Subjects -> METEOROLOGY (Total: 106 journals)
 Showing 1 - 36 of 36 Journals sorted by number of followers Journal of Atmospheric and Solar-Terrestrial Physics       (Followers: 157) Nature Climate Change       (Followers: 149) Journal of the Atmospheric Sciences       (Followers: 81) Atmospheric Research       (Followers: 73) Atmospheric Environment       (Followers: 72) Climatic Change       (Followers: 70) Bulletin of the American Meteorological Society       (Followers: 63) Advances in Climate Change Research       (Followers: 60) Journal of Climate       (Followers: 56) Climate Policy       (Followers: 53) Climate Change Economics       (Followers: 50) Climate Dynamics       (Followers: 45) Advances in Atmospheric Sciences       (Followers: 44) Weather and Forecasting       (Followers: 43) Atmospheric Chemistry and Physics (ACP)       (Followers: 43) American Journal of Climate Change       (Followers: 42) Journal of Applied Meteorology and Climatology       (Followers: 41) Nature Reports Climate Change       (Followers: 40) Atmospheric Science Letters       (Followers: 40) Journal of Hydrology and Meteorology       (Followers: 39) Atmosphere       (Followers: 33) Journal of Atmospheric and Oceanic Technology       (Followers: 33) International Journal of Climate Change Strategies and Management       (Followers: 32) Boundary-Layer Meteorology       (Followers: 32) The Quarterly Journal of the Royal Meteorological Society       (Followers: 32) Journal of Space Weather and Space Climate       (Followers: 30) Monthly Weather Review       (Followers: 30) Meteorology and Atmospheric Physics       (Followers: 29) International Journal of Climatology       (Followers: 28) Space Weather       (Followers: 28) Climate Change Responses       (Followers: 27) Advances in Meteorology       (Followers: 27) Energy & Environment       (Followers: 26) Climate Resilience and Sustainability       (Followers: 26) Journal of Climate Change       (Followers: 25) International Journal of Atmospheric Sciences       (Followers: 25) International Journal of Environment and Climate Change       (Followers: 24) Environmental Dynamics and Global Climate Change       (Followers: 24) Journal of Atmospheric Chemistry       (Followers: 23) Current Climate Change Reports       (Followers: 22) Agricultural and Forest Meteorology       (Followers: 21) Tellus A       (Followers: 21) Global Meteorology       (Followers: 20) Journal of Meteorology and Climate Science       (Followers: 20) Tellus B       (Followers: 20) Journal of Economic Literature       (Followers: 20) Dynamics of Atmospheres and Oceans       (Followers: 19) Weather and Climate Extremes       (Followers: 18) Weatherwise       (Followers: 18) Atmosphere-Ocean       (Followers: 16) Economics of Disasters and Climate Change       (Followers: 16) Atmospheric Chemistry and Physics Discussions (ACPD)       (Followers: 15) Monthly Notices of the Royal Astronomical Society       (Followers: 14) Theoretical and Applied Climatology       (Followers: 14) Atmospheric and Oceanic Science Letters       (Followers: 13) Climate Risk Management       (Followers: 12) Advances in Statistical Climatology, Meteorology and Oceanography       (Followers: 12) Journal of Hydrometeorology       (Followers: 10) The Cryosphere (TC)       (Followers: 8) Climate Research       (Followers: 8) Climate and Energy       (Followers: 8) Climate       (Followers: 7) Journal of the Meteorological Society of Japan       (Followers: 7) Aeolian Research       (Followers: 7) Climate of the Past (CP)       (Followers: 7) Climate Law       (Followers: 6) Journal of Climate Change and Health       (Followers: 6) npj Climate and Atmospheric Science       (Followers: 6) Dynamics and Statistics of the Climate System       (Followers: 6) Carbon Balance and Management       (Followers: 6) Open Journal of Modern Hydrology       (Followers: 5) Bulletin of Atmospheric Science and Technology       (Followers: 5) Open Atmospheric Science Journal       (Followers: 5) Urban Climate       (Followers: 5) Climate Services       (Followers: 4) Journal of Climatology       (Followers: 4) Journal of Integrative Environmental Sciences       (Followers: 4) Frontiers in Climate       (Followers: 4) Russian Meteorology and Hydrology       (Followers: 4) Meteorologische Zeitschrift       (Followers: 4) Journal of Weather Modification       (Followers: 4) Meteorological Applications       (Followers: 4) Acta Meteorologica Sinica       (Followers: 4) Atmospheric Environment : X       (Followers: 3) Oxford Open Climate Change       (Followers: 3) Environmental and Climate Technologies       (Followers: 3) International Journal of Biometeorology       (Followers: 3) International Journal of Image and Data Fusion       (Followers: 3) Atmósfera       (Followers: 2) GeoHazards       (Followers: 2) Journal of Meteorological Research       (Followers: 2) Mediterranean Marine Science       (Followers: 2) Meteorologica       (Followers: 2) 气候与环境研究       (Followers: 2) Weather and Climate Dynamics       (Followers: 1) Modeling Earth Systems and Environment       (Followers: 1) Michigan Journal of Sustainability       (Followers: 1) Earth Perspectives - Transdisciplinarity Enabled       (Followers: 1) Tropical Cyclone Research and Review       (Followers: 1) Ciencia, Ambiente y Clima       (Followers: 1) Climate of the Past Discussions (CPD)       (Followers: 1) Nīvār       (Followers: 1) Meteorological Monographs       (Followers: 1) Studia Geophysica et Geodaetica       (Followers: 1) Revista Iberoamericana de Bioeconomía y Cambio Climático       (Followers: 1) Journal of Agricultural Meteorology Mètode Science Studies Journal : Annual Review
Similar Journals
 Climate DynamicsJournal Prestige (SJR): 2.445 Citation Impact (citeScore): 4Number of Followers: 45      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1432-0894 - ISSN (Online) 0930-7575 Published by Springer-Verlag  [2469 journals]
• Either IOD leading or ENSO leading triggers extreme thermohaline events in
the central tropical Indian Ocean

