Global Atmospheric Circulation Research Articles

Terrestrial Material Input to the Northwest Shelf of Australia Through the Pliocene‐Pleistocene Period and Its Implications on Continental Climates

AbstractBased on biomarkers and bulk organic carbon isotope, we reconstructed a 5‐million‐year history of terrestrial material input to the northwest shelf of Australia. Vegetational organic input continuously decreased through the Pliocene‐Pleistocene period due to decreased vegetation coverage and discharge under general aridification process. Triggered by lowered sea level and drier climates, soil input increased after ∼2.5–2.2 million years ago (Ma). Bulk terrestrial organic input demonstrates stronger variability after ∼1.7 Ma, as influenced by large‐amplitude hydrological swings on the Australian continent. Source of soils shifted between ∼1.5 and 1.2 Ma, along with presence of active dune fields. All lines of evidence together indicate a general wet climate in northwestern Australia during the early Pliocene, a continuously drying trend to the mid‐Pleistocene, and a drier phase with less vegetation coverage and expanded desert during the late Pleistocene, which is modulated by ongoing Indonesian Throughflow constriction and global atmospheric circulations.

North Atlantic Oscillation (NAO) Climate Index Hidden in Ocean Generated Secondary Microseisms

AbstractWith the role of surface winds in the generation of ocean waves, secondary microseisms induced by ocean wave‐wave interactions represent a unique interconnection between the solid Earth, the ocean and global atmospheric circulation patterns. In this study, temporal changes in the ocean generated seismic wavefield in Northeast Atlantic are monitored offshore West of Ireland using ocean bottom seismometers located on top of a thick sedimentary basin. Comparisons with numerical seismic simulations and ocean wave model hindcast data suggest those variations are correlated with changing patterns in ocean wave‐wave interactions closely linked to secondary microseism generation areas. Here we show how those changes, accentuated by the specific structure of the Irish offshore margin, reveal the signature of the North Atlantic Oscillation (NAO) in the Earth’s background seismic wavefield. In the North Atlantic, secondary microseism sources likely fluctuate with the changing storm track in response to variations in the NAO.

RETRACTED ARTICLE: Tropical coastal climate change based on image defogging algorithm and swimming rehabilitation training

This paper first designs and implements an image defogging algorithm based on FPGA. The hardware design mainly includes SDRAM control module, SD card control module, data transmission control module, and convolution neural network calculation module. The SDRAM control module controls the working state of SDRAM; the SD card control module controls the working state of SD card; the data transmission control module controls the data transmission of reading and writing SDRAM; and the convolution neural network module is responsible for the image defogging algorithm. Based on this point, this paper uses the medium complex ocean atmosphere combination model to estimate the SST diversity and climate characteristics of the tropical coastal Pacific and Atlantic Ocean in recent years, and studies and analyzes the influencing factors of the prediction. The atmospheric part of the coupled model is the global atmospheric circulation model CCM3, and the oceanic part is a simplified gravity model of Zebiak Cane type. In addition, an air filter is added to the coupled model to test the impact of natural noise during broadcasting. Finally, the article investigated the positive effect of swimming rehabilitation training on chronic neck pain symptoms of office workers; Objectives were to study the effect of various swimming rehabilitation trainings on neck pain of office workers and investigate the effect of different swimming rehabilitation training cycles on chronic neck pain symptoms of office workers. Objective was to provide a theoretical basis for the development of exercise rehabilitation plan to improve the chronic pain symptoms of office workers. The results showed that breaststroke training and freestyle training were effective in treating neck pain of office workers. In this paper, the application of adaptive image defogging algorithm and the correction of coastal climate change in the rehabilitation training research has promoted the healthy development and progress of swimming rehabilitation training.

Trends and variability in polar sea ice, global atmospheric circulations, and baroclinicity.

