JournalTOCs

Ocean Dynamics
Journal Prestige (SJR): 0.789

Citation Impact (citeScore): 2
Number of Followers: 6

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1616-7228 - ISSN (Online) 1616-7341
Published by Springer-Verlag

[2469 journals]

Potential sea-level rise effects on the hydrodynamics and transport
processes in Hudson–Raritan Estuary, NY–NJ
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  Abstract: Abstract The climatic change has led to the sea-level rise (SLR), which is expected to continue based on the current industrial and human activities. Previous studies indicated that most of estuaries which are of great environmental and economic importance are likely to be affected by SLR. Thus, understanding the hydrodynamic behavior of estuaries under SLR is necessary. This study focuses on the Hudson–Raritan Estuary (HRE) which has been predicted to undergo relatively high SLR rates. The complex geometry of HRE including bays connected by tidal straits along with the multi-tidal inlets necessitates more investigation of the complex hydrodynamics in this region. Here, we studied the potential effect of the projected SLR scenarios to the year 2100 on salinity distribution and transport processes during the dry and wet seasons using the three-dimensional hydrodynamic model (EFDC). The model is validated by the field observations of water level, current velocity, salinity, and temperature distribution in the estuary. A comprehensive analysis of the current sea level (base) and the three projected scenarios of 0.35, 0.55, and 1.05 m rise revealed an increase of the average salt content and the stratification intensity as the water level rises in tributaries, with higher increase rates during the wet season. In addition, the results showed that the water exchange between different regions through tidal straits enhances under SLR scenarios. Furthermore, it was found that SLR amplifies the residual flows in tributaries and suppresses it along Ambrose and Raritan Bay Channels. Finally, our results showed that under SLR, the residence time increases in the tributaries due to changes in estuarine circulation. Conversely, the residence time decreases slightly in downstream of the estuary because of vertical mixing enhancement induced by decrease in stratification. The results provide beneficial information for understanding the response of transport process and circulation to SLR in the Hudson–Raritan Estuary.
  PubDate: 2022-05-07
Propagation of barotropic Kelvin waves around Antarctica
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  Abstract: Abstract Barotropic (i.e., depth-uniform) coastal oceanic Kelvin waves can provide rapid teleconnections from climate and weather events in one location to remote regions of the globe. Studies suggest that barotropic Kelvin waves observed around Antarctica may provide a mechanism for rapidly propagating circulation anomalies around the continent, with implications for continental shelf temperatures along the West Antarctic Peninsula and thus Antarctic ice mass loss rates. However, how the propagation of Kelvin waves around Antarctica is influenced by features such as coastal geometry and variations in bathymetry remains poorly understood. Here we study the propagation of barotropic Antarctic Kelvin waves using a range of idealized model simulations. Using a single-layer linear shallow water model with 1∘ horizontal resolution, we gradually add complexity of continental configuration, realistic bathymetry, variable planetary rotation, and forcing scenarios, to isolate sources and sinks of wave energy and the mechanisms responsible. We find that approximately 75% of sub-inertial barotropic Kelvin wave energy is scattered away from Antarctica as other waves in one circumnavigation of the continent, due mostly to interactions with bathymetry. Super-inertial barotropic Kelvin waves lose nearly 95% of their energy in one circumpolar loop, due to interactions with both coastal geometry and bathymetry. These results help to explain why only sustained signals of low-frequency resonant barotropic Kelvin waves have been observed around Antarctica, and contribute to our understanding of the role of rapid, oceanic teleconnections in climate.