Abstract: Abstract Based on 12 years (2007–2018) of salinity data from the Array for Real-Time Geostrophic Oceanography (Argo) dataset, we found significant positive salinity anomalies in the upper layer of the central tropical Indian Ocean from autumn 2010 to spring 2011 and from autumn 2016 to spring 2017. We used wind, precipitation, outgoing longwave radiation and ocean current data from satellites and reanalysis datasets to analyze the atmospheric conditions, ocean dynamic processes and salinity budget associated with these high salinity events. Our results suggest that surface buoyancy fluxes are not the dominant factor affecting the positive salinity anomalies and that ocean dynamic processes have a more important role. Under the influence of the La Niña events and strong negative Indian Ocean dipole in 2010 and 2016, positive salinity anomalies appeared in the eastern Indian Ocean at the end of 2010 and 2016 as a result of strong westerlies and positive zonal currents. However, because the La Niña event in 2010 was stronger than that in 2016, the salinity anomalies in 2010 were also stronger and the decrease in the following year was both stronger and lasted longer, meaning that the salinity anomalies weakened only gradually. The maximum value of the salinity anomalies in 2011 therefore appeared in January, whereas in 2017 the salinity anomalies first decreased and then increased, with the largest anomalies in March. Salinity budget analyses showed that ocean advection was the main factor leading to the variations in the salinity anomaly during these two periods and that the changes in the zonal velocity in the zonal advection anomalies had the greatest impact. Zonal advection was positive and strongest at the end of 2010 and negative in early 2011, but weakly positive at the end of 2016. In early 2017, the zonal advection was first negative, then became positive and strengthened in spring, so the salinity anomalies in spring 2017 were higher than those in 2011. The freshwater flux had a small, negative effect on the positive salinity anomalies for these two events. The mutual effects of the horizontal advection and the freshwater flux led to high salinity anomalies. The high salinity anomalies reflect the response of the upper ocean to climate events and may influence regional air–sea interactions and large-scale processes.
PubDate: 2022-08-08

• The relative contribution of large-scale circulation and local soil
moisture to summer precipitation over Asian mid-low latitudes