We analyze the polar sea ice distribution and the global sea level pressure (SLP) and baroclinicity distributions over the "satellite" period of 1979-2020. In the Arctic, there are statistically significant sea ice extent (SIE) decreases in all calendar months, and the annual mean has lost 2.22 million km2 over the four decades. The Antarctic SIE, in marked contrast, increased up to 2014, then commenced a remarkable retreat (the annual mean ice extent decreased by 2.03 million km2 in the 3 years to 2017), and subsequently increased to near its long-term average value in 2020. The shifts in seasonal-mean SLP patterns are consistent with a warming planet. At the synoptic scale, we diagnose the changes in the baroclinicity, the mechanism by which cyclones, fronts, and other weather systems are generated. Through a novel presentation, we give an overview of the relative roles of changes in the vertical shear and static stability in influencing the global trends in baroclinicity. In both the Arctic and Antarctic regions, baroclinicity is shown to have increased in each season (with the sole exception of the Arctic in summer). This increase, coupled with midlatitude decreases in baroclinicity, results in poleward shifts of the storm tracks.

Projection Pursuit Regression (PPR) on Statistical Downscaling Modeling for Daily Rainfall Forecasting

Rainfall forecasting has an important role in people's lives. Rainfall forecasting in Indonesia has complex problems because it is located in a tropical climate. Rainfall prediction in Indonesia is difficult due to the complex topography and interactions between the oceans, land and atmosphere. With these conditions, an accurate rainfall forecasting model on a local scale is needed, of course taking into account the information about the global atmospheric circulation obtained from the General Circulation Model (GCM) output. GCM may still be used to provide local or regional scale information by adding Statistical Downscaling (SD) techniques. SD is a regression-based model in determining the functional relationship between the response variable and the predictor variable. Rainfall observations obtained from the Meteorology Climatology and Geophysics Council (BMKG) are a response variable in this study. The predictor variable used in this study is the global climate output from GCM. This research was conducted in a place, namely Kupang City, East Nusa Tenggara because it has low rainfall. The Projection Pursuit Regression (PPR) will be used in this SD method for this study. In PPR modeling, optimization needs to be done and model validation is carried out with the smallest Root Mean Square Error (RMSE) criteria. The expected results must have a pattern between the results of forecasts and observations showing or approaching the observational data. The PPR model is a good model for predicting rainfall because The results of the forecast and observation show that the results of the rainfall forecast are observational data.

Inconsistent Global Kinetic Energy Spectra in Reanalyses and Models

AbstractGlobal upper tropospheric kinetic energy (KE) spectra in several global atmospheric circulation datasets are examined. The datasets considered include the ERA-Interim, JRA-55, and ERA5 reanalyses and two versions of NOAA-GFS analyses at horizontal resolutions ranging from 0.7° to 0.12°. The mesoscale portions of the spectra are found to be highly inconsistent. This is shown to be mainly due to inconsistencies in the scale-dependent numerical damping and in the large contributions to the global mesoscale KE from the KE in convective regions and near orography.The spectra also generally have a steeper mesoscale slope than the -5/3 slope of the observational Nastrom-Gage spectrum pursued at many modeling centers. The sensitivity of the slope in global models to 1) stochastically perturbing diabatic tendencies and 2) decreasing the horizontal hyper-viscosity coefficient is explored in large ensembles of 10-day forecasts made with the NCEP-GFS (0.7° grid) model. Both changes lead to larger mesoscale KE and a flatter spectral slope. The effect is stronger in the modified hyper-viscosity experiment.These results show that (a) despite assimilating vastly more observations than used in the original Nastrom-Gage studies, current high-resolution global analyses still do not converge to a single “true” global mesoscale KE spectrum, and (b) model KE spectra can be made flatter not just by increasing model resolution but also by perturbing model physics and decreasing horizontal diffusion. Such sensitivities and lack of consensus on the spectral slope also raise the possibility that the true global mesoscale spectral slope may not be a precisely -5/3 slope.

