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Publisher: American Geophysical Union (AGU)   (Total: 17 journals)

Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 21, SJR: 2.156, h-index: 61)
Geophysical Research Letters     Full-text available via subscription   (Followers: 46, SJR: 2.668, h-index: 142)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 3, SJR: 2.4, h-index: 109)
J. of Advances in Modeling Earth Systems     Open Access   (Followers: 2, SJR: 0.126, h-index: 2)
J. of Geophysical Research : Atmospheres     Partially Free   (Followers: 20)
J. of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 5)
J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 22)
J. of Geophysical Research : Oceans     Partially Free   (Followers: 15)
J. of Geophysical Research : Planets     Full-text available via subscription   (Followers: 13)
J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 22)
J. of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 14)
Paleoceanography     Full-text available via subscription   (Followers: 4, SJR: 2.16, h-index: 82)
Radio Science     Full-text available via subscription   (Followers: 2, SJR: 0.527, h-index: 47)
Reviews of Geophysics     Full-text available via subscription   (Followers: 19, SJR: 8.837, h-index: 87)
Space Weather     Full-text available via subscription   (Followers: 3, SJR: 0.496, h-index: 16)
Tectonics     Full-text available via subscription   (Followers: 7, SJR: 2.16, h-index: 79)
Water Resources Research     Full-text available via subscription   (Followers: 136, SJR: 1.769, h-index: 110)
Journal Cover Journal of Geophysical Research : Oceans
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     ISSN (Online) 2169-9291
     Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • Dispersion and nonlinear effects in the 2011 Tohoku‐Oki earthquake
           tsunami
    • Authors: Tatsuhiko Saito; Daisuke Inazu, Takayuki Miyoshi, Ryota Hino
      Pages: n/a - n/a
      Abstract: This study reveals the roles of the wave dispersion and nonlinear effects for the 2011 Tohoku‐Oki earthquake tsunami. We conducted tsunami simulations based on the nonlinear dispersive equations with a high‐resolution source model. The simulations successfully reproduced the waveforms recorded in the offshore, deep sea, and focal areas. The calculated inundation area coincided well with the actual inundation for the Sendai Plain, which was the widest inundation area during this event. By conducting sets of simulations with different tsunami equations, we obtained the followings insights into the wave dispersion, nonlinear effects, and energy dissipation for this event. Although the wave dispersion was neglected in most studies, the maximum amplitude was significantly overestimated in the deep sea if the dispersion was not included. The waveform observed at the station with the largest tsunami height (∼2 m) among the deep‐ocean stations also verified the necessity of the dispersion. It is well known that the nonlinear effects play an important role for the propagation of a tsunami into bays and harbors. Additionally, nonlinear effects need to be considered to accurately model later waves, even for offshore stations. In particular, including nonlinear terms rather than the inundation was more important when precisely modeling the waves reflected from the coast.
      PubDate: 2014-08-15T13:08:03.305314-05:
      DOI: 10.1002/2014JC009971
       
  • Quantifying uncertainty sources in the gridded data of sea surface CO2
           partial pressure
    • Authors: Guizhi Wang; Minhan Dai, Samuel S. P. Shen, Yan Bai, Yi Xu
      Pages: n/a - n/a
      Abstract: The bulk uncertainty in the gridded sea surface pCO2 data is crucial in assessing the reliability of the CO2 flux estimated from measurements of air‐sea pCO2 difference, because atmospheric pCO2 are relatively homogeneous and well defined. The bulk uncertainty results from three different sources: analytical error (Em), spatial variance ( σs2), and the bias from undersampling ( σu2). Common uncertainty quantification by standard deviation may mix up the different sources of uncertainty. We have established a simple procedure to determine these three sources of uncertainty using remote sensing‐derived and field‐measured pCO2 data. Em is constrained by the analytical method and data reduction procedures. σs2 is derived from the remotely sensed pCO2 field. σu2 is determined by spatial variance and the effective number of observations, considering, for the first time, the geometric bias introduced by pCO2 sampling. This approach is applied to 1° × 1° gridded pCO2 data collected from the East China Sea. We demonstrate that the spatial distribution of these biases is uneven and that none of them follow the same spatial trend as the standard deviation. σs2 contributes the most to the uncertainty in gridded pCO2 data over those grid boxes with good sampling coverage, while σu2 dominates the total uncertainty in the grid boxes with poor sampling coverage. Application of this procedure to other parts of the global ocean will help to better define the inherent spatial variability of the pCO2 field and thus better interpolate and/or extrapolate pCO2 data, and eventually better constrain air‐sea CO2 fluxes.
      PubDate: 2014-08-15T12:50:33.437005-05:
      DOI: 10.1002/2013JC009577
       
  • Low‐frequency ocean bottom pressure variations in the North Pacific
           in response to time‐variable surface winds
    • Authors: C. Petrick; H. Dobslaw, I. Bergmann‐Wolf, N. Schön, K. Matthes, M. Thomas
      Pages: n/a - n/a
      Abstract: One decade of time‐variable gravity field observations from the GRACE satellite mission reveals low‐frequency ocean bottom pressure (OBP) variability of up to 2.5 hPa centered at the northern flank of the subtropical gyre in the North Pacific. From a 145 year‐long simulation with a coupled chemistry climate model, OBP variability is found to be related to the prevailing atmospheric sea‐level pressure and surface wind conditions in the larger North Pacific area. The dominating atmospheric pressure patterns obtained from the climate model run allow in combination with ERA‐Interim sea‐level pressure and surface winds a reconstruction of the OBP variability in the North Pacific from atmospheric model data only, which correlates favorably (r=0.7) with GRACE ocean bottom pressure observations. The regression results indicate that GRACE‐based OBP observations are indeed sensitive to changes in the prevailing sea‐level pressure and thus surface wind conditions in the North Pacific, thereby opening opportunities to constrain atmospheric models from satellite gravity observations over the oceans.
      PubDate: 2014-08-15T12:45:45.854238-05:
      DOI: 10.1002/2013JC009635
       
  • Low calcium carbonate saturation state in an Arctic inland sea having
           large and varying fluvial inputs: The Hudson Bay system
    • Authors: Kumiko Azetsu‐Scott; Michel Starr, Zhi‐Ping Mei, Mats Granskog
      Pages: n/a - n/a
      Abstract: The Hudson Bay system (HBS) is a shallow inland sea in the Arctic, composed of Hudson Strait, Foxe Basin/Channel, James Bay and Hudson Bay. Dissolved inorganic carbon (DIC) and total alkalinity (TA) measurements were used to investigate the state of ocean acidification, specifically calcium carbonate saturation states (Ω) and pH. The freshwater sources were identified from the relationship between oxygen isotope composition (δ18O) and salinity to understand the role of freshwater in ocean acidification. The saturation state of seawater with respect to calcium carbonate (Ω) in surface water (2300 µmol/kg) were observed in the depths of central Hudson Bay with a pHtotal of 7.49 and Ωarg of 0.37. Over 67% and 22% of the bottom water of Hudson Bay was undersaturated with respect to aragonite and calcite respectively, despite Hudson Bay being very shallow (less than 250m deep). The aragonite saturation horizon in the central Hudson Bay was around 50m.
      PubDate: 2014-08-14T03:23:18.857362-05:
      DOI: 10.1002/2014JC009948
       
  • Scaling and stochastic cascade properties of NEMO oceanic simulations and
           their potential value for GCM evaluation and downscaling
    • Authors: Sébastien Verrier; Michel Crépon, Sylvie Thiria
      Pages: n/a - n/a
      Abstract: Spectral scaling properties have already been evidenced on oceanic numerical simulations and have been subject to several interpretations. They can be used to evaluate classical turbulence theories that predict scaling with specific exponents and to evaluate the quality of GCM outputs from a statistical and multiscale point of view. However, a more complete framework based on multifractal cascades is able to generalize the classical but restrictive second‐order spectral framework to other moment orders, providing an accurate description of probability distributions of the fields at multiple scales. The predictions of this formalism still needed systematic verification in oceanic GCM while they have been confirmed recently for their atmospheric counterparts by several papers. The present paper is devoted to a systematic analysis of several oceanic fields produced by the NEMO oceanic GCM. Attention is focused to regional, idealized configurations that permit to evaluate the NEMO engine core from a scaling point of view regardless of limitations involved by land masks. Based on classical multifractal analysis tools, multifractal properties were evidenced for several oceanic state variables (sea surface temperature and salinity, velocity components…). While first order structure functions estimated a different non‐conservativity parameter H in two scaling ranges, the multi‐order statistics of turbulent fluxes were scaling over almost the whole available scaling range. This multifractal scaling was then parameterized with the help of the Universal Multifractal framework, providing parameters that are coherent with existing empirical literature. Finally, we argue that the knowledge of these properties may be useful for oceanographers. The framework seems very well suited for the statistical evaluation of OGCM outputs. Moreover, it also provides practical solutions to simulate sub‐pixel variability stochastically for GCM downscaling purposes. As an independent perspective, the existence of multifractal properties in oceanic flows seems also interesting for investigating scale‐dependencies in remote‐sensing inversion algorithms.
      PubDate: 2014-08-14T02:57:58.50133-05:0
      DOI: 10.1002/2014JC009811
       
  • Spring carbonate chemistry dynamics of surface waters in the northern East
           China Sea: Water mixing, biological uptake of CO2, and chemical buffering
           capacity
    • Authors: Wei‐dong Zhai; Jian‐fang Chen, Hai‐yan Jin, Hong‐liang Li, Jin‐wen Liu, Xian‐qiang He, Yan Bai
      Pages: n/a - n/a
      Abstract: We investigated sea surface total alkalinity (TAlk), dissolved inorganic carbon (DIC), dissolved oxygen (DO), and satellite‐derived chlorophyll‐a in the connection between the Yellow Sea and the East China Sea (ECS) during April to early May 2007. In spring, Changjiang dilution water (CDW), ECS offshore water, and together with Yellow Sea water (YSW) occupied the northern ECS. Using 16‐day composite satellite‐derived chlorophyll‐a images, several algal blooms were identified in the CDW and ECS offshore water. Correspondingly, biological DIC drawdown of 73 ± 20 μmol kg−1, oversaturated DO of 10–110 μmol‐O2 kg−1, and low fugacity of CO2 of 181–304 μatm were revealed in these two waters. YSW also showed CO2 uptake in spring, due to the very low temperature. However, its intrusion virtually counteracted CO2 uptake in the northern ECS. In the CDW and the ECS offshore water, Revelle factor was 9.3–11.7 and 8.9–10.6, respectively, while relatively high Revelle factor values of 11.4–13.0 were revealed in YSW. In the ECS offshore water, the observed relationship between DIC drawdown and oversaturated DO departed from the Redfield ratio, indicating an effect of chemical buffering capacity on the carbonate system during air–sea re‐equilibration. Given the fact that the chemical buffering capacity slows down the air–sea re‐equilibration of CO2, the early spring DIC drawdown may have durative effects on the sea surface carbonate system until early summer. Although our study is subject to limited temporal and spatial coverage of sampling, these insights are fundamental to understanding sea surface carbonate chemistry dynamics in this important ocean margin.
      PubDate: 2014-08-14T02:54:13.803042-05:
      DOI: 10.1002/2014JC009856
       
  • Temporal and spatial variability of tidal‐fluvial dynamics in the
           St. Lawrence fluvial estuary: An application of nonstationary tidal
           harmonic analysis
    • Authors: Pascal Matte; Yves Secretan, Jean Morin
      Pages: n/a - n/a
      Abstract: Predicting tides in upstream reaches of rivers is a challenge, because tides are highly nonlinear and nonstationary, and accurate short‐time predictions of river flow are hard to obtain. In the St. Lawrence fluvial estuary, tide forecasts are produced using a one‐dimensional model (ONE‐D), forced downstream with harmonic constituents and upstream with daily discharges using 30‐day flow forecasts from Lake Ontario and the Ottawa River. Although this operational forecast system serves its purpose of predicting water levels, information about nonstationary tidal‐fluvial processes that can be gained from it is limited, particularly the temporal changes in mean water level and tidal properties (i.e. constituent amplitudes and phases), which are function of river flow and ocean tidal range. In this paper, a harmonic model adapted to nonstationary tides, NS_TIDE, was applied to the St. Lawrence fluvial estuary, where the time‐varying external forcing is directly built into the tidal basis functions. Model coefficients from 13 analysis stations were spatially interpolated to allow tide predictions at arbitrary locations as well as to provide insights into the spatiotemporal evolution of tides. Model hindcasts showed substantial improvements compared to classical harmonic analyses at upstream stations. The model was further validated by comparison with ONE‐D predictions at a total of 32 stations. The slightly lower accuracy obtained with NS_TIDE is compensated by model simplicity, efficiency and capacity to represent stage and tidal variations in a very compact way, and thus represents a new means for understanding tidal rivers.
      PubDate: 2014-08-14T02:52:13.611913-05:
      DOI: 10.1002/2014JC009791
       
  • Formation of fine sediment deposit from a flash flood river in the
           Mediterranean Sea
    • Authors: Manel Grifoll; Vicenç Gracia, Alfredo Aretxabaleta, Jorge Guillén, Manuel Espino, John C. Warner
      Pages: n/a - n/a
      Abstract: We identify the mechanisms controlling fine deposits on the inner‐shelf in front of the Besòs River, in the northwestern Mediterranean Sea. This river is characterized by a flash flood regime discharging large amounts of water (more than twenty times the mean water discharge) and sediment in very short periods lasting from hours to few days. Numerical model output was compared with bottom sediment observations and used to characterize the multiple spatial and temporal scales involved in offshore sediment deposit formation. A high‐resolution (50 m grid size) coupled hydrodynamic‐wave‐sediment transport model was applied to the initial stages of the sediment dispersal after a storm‐related flood event. After the flood, sediment accumulation was predominantly confined to an area near the coastline as a result of preferential deposition during the final stage of the storm. Subsequent reworking occurred due to wave‐induced bottom shear stress that resuspended fine materials, with seaward flow exporting them towards the mid‐shelf. Wave characteristics, sediment availability and shelf circulation determined the transport after the reworking, and the final sediment deposition location. One‐year simulations of the regional area revealed a prevalent southwestward average flow with increased intensity downstream. The circulation pattern was consistent with the observed fine‐deposit depocenter being shifted southwards from the river mouth. At the southern edge, bathymetry controlled the fine deposition by inducing near‐bottom flow convergence enhancing bottom shear stress. According to the short term and long term analyses a seasonal pattern in the fine deposit formation is expected.
      PubDate: 2014-08-14T02:40:25.707666-05:
      DOI: 10.1002/2014JC010187
       
  • Wind‐modulated buoyancy circulation over the Texas‐Louisiana
           shelf
    • Authors: Zhaoru Zhang; Robert Hetland, Xiaoqian Zhang
      Pages: n/a - n/a
      Abstract: This numerical investigation examines buoyancy‐driven circulation on the Texas‐Louisiana shelf modulated by seasonal winds. In wintertime, with downcoast (in the direction of Kelvin wave propagation) wind forcing, the Mississippi‐Atchafalaya River plume exhibits a bottom‐advected pattern. The plume is fairly wide and the horizontal density gradients span almost across the entire shelf inshore of 50m. Within the plume, vertical shear of alongshore flow is in thermal wind balance with the cross‐shore density gradient, and the shear causes a slight reversal of alongshore flow near the bottom. An alongshore flow estimated by the thermal wind relation, along with an assumption of zero bottom velocity, generally well agrees with the actual flow near the surface in regions deeper than 20 m. In spring and summer, the thermal‐wind‐balance‐derived flow deviates from the actual alongshore flow, and an Ekman flow driven by strong onshore wind makes the major contribution to the deviation. Besides, the summertime upcoast wind component transforms the plume to a surface‐advected state, resulting in reduced cross‐shore density gradients and increasing the relative importance of wind‐driven, barotropic alongshore flow, which contributes to the remaining deviation.
      PubDate: 2014-08-14T02:38:49.412571-05:
      DOI: 10.1002/2013JC009763
       