Abstract: Abstract Understanding the contributions of large-scale atmospheric circulation and local land surface processes to precipitation is essentially important for the climate prediction. This study adopts a dynamic adjustment (DA) approach based on constructed circulation analogs to quantitatively isolate the contribution of atmospheric circulation to summer land precipitation (Pr) over Asian mid-low latitudes during 1980–2019. The atmospheric circulation factor is represented by the 500 hPa geopotential height (Z500), and the residual component after DA is regarded as the contribution from land surface processes via evaporation mainly resulting from soil moisture (SM). The results indicate that the key SM-Pr feedback areas are mainly located in northeast China and the northern Indian Peninsula. The key influencing area of Z500 on the land Pr anomaly shows a “- + -” tripole pattern in the mid-latitude region. Atmospheric circulation determines the magnitude of summer land Pr, while the residual components reflect the land–atmosphere coupling effect and dominate Pr trend. This conclusion is helpful for better understanding the evolution mechanism of summer climate over Asia mid-low latitudes and may also have application value for climate prediction.
PubDate: 2022-08-08

• The influence of the wave trains on the intraseasonal variability of the
East Asian subtropical westerly jet in early and late summer

Abstract: Abstract The East Asian subtropical westerly jet (EASWJ) is one of the most crucial subtropical circulation systems affecting the precipitation over East Asia. Based on the ERA5 dataset, the dominant modes of the intraseasonal variability of the EASWJ in early (May and June) and late (July and August) summer are investigated, respectively, through the empirical orthogonal function (EOF) analysis. The EOF1 in early summer is characterized by the anomalous westerlies centered over the North China and anomalous easterlies centered over the south of Japan. This mode is led by the south-eastward propagating wave train initiating from the Barents Sea, where the ridge of the wave train coincides with an anomalous warm advection in the low level, due to the negative phase of Arctic Dipole (AD). Since lag − 4 days, the East Asia/Western Ruassia (EAWR) teleconnection contributes to the wave trains. The EOF1 in late summer is characterized by the anomalous westerlies centered over the south of Baikal and anomalous easterlies centered over the Central China, which is affected by the two wave trains along different directions. One wave train propagate zonally across Eurasia initiated from North Atlantic, where significant signal of East Atlantic (EA) teleconnection is found as a precursor. When the wave train disperses downstream to Eurasia, the EAWR play a dominant role on the growth and persistence of the EASWJ variability. The other one is similar to the East Asia–Pacific (EAP) teleconnection propagating poleward from the Southern Asia and Western North Pacific, where the active convection anomalies may be a key driver. The intraseasonal wave trains that influence the EASWJ are different between early and late summer probably due to the discrepancies of background status, such as the background temperature gradient and the curviness of the jet climatology.
PubDate: 2022-08-05

• Impact of initialization methods on the predictive skill in NorCPM: an
Arctic–Atlantic case study

Abstract: Abstract The skilful prediction of climatic conditions on a forecast horizon of months to decades into the future remains a main scientific challenge of large societal benefit. Here we assess the hindcast skill of the Norwegian Climate Prediction Model (NorCPM) for sea surface temperature (SST) and sea surface salinity (SSS) in the Arctic–Atlantic region focusing on the impact of different initialization methods. We find the skill to be distinctly larger for the Subpolar North Atlantic than for the Norwegian Sea, and generally for all lead years analyzed. For the Subpolar North Atlantic, there is furthermore consistent benefit in increasing the amount of data assimilated, and also in updating the sea ice based on SST with strongly coupled data assimilation. The predictive skill is furthermore significant for at least two model versions up to 8–10 lead years with the exception for SSS at the longer lead years. For the Norwegian Sea, significant predictive skill is more rare; there is relatively higher skill with respect to SSS than for SST. A systematic benefit from more complex data assimilation approach can not be identified for this region. Somewhat surprisingly, skill deteriorates quite consistently for both the Subpolar North Atlantic and the Norwegian Sea when going from CMIP5 to corresponding CMIP6 versions. We find this to relate to change in the regional performance of the underlying physical model that dominates the benefit from initialization.
PubDate: 2022-08-04