Distribution of 137Cs in lichens, mosses and pine needles along the transect from the north to the south of Western Siberia

The 137Cs content in mosses (Hylocomium splendens), lichens (Cladonia stellaris) and the needles of the Siberian pine (Pinus sibirica) and the common pine (Pinus sylvestris) along the transect from the north to the south of Western Siberia from N. 67.5° to N. 55° has been investigated. The appearance of 137Cs here is linked to the nuclear weapon tests at Novaya Zemlya. The measurements have shown that at all sampling points south of N. 59.6° there is a very sharp decrease in the 137Cs specific activity in all components of the ecosystem (in mosses and lichens by about 20 times, and in the needles of conifers by 100 times) instead of a smooth decrease. This fact can be explained by the existence of the global atmospheric circulation consisting of three circulation cells in the Northern hemisphere. It is just around N. 60° that the boundary between the Polar cell and the circulation cell of midle latitudes is drawn. At this boundary, the counter surface air flows of these cells (in our case, a contaminated flow from the north and a clean one from the south) collide and generate the upward air flows here that take 137Cs away. In addition, there is water vapor condensation in the upward flows resulting in snowfalls, rains and thunderstorms. And with these precipitation events, large amounts of 137Cs should have fallen out to the north of the Polar cell boundary during the Novaya Zemlya tests. The areas south around of N. 60° have been supposed to remain clean, which is what is being observed.

Impact assessment of common bean availability in Brazil under climate change scenarios

CONTEXTBrazil is one of the main producers of common beans (Phaseolus vulgaris L.), which have high nutritional value as human food. The climate changes predicted in the 21st century might be a possible threat to the planet’s food security, given the expected population increase, and hence, increased demand for food. OBJECTIVEThis study aimed to project the impact of climate change on common bean cropping systems using an upscaling climate approach and crop modeling to represent the Brazilian production regions. METHODSWe considered the representative CO2 concentration pathway scenarios (RCPs) 4.5 and 8.5 presented by the 5th IPCC Assessment Report from 20 atmospheric global circulation models covering the main bean-producing region in Brazil. The well-calibrated CROPGRO-Drybean crop model simulated two representative cultivars of the “black” and “colors” types and three cropping seasons applied by Brazilian farmers. RESULTS AND CONCLUSIONSOn average, we found that yield increased by 5.56% and 9.12% for the RCP 4.5 and 8.5 scenarios, respectively. Increased photosynthetic efficiency due to the increased atmospheric CO2 concentration was identified as the main cause of this yield increase. Crop respiration rates increased due to the raised air temperature, and were responsible for increasing the probability (production risk) of not meeting the future domestic demands for grains to 10.13% and 8.34% for the RCP 4.5 and 8.5 scenarios, respectively. For the national supply of grains, estimates pointed to a future in which crop production will probably rely more on area expansion than yield gains by crop intensification. SIGNIFICANCEOur findings emphasize the need for new policies for land utilization and investments in scientific research programs aimed towards genetic adaptation in all main Brazilian crops in the face of potential climate change.

Projection pursuit regression and principal component regression on statistical downscaling using artificial neural network for rainfall prediction in Jember

Rainfall forecasting is essential for Indonesia, which is an agricultural country. Forecasting to see the rainfall needed to anticipate the danger of drought that will harm farmers. However, due to the complexity of topography and the interactions between the oceans, land, and atmosphere in Indonesia, it is difficult to predict rainfall. Therefore, Statistical Downscaling (SD) is needed to provide accurate rainfall predictions by considering the information about global atmospheric circulation obtained from the General Circulation Model (GCM). Statistics Downscaling (SD) modeling is a basic regression model based on the functional relationship between local scales, which is the response variable with the Global Circulation Model (GCM) global scale as a predictor variable. The Statistics Downscaling (SD) method used is Principal Component Regression (PCR) and Projection Pursuit Regression (PPR). The prediction of both methods was conducted by an Artificial Neural Network (ANN). The results showed that the prediction of rainfall in Jember using the PPR + ANN method (with the RMSE value of 79.58723) had better accuracy than the PPR, PCR, and PCR + ANN methods, which had RMSE values of 103.7539, 112.337 and 83.62029, respectively.