  PubDate: 2022-05-05
Physical drivers of pelagic sargassum bloom interannual variability in the
Central West Atlantic over 2010–2020
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  Abstract: Abstract Since 2011, unprecedented pelagic sargassum seaweed blooms have occurred across the tropical North Atlantic, with severe socioeconomic impacts for coastal populations. To investigate the role of physical drivers in post-2010 sargassum blooms in the Central West Atlantic (CWA), conditions are examined across the wider tropical North Atlantic, using ocean and atmospheric re-analyses and satellite-derived datasets. Of particular consequence for the growth and drift of sargassum are patterns and seasonality of winds and currents. Results suggest that in years of exceptionally large sargassum blooms (2015, 2018), the Intertropical Convergence Zone (ITCZ), an area of maximum wind convergence where sargassum naturally accumulates, shifted southward, towards nutrient-rich waters of the Amazon River plume and the equatorial upwelling zone further stimulating sargassum growth. These changes are associated with modes of natural variability in the tropical Atlantic, notably a negative phase of the Atlantic Meridional Mode (AMM) in 2015 and 2018, and a positive phase of the Atlantic Niño in 2018. Negative AMM in these 2 years is also associated with stronger trade winds and enhanced northwest Africa upwelling, probably resulting in stronger southwestward nutrient transport into the eastern part of CWA. Moreover, in contrast with most years, important secondary winter blooms took place in both 2015 and 2018 in the northern part of CWA, associated with excessive wind-driven equatorial upwelling and anomalously strong northwestward nutrient transport.
  PubDate: 2022-05-04
Sedimentological data-driven bottom friction parameter estimation in
modelling Bristol Channel tidal dynamics
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  Abstract: Abstract Accurately representing the bottom friction effect is a significant challenge in numerical tidal models. Bottom friction effects are commonly defined via parameter estimation techniques. However, the bottom friction coefficient (BFC) can be related to the roughness of the sea bed. Therefore, sedimentological data can be beneficial in estimating BFCs. Taking the Bristol Channel and Severn Estuary as a case study, we perform a number of BFC parameter estimation experiments, utilising sedimentological data in a variety of ways. Model performance is explored through the results of each parameter estimation experiment, including applications to tidal range and tidal stream resource assessment. We find that theoretically derived sediment-based BFCs are in most cases detrimental to model performance. However, good performance is obtained by retaining the spatial information provided by the sedimentological data in the formulation of the parameter estimation experiment; the spatially varying BFC can be represented as a piecewise-constant field following the spatial distribution of the observed sediment types. By solving the resulting low-dimensional parameter estimation problem, we obtain good model performance as measured against tide gauge data. This approach appears well suited to modelling tidal range energy resource, which is of particular interest in the case study region. However, the applicability of this approach for tidal stream resource assessment is limited, since modelled tidal currents exhibit a strong localised response to the BFC; the use of piecewise-constant (and therefore discontinuous) BFCs is found to be detrimental to model performance for tidal currents.
  PubDate: 2022-04-27
Evaluation of mixing schemes in the HYbrid Coordinate Ocean Model (HYCOM)
in the tropical Indian Ocean
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  Abstract: Abstract The performance of three different mixing schemes implemented in the HYbrid Coordinate Ocean Model (HYCOM), namely, K-Profile Parameterization (KPP), Goddard Institute of Space Sciences (GISS), and Mellor-Yamada (MY), is evaluated with respect to their simulation of upper ocean properties such as SST and mixed layer depth (MLD) in the tropical Indian Ocean. We analyzed interannual global HYCOM simulations without either data assimilation or SST relaxation for the recent period of 2012–2018. Our analysis shows that simulated SST is generally warmer by 1–2 °C than the observations and that there is little difference in SST between simulations by these different mixing schemes except in specific locations. The simulated MLD, irrespective of the choice of mixing scheme, in general, is deeper than observations in the tropical Indian Ocean, although this MLD bias varies with time and location depending on the mixing scheme choice. Furthermore, none of the mixing schemes analyzed consistently simulated the MLD with minimal error at all locations and for all year in the tropical Indian Ocean. Differences in the amount of cross-equatorial heat transport and the estimated thermal eddy diffusivity, especially in the eastern Indian Ocean are noted. A heat budget analysis signifies the importance of the vertical diffusive heat flux and points to the role of positive shortwave flux bias in determining the warm SST bias. The MLD biases in the simulations are not due to possible wind stress forcing errors. In addition, the wind stress-MLD relationship is stronger for these schemes compared to the observations. The KPP simulated MLD is slightly sensitive to the critical bulk Richardson number and changing it from its default value of 0.25 to 0.15 can marginally improve MLD simulation in the Indian Ocean.