• Correction to: Persistent freshening of the Arctic Ocean and changes in
the North Atlantic salinity caused by Arctic sea ice decline

PubDate: 2022-08-02

• Assessment of the RegCM4-CORDEX-CORE performance in simulating cyclones
affecting the western coast of South America

Abstract: Abstract In this study, we assess the performance of the Regional Climate Model version 4 (RegCM4) in simulating the climatology of the cyclones near the west coast of South America. The synoptic evolution and seasonality of these systems are thoroughly investigated. The analyses are based on four simulations from the CORDEX-CORE Southern America (SA) domain, at 0.25° of horizontal resolution: one driven by ERA-Interim and three driven by different GCMs. The reference dataset is represented by ERA5. Cyclones were detected by an objective scheme in the period 1995–2005 and classified in three different classes: (i) Coastal Lows (CLs) and cyclones affecting the coast (CAC) (ii) crossing and (iii) not crossing the Andes. In general, RegCM4 is able to reproduce the climatology of cyclones affecting the western coast of SA. In particular: (i) CLs are shown to be more frequent in austral summer although their frequency is underestimated by the simulations in this season; (ii) CAC not crossing the Andes represent 76% of all CAC and are more frequent in winter, with simulation underestimating their frequency by ~ 22% due to the differences in the simulated upper-level jets, which tend to get weaker (by ~ 5–10 m s− 1) northwards of 30°S; (iii) the frequency of CAC crossing the Andes tends to be overestimated mainly in winter, which is associated with the combination of the stronger upper-level jets and weaker SLP in the simulations, especially southwards of 40°S.
PubDate: 2022-08-02

• Greenhouse-gas forced changes in the Atlantic meridional overturning
circulation and related worldwide sea-level change

Abstract: Abstract The effect of anthropogenic climate change in the ocean is challenging to project because atmosphere-ocean general circulation models (AOGCMs) respond differently to forcing. This study focuses on changes in the Atlantic Meridional Overturning Circulation (AMOC), ocean heat content ( $$\Delta$$ OHC), and the spatial pattern of ocean dynamic sea level ( $$\Delta \zeta$$ ). We analyse experiments following the FAFMIP protocol, in which AOGCMs are forced at the ocean surface with standardised heat, freshwater and momentum flux perturbations, typical of those produced by doubling $$\hbox {CO}_{{2}}$$ . Using two new heat-flux-forced experiments, we find that the AMOC weakening is mainly caused by and linearly related to the North Atlantic heat flux perturbation, and further weakened by a positive coupled heat flux feedback. The quantitative relationships are model-dependent, but few models show significant AMOC change due to freshwater or momentum forcing, or to heat flux forcing outside the North Atlantic. AMOC decline causes warming at the South Atlantic-Southern Ocean interface. It does not strongly affect the global-mean vertical distribution of $$\Delta$$ OHC, which is dominated by the Southern Ocean. AMOC decline strongly affects $$\Delta \zeta$$ in the North Atlantic, with smaller effects in the Southern Ocean and North Pacific. The ensemble-mean $$\Delta \zeta$$ and $$\Delta$$ OHC patterns are mostly attributable to the heat added by the flux perturbation, with smaller effects from ocean heat and salinity redistribution. The ensemble spread, on the other hand, is largely due to redistribution, with pronounced disagreement among the AOGCMs.
PubDate: 2022-08-02

• Probabilistic forecasts of near-term climate change: verification for
temperature and precipitation changes from years 1971–2000 to
2011–2020

Abstract: Abstract In year 2006, Räisänen and Ruokolainen proposed a resampling ensemble technique for probabilistic forecasts of near-term climate change. Here, the resulting forecasts of temperature and precipitation change from years 1971–2000 to 2011–2020 are verified. The forecasts of temperature change are found to be encouraginly reliable, with just 9% and 10% of the local annual and monthly mean changes falling outside the 5–95% forecast range. The verification statistics for temperature change represent a large improvement over the statistics for a surrogate no-forced-change forecast, and they are largely insensitive to the observational data used. The improvement for precipitation changes is much smaller, to a large extent due to the much lower signal-to-noise ratio of precipitation than temperature changes. In addition, uncertainty in observations is a major complication in verification of precipitation changes. For the main source of precipitation data chosen in the study, 20% and 15% of the local annual and monthly mean precipitation changes fall outside the 5–95% forecast range.
PubDate: 2022-08-01