Changes in Paleovegetation and Paleoclimate in China since the Late Middle Pleistocene: A Case Study of the Dajiuhu Basin

The East Asian monsoon system is an important part of global atmospheric circulation; however, records of the East Asian monsoon from different regions exhibit different evolutionary rhythms. Here, we show a high-resolution record of grain size and pollen data from a lacustrine sediment core of Dajiuhu Lake in Shennongjia, Hubei Province, China, in order to reconstruct the paleovegetation and paleoeclimate evolution of the Dajiuhu Basin since the late Middle Pleistocene (~237.9 ka to the present). The results show that grain size and pollen record of the core DJH-2 are consistent with the δ18O record of stalagmites from Sanbao Cave in the same area, which is closely related to the changes of insolation at the precessional (~20-kyr) scale in the Northern Hemisphere. This is different from the records of the Asian summer monsoon recorded in the Loess Plateau of North China, which exhibited dominant 100-kyr change cyclicities. We suggest that the difference between paleoclimatic records from North and South China is closely related to the east–west-oriented mountain ranges of the Qinling Mountains in central China that blocked weakened East Asia summer monsoons across the mountains during glacial periods.

Response of drylands' water‐cycle to the global warming

AbstractDrylands occupy about 41% of land surface and feed 38% of the world's population, where understanding drylands' water‐cycle is in urgent need. In this study, response of water‐cycle over the drylands to global warming from 1980 to 2015 and its mechanisms have been investigated in detail. The results show that, with the global surface air temperature (SAT) increasing at a rate of 0.03 K⋅year−1 over the drylands, an increased evaporation is found; however, the net water vapour transport over the global drylands appears an overall decreased rate of −0.24 mm⋅year−1. Due to global warming and atmospheric circulation anomalies, the evaporation increases by 1.1 mm⋅year−1, while the precipitation and runoff decrease by −2.32 and −0.8 mm⋅year−1, respectively. In addition, the precipitation conversion rate (PCR) tends to decrease during this period, while the precipitation recycling rate (PRR) shows slightly increasing trend, implying a more dependence of the precipitation on the local evaporation over the drylands. Overall, except the drylands of Africa, it indicates a weakened water‐cycle over the global drylands from 1980 to 2015. Though some findings have been revealed, there still remains some uncertainties due to the observation limitation on the water‐cycle components. Therefore, a comprehensive study including multi‐sourced data and model simulation is expected in the future.

The rotational and divergent components of atmospheric circulation on tidally locked planets

Tidally locked exoplanets likely host global atmospheric circulations with a superrotating equatorial jet, planetary-scale stationary waves, and thermally driven overturning circulation. In this work, we show that each of these features can be separated from the total circulation by using a Helmholtz decomposition, which splits the circulation into rotational (divergence-free) and divergent (vorticity-free) components. This technique is applied to the simulated circulation of a terrestrial planet and a gaseous hot Jupiter. For both planets, the rotational component comprises the equatorial jet and stationary waves, and the divergent component contains the overturning circulation. Separating out each component allows us to evaluate their spatial structure and relative contribution to the total flow. In contrast with previous work, we show that divergent velocities are not negligible when compared with rotational velocities and that divergent, overturning circulation takes the form of a single, roughly isotropic cell that ascends on the day side and descends on the night side. These conclusions are drawn for both the terrestrial case and the hot Jupiter. To illustrate the utility of the Helmholtz decomposition for studying atmospheric processes, we compute the contribution of each of the circulation components to heat transport from day side to night side. Surprisingly, we find that the divergent circulation dominates day-night heat transport in the terrestrial case and accounts for around half of the heat transport for the hot Jupiter. The relative contributions of the rotational and divergent components to day-night heat transport are likely sensitive to multiple planetary parameters and atmospheric processes and merit further study.