  • Relative role of El Niño and IOD forcing on the southern tropical
           Indian Ocean Rossby waves
    • Authors: Soumi Chakravorty; C. Gnanaseelan, J. S. Chowdary, Jing‐Jia Luo
      Pages: n/a - n/a
      Abstract: The role of local air‐sea interactions over the tropical Indian Ocean (TIO) and remote forcing from the tropical Pacific Ocean in the formation and maintenance of southern TIO Rossby waves during El Niño and positive Indian Ocean Dipole (IOD) years is investigated. These Rossby waves are significantly intensified during the El Niño and IOD cooccurrence years, as compared to those during pure El Niño or IOD years. Coupled ocean‐atmosphere model sensitivity experiments reveal that air‐sea coupled processes in the TIO are responsible for the Rossby wave formation and its maintenance from boreal summer to fall, while remote forcing from the Pacific intensifies and maintains these waves up to the following spring. During the cooccurrence years, the Rossby waves are generated by both the persistent equatorial easterlies and off‐equatorial wind stress curl. During pure El Niño years, however, only off‐equatorial wind stress curl exists to drive weak Rossby wave. Asymmetric heating associated with IOD and the mean background easterly vertical wind shear (in the northern hemisphere) during summer and fall excite two symmetric anticyclones in both sides of the equator as atmospheric Rossby wave response, which are responsible for the anomalous equatorial surface easterlies. In contrast, symmetric heat sink over the Maritime Continent in winter associated with El Niño‐induced subsidence and mean easterly vertical shear (in southern hemisphere) are responsible for strong anticyclone in the southern TIO, which supports off‐equatorial wind stress curl.
      PubDate: 2014-08-12T15:46:30.725185-05:
      DOI: 10.1002/2013JC009713
       
  • Intraseasonal to interannual variability of the Atlantic meridional
           overturning circulation from eddy‐resolving simulations and
           observations
    • Authors: Xiaobiao Xu; Eric P. Chassignet, William E. Johns, William J. Schmitz, E. Joseph Metzger
      Pages: n/a - n/a
      Abstract: Results from two 1/12° eddy‐resolving simulations, together with data‐based transport estimates at 26.5°N and 41°N, are used to investigate the temporal variability of the Atlantic meridional overturning circulation (AMOC) during 2004–2012. There is a good agreement between the model and the observation for all components of the AMOC at 26.5°N, whereas the agreement at 41°N is primarily due to the Ekman transport. We found that (1) both observations and model results exhibit higher AMOC variability on seasonal and shorter time scales than on interannual and longer time scales; (2) on intraseasonal and interannual time scales, the AMOC variability is often coherent over a wide latitudinal range, but lacks an overall consistent coherent pattern over the entire North Atlantic; and (3) on seasonal time scales, the AMOC variability exhibits two distinct coherent regimes north and south of 20°N, due to different wind stress variability in the tropics and subtropics. The high AMOC variability south of 20°N in the tropical Atlantic comes primarily from the Ekman transport of the near‐surface water, and is modulated to some extent by the transport of the Antarctic Intermediate water below the thermocline. These results highlight the importance of the surface wind in driving the AMOC variability.
      PubDate: 2014-08-12T15:43:13.315502-05:
      DOI: 10.1002/2014JC009994
       
  • Effect of coastal‐trapped waves and wind on currents and transport
           in the Gulf of California
    • Authors: Manuel O. Gutiérrez; Manuel López, Julio Candela, Rubén Castro, Affonso Mascarenhas, Curtis A. Collins
      Pages: n/a - n/a
      Abstract: Subsurface pressure (SsP) observations from stations inside and outside of the Gulf of California (GC) are used to analyze the relationship between low‐frequency currents, temperature, and transport inside the GC and intraseasonal coastal‐trapped waves (CTWs), which propagate poleward along the coast toward the GC. Correlation functions and coherences of SsP stations were consistent with intraseasonal CTWs splitting in two at the mouth of the gulf: one part enters the gulf, propagates around the gulf, and eventually, toward the mouth, and another part that appears to “jump” the mouth of the gulf and travels poleward along the west coast of the peninsula. The correlation and coherence estimates of SsP at Manzanillo with currents showed that downwelling CTWs generated along‐gulf current anomalies toward the head of the gulf at the mainland shelf of the mouth, whereas at Ballenas Channel sill (San Lorenzo sill) these waves generated current anomalies toward the mouth near the surface (bottom). At the San Lorenzo (SL) sill, downwelling CTWs increased the near‐bottom (∼400 m) temperature and reduced the bottom transport of deep, fresher, and colder water that flows toward the head of the gulf. Cross‐Calibrated Multiplatform winds were used to investigate their relationship with currents. The first empirical orthogonal function of the along‐gulf wind stress showed that wind blowing toward the head of the gulf generated a reduction of bottom transport toward the head of the gulf through the SL sill, and intensified surface geostrophic current fluctuations toward the head of the gulf. There was also significant correlation between inflow bottom transport and outflow surface geostrophic velocities averaged across the gulf, consistent with the exchange pattern for the Northern Gulf.
      PubDate: 2014-08-12T15:34:21.144224-05:
      DOI: 10.1002/2013JC009538
       
  • Can we do better than the grid survey: Optimal synoptic surveys in
           presence of variable uncertainty and decorrelation scales
    • Authors: Sergey Frolov; Bartolame Garau, James Bellingham
      Pages: n/a - n/a
      Abstract: Regular grid (“lawnmower”) survey is a classical strategy for synoptic sampling of the ocean. Is it possible to achieve a more effective use of available resources if one takes into account a priori knowledge about variability in magnitudes of uncertainty and decorrelation scales? In this article, we develop and compare the performance of several path‐planning algorithms: optimized “lawnmower,” a graph‐search algorithm (A*), and a fully nonlinear genetic algorithm. We use the machinery of the best linear unbiased estimator (BLUE) to quantify the ability of a vehicle fleet to synoptically map distribution of phytoplankton off the central California coast. We used satellite and in situ data to specify covariance information required by the BLUE estimator. Computational experiments showed that two types of sampling strategies are possible: a suboptimal space‐filling design (produced by the “lawnmower” and the A* algorithms) and an optimal uncertainty‐aware design (produced by the genetic algorithm). Unlike the space‐filling designs that attempted to cover the entire survey area, the optimal design focused on revisiting areas of high uncertainty. Results of the multivehicle experiments showed that fleet performance predictors, such as cumulative speed or the weight of the fleet, predicted the performance of a homogeneous fleet well; however, these were poor predictors for comparing the performance of different platforms.
      PubDate: 2014-08-12T15:33:00.324955-05:
      DOI: 10.1002/2013JC009521
       
  • Impacts of nonbreaking wave‐stirring‐induced mixing on the
           upper ocean thermal structure and typhoon intensity in the South China Sea
           
    • Authors: Yineng Li; Shiqiu Peng, Jia Wang, Jing Yan
      Pages: n/a - n/a
      Abstract: To investigate the effect of nonbreaking wave‐induced mixing caused by surface wave stirring on the upper ocean thermal structure (UOTS) and the typhoon intensity, a simple nonbreaking wave‐stirring‐induced mixing parameterization (WMP) scheme is incorporated into a regional coupled atmosphere‐ocean model for the South China Sea (SCS), which couples the Princeton Ocean Model (POM) to the Weather Research and Forecasting (WRF) model using the OASIS3 coupler. The results of simulating two selected typhoon cases indicate that the nonbreaking wave‐stirring‐induced mixing has significant impacts on UOTS and the typhoon intensity, and the incorporation of the simple WMP scheme in the coupled model helps to improve the simulation of UOTS and thus the typhoon intensity. In the case that the typhoon intensity is underestimated by the atmosphere model alone, the improvement of initial UOTS by the ocean model with the WMP included can deepen the initial thermocline depth, reduce the effect of SST cooling, and prevent the typhoon intensity from undesired weakening. In the case that the typhoon intensity is overestimated (with strong winds), including the WMP in the ocean model significantly enhances the total vertical mixing rate in the upper ocean, which in turn enhances the SST cooling and thus reduces the typhoon intensity as desired. The results obtained in this study make a contribution to the ongoing efforts of improving the typhoon intensity forecast using a regional atmosphere‐ocean coupled model by worldwide researchers and forecasters, especially for the typhoons in the SCS regions.
      PubDate: 2014-08-12T15:13:54.607721-05:
      DOI: 10.1002/2014JC009956
       
  • Vertical diffusivity of the Western Arctic Ocean halocline
    • Authors: William J. Shaw; Timothy P. Stanton
      Pages: n/a - n/a
      Abstract: A nearly year‐long series of upper ocean temperature, conductivity, and temperature microstructure profiles were collected from an ice camp drifting in the Beaufort Gyre as part of the 1997–1998 Surface Heat Budget of the Arctic Experiment (SHEBA). Geographically, the record includes portions over the deep Canada Basin and the steep bathymetry of the Chukchi Borderlands region. Hydrographically, the record includes “cool,” Pacific‐origin haloclines, which contain a variety of subsurface temperature maxima, and cold haloclines typical of the Eurasian Basins. We present estimates of the vertical turbulent diffusivity derived from the dissipation rate of thermal variance and calculations of the associated vertical heat fluxes. We find that vertical diffusion proceeds at molecular rates in the deep basins and away from topographic features. While still relatively small, diffusivity is enhanced by 1 order of magnitude near and above the Chukchi Borderlands. The enhanced diffusivity is correlated to an increase in water column strain variance above the Borderlands, providing a linkage between bathymetry, internal wave activity and turbulence. The Chukchi Borderlands play a significant role in heat transport in the Western Arctic. They are a pathway for horizontal heat transport and a hot spot for vertical heat transport. Vertical fluxes make a substantial contribution to the energy balance of the sea ice cover in this region. Heat fluxes between the halocline and underlying Atlantic Water are shown to be small and lacking vertical connection near surface waters.
      PubDate: 2014-08-12T15:11:58.18475-05:0
      DOI: 10.1002/2013JC009598
       
  • Seasonal and interannual changes of the Kuroshio intrusion onto the East
           China Sea Shelf
    • Authors: Chau‐Ron Wu; Yi‐Chia Hsin, Tzu‐Ling Chiang, Yong‐Fu Lin, I‐Fong Tsui
      Pages: n/a - n/a
      Abstract: An advanced artificial neural network classification algorithm is applied to 20 years of multisatellite geostrophic velocity data to study the Kuroshio intrusion onto the southern shelf of the East China Sea. The results suggest that the on‐shelf intrusion may occur year round, but winter intrusion events are more frequent than summer events. Both stronger intrusion (which is closely correlated to surface heat flux gradient) and weaker intrusion (which is correlated to wind forcing) occur during wintertime, but the former dominates in late winter while the latter prevails in early winter. There is a significant year‐to‐year variation of the winter on‐shelf intrusion. Although on‐shelf intrusion is the major characteristic of the region during wintertime, seldom intrusion events have been identified in the winters of 1997–1998 and 2002–2003. Two conditions are responsible for the cause of the nonintrusion events. During the two nonintrusion winters, the upstream Kuroshio transport anomaly is insignificant (the Kuroshio is not weakened) and no significant winter cooling off northeast Taiwan. Thus, the Kuroshio tends to flow along the shelf break following the 200 m isobath and on‐shelf intrusion ceases. Those two nonintrusion events take place during the winters when both the Niño 3.4 index and the PDO index are large and positive.
      PubDate: 2014-08-12T15:10:00.406949-05:
      DOI: 10.1002/2013JC009748
       
  • Issue Information
    • Pages: i - v
      PubDate: 2014-08-12T09:39:59.367525-05:
      DOI: 10.1002/jgrc.20352
       
  • Seasonal variability of the Red Sea, from satellite gravity, radar
           altimetry, and in situ observations
    • Authors: John Wahr; David A. Smeed, Eric Leuliette, Sean Swenson
      Pages: n/a - n/a
      Abstract: Seasonal variations of sea surface height (SSH) and mass within the Red Sea are caused mostly by exchange of heat with the atmosphere and by flow through the strait opening into the Gulf of Aden to the south. That flow involves a net mass transfer into the Red Sea during fall and out during spring, though in summer there is an influx of cool water at intermediate depths. Thus, summer water in the south is warmer near the surface due to higher air temperatures, but cooler at intermediate depths. Summer water in the north experiences warming by air‐sea exchange only. The temperature affects water density, which impacts SSH but has no effect on mass. We study this seasonal cycle by combining GRACE mass estimates, altimeter SSH measurements, and steric contributions derived from the World Ocean Atlas temperature climatology. Among our conclusions are: mass contributions are much larger than steric contributions; the mass is largest in winter, consistent with winds pushing water into the Red Sea in fall and out during spring; the steric signal is largest in summer, consistent with surface warming; and the cool, intermediate‐depth water flowing into the Red Sea in spring has little impact on the steric signal, because contributions from the lowered temperature are offset by effects of decreased salinity. The results suggest that the combined use of altimeter and GRACE measurements can provide a useful alternative to in situ data for monitoring the steric signal.
      PubDate: 2014-08-12T09:25:37.972322-05:
      DOI: 10.1002/2014JC010161
       
  • Pathways of basal meltwater from Antarctic ice shelves: A model study
    • Authors: Kazuya Kusahara; Hiroyasu Hasumi
      Pages: n/a - n/a
      Abstract: We investigate spreading pathways of basal meltwater released from all Antarctic ice shelves using a circumpolar coupled ice shelf‐sea ice‐ocean model that reproduces major features of the Southern Ocean circulation, including the Antarctic Circumpolar Current (ACC). Several independent virtual tracers are used to identify detailed pathways of basal meltwaters. The spreading pathways of the meltwater tracers depend on formation sites because the meltwaters are transported by local ambient ocean circulation. Meltwaters from ice shelves in the Weddell and Amundsen—Bellingshausen Seas in surface/subsurface layers are effectively advected to lower latitudes with the ACC. Although a large portion of the basal meltwaters is present in surface and subsurface layers, a part of the basal meltwaters penetrates into the bottom layer through active dense water formation along the Antarctic coastal margins. The signals at the seafloor extend along the topography, showing a horizontal distribution similar to the observed spreading of Antarctic Bottom Water. Meltwaters originating from ice shelves in the Weddell and Ross Seas and in the Indian sector significantly contribute to the bottom signals. A series of numerical experiments in which thermodynamic interaction between the ice shelf and ocean is neglected regionally demonstrates that the basal meltwater of each ice shelf impacts sea ice and/or ocean thermohaline circulation in the Southern Ocean.
      PubDate: 2014-08-12T02:39:34.773313-05:
      DOI: 10.1002/2014JC009915
       
  • Penetration depth of diapycnal mixing generated by wind stress and flow
           over topography in the northwestern Pacific
    • Authors: Ying Li; Yongsheng Xu
      Pages: n/a - n/a
      Abstract: The role of turbulent diapycnal mixing in the northwestern Pacific was estimated by employing a fine‐scale parameterization method based on 6,756 high‐resolution CTD profiles spanning a period of 8 years from the Japan Oceanography Data Center (JODC) and the Kuroshio Extension System Study (KESS). The rate of turbulent mixing in the upper ocean within 300‐1,800 m depth displayed a distinct seasonal cycle, bearing a statistically significant correlation to wind‐induced near‐inertial energy flux (hereafter denoted by WNEF). Enhanced turbulent mixing was also found near the rough seafloor relative to that over smooth topography. Enhanced dissipation at surface and bottom was found to be able to penetrate the ocean interior up to 1,800 m and 3,300 m, respectively, with penetration depths varying with the WNEF and topographic roughness. Our study here provides evidence for the important role of near‐inertial energy input from wind stress and the influence of bottom topography in maintaining mixing in the ocean interior.
      PubDate: 2014-08-12T02:31:00.597022-05:
      DOI: 10.1002/2013JC009681
       