• Wind kinetic energy climatology and effective resolution for the ERA5
reanalysis

Abstract: Abstract ERA5 represents the state of the art for atmospheric reanalyses and is widely used in meteorological and climatological research. In this work, this dataset is evaluated using the wind kinetic energy spectrum. Seasonal climatologies are generated for 30° latitudinal bands in the Northern Hemisphere (periodic domain) and over the North Atlantic area (limited-area domain). The spectra are also assessed to determine the effective resolution of the reanalysis. The results present notable differences between the latitudinal domains, indicating that ERA5 is properly capturing the synoptic conditions. The seasonal variability is adequate too, being winter the most energetic, and summer the least energetic season. The limited area domain results introduce a larger energy density and range. Despite the good results for the synoptic scales, the reanalysis’ spectra are not able to properly reproduce the dissipation rates at mesoscale. This is a source of uncertainties which needs to be taken into account when using the dataset. Finally, a cyclone tropical transition is presented as a case study. The spectrum generated shows a clear difference in energy density at every wavelength, as expected for a highly-energetic status of the atmosphere.
PubDate: 2022-08-01

• Indirect effect of diabatic heating on Mei-yu frontogenesis

Abstract: Abstract Mei-yu fronts are accompanied with the formation of frontal clouds. In addition to its direct effect on Mei-yu fronts through the modification of atmospheric temperature, diabatic heating related to clouds formation also influences frontogenesis indirectly by changing local atmospheric circulation. To quantify such indirect effects, piecewise potential vorticity (PV) inversion is adopted to decompose the process of deformation frontogenesis into several parts associated with distinct PV anomalies. The balanced flow associated with the interior-level diabatic PV anomaly emerges as the most stable and important contributor to the total deformation frontogenesis with the effect of local diabatic PV anomaly in the frontal zone outweighing the effect of remote diabatic PV anomaly. Lower-boundary thermal anomaly (i.e., surface cooling associated with frontal clouds formation) and mean flow provide weak negative and positive contributions to the deformation frontogenesis, respectively. The balanced flow associated with the upper-level PV perturbations is weak at lower-levels, especially in the vicinity of the front zone and thus has negligible contributions to the Mei-yu frontogenesis. The indirect effect of diabatic heating on Mei-yu frontogenesis is generally weaker in magnitude compared to the direct effect of temperature modification as well as the impact of moisture depletion that is also tied to clouds formation. The results presented here add further evidences about the importance of cloud feedback to the evolution of Mei-yu fronts and suggest the necessity of improved model representations of cloud processes in achieving a better simulation and prediction of Mei-yu rainfall.
PubDate: 2022-08-01

• Modes of the BiOS-driven Adriatic Sea thermohaline variability

PubDate: 2022-08-01

• Association of the shift of the South Asian high in June with the diabatic
heating in spring

Abstract: Abstract In this paper, we define the index of the South Asian High (SAH) core position and use correlation analysis and ERA-Interim reanalysis data during 1979–2018 to identify spring latent heating configurations in the central Indian Ocean–southwestern Tibetan Plateau that provide leading signals for the SAH shift in June via the apparent moisture sink. These leading signals in boreal spring have a clear physical significance, and are characterized by a contrast in the meridional apparent moisture sink between the central Indian Ocean (IO) and the southwestern Tibetan Plateau (SWTP). When the spring apparent moisture sink contrast between the central IO and the SWTP is higher than normal, the heating pattern induces an anomalous vertical circulation that enhances the coupling between the mid-level convection and upper-level divergence over the central IO-SWTP. The upper-level divergent circulation in the upper reaches of the SAH track favors the development of the SAH before June, and thus the SAH shifts farther northwestward than normal in June. When the spring apparent moisture sink contrast is lower than normal, the atmospheric response is reversed, causing the SAH to shift farther southeastward than normal. Numerical experiments have confirmed the driving role of the meridional apparent moisture sink contrast in the central IO-SWTP and the associated physical processes. Further analyses reveal a significant and persistent correlation between the apparent moisture sink contrast in late March to late May and the SAH meridional position in June. The spring meridional apparent moisture sink contrast is therefore a reasonable predictor in forecasting the SAH shift in June.
PubDate: 2022-08-01