Proposed scheme for modeling of ocean equatorial currents in the phase of El Niño and La Niña: Implementation of the mesoscale turbulence theory

El Niño is a phenomenon of the catastrophic increase of surface temperature in the eastern part of the Pacific Ocean. It has a significant impact to weather of the American continent and western regions of the tropical Pacific, as well as on the weather and climate of entirely the Earth. Most important factors influencing El Niño are the wind, ocean currents and slope of the water surface (and temperature resulting from these factors) at the equator in the Pacific Ocean. The paper considers results of mathematical modeling of the equatorial Pacific Ocean currents in the El Niño and La Niña phases using the theory of mesoscale turbulence. This theory has been successfully tested in modeling of global circulation of atmosphere and ocean (Arsen’yev et al., 2010) and it has been able to calculate the ocean current changes at equator under changing external conditions. It is shown that the water currents at the equator have a four-tier vertical structure. The surface trade-wind current is located above the subsurface undercurrent, below which we observe the intermediate current, turning into the equatorial deep counter flow. When El Niño begins, the currents are rearranged, change signs and sometimes merge with each other. In the phase of maximum development of the phenomenon there is a two-tier structure: (1) surface current heading the American coast is underlain (below the depth of 440 m) by (2) deep equatorial current directed to the Indonesian coast. The theoretical calculations are compared with the physical observations of ocean currents in the El Niño and La Niña phases. The obtained results indicate that the proposed mathematical apparatus makes it possible to explain the set of physical observations in the Pacific Ocean.

Novel dynamical indices for the variations of the western Pacific subtropical high based on three-pattern decomposition of global atmospheric circulation in a warming climate

Previous studies have often used the 500 hPa geopotential height to define indices of the western Pacific subtropical high (WPSH). However, some studies reported that global warming caused a significant increase in geopotential height, particularly at the middle and lower latitudes, leading artificial results about long-term trend of the WPSH. To avoid the spurious signals resulting from global warming, this study first redefines the area, intensity, westward ridge point and ridge line indices of the WPSH by adopting the stream function R of horizontal circulation in the three-pattern decomposition of global atmospheric circulation (3P-DGAC). Subsequently, the climatic characteristics of the WPSH in summer are investigated by applying the new indices based on four reanalysis datasets. The results show that the circulation features of the WPSH could be revealed by the stream function R in 3P-DGAC. Moreover, the rain belt over East Asia is located at the northwest periphery of the zero-value isoline of the stream function R. We conclude that the climatological average WPSH is contracted and retreated eastward during 1979–2018 relative to 1948–1978. Nevertheless, by analyzing interdecadal changes of the time series of the new indices during 1948–2018, we find that area and intensity indices decrease with time before the end of 1970s and increase slightly with time after the end of 1970s, the western ridge point index moves eastward with time before the end of the 1970s and moves westward slightly with time after the end of 1970s, as well as there is no obvious interdecadal variations in the ridge line index. Because of the evident dynamical meaning, the stream function R in 3P-DGAC can be used as an objective indicator to describe the interdecadal variation of the WPSH under global warming.

Вплив глобальної сейсмічної активності на процеси в атмосфері й іоносфері

In recent decades, ideas about earthquakes (EQ) have been formed as a final stage of a planetary continuous self-organizing tectonic process with periods of accumulation and relaxation of tectonic stresses. However, the scientific literature still presents studies of the response of atmospheric and ionospheric processes to individual strong EQs. In this paper, for the first time, the relationship between processes in the lithosphere, troposphere, and ionosphere is considered, taking into account new ideas about the seismic process as a global phenomenon and on the background of processes caused by space weather. Both planetary data (EQ, total electron content (TEC) of the ionosphere) and data (atmospheric pressure, critical frequency of the F2 layer of the ionosphere) of widely spaced observation points in the western and eastern hemispheres were used. To increase the reliability of statistical results, 4 independent databases of daily data for 2007–2015 were used. Stable effects of global seismic activity (GSA) in the considered parameters are established. Thus, the critical frequency of the F2 region with a sharp increase in the GSA increases by 0.4–0.5 MHz. This effect is quite stable and manifests itself almost simultaneously at ionospheric stations of the eastern and western hemispheres, as well as in planetary TEC values. At the same time, in the ionospheric variations, as before, the influence of both the troposphere (especially at a low level of solar activity) and space weather is traced, the characteristics of which in 75 % of cases also show an association with GSA. Therefore, space weather often but not always can act as a trigger on the EQs. In general, in the western hemisphere, the minimum atmospheric pressure occurs earlier than in the eastern, which leads to a noticeable increase in the pressure difference between the hemispheres by 10 mm. Hg., that indicates the relationship between global seismicity and global atmospheric circulation. The established GSA effects, as a rule, have the character of not a local short-term burst, but a jump followed by a gradual decrease (increase) of the index until the next active period (saw-toothed curve), i.e., the influence of the lithosphere on the overlying layers is continuous and is cyclical in nature, probably due to the cyclical nature of tectonic processes. Most likely, several different couplings between geospheres are realized at the same time, partially synchronized by changes in space weather, which requires new physical mechanisms to explain them.