  • Simulated tomographic reconstruction of ocean current profiles in a
           bottom‐limited sound channel
    • Authors: Naokazu Taniguchi; Chen‐Fen Huang
      Pages: n/a - n/a
      Abstract: Tomographic reconstruction of the vertical current profile in a bottom‐limited sound channel requires solving a difficult ray identification problem. An approach to deal with this problem is a ray group method in which received arrival pulses are divided into several ray groups according to the characteristics of the arrival patterns. The method is validated using numerically simulated reciprocal acoustic transmission in a synthetic ocean in the Luzon Strait, where the Kuroshio Current has speeds as high as 1.2 m/s, for both narrowband and broadband signals. Four ray groups are found for the synthetic data; these are chosen based on arrival time. The differential travel time is determined by pairing up the reciprocal arrival peaks and then averaging the differential travel times within the selected time windows. Compared with the narrowband case, the estimated broadband differential travel time is more consistent with that computed from the current magnitude in the synthetic ocean. The vertical current profile is reconstructed from the broadband differential travel times by a generalized Tikhonov regularization approach. The data weighting matrix includes observation error in picking and pairing travel times and model parameter error due to path length uncertainty. The time series of the reconstructed current agrees with the synthetic ocean current; the fractional residual variance is 0.013 for the surface layer and 0.01 for the entire water column. The ray group method mitigates the ray identification problem in the bottom‐limited environment and could offer valuable data regarding the range‐integrated current velocity.
      PubDate: 2014-08-11T09:40:52.278561-05:
      DOI: 10.1002/2014JC009885
       
  • Effects of super typhoons on cyclonic ocean eddies in the western North
           Pacific: A satellite data‐based evaluation between 2000 and 2008
    • Authors: Liang SUN; Ying‐Xin Li, Yuan‐Jian Yang, Qiaoyan Wu, Xue‐Tao Chen, Qiu‐Yang Li, Yu‐Bin Li, Xian Tao
      Pages: n/a - n/a
      Abstract: A composite time series of the merged satellite altimeters sea surface height anomaly (SSHA) data and satellite‐observed sea surface temperature (SST) data were used to identify eddies in the Western North Pacific Ocean (WNPO), where there were numbers of intense typhoons. This study systematically investigated 15 super typhoons during the period of 2000‐2008 in the WNPO to study their impacts on the pre‐typhoon ocean features, e.g., the cyclonic ocean eddy (COE) feature (closed contours of SSHA < ‐6 cm) and neutral condition (SSHA between ‐6 and 6 cm). Two new COEs are generated by two super typhoons, and 18 pre‐existing COEs are intensified by 13 super typhoons. 5 of the 13 super typhoons each influenced two pre‐exisiting COEs. Although the typhoon‐induced maximum cooling centers had a right bias along the tracks due to wind conditions, pre‐existing COEs also play a significant role in determining the strength and location of large SST cooling. Three possible factors (maximum wind speed, typhoon translation speed and the typhoon forcing time, Tf) are employed to explain the interactions. Above all, the changes of the COE geometric and physical parameters (e.g., effective radius, area, SST, SSHA, and eddy kinetic energy) were mostly related to the typhoon forcing time, Tf. This is because Tf is a parameter that is a combination of the typhoon’s translation speed, intensity and size. Although the typhoons may significantly impact COEs, such samples were not commonly observed. Thus, the impact of typhoon on the strength of COEs is generally inefficient.
      PubDate: 2014-08-11T06:58:40.337463-05:
      DOI: 10.1002/2013JC009575
       
  • The pattern and variability of winter Kuroshio intrusion northeast of
           Taiwan
    • Authors: Xiaohui Liu; Changming Dong, Dake Chen, Jilan Su
      Pages: n/a - n/a
      Abstract: The variations of the Kuroshio path and velocity northeast of Taiwan are analyzed based on along‐track satellite altimeter data as well as high‐resolution model experiments. Observations reveal that in winter the Kuroshio intrusion into the East China Sea (ECS) at this location is manifested by a secondary maximum current core (SMCC) shoreward of the Kuroshio's main path. The SMCC varies significantly on interannual time scale, and its variability is strikingly out of phase with that of the Kuroshio entering the ECS, meaning that the stronger the Kuroshio, the weaker the SMCC, and vice versa. Model experiments corroborate the observational results and, more importantly, indicate that the Kuroshio intrusion here follows two primary routes, a large anticyclonic loop that separates from the Kuroshio at the northern end of Taiwan and moves forward to form the SMCC, and a straight northward path onto the shelf when the Kuroshio turns sharply eastward along the continental slope of the ECS. The intrusion is controlled by both local forcing and remote effect, with its pattern and variability depending mostly on the local heat flux and the inertia of the Kuroshio Current.
      PubDate: 2014-08-11T04:30:59.430707-05:
      DOI: 10.1002/2014JC009879
       
  • SAR observation and numerical modeling of tidal current wakes at the East
           China Sea offshore wind farm
    • Authors: XiaoMing Li; Lequan Chi, Xueen Chen, YongZheng Ren, Susanne Lehner
      Pages: n/a - n/a
      Abstract: A TerraSAR‐X (TS‐X) Synthetic Aperture Radar (SAR) image acquired at the East China Sea offshore wind farm presents distinct wakes at a kilometer scale on the lee of the wind turbines. The presumption was that these wakes were caused by wind movement around turbine blades. However, wind analysis using spaceborne radiometer data, numerical weather prediction, and in situ measurements suggest that the prevailing wind direction did not align with the wakes. By analyzing measurement at the tidal gauge station and modeling of the tidal current field, these trailing wakes are interpreted to have formed when a strong tidal current impinged on the cylindrical monopiles of the wind turbines. A numerical simulation was further conducted to reproduce the tidal current wake under such conditions. Comparison of the simulated surface velocity in the wake region with the TS‐X sea surface backscatter intensity shows a similar trend. Consequently, turbulence intensity (T.I.) of the tidal current wakes over multiple piles is studied using the TS‐X observation. It is found that the T.I. has a logarithmic relation with distance. Furthermore, another case study showing wakes due to wind movement around turbine blades is presented to discuss the differences in the tidal current wakes and wind turbine wakes. The conclusion is drawn that small‐scale wakes formed by interaction of the tidal current and the turbine piles could be also imaged by SAR when certain conditions are satisfied. The study is anticipated to draw more attentions to the impacts of offshore wind foundations on local hydrodynamic field.
      PubDate: 2014-08-11T04:11:30.957143-05:
      DOI: 10.1002/2014JC009822
       
  • Assessing the temporal variability in extreme storm‐tide time series
           for coastal flood risk assessment
    • Authors: N. Quinn; M. Lewis, M. P. Wadey, I. D. Haigh
      Pages: n/a - n/a
      Abstract: The probability of extreme storm‐tide events has been extensively studied; however, the variability within the duration of such events and implications to flood risk is less well understood. This research quantifies such variability during extreme storm‐tide events (the combined elevation of the tide, surge, and their interactions) at 44 national tide gauges around the UK. Extreme storm‐tide events were sampled from water level measurements taken every 15 min between 1993 and 2012. At each site, the variability in elevation at each time step, relative to a given event peak, was quantified. The magnitude of this time series variability was influenced both by gauge location (and hence the tidal and nontidal residual characteristics) and the time relative to high water. The potential influence of this variability on coastal inundation was assessed across all UK gauge sites, followed by a detailed case study of Portsmouth. A two‐dimensional hydrodynamic model of the Portsmouth region was used to demonstrate that given a current 1 in 200 year storm‐tide event, the predicted number of buildings inundated differed by more than 30% when contrasting simulations forced with the upper and lower bounds of the observed time series variability. The results indicate that variability in the time series of the storm‐tide event can have considerable influence upon overflow volumes, hence with implications for coastal flood risk assessments. Therefore, further evaluating and representing this uncertainty in future flood risk assessments is vital, while the envelopes of variability defined in this research provides a valuable tool for coastal flood modelers.
      PubDate: 2014-08-11T04:10:37.119922-05:
      DOI: 10.1002/2014JC010197
       
  • Near‐surface temperature gradient in a coastal upwelling regime
    • Authors: H. Maske; J. Ochoa, C. O. Almeda‐Jauregui, M. C. Ruiz‐de la Torre, R. Cruz‐López, J. R. Villegas‐Mendoza
      Pages: n/a - n/a
      Abstract: In oceanography, a near homogeneous mixed layer extending from the surface to a seasonal thermocline is a common conceptual basis in physics, chemistry, and biology. In a coastal upwelling region 3 km off the coast in the Mexican Pacific, we measured vertical density gradients with a free‐rising CTD and temperature gradients with thermographs at 1, 3, and 5 m depths logging every 5 min during more than a year. No significant salinity gradient was observed down to 10 m depth, and the CTD temperature and density gradients showed no pronounced discontinuity that would suggest a near‐surface mixed layer. Thermographs generally logged decreasing temperature with depth with gradients higher than 0.2 K m−1 more than half of the time in the summer between 1 and 3 m, 3 and 5 m and in the winter between 1 and 3 m. Some negative temperature gradients were present and gradients were generally highly variable in time with high peaks lasting fractions of hours to hours. These temporal changes were too rapid to be explained by local heating or cooling. The pattern of positive and negative peaks might be explained by vertical stacks of water layers of different temperatures and different horizontal drift vectors. The observed near‐surface gradient has implications for turbulent wind energy transfer, vertical exchange of dissolved and particulate water constituents, the interpretation of remotely sensed SST, and horizontal wind‐induced transport.
      PubDate: 2014-08-11T04:08:38.524388-05:
      DOI: 10.1002/2014JC010074
       
  • Observed bottom boundary layer transport and uplift on the continental
           shelf adjacent to a western boundary current
    • Authors: A. Schaeffer; M. Roughan, J. E. Wood
      Pages: n/a - n/a
      Abstract: Western boundary currents strongly influence the dynamics on the adjacent continental shelf and in particular the cross‐shelf transport and uplift through the bottom boundary layer. Four years of moored in situ observations on the narrow southeastern Australian shelf (in water depths of between 65 and 140 m) were used to investigate bottom cross‐shelf transport, both upstream (30°S) and downstream (34°S) of the separation zone of the East Australian Current (EAC). Bottom transport was estimated and assessed against Ekman theory, showing consistent results for a number of different formulations of the boundary layer thickness. Net bottom cross‐shelf transport was onshore at all locations. Ekman theory indicates that up to 64% of the transport variability is driven by the along‐shelf bottom stress. Onshore transport in the bottom boundary layer was more intense and frequent upstream than downstream, occurring 64% of the time at 30°S. Wind‐driven surface Ekman transport estimates did not balance the bottom cross‐shelf flow. At both locations, strong variability was found in bottom water transport at periods of approximately 90–100 days. This corresponds with periodicity in EAC fluctuations and eddy shedding as evidenced from altimeter observations, highlighting the EAC as a driver of variability in the continental shelf waters. Ocean glider and HF radar observations were used to identify the bio‐physical response to an EAC encroachment event, resulting in a strong onshore bottom flow, the uplift of cold slope water, and elevated coastal chlorophyll concentrations.
      PubDate: 2014-08-11T04:07:29.19617-05:0
      DOI: 10.1002/2013JC009735
       
  • Active‐passive synergy for interpreting ocean L‐band
           emissivity: Results from the CAROLS airborne campaigns
    • Authors: A. C. H. Martin; J. Boutin, D. Hauser, E. P. Dinnat
      Pages: n/a - n/a
      Abstract: The impact of the ocean surface roughness on the ocean L‐band emissivity is investigated using simultaneous airborne measurements from an L‐band radiometer (CAROLS) and from a C‐band scatterometer (STORM) acquired in the Gulf of Biscay (off‐the French Atlantic coasts) in November 2010. Two synergetic approaches are used to investigate the impact of surface roughness on the L‐band brightness temperature (Tb). First, wind derived from the scatterometer measurements is used to analyze the roughness contribution to Tb as a function of wind and compare it with the one simulated by SMOS and Aquarius roughness models. Then residuals from this mean relationship are analyzed in terms of mean square slope derived from the STORM instrument. We show improvement of new radiometric roughness models derived from SMOS and Aquarius satellite measurements in comparison with prelaunch models. Influence of wind azimuth on Tb could not be evidenced from our data set. However, we point out the importance of taking into account large roughness scales (>20 cm) in addition to small roughness scale (5 cm) rapidly affected by wind to interpret radiometric measurements far from nadir. This was made possible thanks to simultaneous estimates of large and small roughness scales using STORM at small (7–16°) and large (30°) incidence angles.
      PubDate: 2014-08-11T04:06:08.279911-05:
      DOI: 10.1002/2014JC009890
       
  • An intercomparison of Arctic ice drift products to deduce uncertainty
           estimates
    • Authors: Hiroshi Sumata; Thomas Lavergne, Fanny Girard‐Ardhuin, Noriaki Kimura, Mark A. Tschudi, Frank Kauker, Michael Karcher, Rüdiger Gerdes
      Pages: n/a - n/a
      Abstract: An intercomparison of four low‐resolution remotely sensed ice‐drift products in the Arctic Ocean is presented. The purpose of the study is to examine the uncertainty in space and time of these different drift products. The comparison is based on monthly mean ice drifts from October 2002 to December 2006. The ice drifts were also compared with available buoy data. The result shows that the differences of the drift vectors are not spatially uniform, but are covariant with ice concentration and thickness. In high (low) ice‐concentration areas, the differences are small (large), and in thick (thin) ice‐thickness areas, the differences are small (large). A comparison with the drift deduced from buoys reveals that the error of the drift speed depends on the magnitude of the drift speed: larger drift speeds have larger errors. Based on the intercomparison of the products and comparison with buoy data, uncertainties of the monthly mean drift are estimated. The estimated uncertainty maps reasonably reflect the difference between the products in relation to ice concentration and the bias from the buoy drift in relation to drift speed. Examinations of distinctive features of Arctic sea ice motion demonstrate that the transpolar drift speed differs among the products by 13% (0.32 cm s−1) on average, and ice drift curl in the Amerasian Basin differs by up to 24% (3.3 × 104 m2 s−1). These uncertainties should be taken into account if these products are used, particularly for model validation and data assimilation within the Arctic.
      PubDate: 2014-08-08T14:05:53.760363-05:
      DOI: 10.1002/2013JC009724
       
  • Global observations of quasi‐zonal bands in microwave sea surface
           temperature
    • Authors: C. E. Buckingham; P. C. Cornillon, F. Schloesser, K. M. Obenour
      Pages: n/a - n/a
      Abstract: Global observations of quasi‐zonal jet‐like structures have recently been reported in estimates of upper ocean circulation. To date, these observations have come primarily from float‐derived and altimeter‐derived estimates of zonal velocity. Here, we explore the existence of similar structures in the ocean using satellite‐derived estimates of sea surface temperature (SST) from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR‐E). Applying an ocean front detection algorithm globally to microwave measurements of SST, we find that repeated ocean fronts occur along quasi‐zonal bands in a multiyear (2002–2011) average of detections. Such a pattern is also observed in SST gradient magnitude. Composite analyses of SST, sea surface height (SSH), and upper ocean temperatures from Argo profiling floats suggest repeated fronts in the subtropics occur as a result of neighboring anticyclonic and cyclonic eddies. Horizontal advection in the presence of a background temperature gradient likely plays a role as evidenced by the tilt of temperature anomalies with depth. High gradient events found within the bands are observed to propagate westward with speed comparable to mesoscale eddies and we estimate these events explain 20% of the observed variance in SST gradient magnitude (2002–2011). In a final analysis, we regress the decay of the bands with averaging period and observe mild‐to‐strong persistence throughout much of the World Ocean. These findings support the view that propagating eddies help give rise to the bands. Whether or not eddies follow preferred paths remain unanswered.
      PubDate: 2014-08-08T14:05:21.923121-05:
      DOI: 10.1002/2014JC010088
       
  • Interannual variability of the Kuroshio onshore intrusion along the East
           China Sea shelf break: Effect of the Kuroshio volume transport
    • Authors: Chuanyu Liu; Fan Wang, Xinping Chen, Jin‐Song von Storch
      Pages: n/a - n/a
      Abstract: The interannual variability of the Kuroshio onshore intrusion (KOI) across the East China Sea (ECS) shelf break and its response to the ECS Kuroshio volume transport (KVT) during 1993~2010 are studied based on a high resolution, real time and global ocean general circulation model. Since variability of KVT is mainly determined in the interior Pacific, it is rather a remote than a local factor for the local ECS KOI. On interannual time scales, KVT affects KOI not only in the net volume transport across the entire shelf break but also in the spatial pattern along the shelf break. When KVT increases, the intrusion decreases (increases) upstream (downstream) of the major intrusion region northeast of Taiwan, the retreating increases (decreases) upstream (downstream) of the main veering region southwest of Kyushu. These patterns are caused by cyclonic eddies induced by the seaward deflection of the Kuroshio axis from the shelf break, which ultimately results from the KVT increase. A diagnostic mechanism of KOI ~ M sin(θ) h–1 is proposed, where h is the bottom depth, θ is the angle between isobaths and the vertically averaged current, and M is the absolute volume transport at the shelf break. θ is large in the major intrusion/retreating regions and stable on interannual time scales while M changes with opposite signs between upstream and downstream of the major intrusion/retreating regions. The mechanism explains well the relation of local KVT and the spatial pattern of KOI along the shelf break, in both the mean state and the interannual variations.
      PubDate: 2014-08-08T11:59:35.237931-05:
      DOI: 10.1002/2013JC009653
       