• Impact of highest maximum sustained wind speed and its duration on storm
surges and hydrodynamics along Krishna–Godavari coast

Abstract: Abstract The storm surge and hydrodynamics along the Krishna–Godavari (K–G) basin are examined based on numerical experiments designed from assessing the landfalling cyclones in Bay of Bengal (BoB) over the past 38 years with respect to its highest maximum sustained wind speed and its duration. The model is validated with the observed water levels at the tide gauge stations at Visakhapatnam during 2013 Helen and 2014 Hudhud. Effect of gradual and rapid intensification of cyclones on the peak water levels and depth average currents are examined and the vulnerable locations are identified. The duration of intensification of a rapidly intensifying cyclone over the continental shelf contributed to about 10–18% increase in the peak water levels, whereas for the gradually intensifying cyclone the effect is trivial. The inclusion of the wave-setup increased the peak water levels up to 39% compared to those without wave-setup. In the deep water region, only rapidly intensifying cyclones affected the peak MWEs. Intensification over the continental slope region significantly increases the currents along the shelf region and coast. The effect on peak maximum depth averaged current extends up to 400 km from the landfall location. Thus, it is necessary to consider the effect of various combinations of the highest cyclone intensity and duration of intensification for identifying the worst scenarios for impact assessment of coastal processes and sediment transport. The study is quite useful in improving the storm surge prediction, in preparedness, risk evaluation, and vulnerability assessment of the coastal regions in the present changing climate.
PubDate: 2022-08-01

• On the weakening of northward propagation of intraseasonal oscillations
during positive Indian Ocean Dipole events

Abstract: Abstract The northward propagation of intraseasonal oscillations (ISO) is one of the major modes of variability in the tropics during boreal summers, associated with active and break spells of monsoon rainfall over the Indian region. These northward propagations modulate the Indian summer monsoon rainfall. The northward march starts close to the equator over warm waters of the Indian Ocean and continues till the foothills of the Himalayas. In this study, we investigate the influence of Indian Ocean Dipole (IOD) on northward propagations. We show that northward propagations tend to be weaker during positive Indian Ocean Dipole (pIOD) events. The “moisture mode” framework is used to understand the processes responsible for the weakening of northward propagations during pIOD years. Our analyses show that moistening caused by the horizontal advection is the major contributor for the northward propagations during negative IOD (nIOD) years, and its amplitude is much smaller during pIOD years. Further analyses revealed that the reduction in the advection of the background entropy/moisture by zonal wind perturbations during pIOD is primarily responsible for the reduction in the horizontal advection. The mean structure of entropy between 925 and 500 hpa levels remained similar over most of the Asian monsoon region across the contrasting IOD years, and the reason for weaker northward propagations can be attributed to the weaker zonal wind perturbations at intraseasonal timescales. These weaker zonal wind perturbations during ISO events in pIOD years results from weak Rossby Vortex lobes. The weakening of Rossby wave response owing to cooler than average sea surface temperatures in the South-East Equatorial Indian Ocean and warmer than average West Equatorial Indian Ocean is proposed to be the possible reason for the weakening of northward propagations during pIOD years.
PubDate: 2022-08-01

• The water mass transformation framework and variability in hurricane
activity

Abstract: Abstract Hurricane activity has been higher since 1995 than in the 1970s and 1980s. This rise in activity has been linked to a warming Atlantic. In this study, we consider variability of the volume of water warmer than 26.5 ºC, considered widely to be the temperature threshold crucial to hurricane development. We find the depth of the 26.5 ºC isotherm better correlated with seasonal hurricane counts than SST in the early part of the Atlantic hurricane season in some regions. The volume of water transformed by surface heat fluxes to temperatures above 26.5 ºC is directly calculated using the Water Mass Transformation framework. This volume is compared with the year-to-year changes in the volume of water of this temperature to see how much of the volume can be explained using this calculation. In some years, there is notable correspondence between transformed and observed volume anomalies, but anomalies in other years must be largely associated with other processes, such as the divergence of horizontal heat transport associated with the AMOC. This technique provides evidence that, in a given year, coordinated physical mechanisms are responsible for the build-up of anomalous ocean heat; not only net surface heat exchange but also the convergence of horizontal heat transport from ocean currents, to provide fuel for larger numbers of intense hurricanes.
PubDate: 2022-08-01