Phase Shift of Planetary Waves and Wave–Jet Resonance on Tidally Locked Planets

Abstract Recent studies found that atmospheric superrotation (i.e., west-to-east winds over the equator) on tidally locked planets can modify the phase of planetary waves. But a clear relationship between the superrotation and the magnitude of the phase shift was not examined. In this study, we re-investigate this problem using a 2D linear shallow-water model with a specified uniform zonal flow. We find that the degree of the phase shift is a monotonic but nonlinear function of the strength of the mean flow and the phase shift has two limits of -π and +π. The existence of these limits can be explained using the energy balance of the whole system. We further show that a resonance between the Rossby wave and the mean flow occurs when the speed of an eastward jet approaches to the westward phase speed of the Rossby wave, or a resonance between the Kelvin wave and the mean flow happens when the speed of a westward jet approaches to the eastward phase speed of the Kelvin wave. The resonance mechanism is the same as that found in the previous studies on Earth and hot Jupiters. Moreover, in the spin-up period of a 3D global atmospheric general circulation simulation for tidally locked rocky planet, we also find these two phenomena: phase shift and wave–jet resonance. This study improves the understanding of wave–mean-flow interactions on tidally locked planets.

Пирогенное преобразование геосистем Западного Прибайкалья: факторы, условия, современное состояние

The factors of pyrogenic impact on the taiga geosystems of the Western Baikal region against the background of the modern transformation of the global atmospheric circula-tion are studied in the paper. The results of world scientific research on modeling climate change and related adverse weather phenomena (prolonged droughts, thunderstorm activity, etc.) are presented. The natural factors contributing to the increase in the pyrogenic transformation of geosystems are described. The study of the spatio-temporal distribution of fires is carried out on the basis of data from remote sensing of the Earth. Information about unfavorable weather conditions and dangerous hydrometeorological phenomena, data on atmospheric phenomena (thunderstorm activity), daily values of air temperature and soil temperature under natural cover at different depths are analyzed in order to factorial analysis of forest fire sources in the study area. The characteristic of the current stage of geosystems is given based on field research conducted in June 2020. It was revealed that catastrophic fires registered in the study area in 1997 and 2015 occurred against the background of minimal thunderstorm activity. At the same time, in the central part of the Western Baikal region thunderstorms were the leading factor in the 2015 fires. Five years after the fire, the restoration of mountain taiga light coniferous forests is characterized by the predominance of the community of Chamaenerion angustifolium (L.) Scop. The successional dynamics of the geosystems of mountain taiga dark coniferous forests is going through the Betula rotundifolia Spach. with Ledum palustre L. and cereal-forb ground cover. Undergrowth of tree species (mainly pine) is rare and uneven about 800–1200 specimens per hectare.