  • Mesoscale eddy effects on the subduction of North Pacific mode waters
    • Authors: Lixiao Xu; Shang‐Ping Xie, Julie L. McClean, Qinyu Liu, Hideharu Sasaki
      Pages: n/a - n/a
      Abstract: Mesoscale eddy effects on the subduction of North Pacific mode waters are investigated by comparing observations and ocean general circulation models where eddies are either parameterized or resolved. The eddy‐resolving models produce results closer to observations than the noneddy‐resolving model. There are large discrepancies in subduction patterns between eddy‐resolving and noneddy‐resolving models. In the noneddy‐resolving model, subduction on a given isopycnal is limited to the cross point between the mixed layer depth (MLD) front and the outcrop line whereas in eddy‐resolving models and observations, subduction takes place in a broader, zonally elongated band within the deep mixed layer region. Mesoscale eddies significantly enhance the total subduction rate, helping create remarkable peaks in the volume histogram that correspond to North Pacific subtropical mode water (STMW) and central mode water (CMW). Eddy‐enhanced subduction preferentially occurs south of the winter mean outcrop. With an anticyclonic eddy to the west and a cyclonic eddy to the east, the outcrop line meanders south, and the thermocline/MLD shoals eastward. As eddies propagate westward, the MLD shoals, shielding the water of low potential vorticity from the atmosphere. The southward eddy flow then carries the subducted water mass into the thermocline. The eddy subduction processes revealed here have important implications for designing field observations and improving models.
      PubDate: 2014-08-08T10:28:21.411177-05:
      DOI: 10.1002/2014JC009861
       
  • Layered mixing on the New England Shelf in summer
    • Authors: Jianing Wang; Blair J. W. Greenan, Youyu Lu, Neil S. Oakey, William J. Shaw
      Pages: n/a - n/a
      Abstract: The layered structure of stratification and mixing on the New England Shelf (NES) in summer is examined by analyzing a comprehensive set of observations of hydrography, currents and turbulence. A clear distinction in mixing characteristics between the mid‐column water (consisting of sub‐surface stratification, mid‐depth weak stratification and lower‐layer stratification) and a well‐mixed bottom boundary layer (BBL) is revealed. The combination of subtidal Ekman onshore bottom transport and cross‐shore density gradient created a lower‐layer stratification that inhibited the upward extension of the BBL turbulence. The BBL mixing was related to strong shear generated by bottom stress, and the magnitude and periodic variation of BBL mixing was determined by both the tidal and subtidal flows. Mixing in the mid‐column water occurred under stably‐stratified conditions and showed correspondence with the occurrence of near‐inertial and semi‐diurnal internal waves. Positive correlations between buoyancy frequency squared (N2) and shear variance (S2), S2 and dissipation rate (ε), N2 and ε are established in the mid‐column, but not in the BBL. The mid‐column ε was reasonably described by a slightly modified MacKinnon‐Gregg (MG) model.
      PubDate: 2014-08-07T04:37:56.573516-05:
      DOI: 10.1002/2014JC009947
       
  • Periodicity and patterns of ocean wind and wave climate
    • Authors: Justin E. Stopa; Kwok Fai Cheung
      Pages: n/a - n/a
      Abstract: The Climate Forecast System Reanalysis (CFSR) provides a wealth of information spanning 1979 to 2009 for investigation of ocean wind and wave climate. Preprocessing of the data removes the dominant seasonal signals and creates time series of semi‐monthly averaged wind speed and significant wave height over a 0.5º global grid. We perform an empirical orthogonal function (EOF) analysis to extract the dominant space‐time patterns. The results for the three major ocean basins show strong zonal structures in the winds and saturation of the swells corroborating prior works with various datasets. We reexamine the CFSR data in the frequency domain to identify periodic signals associated with published climate indices. The Fourier transform generates spectra ranging from 1 month to 15 years period for an EOF analysis. The results demonstrate dominance of the Arctic Oscillation in the Atlantic basin with a broad range of intra‐annual signals off the European coasts. The Indian and Pacific Oceans are strongly influenced by inter‐annual cycles of the El Niño Southern Oscillation (ENSO) and the Antarctica Oscillation. The Indian Ocean also has strong intra‐annual components ranging from 50 to 80 day period. The ENSO proves to be a ubiquitous signal around the globe, and in particular, saturates the Pacific with strong influences in the Equatorial region and the Southern Hemisphere Westerlies. A commonality of all basins is that the magnitude and the spatial structure of the intra‐annual and inter‐annual signals are similar suggesting a wide range of periods in each of the climate cycles examined.
      PubDate: 2014-08-07T04:27:12.943945-05:
      DOI: 10.1002/2013JC009729
       
  • On the nature of the sea ice albedo feedback in simple models
    • Authors: W. Moon; J. S. Wettlaufer
      Pages: n/a - n/a
      Abstract: We examine the nature of the ice‐albedo feedback in a long standing approach used in the dynamic‐thermodynamic modeling of sea ice. The central issue examined is how the evolution of the ice area is treated when modeling a partial ice cover using a two‐category‐thickness scheme; thin sea ice and open water in one category and “thick” sea ice in the second. The problem with the scheme is that the area‐evolution is handled in a manner that violates the basic rules of calculus, which leads to a neglected area‐evolution term that is equivalent to neglecting a leading‐order latent heat flux. We demonstrate the consequences by constructing energy balance models with a fractional ice cover and studying them under the influence of increased radiative forcing. It is shown that the neglected flux is particularly important in a decaying ice cover approaching the transitions to seasonal or ice‐free conditions. Clearly, a mishandling of the evolution of the ice area has leading‐order effects on the ice‐albedo feedback. Accordingly, it may be of considerable importance to re‐examine the relevant climate model schemes and to begin the process of converting them to fully resolve the sea ice thickness distribution in a manner such as remapping, which does not in principle suffer from the pathology we describe.
      PubDate: 2014-08-05T02:56:16.22264-05:0
      DOI: 10.1002/2014JC009964
       
  • Observations of rain‐induced near‐surface salinity anomalies
    • Authors: William E. Asher; Andrew T. Jessup, Ruth Branch, Dan Clark
      Pages: n/a - n/a
      Abstract: Vertical salinity gradients in the top few meters of the ocean surface can exist due to the freshwater input from rain. If present, surface gradients complicate comparing salinity measured at depths of a few meters to salinities retrieved using L‐band microwave radiometers such as SMOS and Aquarius. Therefore, understanding the spatial scales and the frequency of occurrence of these vertical gradients and the conditions under which they form will be important in understanding sea surface salinity maps provided by microwave radiometers. Salinity gradients in the near‐surface ocean were measured using a towed profiler that profiled salinity in the top two meters of the ocean with a minimum measurement depth of 0.1 m. In addition, an underway salinity profiling system was installed on the R/V Thomas G. Thompson. This measured near‐surface salinity at depths of 1 m and 2 m. Both the towed profiler and the underway system found the occurrence of negative salinity anomalies (i.e., salinity decreasing towards the surface) was correlated with the presence of rain. The magnitude of the anomaly (i.e. the difference between salinity at 0.1 m and the salinity at 0.26 m) was proportional to the cube of the rain rate for rain rate, R, greater than 6 mm h−1. From this, for R > 15 to 22 mm h−1, depending on the areal extent of the salinity anomalies, rain can cause scene‐averaged salinity offsets that are as large as the accuracy goal for Aquarius of 0.1 o/oo.
      PubDate: 2014-08-05T02:54:01.952519-05:
      DOI: 10.1002/2014JC009954
       
  • Observed wintertime tidal and subtidal currents over the continental shelf
           in the northern South China Sea
    • Authors: Ruixiang Li; Changsheng Chen, Huayong Xia, Robert C. Beardsley, Maochong Shi, Zhigang Lai, Huichan Lin, Yanqing Feng, Changjian Liu, Qichun Xu, Yang Ding, Yu Zhang
      Pages: n/a - n/a
      Abstract: Synthesis analyses were performed to examine characteristics of tidal and subtidal currents at eight mooring sites deployed over the northern South China Sea (NSCS) continental shelf in the 2006‐2007 and 2009‐2010 winters. Rotary spectra and harmonic analysis results showed that observed tidal currents in the NSCS were dominated by baroclinic diurnal tides with phases varying both vertically and horizontally. This feature was supported by the CC‐FVCOM results, which demonstrated that the diurnal tidal flow over this shelf was characterized by baroclinic Kelvin waves with vertical phase differences varying in different flow zones. The northeasterly wind‐induced southwestward flow prevailed over the NSCS shelf during winter, with episodic appearances of meso‐scale eddies and a bottom‐intensified buoyancy‐driven slope water intrusion. The moored current records captured a warm‐core anticyclonic eddy, which originated from the southwestern coast of Taiwan and propagated southwestward along the slope consistent with a combination of β‐plane and topographic Rossby waves. The eddy was surface‐intensified with a swirl speed of >50 cm/s and a vertical scale of ˜400 m. In absence of eddies and onshore deep slope water intrusion, the observed southwestward flow was highly coherent with the northeasterly wind stress. Observations did not support the existence of the permanent wintertime South China Sea Warm Current (SCSWC). The definition of SCSWC, which was based mainly on thermal wind calculations with assumed level of no motion at the bottom, needs to be interpreted with caution since the observed circulation over the NSCS shelf in winter included both barotropic and baroclinic components.
      PubDate: 2014-08-04T02:27:53.870112-05:
      DOI: 10.1002/2014JC009931
       
  • Feedbacks between ice cover, ocean stratification, and heat content in
           Ryder Bay, western Antarctic Peninsula
    • Authors: Hugh J. Venables; Michael P. Meredith
      Pages: n/a - n/a
      Abstract: A multi‐year, all‐season time series of water column physical properties and sea ice conditions in Ryder Bay, at the western Antarctic Peninsula (WAP), is used to assess the effects on the ocean of varying ice cover. Reduced ice cover leads to increased mixing and heat loss in the winter. The reduction in stratification persists into the following summer, preconditioning the water column to a greater vertical extent of surface‐driven mixing. This leads to an increased amount of heat from insolation being mixed down, affecting approximately the top 100m. The increased heat uptake in summer exceeds the heat lost the preceding winter, giving the initially counter‐intuitive effect that enhanced winter cooling generates warmer temperatures in the following summer and autumn. This process is therefore a positive feedback on sea ice, as reduced sea ice leads to increased heat content in the ocean the following autumn. It also causes increased winter atmospheric temperatures due to the increased winter heat loss from the ocean. In the deeper part of the water column, heat and carbon stored in the Circumpolar Deep Water (CDW) layer are released by deep mixing events. At these depths, conditions are restored by advection and vertical mixing on multi‐year timescales. In recent years, stronger deep mixing events in winter have led to a persistent reduction in CDW temperatures at the study site. Ocean glider data demonstrate the representativeness of these results across the wider region of Marguerite Bay, within which Ryder Bay is situated.
      PubDate: 2014-08-04T02:22:08.109135-05:
      DOI: 10.1002/2013JC009669
       
  • Vertical gradient correction for the oceanographic Atlas of the East Asian
           Seas
    • Authors: You‐Soon Chang; Hong‐Ryeol Shin
      Pages: n/a - n/a
      Abstract: Regional climatology around the East Asian Seas has been developed by an international collaboration between the National Oceanic Data Center and the Korea Oceanic Data Center. It provides reliable information on temperature and salinity climatological fields with high resolution (0.1 ° by 0.1 ° by 137 levels). However, there is a problem around near‐bottom areas where topographic change is steep and observations are not available near the bottom. This study resolves this problem using a vertical gradient correction method when the profile is statically unstable. The stability is determined based on the Brunt‐Väisälä frequency with individual temperature and salinity profiles. Topographic‐following mapping technique employing the potential vorticity constraint term is used to construct a vertical gradient database for the temperature and salinity at every grid point. The results show that the correction is effective for eliminating large erroneous vertical gradients around near‐bottom areas. In addition, we show the importance of the optimal length scale to construct a precise vertical gradient database in a particular area such as the northern shelf of Taiwan. We expect that our revised high resolution climatological mean fields will serve as important data for relevant studies around the East Asian Seas.
      PubDate: 2014-08-04T02:19:36.928533-05:
      DOI: 10.1002/2014JC009845
       
  • Interdecadal changes in snow depth on Arctic sea ice
    • Authors: Melinda A. Webster; Ignatius G. Rigor, Son V. Nghiem, Nathan T. Kurtz, Sinead L. Farrell, Donald K. Perovich, Matthew Sturm
      Pages: n/a - n/a
      Abstract: Snow plays a key role in the growth and decay of Arctic sea ice. In winter, it insulates sea ice from cold air temperatures, slowing sea ice growth. From spring into summer, the albedo of snow determines how much insolation is absorbed by the sea ice and underlying ocean, impacting ice melt processes. Knowledge of the contemporary snow depth distribution is essential for estimating sea ice thickness and volume, and for understanding and modeling sea ice thermodynamics in the changing Arctic. This study assesses spring snow depth distribution on Arctic sea ice using airborne radar observations from Operation IceBridge for 2009‐2013. Data were validated using coordinated in situ measurements taken in March 2012 during the BRomine, Ozone, and Mercury EXperiment (BROMEX) field campaign. We find a correlation of 0.59 and root‐mean‐square error of 5.8 cm between the airborne and in situ data. Using this relationship and IceBridge snow thickness products, we compared the recent results with data from the 1937, 1954‐1991 Soviet drifting ice stations. The comparison shows thinning of the snow pack, from 35.1 ± 9.4 cm to 22.2 ± 1.9 cm in the western Arctic, and from 32.8 ± 9.4 cm to 14.5 ± 1.9 cm in the Beaufort and Chukchi seas. These changes suggest a snow depth decline of 37 ± 29% in the western Arctic and 56 ± 33% in the Beaufort and Chukchi seas. Thinning is negatively correlated with the delayed onset of sea ice freeze‐up during autumn.
      PubDate: 2014-08-02T01:10:32.607412-05:
      DOI: 10.1002/2014JC009985
       
  • Validation of Aquarius sea surface salinity with in situ measurements from
           Argo floats and moored buoys
    • Authors: Wenqing Tang; Simon H. Yueh, Alexander G. Fore, Akiko Hayashi
      Pages: n/a - n/a
      Abstract: We validate sea surface salinity (SSS) retrieved from Aquarius instrument on SAC‐D satellite with in situ measurements by Argo floats and moored buoy arrays. We assess the error structure of three Aquarius SSS products: the standard product processed by Aquarius Data Processing System (ADPS) and two datasets produced at the Jet Propulsion Laboratory (JPL): the Combined Active‐Passive algorithm with and without rain correction, CAP and CAP_RC respectively. We examine the effect of various filters to prevent unreliable point retrievals from entering Level‐3 averaging, such as land or ice contamination, radio‐frequency‐interference (RFI), and cold water. Our analyses show that Aquarius SSS agrees well with Argo in a monthly average sense between 40°S and 40°N except in the Eastern Pacific Fresh Pool and Amazon River outflow. Buoy data within these regions show excellent agreement with Aquarius but have discrepancies with the Argo gridded products. Possible reasons include strong near surface stratification and sampling problems in Argo in regions with significant western boundary currents. We observe large root‐mean‐square (RMS) difference and systematic negative bias between ADPS and Argo in the tropical Indian Ocean and along the Southern Pacific Convergence Zone. Excluding these regions removes the suspicious seasonal peak in the monthly RMS difference between the Aquarius SSS products and Argo. Between 40°S and 40°N, the RMS difference for CAP is less than 0.22 PSU for all 28 months, CAP_RC has essentially met the monthly 0.2 PSU accuracy requirement, while that for ADPS fluctuates between 0.22 and 0.3 PSU.
      PubDate: 2014-08-02T00:49:13.424573-05:
      DOI: 10.1002/2014JC010101
       