• Distribution of extreme rainfall events and their environmental controls
in the West African Sahel and Soudan

Abstract: Abstract West African Sahel and Soudan extreme rainfall events are impactful when strong mesoscale convective systems (MCSs) produce large amounts of rainfall in short periods. NASA IMERG rainfall estimates and the ERA5 reanalysis are examined to understand where the top 100 highest 12Z–12Z 24-h rainfall totals and MCS storm genesis occur, and to assess the relative importance of environmental conditions in their generation including the influence of atmospheric moisture and vertical wind shear. Most of the top 100 events are located south of 14° N over the Soudan. Events cluster over three regions, namely, Mali, Burkina Faso, and northern Nigeria. The associated MCSs are typically not locally generated, forming instead at distances greater than 100 km upstream. Composites reveal that a significant increase in atmospheric moisture content occurs prior to development, but there is no evidence of significant changes in the 600–925 hPa vertical wind shear. This indicates that changes in vertical wind shear are less influential in extreme storm development than atmospheric moisture preconditioning. The top 10 events are further evaluated. A change in these storms’ direction and speed near the maximum rainfall location is common, suggesting the MCSs are reorganizing around peak rainfall intensity time. Three atmospheric conditions are associated with these events. They are (1) moisture preconditioning of the atmosphere, (2) interaction of the storm in the wake of a region of anticyclonic flow, and (3) interaction of the storm in the wake of a region of anticyclonic flow and the Sahel/tropical dryline boundary.
PubDate: 2022-08-01

• Coupled climate response to Atlantic Multidecadal Variability in a
multi-model multi-resolution ensemble

Abstract: Abstract North Atlantic sea surface temperatures (SSTs) underwent pronounced multidecadal variability during the twentieth and early twenty-first century. We examine the impacts of this Atlantic Multidecadal Variability (AMV), also referred to as the Atlantic Multidecadal Oscillation (AMO), on climate in an ensemble of five coupled climate models at both low and high spatial resolution. We use a SST nudging scheme specified by the Coupled Model Intercomparision Project’s Decadal Climate Prediction Project Component C (CMIP6 DCPP-C) to impose a persistent positive/negative phase of the AMV in the North Atlantic in coupled model simulations; SSTs are free to evolve outside this region. The large-scale seasonal mean response to the positive AMV involves widespread warming over Eurasia and the Americas, with a pattern of cooling over the Pacific Ocean similar to the Pacific Decadal Oscillation (PDO), together with a northward displacement of the inter-tropical convergence zone (ITCZ). The accompanying changes in global atmospheric circulation lead to widespread changes in precipitation. We use Analysis of Variance (ANOVA) to demonstrate that this large-scale climate response is accompanied by significant differences between models in how they respond to the common AMV forcing, particularly in the tropics. These differences may arise from variations in North Atlantic air-sea heat fluxes between models despite a common North Atlantic SST forcing pattern. We cannot detect a widespread effect of increased model horizontal resolution in this climate response, with the exception of the ITCZ, which shifts further northwards in the positive phase of the AMV in the higher resolution configurations.
PubDate: 2022-08-01