  PubDate: 2022-04-15
Changes in tidal asymmetry in the German Wadden Sea
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  Abstract: Abstract The recent morphological development of the German Wadden Sea (North Sea, Europe) has been characterized by expanding intertidal flats and deepening, narrowing tidal channels at declining subtidal volume. This study analyzes the effect of these changes on tidal asymmetry, based on numerical modeling with high-resolution bathymetry data, and discusses possible adaptations of the import and export behavior in intertidal systems. As common descriptors of tidal asymmetry may show a high spatial variability in bathymetrically complex intertidal systems, we develop a novel subregion averaging approach for a more robust trend estimation. Our data reveal a statistically significant decrease in flood and flood current duration in the period from 1996 to 2016 resulting in declining flood dominance or enhanced ebb dominance in most tidal basins of the German Wadden Sea. Mean and peak current asymmetry also indicate significant decreases in mean flood current magnitude. We relate decreasing flood dominance mostly to local bathymetric volume changes rather than tidal amplitude. However, it appears likely that the sum of local effects facilitates the adaptation of regional tidal dynamics which affects especially the northern German Bight. This regional shift is explained by the deceleration of rising tides due to increased friction on laterally expanded intertidal flats and decreased subtidal channel volume. The decrease in flood or increase in ebb dominance, respectively, indicates that the recent trend of sediment accretion in Wadden Sea areas may cease soon.
  PubDate: 2022-04-12
Seasonal and spatial variations in spice generation in the South Indian
Ocean salinity maxima
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  Abstract: Abstract Spiciness anomalies generated in the salinity maxima region are important for several atmospheric and oceanic factors as they move along the geostrophic pathways towards the equator and resurface. Subduction and injection mechanisms are responsible for the spiciness generation in the South Indian Ocean (SIO) salinity maxima region. Using ECCO data from 1992 to 2017, here we study monthly variations of spiciness associated with both of these mechanisms in the SIO salinity maxima region. Using a Lagrangian approach, we estimated the monthly evolution of the subduction rate. A maximum subduction rate of 35–38 m/mon occurs during September and consequently decreases towards the end of the year. The effective subduction rate in the salinity maxima region shows the dominance of temporal induction (mixed layer tendency) term, with a sharp gradient in total subduction rate along the 30∘S associated with large mixed layer depth variation. Further, a high Turner angle (> 66∘) to the south of 30∘S confirms the generation of spiciness by injection mechanism. We found that the decrease in mixed layer salt (MLS) coincides with the increase in salinity below the mixed layer. To explore the significance of MLS changes in spiciness generation, we further addressed the monthly evolution of spiciness through MLS budget. Our results suggest that the entrainment and meridional advection terms are key to monthly variations in MLS changes and thus the spiciness.
  PubDate: 2022-04-08
High-resolution downscaling of CMEMS oceanographic reanalysis in the area
of the Tuscany Archipelago (Italy)
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  Abstract: Abstract A native nested configuration of the ROMS model is implemented on the marine area between the Ligurian and Tyrrhenian basins, which includes the Tuscany Archipelago. Initial and boundary conditions are provided by the CMEMS Mediterranean Sea Physical Reanalysis product (1/16°), feeding the parent ROMS model (BLUE, 1/72°), in which a high-resolution grid is nested (PURPLE, 1/216°). Atmospheric forcing comes from a downscaled version of ERA5 reanalysis. Temperature and salinity profiles from gliders and floats, and HF-radar-derived surface currents, are compared to model outputs within the high-resolution area for the whole year 2017. Results show the downscaling procedure is able to reduce model errors for temperature profiles, whereas errors in salinity profiles remain comparable. However, the downscaled model cannot recover large errors inherited from the parent one. The mean bias largest values found in both temperature and salinity profiles may be explained by a model underestimation of the depth of stable stratification limit with respect to field data. Errors in surface currents are reduced for the downscaled dynamics and appear to be uncorrelated to the original CMEMS product, being surface dynamics less affected by initial condition than by atmospheric forcing. A simple scalar metric, to quantify the error in the surface current vector fields from observations and models, is proposed. The novel metric allows to better quantify the improvement gained by the downscaling procedure.