  • Mesoscale variability and its seasonality in the Solomon and Coral Seas
    • Authors: Hristina G. Hristova; William S. Kessler, James C. McWilliams, M. Jeroen Molemaker
      Pages: n/a - n/a
      Abstract: High‐resolution (4 km) climatologically forced ocean model, validated by altimetry and glider data, is used to characterize the vertical and seasonal variations of mesoscale variability in the Solomon and Coral Seas. The highest eddy kinetic energy (EKE) in the southwest Pacific is found subsurface in the Gulf of Papua, at the depth of the low‐latitude western boundary current velocity core. Variability associated with the western boundary current, especially downstream of topographic obstacles, dominates the thermocline and intermediate level EKE. By contrast, surface EKE is generally enhanced in the southwest Pacific with a pronounced annual cycle that has a phase difference between small‐scale and large‐scale variability. Large mesoscale eddies account for most of the surface EKE and its annual modulation. The June maximum of surface EKE in the Solomon Sea and the December maximum in the Coral Sea can be accounted for by local instabilities of large‐scale currents. Small mesoscale eddies, predominantly cyclonic, are abundant in late winter (August to September), coinciding with the timing of deepest mixed layer and strongest vertical velocity. They contribute to the spatially uniform surface‐enhanced EKE over the top 100 m, not associated with the western boundary current. In the Coral Sea, small mesoscale eddies are generated mostly by open‐ocean surface baroclinic instabilities, while in the land‐bounded Solomon Sea near‐boundary instabilities and topographic generation are also important.
      PubDate: 2014-07-31T10:10:04.405758-05:
      DOI: 10.1002/2013JC009741
       
  • A new approach to discriminate dinoflagellate from diatom blooms from
           space in the East China Sea
    • Authors: Shaoling Shang; Jingyu Wu, Bangqin Huang, Gong Lin, Zhongping Lee, James Liu, Shaoping Shang
      Pages: n/a - n/a
      Abstract: Dinoflagellate and diatom blooms often occur in the East China Sea (ECS) during spring and summer. Some of the dinoflagellate blooms are toxic, resulting in widespread economic damage. In order to mitigate the negative impacts, remote‐sensing methods that can effectively and accurately discriminate between bloom types are demanded for early warning and continuous monitoring of bloom events at large scales. An in situ bio‐optical data set collected from diatom and dinoflagellate blooming waters indicates that the two types of blooms exhibited distinctive differences in the shapes and magnitudes of remote‐sensing reflectance (Rrs). The ratio of in situ measured Rrs spectral slopes at two spectral ranges (443–488 and 531–555 nm, bands available with the moderate resolution imaging spectrometer (MODIS) sensor), abbreviated as BI (representing bloom index), was found effective in differentiating dinoflagellates from diatoms. Reflectance model simulations, which were carried out using in situ and algal culture data as input, provided consistent results. A classification approach for separating dinoflagellate from diatom blooms in the ECS was then developed: When fluorescence line height (FLH) is doubled over the background level and total absorption coefficient at 443 nm ≥ 0.5 m−1, if 0.0
      PubDate: 2014-07-31T10:07:42.687015-05:
      DOI: 10.1002/2014JC009876
       
  • The surface mixed layer heat budget from mooring observations in the
           central Indian Ocean during Madden–Julian Oscillation events
    • Authors: Nan‐Hsun Chi; Ren‐Chieh Lien, Eric A. D'Asaro, Barry B. Ma
      Pages: n/a - n/a
      Abstract: The oceanic surface mixed layer heat budget in the central equatorial Indian Ocean is calculated from observations at two mooring sites (0°S 79°E and 1.5°S 79°E) during three active and calm phases of Madden–Julian Oscillation (MJO) events between September 2011 and January 2012. At both mooring locations, the surface mixed layer is generally heated during MJO calm phases. During MJO active phases at both mooring locations, the surface mixed layer is always cooled by the net surface heat flux and also sometimes by the turbulent heat flux at the bottom of the surface mixed layer. The turbulent heat flux at the bottom of the surface mixed layer, however, varies greatly among different MJO active phases and between the two mooring locations. A barrier layer exerts control on the turbulent heat flux at the base of the surface mixed layer; we quantify this barrier layer strength by a “barrier layer potential energy,” which depends on the thickness of the barrier layer, the thickness of the surface mixed layer, and the density stratification across the isothermal layer. During one observed MJO active phase, a strong turbulent heat flux into the mixed layer was diagnosed, despite the presence of a 10−20 m thick barrier layer. This was due to the strong shear across the barrier layer driven by the westerly winds, which provided sufficient available kinetic energy to erode the barrier layer. To better simulate and predict net surface heat fluxes and the MJO, models must estimate the oceanic barrier layer potential energy, background shear, stratification, and surface forcing accurately.
      PubDate: 2014-07-31T09:50:34.650752-05:
      DOI: 10.1002/2014JC010192
       
  • How much does heat content of the western tropical Pacific Ocean modulate
           the South China Sea summer monsoon onset in the last four decades?
    • Authors: Junqiao Feng; Dunxin Hu
      Pages: 4029 - 4044
      Abstract: The role of the western tropical Pacific Ocean heat content in the South China Sea summer monsoon (SCSSM) onset is investigated in the present paper, by using atmospheric data from NCEP and ocean subsurface temperature data from Japan Meteorology Agency. It is showed from the result that the heat content (HC) of the upper 400 m layer in the western tropical Pacific (WTP), especially in the region of (130°E–150°E, 0°N–14°N) in the last four decades, is a good predictive indicator for the SCSSM onset. Positive (negative) HC anomalies can induce a strong (weak) convection over the WTP, leading to stronger (weaker) Walker circulation and weaker (stronger) western North Pacific subtropical high (WNPSH) in the boreal spring. Consequently, the anomalous westerly (easterly) in the tropical Indian Ocean is favorable (unfavorable) for the airflow into the SCS and for an early (late) WNPSH retreat from the SCS and hence for an early (late) SCSSM onset. It is elucidated that the long‐term trend of SCSSM onset changes its sign around 1993/94 from decline to rise, which is responding and attributed to the WTP HC trend. During the period of 1971–1993, the WTP HC shows a significant decrease trend. In particular, a significant decline trend is observed in the HC difference between the WTP and western tropical Indian Ocean, which causes an easterly trend in the SCS and strengthened WNPSH trend, leading to a late onset trend of SCSSM. The situation is reverse after 1993/94.
      PubDate: 2014-07-01T11:19:46.491595-05:
      DOI: 10.1002/2013JC009683
       
  • Impact of Aquarius sea surface salinity observations on coupled forecasts
           for the tropical Indo‐Pacific Ocean
    • Authors: Eric Hackert; Antonio J. Busalacchi, Joaquim Ballabrera‐Poy
      Pages: 4045 - 4067
      Abstract: This study demonstrates the impact of gridded in situ and Aquarius sea surface salinity (SSS) on coupled forecasts for August 2011 until February 2014. Assimilation of all available subsurface temperature (ASSIM_Tz) is chosen as the baseline and an optimal interpolation of all in situ salinity (ASSIM_Tz_SSSIS) and Aquarius SSS (ASSIM_Tz_SSSAQ) are added in separate assimilation experiments. These three are then used to initialize coupled experiments. Including SSS generally improves NINO3 sea surface temperature anomaly validation. For ASSIM_Tz_SSSIS, correlation is improved after 7 months, but the root mean square error is degraded with respect to ASSIM_Tz after 5 months. On the other hand, assimilating Aquarius gives significant improvement versus ASSIM_Tz for all forecast lead times after 5 months. Analysis of the initialization differences with the baseline indicates that SSS assimilation results in an upwelling Rossby wave near the dateline. In the coupled model, this upwelling signal reflects at the western boundary eventually cooling the NINO3 region. For this period, coupled models tend to erroneously predict NINO3 warming, so SSS assimilation corrects this defect. Aquarius is more efficient at cooling the NINO3 region since it is relatively more salty in the eastern Pacific than in situ SSS which leads to increased mixing and upwelling which in turn sets up enhanced west‐to‐east SST gradient and intensified Bjerknes coupling. A final experiment that uses subsampled Aquarius at in situ locations infers that high‐density spatial sampling of Aquarius is the reason for the superior performance of Aquarius versus in situ SSS.
      PubDate: 2014-07-03T10:47:07.660237-05:
      DOI: 10.1002/2013JC009697
       
  • A comparative study of sea level reconstruction techniques using 20 years
           of satellite altimetry data
    • Authors: M. W. Strassburg; B. D. Hamlington, R. R. Leben, K.‐Y. Kim
      Pages: 4068 - 4082
      Abstract: Sea level reconstructions extend spatially dense data sets, such as those from satellite altimetry, by decomposing the data set into basis functions and fitting those functions to in situ tide gauge measurements with a longer temporal record. We compare and evaluate two methods for reconstructing sea level through an idealized study. The compared sea level reconstruction methods differ in the technique for calculating basis functions, i.e., empirical orthogonal functions (EOFs) versus cyclostationary EOFs (CSEOFs). Reconstructions are created using Archiving, Validation, and Interpretation of Satellite Oceanographic (AVISO) satellite altimetry data and synthetic tide gauges. Synthetic tide gauge records are simulated using historical distributions and real high‐frequency signal to test reconstruction skill. The CSEOF reconstructions show high skill in reproducing variations in global mean sea level (GMSL) and ocean climate indices, and are affected less by both limited tide gauge distribution and added high‐frequency tide gauge signal than EOF reconstructions. Typically, CSEOF reconstructions slightly underestimate sea level amplitudes while EOF reconstructions overestimate sea level amplitudes, in some cases, significantly. Both of these results are accentuated with decreasing quality of the synthetic tide gauge data set. Additionally, we investigate how the reconstructions differ when reconstructing with more of the variance retained in the basis functions. Increasing the variance explained by the basis functions from 70% to 90% reduces the efficacy of an EOF reconstruction to reproduce common ocean indices when noise is included in the tide gauge data sets. These results show that in the idealized comparative cases examined the CSEOF method of sea level reconstruction creates more robust reconstructions, especially when less than ideal tide gauge data are used.
      PubDate: 2014-07-03T11:05:19.167928-05:
      DOI: 10.1002/2014JC009893
       
  • The evolution of tides and tidal dissipation over the past 21,000 years
    • Authors: S.‐B. Wilmes; J. A. M. Green
      Pages: 4083 - 4100
      Abstract: The 120 m sea‐level drop during the Last Glacial Maximum (LGM; 18–22 kyr BP) had a profound impact on the global tides and lead to an increased tidal dissipation rate, especially in the North Atlantic. Here, we present new simulations of the evolution of the global tides from the LGM to present for the dominating diurnal and semidiurnal constituents. The simulations are undertaken in time slices spanning 500–1000 years. Due to uncertainties in the location of the grounding line of the Antarctic ice sheets during the last glacial, simulations are carried out for two different grounding line scenarios. Our results replicate previously reported enhancements in dissipation and amplitudes of the semidiurnal tide during LGM and subsequent deglaciation, and they provide a detailed picture of the large global changes in M2 tidal dynamics occurring over the deglaciation period. We show that Antarctic ice dynamics and the associated grounding line location have a large influence on global semidiurnal tides, whereas the diurnal tides mainly experience regional changes and are not impacted by grounding line shifts in Antarctica.
      PubDate: 2014-07-07T12:38:27.616777-05:
      DOI: 10.1002/2013JC009605
       
  • Modeled diurnally varying sea surface temperatures and their influence on
           surface heat fluxes
    • Authors: Rachel R. Weihs; Mark. A. Bourassa
      Pages: 4101 - 4123
      Abstract: A diurnal warming model is used to create a new data set of global, diurnally varying sea surface temperatures (dSSTs) and surface turbulent heat fluxes over a 5 year period. The magnitude of diurnal warming is primarily a function of low wind speed and net heat flux. Differences between each of the surface turbulent fluxes with and without a diurnally varying SST are examined on hourly, daily, and seasonal time scales. Over a 2 month period, maximum averaged diurnal warming is as large as 0.3°C, and latent heat flux is underestimated by as much as 8 W/m2 in the Indian Ocean. They also exceed roughly 0.7°C and 10 W/m2, respectively, up to 25% of the total daytime in the Atlantic. A best‐case approach validation shows the model overestimates peak warming and underestimates the duration of the cycle, though the average error is quite small. The model is tested under a variety of wind speed, solar radiation, and precipitation conditions to examine the impact of potential biases or error in the input data. To test the impact of a positive bias in the wind speeds, diurnal warming magnitudes are recomputed with an adjusted wind under near‐neutral conditions. Compared to the original data, diurnal warming can increase by as much as 1.5°C on an hourly scale but generally is
      PubDate: 2014-07-08T13:48:31.961869-05:
      DOI: 10.1002/2013JC009489
       
  • Subtropical surface layer salinity budget and the role of mesoscale
           turbulence
    • Authors: Julius Busecke; Arnold L. Gordon, Zhijin Li, Frederick M. Bingham, Jordi Font
      Pages: 4124 - 4140
      Abstract: The subtropical North Atlantic exhibits the saltiest surface waters of the open ocean. Eventually that water subducted from the surface and exported toward the Equator, as a subsurface salinity maximum (S‐max) forming the lower limb of the subtropical cell. Climatologically, the winter subtropical surface water, coinciding with the deepest mixed layer of ∼100 m, is saltier and colder than the S‐max. Towed CTD measurements in March/April 2013 (a component of the field program SPURS) within the North Atlantic subtropical surface salinity maximum reveal several relatively fresh, warm anomalies, which deviate strongly from climatological conditions. These features introduce a large amount of freshwater into the subtropical region, exceeding the amount introduced by local rain events. Observed scales and evolution of the features strongly suggest a connection to mesoscale dynamics. This is supported by high‐resolution regional model output, which produces an abundance of features that are similar in scale and structure to those observed. It is hypothesized that turbulent transport in the surface ocean is a crucial process for setting mixed layer characteristics, which spread into S‐max stratum. High variability in the EKE implies a high potential for interannual variability in the resulting S‐max water properties by ocean dynamics in addition to the variability caused by air sea fluxes. This has likely consequences to the meridional transport of heat and freshwater of the subtropical cell in the North Atlantic and to the larger‐scale ocean and climate system.
      PubDate: 2014-07-08T14:30:07.061624-05:
      DOI: 10.1002/2013JC009715
       
  • Snow depth of the Weddell and Bellingshausen sea ice covers from IceBridge
           surveys in 2010 and 2011: An examination
    • Authors: R. Kwok; T. Maksym
      Pages: 4141 - 4167
      Abstract: We examine the snow radar data from the Weddell and Bellingshausen Seas acquired by eight IceBridge (OIB) flightlines in October of 2010 and 2011. In snow depth retrieval, the sidelobes from the stronger scattering snow‐ice (s‐i) interfaces could be misidentified as returns from the weaker air‐snow (a‐s) interfaces. In this paper, we first introduce a retrieval procedure that accounts for the structure of the radar system impulse response followed by a survey of the snow depths in the Weddell and Bellingshausen Seas. Limitations and potential biases in our approach are discussed. Differences between snow depth estimates from a repeat survey of one Weddell Sea track separated by 12 days, without accounting for variability due to ice motion, is −0.7 ± 13.6 cm. Average snow depth is thicker in coastal northwestern Weddell and thins toward Cape Norvegia, a decrease of >30 cm. In the Bellingshausen, the thickest snow is found nearshore in both Octobers and is thickest next to the Abbot Ice Shelf. Snow depth is linearly related to freeboard when freeboards are low but diverge as the freeboard increases especially in the thicker/rougher ice of the western Weddell. We find correlations of 0.71–0.84 between snow depth and surface roughness suggesting preferential accumulation over deformed ice. Retrievals also seem to be related to radar backscatter through surface roughness. Snow depths reported here, generally higher than those from in situ records, suggest dissimilarities in sample populations. Implications of these differences on Antarctic sea ice thickness are discussed.
      PubDate: 2014-07-08T13:44:01.984879-05:
      DOI: 10.1002/2014JC009943
       