• Lagged oceanic effects on the East African short rains

Abstract: Abstract The East African ‘short rains’ in October–December (OND) exhibit large interannual variability. Drought and flooding are not unusual, and long-range rainfall forecasts can guide planning and preparedness for such events. Although seasonal forecasts based on dynamical models are making inroads, statistical models based on sea surface temperature (SST) precursors are still widely used, making it important to better understand the strengths and weaknesses of such models. Here we define a simple statistical forecast model, which is used as a tool to shed light on the dynamics that link SSTs and rainfall across time and space, as well as on why such models sometimes fail. Our model is a linear regression, where the August states of El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) predict about 40% of the short rains variability in 1950–2020. The forecast errors are traced back to the initial SSTs: too-wet (too-dry) forecasts are linked linearly to positive (negative) initial ENSO and IOD states in August. The link to the initial IOD state is mediated by changes in the IOD between August and OND, highlighting a physical mechanism for prediction busts. We also identify asymmetry and nonlinearity: when ENSO and/or the IOD are positive in August, the range and variance of OND forecast errors are larger than when the SST indices are negative. Upfront adjustments of predictions conditional on initial SSTs would have helped in some years with large forecast busts, such as the dry 1987 season during a major El Niño, for which the model erroneously predicts copious rainfall, but it would have exacerbated the forecast in the wet 2019 season, when the IOD was strongly positive and the model predicts too-dry conditions.
PubDate: 2022-08-01

• Relationship between summer extreme precipitation anomaly in Central Asia
and surface sensible heat variation on the Central-Eastern Tibetan Plateau

Abstract: Abstract In the context of global warming, the frequency and intensity of extreme weather and climate events have increased, especially in Central Asia (CA). In this study, we investigate the characteristics of summer extreme precipitation (SEP) in CA and its relationship with the surface sensible heat (SSH) variation over the central–eastern Tibetan Plateau (CETP). The results suggest that the distribution of SEP in CA is extremely uneven, and the SEP thresholds range from 2 to 32 mm/day, and 80% of them are concentrated in 4–10 mm/day. Both the total amount of SEP and the number of SEP days show significant increasing trends, with the climatic tendencies of 4.4 mm/decade and 0.4 day/decade, respectively. The SSH anomalies over the CETP can affect the SEP and summer drought in CA by regulating the strength of South Asia High (SAH) and the subtropical jet over CA. The strong SSH anomalies over the CETP in late spring (April–May) can be transmitted from the lower to the upper layers through the continuous heating to the atmosphere and lead to the anomalously strong subtropical high over northern Africa and the Arabian Peninsula, the anomalously weak subtropical westerly jet over CA and the anomalously strong SAH in summer. At the same time, the Ural ridge strengthens, the CA trough weakens, and the northern CA is controlled by an anomaly of warm high-pressure ridge. Therefore, the anomaly of water vapor convergence in northern CA weakens. The SEP there will be abnormally less, and the summer drought intensifies. When the SSH over CETP is anomalously weak in late spring, the key circulations are just the opposite. Furthermore, the anomalous water vapor from the Arctic, North Atlantic and western Pacific converges in northern CA and northern Xinjiang, China, which is conducive to the generation of widespread extreme precipitation and the alleviation of summer drought in these regions.
PubDate: 2022-08-01

• Feedback of tropical cyclones on El Niño diversity. Part II: possible
mechanism and prediction

Abstract: Abstract Part I of this study has shown that the tropical cyclones (TCs) over the western North Pacific (WNP) can affect El Niño diversity. In this part, we further explore the possible mechanism of this phenomenon: Compared with the composite situation of all El Niño months, when the preceding (3 months earlier) accumulated cyclone energy (ACE) is strong, the Walker circulation is further weakened and the east–west thermocline gradient is reduced. The eastward transport of warm sea water over the western Pacific is enhanced, the center of the maximum positive sea surface temperature (SST) anomalies is located in the equatorial eastern Pacific, supporting for the development of the eastern-Pacific (EP) El Niño. In contrast, compared with the composite situation of all El Niño months, when the preceding ACE is weak, the Walker circulation is enhanced and the east–west thermocline gradient is strengthened. Thus, the center of the maximum positive SST anomalies is limited to the equatorial central Pacific, supporting for the development of the central-Pacific (CP) El Niño. The modulation of thermocline depth by the WNP TCs mainly results from Kelvin wave propagation and Ekman pumping. In addition, WNP TCs are verified to contribute to the prediction of both the phase-locking of the peak of EP and CP El Niño events and the rapid decrease in SST anomalies during the decaying period of two types of El Niño.
PubDate: 2022-08-01

JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762