  PubDate: 2022-03-17
Spatial variability of currents associated with different cold fronts
along the southern Texas coast
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  Abstract: Abstract Wind and current measurements collected between February and March 2017 at three sites in the southern Texas coast were used to determine along-shelf flow variations induced by episodic synoptic-scale cold fronts and to quantify the relevant terms in the inner-shelf along-shelf momentum budget. Inner-shelf flows were wind-driven, but significant along-shelf variations existed between the northern and southern sites. Cold fronts induced downcoast mean, surface and bottom flows along the study site. Strongest downcoast flows occurred in the surface in the northern and southern ends, while these were weaker in the center. Flows averaged over a longer period of time showed the presence of a convergence zone in the central site, off Port Mansfield. Spatial variations of the along-shelf wind stress were the main cause for the flow convergence in the surface layer at the central site. Most intense surface flows occurred in the north (along-shelf wind speeds of > 10 ms−1), less affected by southeasterly (upcoast) Trade winds. Low-energy cold fronts (along-shelf wind speeds of < 10 ms−1) were unable to completely reverse the wind direction towards the south (downcoast) in the southern and central sites, due to the stronger influence of Trade winds. Surface wind stress and pressure gradients were the dominant terms in the along-shelf momentum budget, while the bottom stress and Coriolis terms were considered negligible. The wind-stress term was dominant in the north, while pressure gradients associated with local sea-level responses to the wind forcing were dominant in the southern site. This study highlights the importance of pre-front wind characteristics in spatial variations of the along-shelf flow during cold fronts.
  PubDate: 2022-03-16
Analysis of the annual mean energy cycle of the Black Sea circulation for
the climatic, basin-scale and eddy regimes
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  Abstract: Abstract This work presents an analysis of the Lorenz energy cycles derived from the simulation results of the Black Sea circulation. Three numerical experiments are carried out based on an eddy-resolving z-model with a horizontal resolution of 1.6 km and taking into account different atmospheric forcing: climatic data, 2011, and 2016. The annual mean circulation for these time intervals reflects the climatic basin-scale, basin-scale (2011) and eddy (2016) regimes. Main differences between experiments are (1) the intensity of atmospheric fluxes and (2) SST assimilation and direct consideration of shortwave radiation in the realistic forcing simulations. The Lorenz energy cycles components are considered in detail. Some common features between climatic and realistic energetics are detected. The annual mean energy conversion from mean motion to the eddy is observed for all circulation regimes. Also, it is obtained that the annual mean buoyancy work enhances the mean current for all experiments, which evidences about maintaining of isopycnal surfaces slope such that a condition for converting available potential energy into kinetic energy is realized. Qualitative difference in the energy transfers for the climatic calculation, basin-scale and eddy regimes is revealed. Conversion from the eddy kinetic energy to eddy available potential energy is observed only for climatic circulation. For the basin-scale circulation the eddy kinetic energy is increasing mainly due to the transfer from the mean current kinetic energy through barotropic instability. The growth of the eddy kinetic energy for the eddy regime is provided by conversion of the available potential energy due to baroclinic instability.
  PubDate: 2022-03-15
Stability analysis of finite amplitude interfacial waves in a two-layer
fluid in the presence of depth uniform current
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  Abstract: Abstract A fourth-order nonlinear evolution equation of interfacial progressive waves in two-layer fluids of finite depths is derived in the case when there is a depth uniform current in the lower fluid. Based on this equation, stability analysis is then determined of a plane progressive wave. Discourses are provided for both air–water interface and a Boussinesq approximation. Graphs are plotted for maximum growth rate of instability as a function of wave steepness. Two-dimensional instability regions in the perturbed wavenumber plane and three-dimensional contour plots of growth rate of instability are also drawn. Starting from third-order nonlinear Schrödinger equation in one spatial dimension, we have additionally found the effect of depth uniform current on Peregrine breather. The present fourth-order analysis shows significant deviation from the third-order analysis and produces results consistent with the exact numerical results.