  • Calibration of sea ice dynamic parameters in an ocean‐sea ice model
           using an ensemble Kalman filter
    • Authors: F. Massonnet; H. Goosse, T. Fichefet, F. Counillon
      Pages: 4168 - 4184
      Abstract: The choice of parameter values is crucial in the course of sea ice model development, since parameters largely affect the modeled mean sea ice state. Manual tuning of parameters will soon become impractical, as sea ice models will likely include more parameters to calibrate, leading to an exponential increase of the number of possible combinations to test. Objective and automatic methods for parameter calibration are thus progressively called on to replace the traditional heuristic, “trial‐and‐error” recipes. Here a method for calibration of parameters based on the ensemble Kalman filter is implemented, tested and validated in the ocean‐sea ice model NEMO‐LIM3. Three dynamic parameters are calibrated: the ice strength parameter P*, the ocean‐sea ice drag parameter Cw, and the atmosphere‐sea ice drag parameter Ca. In twin, perfect‐model experiments, the default parameter values are retrieved within 1 year of simulation. Using 2007–2012 real sea ice drift data, the calibration of the ice strength parameter P* and the oceanic drag parameter Cw improves clearly the Arctic sea ice drift properties. It is found that the estimation of the atmospheric drag Ca is not necessary if P* and Cw are already estimated. The large reduction in the sea ice speed bias with calibrated parameters comes with a slight overestimation of the winter sea ice areal export through Fram Strait and a slight improvement in the sea ice thickness distribution. Overall, the estimation of parameters with the ensemble Kalman filter represents an encouraging alternative to manual tuning for ocean‐sea ice models.
      PubDate: 2014-07-08T13:57:18.710133-05:
      DOI: 10.1002/2013JC009705
       
  • Standing wave modes observed in the South China Sea deep basin
    • Authors: Quanan Zheng; Jianyu Hu, Benlu Zhu, Ying Feng, Young‐Heon Jo, Zhenyu Sun, Jia Zhu, Hongyang Lin, Junyi Li, Ying Xu
      Pages: 4185 - 4199
      Abstract: This study deals with standing wave or seiche events using cruise observations, satellite altimeter data, and theoretical analysis. Cruise missions in summer 2007 and 2009 detected internal oscillation signals in the South China Sea (SCS) deep basin. The signals have average wavelengths of 320 and 390 km and the maximum amplitudes of 50–100 m at layers 500–700 m and 1500–1700 m. Satellite altimeter sea level anomaly (SLA) images and the second intrinsic mode function (IMF2) images derived from the empirical mode decomposition (EMD) analysis show that the observed internal oscillations are a portion of 2‐D seiche modes, which lasted for at least 2 weeks. We recognize that the observed internal oscillation signals represent seiche modes H5,3 and H5,1 derived from a rectangular model ocean basin with a uniform depth, a west‐east length of 1000 km and a north‐south width of 800 km. Statistical analysis of standing wave modes H4,0, H5,1, and H5,3 with the average wavelength of 500, 390, and 320 km indicates that from 1993 to 2012 (1045 weeks), total 94 events with total temporal coverage of 218 weeks are affirmed. The total occurrence frequency is 20.9%. Histograms of annual distributions of seiche events and timespans show an interannual variability of about 9 years, with peak years 1993, 1994, 1998, 2001, and 2011. While monthly distributions show an intraseasonal variability double‐peaked in May and October, transit periods of East Asia monsoon in the SCS.
      PubDate: 2014-07-08T14:52:47.554898-05:
      DOI: 10.1002/2014JC009957
       
  • Estimation of the barrier layer thickness in the Indian Ocean using
           Aquarius Salinity
    • Authors: Clifford S. Felton; Bulusu Subrahmanyam, V. S. N. Murty, Jay F. Shriver
      Pages: 4200 - 4213
      Abstract: Monthly barrier layer thickness (BLT) estimates are derived from satellite measurements using a multilinear regression model (MRM) within the Indian Ocean. Sea surface salinity (SSS) from the recently launched Soil Moisture and Ocean Salinity (SMOS) and Aquarius SAC‐D salinity missions are utilized to estimate the BLT. The MRM relates BLT to sea surface salinity (SSS), sea surface temperature (SST), and sea surface height anomalies (SSHA). Three regions where the BLT variability is most rigorous are selected to evaluate the performance of the MRM for 2012; the Southeast Arabian Sea (SEAS), Bay of Bengal (BoB), and Eastern Equatorial Indian Ocean (EEIO). The MRM derived BLT estimates are compared to gridded Argo and Hybrid Coordinate Ocean Model (HYCOM) BLTs. It is shown that different mechanisms are important for sustaining the BLT variability in each of the selected regions. Sensitivity tests show that SSS is the primary driver of the BLT within the MRM. Results suggest that salinity measurements obtained from Aquarius and SMOS can be useful for tracking and predicting the BLT in the Indian Ocean. Largest MRM errors occur along coastlines and near islands where land contamination skews the satellite SSS retrievals. The BLT evolution during 2012, as well as the advantages and disadvantages of the current model are discussed. BLT estimations using HYCOM simulations display large errors that are related to model layer structure and the selected BLT methodology.
      PubDate: 2014-07-08T13:43:02.866167-05:
      DOI: 10.1002/2013JC009759
       
  • Ocean variability contributing to basal melt rate near the ice front of
           Ross Ice Shelf, Antarctica
    • Authors: Isabella B. Arzeno; Robert C. Beardsley, Richard Limeburner, Breck Owens, Laurie Padman, Scott R. Springer, Craig L. Stewart, Michael J. M. Williams
      Pages: 4214 - 4233
      Abstract: Basal melting of ice shelves is an important, but poorly understood, cause of Antarctic ice sheet mass loss and freshwater production. We use data from two moorings deployed through Ross Ice Shelf, ∼6 and ∼16 km south of the ice front east of Ross Island, and numerical models to show how the basal melting rate near the ice front depends on sub‐ice‐shelf ocean variability. The moorings measured water velocity, conductivity, and temperature for ∼2 months starting in late November 2010. About half of the current velocity variance was due to tides, predominantly diurnal components, with the remainder due to subtidal oscillations with periods of a few days. Subtidal variability was dominated by barotropic currents that were large until mid‐December and significantly reduced afterward. Subtidal currents were correlated between moorings but uncorrelated with local winds, suggesting the presence of waves or eddies that may be associated with the abrupt change in water column thickness and strong hydrographic gradients at the ice front. Estimated melt rate was ∼1.2 ± 0.5 m a−1 at each site during the deployment period, consistent with measured trends in ice surface elevation from GPS time series. The models predicted similar annual‐averaged melt rates with a strong annual cycle related to seasonal provision of warm water to the ice base. These results show that accurately modeling the high spatial and temporal ocean variability close to the ice‐shelf front is critical to predicting time‐dependent and mean values of meltwater production and ice‐shelf thinning.
      PubDate: 2014-07-09T12:34:18.479348-05:
      DOI: 10.1002/2014JC009792
       
  • Pathways of the Agulhas waters poleward of 29°S
    • Authors: Jinbo Wang; Matthew R. Mazloff, Sarah T. Gille
      Pages: 4234 - 4250
      Abstract: Passive tracers are advected in a Southern Ocean State Estimate (SOSE) to map the pathways of Agulhas waters, with a focus on determining where the Agulhas waters intrude into the Antarctic Circumpolar Current (ACC). Results show that Agulhas waters spread into all three ocean basins within 3 years of release. After leaving the African continent, the mean Agulhas water pathway tilts northwest toward the South Atlantic and southeast toward the ACC. The majority (from 60% to 100% depending on specific water mass) of the Agulhas waters stay in the South Indian Ocean north of the Sub‐Antarctic Front. From 10 to 28% enters the South Atlantic Ocean through the boundary current along the southern tip of South Africa and via Agulhas rings in the retroflection region. Up to 12% of intermediate depth Agulhas waters enter the ACC. Most of the tracer transport into the ACC occurs just downstream of the Kerguelen Plateau, which clearly demonstrates the importance of topography in elevating cross‐frontal exchange. Agulhas waters also contribute to Sub‐Antarctic Mode Water formation in the Southeast Indian Ocean by lateral advection. The surface Agulhas waters are preconditioned by strong surface buoyancy loss before turning into mode water, while the intermediate Agulhas waters are advected to the mode water formation region along isopycnals before being drawn into the mixed layer.
      PubDate: 2014-07-09T12:34:23.552228-05:
      DOI: 10.1002/2014JC010049
       
  • The nascent Kuroshio of Lamon Bay
    • Authors: Arnold L. Gordon; Pierre Flament, Cesar Villanoy, Luca Centurioni
      Pages: 4251 - 4263
      Abstract: A northward flowing current, emanating from the North Equatorial Current (NEC) bifurcation at the Philippine margin, enters Lamon Bay along Luzon's eastern coast. There the NEC tropical water masses merge with subtropical water of the western North Pacific to form the Kuroshio. A northward flowing western boundary current is first observed near 16.5°N, marking the initiation of the Kuroshio. The current feeding into the nascent Kuroshio of Lamon Bay is bracketed by an anticyclonic dipole to its northeast and a cyclonic dipole to its southwest. Ship‐based observational programs in the spring seasons of 2011 and 2012 detect a shift of the Lamon Bay thermohaline stratification with marked enrichment of NEC tropical thermocline water in 2012 relative to a dominant western North Pacific subtropical stratification of 2011. Temperature‐salinity time series from moorings spanning the two ship‐based observations identify the timing of the transition as December 2011. The NEC bifurcation was further south in May 2012 than in May 2011. We suggest that the more southern bifurcation in May 2012 induced increased NEC thermocline water injection into Lamon Bay and nascent Kuroshio, increasing the linkage of the western North Pacific subtropical and tropical thermoclines. This connection was reduced in May 2011 as the NEC bifurcation shifted into a more northerly position and western North Pacific subtropical thermocline dominated Lamon Bay stratification.
      PubDate: 2014-07-10T12:51:12.752646-05:
      DOI: 10.1002/2014JC009882
       
  • Semidiurnal tidal currents in the deep ocean near the East Pacific Rise
           between 9° and 10°N
    • Authors: Xinfeng Liang
      Pages: 4264 - 4277
      Abstract: Spatial and temporal variations of the semidiurnal tidal currents, especially the baroclinic components, in the deep ocean near a segment of the East Pacific Rise (EPR) are examined using observations from a set of current meter moorings. Over the ridge crest, the baroclinic semidiurnal tidal current is dominated by the zonal component and is coherent along the observed ridge segment. In the direction across the ridge crest, the baroclinic semidiurnal tidal current is not coherent and its magnitude decreases away from the ridge crest. Vertically, the baroclinic semidiurnal tidal current covaries in a few hundred meters near the seafloor. Both the semidiurnal kinetic energy (KE) and shear show significant subinertial temporal variations. By comparing with background forcings, the author found that the subinertial variation of the semidiurnal tides over the ridge crest is related to both the spring‐neap cycles and the eddy‐induced low‐frequency flows in the deep ocean, particularly their cross‐ridge components. The observation that the baroclinic tidal currents at the axial stations flowing perpendicularly to the ridge crest suggests that the baroclinic semidiurnal tides at the axial stations are generated locally. It is therefore probable that the subinertial variation of the baroclinic semidiurnal tides near the EPR is due to the eddy‐modulated internal tide generation. Since the mesoscale eddies in the eastern tropical Pacific vary with the state of the climate, the observed eddy‐modulated internal tide generation connects climate change and variability to the physical and biogeochemical dynamics in the deep ocean and implies an unexplored feedback mechanism potentially affecting the climate system.
      PubDate: 2014-07-10T12:37:07.914739-05:
      DOI: 10.1002/2013JC009522
       
  • Surface circulation in the Gulf of California in summer from surface
           drifters and satellite images (2004–2006)
    • Authors: M. F. Lavín; Rubén Castro, Emilio Beier, Carlos Cabrera, Victor M. Godínez, A. Amador‐Buenrostro
      Pages: 4278 - 4290
      Abstract: Surface drifters released in the Gulf of California between June 2004 and August 2006 are used to describe the surface circulation in late spring and summer. In the June to September mean, there was a poleward coastal current on the shelf and slope of the mainland side of the Gulf, with mean speed ∼0.3 m/s; it reached the northern Gulf and joined the cyclonic circulation typical of this zone in summer. In the western half of the southern Gulf, the drifters presented recirculating currents that are due to mesoscale eddies that appear to dominate the surface circulation in summer. In June 2004, the coastal current presented an enhancement event with mean speed around 0.60 m/s and maximum ∼0.80 m/s. It took ∼20 days for a particular drifter to travel the 1000 km from the Gulf entrance to the head. This strengthening of the coastal current was apparent in chlorophyll a and SST satellite images, the drifters following closely the intrusion of warm, chlorophyll‐poor surface water from outside the Gulf. The drifters and the satellite images suggest that the current‐enhancement event lasted less than a month. This mesoscale event was linked with a mesoscale remote forcing in the tropical Pacific coast and with a mesoscale local forcing of the wind. These events seem to occur every year, and are probably important in carrying organisms and properties from the entrance to the whole length of the Gulf.
      PubDate: 2014-07-12T06:23:31.520902-05:
      DOI: 10.1002/2013JC009345
       
  • Shelf water and chlorophyll export from the Hatteras slope and outer shelf
    • Authors: James H. Churchill; Glen G. Gawarkiewicz
      Pages: 4291 - 4304
      Abstract: Using high‐resolution data acquired from a shipboard ADCP and a towed Scanfish equipped with a CTD and fluorometer, we examine the properties and transport of Middle Atlantic Bight (MAB) shelf water over a region of the Hatteras outer shelf and slope where MAB shelf water is commonly deflected offshore and entrained into the Gulf Stream. The data are from a period in early August 2004 when the seasonal pycnocline of the MAB is well developed and situated over a weakly stratified, near‐bottom shelf water mass commonly referred to as the cold pool. Our data show chlorophyll‐rich cold pool water carried rapidly southward over the slope and outer shelf, at a rate of up to 60 cm s−1, as part of the shelf‐edge frontal jet. This southward transport of chlorophyll‐rich cold pool water is shunted eastward and entrained into the Gulf Stream. However, the latitude band over which this export occurs varies significantly over the 7 day course of our study, a variation which is linked to an order 50 km shift in the latitude at which the Gulf Stream separates from the continental margin. The coupled rapid translation of the Gulf Stream frontal separation and the cold pool export zone is likely to have a significant impact on the movement and accumulation of biogenic material over the Hatteras slope and rise.
      PubDate: 2014-07-16T10:20:19.828531-05:
      DOI: 10.1002/2014JC009809
       
  • Ocean subsurface studies with the CALIPSO spaceborne lidar
    • Authors: Xiaomei Lu; Yongxiang Hu, Charles Trepte, Shan Zeng, James H. Churnside
      Pages: 4305 - 4317
      Abstract: The primary objective of the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission is to study the climate impact of clouds and aerosols in the atmosphere. However, recent studies have demonstrated that CALIPSO also collects information about the ocean subsurface. The objective of this study is to estimate the ocean subsurface backscatter from CALIPSO lidar measurements. The effects of the lidar receiver's transient response on the attenuated backscatter were first removed in order to obtain the correct attenuated backscatter profile. The empirical relationship between sea surface lidar backscatter and wind speed was used to estimate the theoretical ocean surface backscatter. Then the two‐way atmospheric transmittance was estimated as the ratio between the corrected ocean surface backscatter and the theoretical one. The ocean subsurface backscatter was finally derived from the subsurface attenuated backscatter divided by the two‐way atmospheric transmittance. Significant relationships between integrated subsurface backscatter and chlorophyll‐a concentration and between integrated subsurface backscatter and particulate organic carbon were found, which indicate a potential use of CALIPSO lidar to estimate global chlorophyll‐a and particulate organic carbon concentrations.
      PubDate: 2014-07-16T10:32:25.066959-05:
      DOI: 10.1002/2014JC009970
       