Runoff change controlled by combined effects of multiple environmental factors in a headwater catchment with cold and arid climate in northwest China

The limited runoff in cold and arid regions is sensitive to environmental changes, and it is thus urgent to explore the change and controlling factors of runoff under the background of global warming and intensified human activities. However, previous studies have rarely considered the combined effects of multiple controlling factors at varying scales over time. With the headwater region of the Manas River in northwest China as the study area, we investigated the change in runoff for the period of 1954–2016 and its relationship with regional environmental factors (e.g. precipitation PCP, temperature TMP, potential evapotranspiration ET0, snow cover extent SCE, land use, and normalized difference vegetation index NDVI) and/or global atmospheric circulation (e.g. North Atlantic Oscillation NAO, Arctic Oscillation AO, Pacific Interdecadal Oscillation PDO, and El Nino Southern Oscillation ENSO). In particular, the combined effects of multiple environmental factors were determined at different scales by the multiple wavelet coherence. The annual runoff significantly increased at a rate of 0.508 × 108 m3/decade, and the climate tended to be warmer and wetter. Among the regional and global environmental factors, NDVI and ENSO were the single factor mostly correlated with runoff, while NDVI-TMP and ENSO-PDO were the combined factors with the stronger relations on runoff, respectively. The regional environmental factors had larger impacts on runoff than the global environmental factors, and the natural factors outperformed human activities in controlling runoff. The accelerated melting of snow/glacier induced by the increasing temperature dominated runoff change, and the increasing water inputs from wetter climate may play a second role in runoff. The runoff characteristics in cold and arid regions seem to be different from those regions with little snow/glacier, which should be paid more attention. The employed multiple wavelet coherence is helpful in determining the processes dominating runoff change.

Middle Miocene Intensification of South Asian Monsoonal Rainfall

AbstractDuring the middle Miocene, Earth's climate changed from a global warm period (Miocene Climatic Optimum) into a colder one with the expansion of the Antarctic ice sheet. This prominent climate transition was also a period of drastic changes in global atmospheric circulation. The development of the South Asian monsoon is not well understood and mainly derived from proxy records of wind strength. Data for middle Miocene changes in rainfall are virtually non‐existent for India and the Arabian Sea prior to 11 Ma. This study presents planktic foraminiferal trace element (Mg/Ca and Ba/Ca) and stable oxygen isotope records from NGHP‐01 Site 01A off the coast of West India in the Eastern Arabian Sea (EAS) to reconstruct the regional surface hydrography and hydroclimate in the South Asian monsoon (SAM) region during the middle Miocene. The Ba/Ca and local seawater δ18O (δ18Osw) changes reveal a notable gradual increase in SAM rainfall intensity during the middle Miocene. Additionally to this long‐term increase in precipitation, the seawater δ18O is punctuated by a prominent decrease, i.e. freshening, at ~14 Ma contemporary with Antarctic glaciation. This suggests that Southern Ocean Intermediate Waters (SOIW) transmitted Antarctic salinity changes into the Arabian Sea via an “oceanic tunnel” mechanism. The middle Miocene increase in SAM rainfall is consistent with climate model simulations of an overall strengthening Asian monsoon from the Eocene to the middle/late Miocene with a further acceleration after the middle Miocene climate transition.

A nonstationary analysis for investigating the multiscale variability of extreme surges: case of the English Channel coasts

Abstract. This research examines the nonstationary dynamics of extreme surges along the English Channel coasts and seeks to make their connection to the climate patterns at different timescales by the use of a detailed spectral analysis in order to gain insights into the physical mechanisms relating the global atmospheric circulation to the local-scale variability of the monthly extreme surges. This variability highlights different oscillatory components from the interannual (∼1.5, ∼2–4, ∼5–8 years) to the interdecadal (∼12–16 years) scales with mean explained variances of ∼25 %–32 % and ∼2 %–4 % of the total variability, respectively. Using the two hypotheses that the physical mechanisms of the atmospheric circulation change according to the timescales and their connection with the local variability improves the prediction of the extremes, we have demonstrated statistically significant relationships of ∼1.5, ∼2–4, ∼5–8 and 12–16 years with the different climate oscillations of sea level pressure, zonal wind, North Atlantic Oscillation and Atlantic Multidecadal Oscillation, respectively. Such physical links have been used to implement the parameters of the time-dependent generalized extreme value (GEV) distribution models. The introduced climate information in the GEV parameters has considerably improved the prediction of the different timescales of surges with an explained variance higher than 60 %. This improvement exhibits their non-linear relationship with the large-scale atmospheric circulation.