  PubDate: 2022-03-04
  DOI: 10.1007/s10236-022-01503-1
The impact of remote temperature anomalies on the strength and position of
the Gulf Stream and on coastal sea level variability: a model sensitivity
study
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  Abstract: Abstract A regional numerical ocean model of the Gulf Stream (GS) and the US East Coast was used to conduct sensitivity experiments of the dynamic response to temperature anomalies originated at different Atlantic locations. In a series of experiments, temperature anomalies were injected into the model domain through inflow boundary conditions at either the Florida Current (FC), the Slope Current (SC), or the Sargasso Sea (SS), while holding all other inflows/outflows unchanged. The strong currents and meso-scale variability of the GS system result in fast transport of anomalies throughout the model domain and immediate response within days. During a period of 60 days, remote temperature anomalies of ± 2 °C induced about 5–12 cm change in coastal sea level, about 0.5–1.0 ms−1 change in velocity, and about 30–50 km shift in the GS position, and a significant increase in kinetic energy of the whole GS system. Warm anomaly entering into the GS from the south through the FC had the strongest impact, strengthening the GS and temporally lowering coastal sea level by as much as ~ 10 cm, compared with coastal sea level drop of ~ 2–3 cm when the same warm anomaly was coming from the SS. Cold or warm anomalies coming from the north through the SC caused a large shift in the GS path, which moved onshore in the Mid-Atlantic Bight (MAB) and offshore in the South Atlantic Bight (SAB). Observations taken in 2017 when 3 hurricanes disrupted the GS flow show similar links between temperature anomalies, the GS, and coastal sea level, as in the idealized model simulations. The results demonstrated how temperature anomalies due to storms or uneven climate warming can cause variations on the coast and increased kinetic energy near western boundary currents. Since coastal sea level is positively correlated with temperature, but negatively correlated with the strength of the GS, the non-linear combination of the two factors can result in unexpected spatiotemporal variability in coastal sea level. The study provides better understanding of how remote signals affect the coast.
  PubDate: 2022-02-25
  DOI: 10.1007/s10236-022-01500-4
Time-dependent plume front positioning and its dynamics coupled with
seasonal river efflux
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  Abstract: Abstract The time-dependent plume front positioning with respect to different tidal phases and its dynamics coupled with seasonal river efflux on the shelf off Kochi, southwest coast of India, was investigated using Finite Volume Community Ocean Model (FVCOM). This region is linked with a monsoonal estuary, characterised by a mixed semidiurnal tide (1 m) and exhibited features of small and large-scale plumes. The interaction between river efflux and tidal phases modulates plume fronts on the shelf, where the density gradients are fortified or weakened by mixing dynamics. Even though the heavy river efflux in the summer monsoon imparts significant momentum on the shelf, the range of frontal fluctuation was curtailed to 2 km by strong monsoon currents. During the transient phase of the season (fall inter-monsoon), the tidal forcings on plume positioning overwhelm the shelf currents, such that the plume front fluctuates between 5 and 17 km from the inlet (range increasing to ~12 km). During low tides, the region near the inlets was almost homogenised (Rd<1), while during high tides, the region became more stratified due to the transport of high saline coastal water towards the inlet and also by the decreasing kinetic energy (Richardson number, Rd>1). The location of frontal zones suitable for the propagation of internal waves (Froude number, F≤ 1) changes as a result of the competition between river efflux and tide-topography interaction. Strong stratified plume frontal regions with high Brunt Vaisala Frequency (N) could be active zones of internal wave generation when the flow decelerates from supercritical to subcritical during the summer monsoon. The release of accumulated potential energy during the transition from high tide to low tide generates the hydraulic jump. This disturbance in the Nmax zone together with F ≤ 1 condition (supercritical flow changed to subcritical flow) favours the generation and propagation of plume-induced internal waves on the shelf. Satellite imageries demonstrate such propagation of plume-generated internal waves on the shelf off Kochi.
  PubDate: 2022-02-17
  DOI: 10.1007/s10236-022-01499-8
Tidal simulation revisited
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  Abstract: Abstract Accurate representation of tides is a pre-requisite for simulating many complex coastal processes. This study examines several most important factors for rigorous validation of nearshore tides: bottom friction, quality of DEM (Digital Elevation Model) information, horizontal resolution of model mesh, and 3D baroclinic effects. The results demonstrate that a rigorous model validation against tide gauge observation requires (1) good-quality DEM information be available; (2) locally very high mesh resolution (which has not been used in previous models) be used to capture the small-scale bathymetric/geometric features near the tide gauges; and (3) 3D effects be included. On the other hand, attempts to compensate errors by tuning other parameters such as bottom friction might produce erroneous results away from the validation sites, as tides undergo complex nonlinear transformations in the nearshore regime. Consequently, a most skilled tidal simulation should use a 3D model with locally very high resolution to faithfully represent DEMs of good quality (not just high resolution). Our results also highlight the central role played by the bathymetry on coastal processes.