  • Southern Ocean jets and how to find them: Improving and comparing common
           jet detection methods
    • Authors: Christopher C. Chapman
      Pages: 4318 - 4339
      Abstract: This study undertakes a detailed comparison of different methods used for detecting and tracking oceanic jets in the Southern Ocean. The methods under consideration are the gradient thresholding method, the probability density function (PDF) method, and the contour method. Some weaknesses of the gradient thresholding method are discussed and an enhancement (the WHOSE method), based on techniques from signal processing, is proposed. The WHOSE method is then compared to the other three methods. Quantitative comparison is undertaken using synthetic sea‐surface height fields. The WHOSE method and the contour method are found to perform well even in the presence of a strong eddy field. In contrast, the standard gradient thresholding and PDF methods only perform well in high signal‐to‐noise ratio situations. The WHOSE, PDF, and the contour methods are then applied to data from the eddy‐resolving Ocean General Circulation Model for the Earth Simulator. While the three methods are in broad agreement on the location of the main ACC jets, the nature of the jet fields they produce differ. In particular, the WHOSE method reveals a fine‐scale jet field with complex braiding behavior. It is argued that this fine‐scale jet field may affect the calculation of eddy diffusivities. Finally, recommendations based on this study are made. The WHOSE and gradient thresholding methods are more suitable for the study of jets as localized strong currents, useful for studies of tracer fluxes. The contour and PDF methods are recommended for studies linking jets to hydrographic fronts.
      PubDate: 2014-07-16T10:45:25.449486-05:
      DOI: 10.1002/2014JC009810
       
  • Extensive hydrogen supersaturations in the western South Atlantic Ocean
           suggest substantial underestimation of nitrogen fixation
    • Authors: Robert M. Moore; Markus Kienast, Michael Fraser, John J. Cullen, Curtis Deutsch, Stephanie Dutkiewicz, Michael J. Follows, Christopher J. Somes
      Pages: 4340 - 4350
      Abstract: The nitrogen cycle is fundamental to Earth's biogeochemistry. Yet major uncertainties of quantification remain, particularly regarding the global oceanic nitrogen fixation rate. Hydrogen is produced during nitrogen fixation and will become supersaturated in surface waters if there is net release from diazotrophs. Ocean surveys of hydrogen supersaturation thus have the potential to illustrate the spatial and temporal distribution of nitrogen fixation and to guide the far more onerous but quantitative methods for measuring it. Here we present the first transect of high resolution measurements of hydrogen supersaturations in surface waters along a meridional 10,000 km cruise track through the Atlantic. We compare measured saturations with published measurements of nitrogen fixation rates and also with model‐derived values. If the primary source of excess hydrogen is nitrogen fixation and has a hydrogen release ratio similar to Trichodesmium, our hydrogen measurements would point to similar rates of fixation in the North and South Atlantic, roughly consistent with modeled fixation rates but not with measured rates, which are lower in the south. Possible explanations would include any substantial nitrogen fixation by newly discovered diazotrophs, particularly any having a hydrogen release ratio similar to or exceeding that of Trichodesmium; undersampling of nitrogen fixation south of the equator related to excessive focus on Trichodesmium; and methodological shortcomings of nitrogen fixation techniques that cause a bias toward colonial diazotrophs relative to unicellular forms. Alternatively, our data are affected by an unknown hydrogen source that is greater in the southern half of the cruise track than the northern.
      PubDate: 2014-07-16T11:55:20.416386-05:
      DOI: 10.1002/2014JC010017
       
  • Long‐term trends in the East Australian Current separation latitude
           and eddy driven transport
    • Authors: P. Cetina‐Heredia; M. Roughan, E. van Sebille, M. A. Coleman
      Pages: 4351 - 4366
      Abstract: An observed warming of the Tasman Sea in recent decades has been linked to a poleward shift of the maximum wind stress curl, and a strengthening of the poleward flow along the coast of southeastern Australia. However, changes in the East Australian Current (EAC) separation latitude, as well as in the contribution of the EAC, the EAC extension and its eddy field to the total southward transport due to such a strengthening remain unknown. This study uses 30 years (1980–2010) of the Ocean Forecast for the Earth Simulator (OFES) sea surface height and velocity outputs to obtain a three decade long‐time series of (i) the EAC separation latitude, (ii) the southward transport along the coast of southeastern Australia (28°S–39°S), and (iii) the southward transport across the EAC separation latitude. A Lagrangian approach is implemented and the spin parameter Ω is used to provide a quantitative distinction between the transports occurring outside and inside (cyclonic and anticyclonic) eddies. Significant positive trends of the low pass southward transports indicate that the intensification of the poleward flow has occurred both within the EAC and in the EAC extension. In addition, a significant increase in southward transport inside and outside eddies is found. Importantly, the contribution of eddy driven transport has a large temporal variability and shows a sharp increase from 2005 onward. Finally our results show that the EAC has not penetrated further south but it has separated more frequently at the southernmost latitudes within the region where it typically turns eastward.
      PubDate: 2014-07-16T11:52:49.805696-05:
      DOI: 10.1002/2014JC010071
       
  • Cross‐shore tracer exchange between the surfzone and
           inner‐shelf
    • Authors: Kai Hally‐Rosendahl; Falk Feddersen, R. T. Guza
      Pages: 4367 - 4388
      Abstract: Cross‐shore tracer exchange between the surfzone and inner‐shelf is examined using temperature and dye measurements at an approximately alongshore‐uniform beach. An alongshore‐oriented plume is created by releasing dye continuously for 4.5 h in a surfzone alongshore current. The plume is sampled for 13 h from the release point to 700 m downstream, between the shoreline and 250 m offshore (6 m water depth). Within the surfzone (≤2 m depth), water is relatively warm, and dye is vertically well mixed. On the inner‐shelf (3–6 m depth), alongshore currents are weak, and elevated temperature and dye co‐occur in 25–50 m wide alongshore patches. Within the patches, dye is approximately depth‐uniform in the warm upper 3 m where thermal stratification is weak, but decreases rapidly below 3 m with a strong thermocline. Dye and temperature vertical gradients are correlated, and dye is not observed below 18 °C. The observations and a model indicate that, just seaward of the surfzone, thermal stratification inhibits vertical mixing to magnitudes similar to those in the ocean interior. Similar surfzone and inner‐shelf mean alongshore dye dilution rates are consistent with inner‐shelf dye properties being determined by local cross‐shore advection. The alongshore‐patchy and warm inner‐shelf dye is ejected from the surfzone by transient rip currents. Estimated Stokes drift driven cross‐shore exchange is small. The transient rip current driven depth‐normalized heat flux out of the surfzone has magnitude similar to those of larger‐scale shelf processes. Dye recycling, from the inner‐shelf back to the surfzone, is suggested by relatively long surfzone dye residence times.
      PubDate: 2014-07-17T08:27:12.145058-05:
      DOI: 10.1002/2013JC009722
       
  • Mechanisms of the disappearance of sea surface temperature fronts in the
           subtropical North Pacific Ocean
    • Authors: Chunhua Qiu; Hiroshi Kawamura, Huabin Mao, Jiaxue Wu
      Pages: 4389 - 4398
      Abstract: The disappearance mechanisms of subtropical sea surface temperature (SST) fronts occurring from May to August were examined quantitatively using a simple mixed‐layer model. Weekly 2.5° data sets were matched up between satellite and in situ observations, including cloud‐free SST from Advanced Microwave Scanning Radiometer‐Earth Observing System (AMSR‐E) and Global Temperature and Salinity Profile Program (GTSPP) data. A 1.5 mixed‐layer model used in this study assumed that the temporal variation of the SST gradient was controlled by the resultant effect among the net heat flux, temperature advection (including Ekman and geostrophic), and the temperature entrainment at the bottom of the mixed layer. The net heat flux was found to provide a dominant contribution to the weakening of the SST front (decreasing SST gradient), while the temperature advection and the bottom entrainment were relatively weak. Decomposition of the net heat flux revealed that the meridional gradient of the latent heat flux is a direct factor in the weakening of the SST front, while the shortwave radiation could have indirect effects. The meridional gradient of the latent heat flux is induced by southerly winds, which in turn causes the weakening and disappearance of the SST front. Comparison of weekly and monthly averaged SST gradient modeling results with in situ observations demonstrated that the weekly SST gradient in the model agrees closely with AMSR‐E observations, but there was a large difference between the monthly SST gradient in the model and in the observations.
      PubDate: 2014-07-18T13:36:47.042097-05:
      DOI: 10.1002/2014JC010142
       
  • Historical wave height trends in the South and East China Seas,
           1911–2010
    • Authors: Lingli Wu; Xiaolan L. Wang, Yang Feng
      Pages: 4399 - 4409
      Abstract: This study reconstructs 6 hourly significant wave heights (Hs) in the South and East China Seas for the period 1871–2010, using the Twentieth Century Reanalysis ensemble of mean sea level pressure (SLP) fields and a multivariate regression model to represent the Hs‐SLP relationship in each study area. The regression model was calibrated and validated using the ERA‐Interim reanalysis of Hs and SLP for the period 1981–2010. These reconstructions were found to reproduce reasonably well the seasonal mean and maximum Hs climates as represented by the ERA40 and ERA‐Interim wave reanalyses. For each study area, an ensemble of 56 members of 6 hourly Hs was reconstructed for each grid point. The regional mean series of the ensemble mean of the reconstructed consecutive monthly mean Hs was tested for temporal homogeneity, which identified a few discontinuities in the pre‐1946 period and led to the exclusion of the reconstructed Hs for 1871–1910 from trend analysis (due to data uncertainty and inhomogeneity). Each 6 hourly Hs time series for the period 1911–2010 was homogenized for the identified discontinuities, before being used to derive annual and seasonal mean and maximum Hs for trend analysis. The trend analysis results show that, in both study areas, the 1911–2010 wave height trends are dominantly negative, with the exception that the seasonal maximum significant wave heights seem to have increased in summer and spring in the central South China Sea and in summer in the East China Sea.
      PubDate: 2014-07-18T13:43:19.723092-05:
      DOI: 10.1002/2014JC010087
       
  • ITCZ and ENSO pacing on East Asian winter monsoon variation during the
           Holocene: Sedimentological evidence from the Okinawa Trough
    • Authors: Xufeng Zheng; Anchun Li, Shiming Wan, Fuqing Jiang, Shuh Ji Kao, Cody Johnson
      Pages: 4410 - 4429
      Abstract: Deep‐sea fan sediments provide an excellent geological archive for paleoenvironment reconstruction. Grain size, clay mineral and elemental (Ti, Fe, Ca) compositions were measured for a core retrieved from a submarine fan in the Okinawa Trough. Varimax‐rotated Principal Component Analysis (V‐PCA) on time‐evolution of grain size spectrum reveals that, since the Holocene, sediment was transported mainly by the benthic nepheloid layer (33%) and upper layers (33%) which is driven by the East Asian winter monsoon (EAWM). The intensification of the Kuroshio Current during the Holocene, masks the fluvial signal of the summer monsoon and obstructs clay minerals derived from the Yellow River, a major contributor prior to 12 ka BP. A new grain size index (GSI), which represents the EAWM well, exhibits a negative correlation with the δ18O record in Dongge Cave, China during the Holocene when sea level was relatively steady. This anticorrelation suggests the southward migration of the Intertropical Convergence Zone (ITCZ). The consistency among our records and rainfall records in Peru, Ti counts in the Cariaco Basin, monsoon records in Oman and the averaged summer insolation pattern at 30°N further support the ITCZ's impact on monsoon systems globally. Cross‐Correlation Analyses for GSI and log(Ti/Ca) against δ18O record in Dongge Cave reveal a decoupling between the East Asian winter and summer monsoon during 5500–2500 cal yr BP, with greater complexity in the last 2500 years. This can be attributed to exacerbated ENSO mode fluctuations and possibly anthropogenic interference superimposed on insolation and ITCZ forcing.
      PubDate: 2014-07-21T09:00:39.872357-05:
      DOI: 10.1002/2013JC009603
       
  • Seasonal migration of the Yellow Sea Bottom Cold Water
    • Authors: Bin Wang; Naoki Hirose, Boonsoon Kang, Katsumi Takayama
      Pages: 4430 - 4443
      Abstract: The three‐dimensional motion of the Yellow Sea Bottom Cold Water (YSBCW) and the relevant dynamical factors are studied using a regional circulation model and the two‐way Lagrangian particle tracking method (PTM). The simulated results are in good agreement with hydrographic observations. The trajectories of the modeled particles show that the subsurface cold heavy water mass from the northern part of the Yellow Sea gradually sinks into deeper layers along the western slope of the Yellow Sea trough with a southward movement from spring to summer. The cold water mass gradually gathers speed from early March to July or August, and eventually reaches its southernmost location in late September or early October. Furthermore, sensitivity experiments demonstrate that tide‐induced residual currents under baroclinic conditions are the dominant factor driving deep circulation during summertime in the Yellow Sea. The summer southerly wind and strong surface solar radiation are the secondary factors influencing the southward migration. This study also proposes an improved delimitation for the YSBCW based on temperature statistics in the central basin (deeper than 40 m) between 35°N and 39°N in March with an increase in rate of approximately 0.7°C/month, which is more appropriate than the constants of the 8°C or 10°C isotherms frequently used.
      PubDate: 2014-07-21T08:40:29.803864-05:
      DOI: 10.1002/2014JC009873
       
  • Zonal momentum budget along the equator in the Indian Ocean from a
           high‐resolution ocean general circulation model
    • Authors: Motoki Nagura; Michael J. McPhaden
      Pages: 4444 - 4461
      Abstract: This study examines the zonal momentum budget along the equator in the Indian Ocean in a high‐resolution ocean general circulation model. Wyrtki Jets, wind‐driven eastward flows in the upper 100 m that appear typically twice per year in boreal spring and fall, are a prominent feature of the ocean circulation in this region. Our results indicate that nonlinearity associated with these jets is an important element of the zonal momentum budget, with wind driven eastward momentum advected downward into the thermocline. This advection results in annually averaged zonal currents that flow against the zonal pressure gradient in the upper 200 m, such that there is no mean subsurface undercurrent in the Indian Ocean as there is in the Pacific and Atlantic Oceans. Zonal momentum is further distributed along the equator by zonal advection, with eastward flow substantially enhanced in the eastern basin relative to the western basin. Meridional advection, though generally weak, tends to decelerate surface eastward flow along the equator. These results contrast with those from previous idealized wind‐forced model experiments that primarily emphasized the importance of vertical momentum advection. Also, beyond semiannual period fluctuations, significant momentum advection results from a broad range of interacting processes, spanning intraseasonal to interannual time scales. We conclude that proper simulation of zonal flows along the equator in the Indian Ocean, including their climatically relevant impacts on the mass and heat balance, requires accurate representation of nonlinearities that derive from a broad range of time and space scales.
      PubDate: 2014-07-21T14:11:56.157489-05:
      DOI: 10.1002/2014JC009895
       
  • Transient modulation of Kuroshio upper layer flow by directly impinging
           typhoon Morakot in east of Taiwan in 2009
    • Authors: Zhe‐Wen Zheng; Quanan Zheng, Chia‐Ying Lee, Ganesh Gopalakrishnan
      Pages: 4462 - 4473
      Abstract: This study deals with the modulation of the Kuroshio upper layer flow (KULF) in response to the passage of Typhoon Morakot in 2009, using Regional Oceanic Modeling System (ROMS) and in situ measurements from Argos drifters and Argo floats. The analysis of the simulated current fields near the typhoon track revealed an intermittency phenomenon of the KULF, which was almost shut down for at least 6 hours. The process begun 2 days prior to the approach of typhoon center due to blockage of the KULF by the steadily northerly winds, and lasted for more than 2 days, simultaneously shifting the Kuroshio main stream (KMS) path. When the Morakot gradually moved closely to the Kuroshio, the KMS shifted vertically from the surface layer to deeper layer of 50 – 100 m depth, and the maximum current speed in the KMS decreased from more than 1.3 m s−1 to less than 1.1 m s−1. When the Morakot center approached about 100 km to the original position of the Kuroshio, the KULF spread eastward for 1.5 degrees at 24°N. When the Morakot center moved to the original position of the KMS, the Kuroshio abruptly rushed with a maximum speed near 1.4 m s−1. Meanwhile, an offshore cool jet originating from southeastern tip of Taiwan was generated and extended northward along the Kuroshio. In the cool jet, the lowest temperature reached about 5°C lower than the ambient waters. Modeled current variations and the cool jet during the Morakot passage were validated by in situ measurements.
      PubDate: 2014-07-22T11:13:55.302629-05:
      DOI: 10.1002/2014JC010090
       
  • Impacts of typhoon megi (2010) on the South China Sea
    • Authors: Dong Shan Ko; Shenn‐Yu Chao, Chun‐Chieh Wu, I‐I Lin
      Pages: 4474 - 4489
      Abstract: In October 2010, typhoon Megi induced a profound cold wake of size 800 km by 500 km with sea surface temperature cooling of 8°C in the South China Sea (SCS). More interestingly, the cold wake shifted from the often rightward bias to both sides of the typhoon track and moved to left in a few days. Using satellite data, in situ measurements and numerical modeling based on the East Asian Seas Nowcast/Forecast System (EASNFS), we performed detailed investigations. To obtain realistic typhoon‐strength atmospheric forcing, the EASNFS applied typhoon‐resolving Weather Research and Forecasting (WRF) model wind field blended with global weather forecast winds from the U.S. Navy Operational Global Atmospheric Prediction System (NOGAPS). In addition to the already known impacts from the slow typhoon translation speed and shallow pre‐exiting ocean thermocline, we found the importance of the unique geographical setting of the SCS and the NE monsoon. As the event happened in late October, NE monsoon already started and contributed to the southwestward ambient surface current. Together with the topographicβ effect, the cold wake shifted westward to the left of Megi's track. It was also found that Megi expelled waters away from the SCS and manifested as a gush of internal Kelvin wave exporting waters through the Luzon Strait. The consequential sea level depression lasted and presented a favorable condition for cold dome development. Fission of the north‐south elongated cold dome resulted afterward and produced two cold eddies that dissipated slowly thereafter.
      PubDate: 2014-07-22T13:09:29.125478-05:
      DOI: 10.1002/2013JC009785
       
  • Satellite views of the episodic terrestrial material transport to the
           southern Okinawa Trough driven by typhoon
    • Authors: Xianqiang He; Yan Bai, Chen‐Tung Arthur Chen, Yi‐Chia Hsin, Chau‐Ron Wu, Weidong Zhai, Zhiliang Liu, Fang Gong
      Pages: 4490 - 4504
      Abstract: Using satellite‐derived water transparency (alias Secchi depth) images, we found clear signals of terrestrial material transport to the southern Okinawa Trough triggered by the Typhoon Morakot in August 2009. Three sources were identified: one is from the eastern coast of Taiwan, another is from the western coast of Taiwan, and the other is from the coast of mainland China. Carried by northward flows, typhoon‐triggered terrestrial materials from both sides of Taiwan's coasts were transported to the region northeast of Taiwan. Moreover, the terrestrial material from the coast of mainland China could cross the Taiwan Strait and be further transported to the region northeast of Taiwan. These typhoon‐induced terrestrial materials off northeastern Taiwan could then be transported to the southern Okinawa Trough along the western edge of the Kuroshio. In addition to the particulate terrestrial material transported, nutrients might also be transported to the Kuroshio main stream. A significant phytoplankton bloom was observed along the Kuroshio path for about 300 km off northeast of Taiwan. Our results indicate that episodic cyclone‐driven terrestrial material transport could be another source of mud in the southern Okinawa Trough.
      PubDate: 2014-07-22T13:10:56.738761-05:
      DOI: 10.1002/2014JC009872
       
  • Summer primary productivity and phytoplankton community composition driven
           by different hydrographic structures in the East/Japan Sea and the Western
           Subarctic Pacific
    • Authors: Jung Hyun Kwak; Sang Heon Lee, Jeomshik Hwang, Young‐Sang Suh, Hyun Park, Kyung‐Il Chang, Kyung‐Ryul Kim, Chang‐Keun Kang
      Pages: 4505 - 4519
      Abstract: The East/Japan Sea (EJS) is a highly productive marginal sea in the northwest Pacific, consisting of three basins (Ulleung Basin: UB, Yamato Basin: YB, and Japan Basin: JB). To find causes of the reportedly high primary productivity in summer in the EJS, especially in the UB, we measured primary productivity, phytoplankton composition, and other environmental variables. The water column was strongly stratified in the EJS compared with the Western Subarctic Pacific (WSP). Integrated primary productivity was two times higher in the EJS (612 mg C m−2 d−1) than in the WSP (291 mg C m−2 d−1). The vertical distributions of physicochemical and biological factors confirmed that production in the subsurface chlorophyll maximum layer in the study regions was an important factor regulating primary productivity within the water column. While picoplankton (
      PubDate: 2014-07-23T09:03:04.906483-05:
      DOI: 10.1002/2014JC009874
       
  • Inversion of submesoscale patterns from a high‐resolution Solomon
           Sea model: Feasibility assessment
    • Authors: Lucile Gaultier; Bughsin' Djath, Jacques Verron, Jean‐Michel Brankart, Pierre Brasseur, Angelique Melet
      Pages: 4520 - 4541
      Abstract: A high‐resolution realistic numerical model of the Solomon Sea, which exhibits a high level of variability at mesoscales and submesoscales, is used to explore new avenues for data assimilation. Image data assimilation represents a powerful methodology to integrate information from high‐resolution observations such as satellite sea surface temperature or chlorophyll, or high‐resolution altimetric sea surface height that will be observed in the forthcoming SWOT mission. The present study investigates the feasibility and accuracy of the inversion of the dynamical submesoscale information contained in high‐resolution images of sea surface temperature (SST) or salinity (SSS) to improve the estimation of oceanic surface currents. The inversion method is tested in the context of twin experiments, with SST and SSS data provided by a model of the Solomon Sea. For that purpose, synthetic tracer images are built by binarizing the norm of the gradient of SST, SSS or spiciness. The binarized tracer images are compared to the dynamical image which is derived from the Finite‐Size Lyapunov Exponents. The adjustment of the dynamical image to the tracer image provides the optimal correction to be applied on the surface velocity field. The method is evaluated by comparing the result of the inversion to the reference model solution. The feasibility of the inversion of various images (SST, SSS, both SST and SSS or spiciness) is explored on two small areas of the Solomon Sea. We show that errors in the surface velocity field can be substantially reduced through the inversion of tracer images.
      PubDate: 2014-07-23T12:15:48.067309-05:
      DOI: 10.1002/2013JC009660
       
  • Hurricane Sandy storm surges observed by HY‐2A satellite altimetry
           and tide gauges
    • Authors: Nan Chen; Guoqi Han, Jingsong Yang, Dake Chen
      Pages: 4542 - 4548
      Abstract: Hurricane Sandy made landfall to the northeast of Atlantic City, New Jersey at 23:30 UTC on 29 October 2012 and caused large storm surges and devastating flooding along the New Jersey and New York coasts. Here we combine sea surface height measurements from the HaiYang‐2A (HY‐2A) satellite altimeter with coastal tide‐gauge data to study the features of the Hurricane Sandy storm surges. The HY‐2A altimeter captured the cross‐shelf profile of surge at the time of Sandy's peak surge, with a surge magnitude of about 1.83 m at the coast and a cross‐shelf decaying scale of 68 km. The altimetric surge magnitude agrees approximately with tide‐gauge estimate of 1.73 m at nearby Montauk. Further analysis suggests that continental shelf waves were generated during the passage of Sandy. The continental shelf wave observed by altimetry has a propagating speed of 6.5 m/s. The post landfall free shelf wave at Atlantic City observed by tide gauges has a propagating phase speed of 6.8 m/s and cross‐shelf e‐folding scale of 75 km. In contrast, the post landfall sea level oscillation at Montauk is not associated with a continental shelf wave. The study indicates that satellite altimetry is capable of observing and useful for understanding features of storm surges, complementing existing coastal tide gauges.
      PubDate: 2014-07-24T11:13:10.170918-05:
      DOI: 10.1002/2013JC009782
       
  • Variability of sea‐ice in the northern Weddell Sea during the 20th
           century
    • Authors: E. J. Murphy; A. Clarke, N. J. Abram, J. Turner
      Pages: 4549 - 4572
      Abstract: The record of winter fast‐ice in the South Orkney Islands, northern Weddell Sea, Antarctica, is over a century long and provides the longest observational record of sea‐ice variability in the Southern Hemisphere. Here we present analyses of the series of fast‐ice formation and breakout dates from 1903 to 2008. We show that over the satellite era (post‐1979), the timing of both final autumn formation and complete spring breakout of fast‐ice is representative of the regional sea‐ice concentrations (SIC) in the northern Weddell Sea, and associated with atmospheric conditions in the Amundsen Sea region to the west of the Antarctic Peninsula. Variation in the fast‐ice breakout date is influenced by the intensity of the westerly/north‐westerly winds associated with the Southern Annular Mode (SAM). In contrast, the date of ice formation displays correlations with regional oceanic and sea‐ice conditions over the previous 18 months, which indicate a preconditioning during the previous summer and winter, and exhibits variability associated with variation in tropical Pacific sea‐surface temperature (i.e., the El Niño‐Southern Oscillation, ENSO). A reduction in fast‐ice duration at the South Orkney Islands around the 1950s was associated with both later formation and earlier breakout. However, there were marked changes in variability (with periodicities of 3–5, 7–9, and 20 years) in each of the series and in their relationships with ENSO and SAM, indicating the need for caution in interpreting changes in ice conditions based on shorter‐term satellite series.
      PubDate: 2014-07-28T09:30:26.981126-05:
      DOI: 10.1002/2013JC009511
       
  • Inferring deep ocean tidal energy dissipation from the global
           high‐resolution data‐assimilative HAMTIDE model
    • Authors: E. Taguchi; D. Stammer, W. Zahel
      Pages: 4573 - 4592
      Abstract: Energy dissipation rates of eight major semidiurnal and diurnal tidal constituents are inferred using a barotropic data assimilative tide model with 7.5' spatial resolution. Dynamical residuals and dynamical residual power, estimated through the assimilation procedure as a correction for model uncertainties, constitute an essential contribution to deep‐ocean and shallow‐seas dissipation rates. Resulting total dissipation rates amount to 3.54 TW, of which 2.44 TW (69%) are accounted for by the M2 component alone. Concentrating on the deep ocean (> 1000 m water depth), the dissipation by all eight constituents amounts to 1.42 TW, and 0.93 TW just for the M2 component. These results are higher by 19% and 38% than dissipation rates estimated by Egbert and Ray (2003), respectively. Of the globally dissipated 2.44TWM2 energy, 1.24 TW are estimated to arise from bottom drag and eddy turbulence, 1.20 TW from residual power. For just the deep ocean, respective numbers amount to 0.10 TW for bottom drag and eddy turbulence, 1.07 TW for barotropic‐to‐baroclinic energy conversion due to the internal wave drag. Interpreting negative residual power −0.24 TW as a potential tidal energy source, a net surface‐to‐internal tide M2 energy conversion would amount to 0.83 TW.
      PubDate: 2014-07-28T09:42:27.784065-05:
      DOI: 10.1002/2013JC009766
       
  • Twentieth century sea surface temperature and salinity variations at Timor
           inferred from paired coral δ18O and Sr/Ca measurements
    • Authors: Sri Yudawati Cahyarini; Miriam Pfeiffer, Intan Suci Nurhati, Edvin Aldrian, Wolf‐Christian Dullo, Steffen Hetzinger
      Pages: 4593 - 4604
      Abstract: The Indonesian Throughflow (ITF), which represents the global ocean circulation connecting the Pacific Warm Pool to the Indian Ocean, strongly influences the Indo‐Pacific climate. ITF monitoring since the late 1990s using mooring buoys have provided insights on seasonal and interannual time scales. However, the absence of longer records limits our perspective on its evolution over the past century. Here, we present sea surface temperature (SST) and salinity (SSS) proxy records from Timor Island located at the ITF exit passage via paired coral δ18O and Sr/Ca measurements spanning the period 1914–2004. These high‐resolution proxy based climate data of the last century highlights improvements and cautions when interpreting paleoclimate records of the Indonesian region. If the seasonality of SST and SSS is not perfectly in phase, the application of coral Sr/Ca thermometry improves SST reconstructions compared to estimates based on coral δ18O only. Our records also underline the importance of ocean advection besides rainfall on local SSS in the region. Although the El Niño/Southern Oscillation (ENSO) causes larger anomalies relative to the Indian Ocean Dipole (IOD), Timor coral‐based SST and SSS records robustly correlate with IOD on interannual time scales, whereas ENSO only modifies Timor SST. Similarly, Timor SST and SSS are strongly linked to Indian Ocean decadal‐scale variations that appear to lead Timor oceanographic conditions by about 1.6–2 years. Our study sheds new light on the complex signatures of Indo‐Pacific climate modes on SST and SSS dynamics of the ITF.
      PubDate: 2014-07-31T09:24:48.108186-05:
      DOI: 10.1002/2013JC009594
       
  • Coastal cape and canyon effects on wind‐driven upwelling in northern
           Taiwan Strait
    • Authors: Zhaoyun Chen; Xiao‐Hai Yan, Yuwu Jiang
      Pages: 4605 - 4625
      Abstract: A combination of observations and numerical model is used to reveal the upwelling features and mechanisms in the northern Taiwan Strait during summer. In situ data give evidence of the upwelling in the form of thermocline tilting upward onshore. The remote sensing data show a strip of upwelling in the coastal region, which occurs more than half a summer. The upwelling probability map indicates there are two upwelling cores, one located downstream of Pingtan Island formed as cape effect and the other over the coastal canyon off the Sansha Bay. Remote sensing data and numerical model results suggest that the southerly wind plays a key role in shaping this upwelling strip, while the tides regulate the upwelling location through tidal mixing effect in the shallow water region, especially lee of Pingtan Island. Further numerical experiments using idealized cape and coastal canyon topography show that vertical velocity is intensified downstream of the cape and canyon. The vorticity equation shows that relative vorticity change along a streamline and frictional diffusion of vorticity are responsible for the vertical velocity off the cape and within and around the canyon. According to the conservation of potential vorticity, the variation of relative vorticity along a streamline over irregular topography, e.g., cape and canyon, is the main mechanism for the two upwelling cores in the northern Taiwan Strait.
      PubDate: 2014-07-31T09:35:40.523367-05:
      DOI: 10.1002/2014JC009831
       
  • Validation of Aquarius sea surface salinity with Argo: Analysis of error
           due to depth of measurement and vertical salinity stratification
    • Authors: Robert Drucker; Stephen C. Riser
      Pages: 4626 - 4637
      Abstract: We validate Aquarius sea surface salinities against Argo 1–7 m salinities for the period 27 August 2011 through 1 October 2013, a period of ∼25 months. The validation consists of comparison of 20,149 collocated Argo/Aquarius data pairs. The global mean of the difference between Aquarius and Argo salinities  is +0.018 PSU, with latitudinal variations of approximately ±0.2 PSU. The standard deviation of this difference ranges from about 0.3 PSU in the tropics to 0.7 PSU at high latitudes. We discuss errors due to geographic and temporal displacement and depth of measurement and show that these are insignificant for global validation of Aquarius. In particular, we use NASA's Tropical Rainfall Measuring Mission 3B42 product to analyze the contribution of vertical salinity stratification in the ocean to validation error. This salinity stratification is important for understanding the hydrological cycle of the oceans and has been cited as a potential source of error in validation of satellite‐based sea surface salinity because of the ∼1–7 m minimum depth of most Argo profiles. We show evidence of heavy precipitation events causing stratification greater than 0.1 PSU and lasting ∼2–8 h, but note that these events occur infrequently and contribute less than 0.03 PSU bias in the tropics and 0.025 PSU globally. It is demonstrated that the existing global Argo array provides sufficient data for large‐scale validation of Aquarius sea surface salinity. We also discuss the potential to exploit large salinity gradients in the upper mixed layer as a signature of rain in the tropical ocean.
      PubDate: 2014-07-31T09:46:01.318192-05:
      DOI: 10.1002/2014JC010045
       
 
 
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