  PubDate: 2022-02-05
  DOI: 10.1007/s10236-022-01498-9
Evaluation of wave model performance in the South Atlantic Ocean: a study
about physical parameterization and wind forcing calibration
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  Abstract: Abstract This paper evaluates the performance of the spectral wave model WAVEWATCH III for the South Atlantic Ocean forced by wind inputs from the most recent reanalyses, NCEP/CFSR and ECMWF/ERA5, combined with two different source terms: ST4 and ST6. A calibration is performed considering 1 year (2012) and 31 simulations, evaluated against altimeter and buoy data through six error metrics and Q-Q plots. Assessment results suggest that both ST4 and ST6 provide good results when WAVEWATCH III is properly adjusted for the wind input. Nevertheless, the wave model presents a positive bias of significant wave height when forced by CFSR winds that requires attention. The investigation in the spectral domain indicates a better performance of wave simulations forced by ERA5 winds, especially for wave periods below 10 s. For wave periods above 10 s, the choice of source term package becomes more important. In this regard, ST4 parameterization combined with ERA5 winds presents the best results for the region. The optimal range of calibration parameters for each wind input and source term package is reported and discussed.
  PubDate: 2022-01-28
  DOI: 10.1007/s10236-021-01495-4
Smooth particle hydrodynamics modelling of liquid-sediment system and
coastal wave breaker
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  Abstract: Abstract In this paper, a two-phase coastal liquid-sediment system and a wave breaker were numerically simulated using a particle-based smooth particle hydrodynamics (SPH). To verify the accuracy of SPH numerical scheme and model, a simplified liquid-sediment test case was constructed for validation using particle image velocimetry (PIV) experiment. Quantitatively, the discrepancies of the probed velocities are less than 9.32%. Moreover, both the sediment and flow profiles obtained numerically and experimentally are qualitatively comparable. Through SPH simulation, the exact mechanism of beach profile erosion was visualized. Thus, the veracity of the developed SPH numerical model was affirmed and justified. Using similar numerical approach, the variation effects of wave frequency on the characteristics of breaking wave were investigated. Five liquid-sediment cases of sinusoidal waves of varying frequencies from 0.2 to 1.0 Hz were studied. The characteristics of breaking waves were determined as surging or collapsing, plunging and spilling in the ascending order of wave frequency. Subsequently, the correlation between Iribarren number and Froude number was analyzed to observe the effect of wave breaker types on the beach erosion profile. Furthermore, two statistically correlated equations were formulated to relate wave frequency to Iribarren number and wave height. Finally, generalized plot of Iribarren number against Froude number was developed to determine the characteristics of the breaker wave at different slope angles. Overall, the presented SPH numerical scheme was found viable in simulating coastal problems, for instance, sediment transport and breaking wave impact on erosion.
  PubDate: 2022-01-28
  DOI: 10.1007/s10236-021-01489-2
The simulation of sediment transport and erosion caused by free-surface
flow based on two-phase SPH model with the improved Shields criterion
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  Abstract: Abstract In this paper, a two-phase model based on the SPH method is established using the Newtonian fluid and non-Newtonian fluid to describe water and sediment respectively. In this model, the Oldroyd-B constitutive model and the modified Shields criterion by sediment thickness and sediment interface slope are used to predict sediment transport and erosion caused by free-surface flow. The drag force of the water flow on the sediment is also considered. In addition, a series of correction techniques, including the kernel gradient correction technique, density re-initialization, treatment of solid boundary, and velocity correction technique, has been used. The dynamic processes of sediment transport and erosion under three different scouring conditions are simulated and analyzed by the two-phase model. Compared with the simulated and/or experimental results from earlier studies, the results show that the two-phase SPH model can capture the principal phenomena of sediment transport and erosion caused by free-surface flow.
  PubDate: 2022-01-25
  DOI: 10.1007/s10236-022-01497-w
Evolution of sea-level trends along the Norwegian coast from 1960 to 2100
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  Abstract: Abstract A first national analysis of the evolution of sea-level rates along the Norwegian coast for the period 1960–2100 has been accomplished by exploring tide-gauge records, relative sea-level projections, and detection techniques for acceleration. Firstly, sea-level rates for the two study periods 1960–2020 and 1991–2020 were estimated. Along the Norwegian coast, relative sea-level rates show significant spatial variation due to glacial isostatic adjustment. Moreover, the coastal average sea-level rate for the period 1991–2020 is significantly higher than for the period 1960–2020. Accelerations were then estimated for all combinations of start years and study periods longer than 30 years by including quadratic coefficients in regression models. It was found that the estimates strongly depend on the study period and do not provide confident estimates of climate change driven variation in the sea level along the Norwegian coast. Secondly, non-linear trends in relative sea level were reconstructed from Singular-Spectrum Analysis, which at several tide gauges revealed low rates in the 1970s, maximum rates around 1990, and declining rates thereafter. From the reconstructed trends, significant positive acceleration in the relative sea level was estimated for the period 1960–2020, while accelerations less than zero were detected for the period 1991–2020. However, the estimates for the recent period appear not robust due to the influence of decadal and multidecadal variation characterizing Norwegian tide-gauge records. Finally, by artificially extending the tide-gauge records by projections, the time when unprecedented high sea-level rates emerge was identified. With projections calculated for the intensive emission scenario RCP8.5, the climate signal of the relative sea level emerges at earliest in the late 2030s. The time of emergence is typically 5 to 10 years later if reanalysis of sea-level pressure and wind speed are used to reduce decadal variation in the tide-gauge records. This is because the meteorological regressors, as a side effect, introduce serial correlations that lead to rate estimates with enlarged standard errors. An important implication of the findings is that a possible absence of record high sea-level rates in the 2020s and 2030s does not falsify that relative sea level along the Norwegian coast is consistent with projections of RCP8.5.
  PubDate: 2022-01-22
  DOI: 10.1007/s10236-021-01492-7
Spectral wave characteristics in the coastal waters of the central west
coast of India during tropical cyclone Kyarr
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  Abstract: Abstract The study presents the assessment of spectral wave conditions in the coastal waters of the central west coast of India based on data from waverider buoys at two locations during the passage of tropical cyclone Kyarr. Due to the impact of the tropical cyclone, at 15 m water depth, the annual maximum significant wave height of 5.1 m occurred in October for the first time in the last 42 years. Though the cyclone track was close to the location Vengurla, maximum energy waves are observed at Karwar, a location ~ 125 km south of Vengurla due to the super-imposition of the cyclonic waves with the comparatively high energy long-period swells existing at Karwar. The high-frequency slope of the wave spectra becomes steep due to cyclone with a value close to − 4. Wave spectrum during cyclones is better represented by the JONSWAP spectrum with modified parameters, and the maximum value of peak enhancement factor observed during the cyclone period agrees with the mean value (3.3) suggested by the JONSWAP study. The wave heights obtained from the numerical model are also compared with the measured values. The spatial variation in waves has been investigated using the ERA5 reanalysis data.
  PubDate: 2022-01-14
  DOI: 10.1007/s10236-022-01496-x
Physical-Ecological Response of the California Current System to ENSO
events in ROMS-NEMURO
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  Abstract: Abstract We analyze the bottom-up El Niño/Southern Oscillation (ENSO) driven physical-biological response of the California Current System (CCS) in a high-resolution, “eddy-scale” ocean model with multiple classes of phytoplankton and zooplankton forced with observed winds over the time period 1959–2007. The response of the sea surface temperature anomalies over the CCS is asymmetrical, with La Niña events being more consistently cold than El Niño events are consistently warm, which is in agreement with previous studies. The biogeochemical and ecological response is represented by ENSO composite anomalies, lag correlations with an ENSO index, and histograms for ENSO years. The results show trophic level interactions during El Niño and La Niña events in which the larger components (diatoms, euphausiids, and copepods) are suppressed in the coastal upwelling zones during El Niño, while the smaller components (flagellates and ciliates) are enhanced. In addition, standing eddies of the CCS modulate the latitudinal structure of the ecological response to ENSO. The results point towards future research to understand how bottom-up changes may lead to variability of patterns in ecological response, including fish populations and top predators.
  PubDate: 2021-12-29
  DOI: 10.1007/s10236-021-01490-9