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In this paper, climatic analysis of non-precipitation periods (NPP) in Lithuania was performed, assessing their recurrence and trends from 1991 to 2020 using two criteria – when precipitation was

Even though winter land–sea thermal contrast (LSC) is expected to undergo a strong weakening in the future warmer climate, its effects have been poorly investigated. Here we run a set of idealized winter simulations featuring reduced LSC in the Northern Hemisphere (NH) extratropics, or in individual extratropical sectors of the NH (Atlantic and Pacific), using an intermediate-complexity atmospheric general circulation model. Reduced LSC is obtained by imposing a warming of surface land temperatures in East Asia and North America. For similar warming intensities over the two regions, the response of the model to East Asia forcing is significantly stronger and dominates the response to the sum of the two forcing patterns. We find that the LSC reduction causes a weakening and poleward shift of the midlatitude jet streams, and a strong interference with zonal wavenumbers 1 and 2. In particular, East Asian warming reduces the amplitude of waves 1 and 2, producing a strengthening of the stratospheric vortex, while a weaker vortex due to a moderate amplification of wave 1 is detected when warming North America. Eventually, stratospheric signals propagate downward in the troposphere affecting the midlatitude winter NH even remotely from the forcing. In this work we pinpoint some mechanisms by which weakened winter LSC influences the NH extratropical circulation: the results may become useful to interpret the response to long-term projections displaying reduced LSC along with other climate change forcing patterns.

International audience; Continued Amazonian deforestation perturbs the surface turbulent fluxes which are important for building the conditions for the wet season onset in the southern Amazon. This work evaluates the impacts of tropical deforestation on the onset and development of the Amazonian rainy season using a weather typing approach. We use 19-year simulations (2001-2019) with the Regional Earth System Model from the Institute Pierre Simone Laplace (RegIPSL) with twin control/deforestation experiments. RegIPSL represents the dominant modes or the atmospheric circulation patterns (CPs) of the daily-to-decadal circulation variability in tropical South America, and the evolution of atmospheric and surface conditions along the dry-to-wet transition period. According to RegIPSL, forests and crops contribute differently to the onset. During the dry-to-wet transition period, croplands/grasslands present a stronger shallow convection driven by a higher atmospheric temperature. Large-scale subsidence suppresses low-level convection in the region and deep convection only persists over forests where the atmosphere presents more convective potential energy. After the onset and the establishment of large-scale rainfall structures, both land covers behave similarly in terms of surface fluxes. Deforestation decreases the frequency of the CP typically linked to the onset. Changes in the spatial structure and frequency of the wet season CPs reinforce the hypothesis of a deforestation-induced dry season lengthening. Variations in the CP frequency and characteristic rainfall have opposite effects on accumulated rainfall during the dry-to-wet transition period. Whereas alterations in frequency are associated with a regional circulation response, changes in the CP characteristic rainfall correspond to a local response to deforestation.

The variability and dynamics of the Asian monsoon (AM, hereafter indicates both of the summer and winter monsoons.) at orbital and millennial timescales has attracted wide interest. Chinese loess deposits, covering an area of ~500 × 103 km2 and with a thickness of several tens to more than three hundred meters, is an ideal continental archive to reconstruct AM variations during the Quaternary epoch. Over the past thirty years, since the earliest paper published in an international journal that linked the Asian monsoon and Chinese loess deposits, many studies have been undertaken focusing on this research topic. These results have greatly deepened our understanding of the variations of the AM climate and their driving mechanisms during the past ~2.6 Myr. In this paper, we emphasize recent progress on the AM variability and dynamics revealed by Chinese loess records; in particular, we discuss the reliability and precision of the timescale and the monsoon proxy indicators for the loess-paleosol sequences, which are two fundamental aspects for understanding AM behavior. We analyze what we know and discuss what we do not know about the AM. We refine the timescale for the typical loess-paleosol sequence in the central Chinese Loess Plateau (CLP), which can be used as a new timescale to study palaeoclimate and palaeoenvironmental changes in the monsoonal Asia. We conclude that low-latitude insolation changes induced by precession, and global ice volume, temperature at high-latitudes, as well as sea-level changes forced variations of the AM at orbital time scales. High-latitude cooling events and low-latitude hydroclimate process at millennial time scales, such as climate changes associated with Heinrich events and Dansgaard-Oeschger cycles in Northern Atlantic and Greenland, have also modulated AM variability. We suggest that high-latitude forcing of AM variations occurs through ocean and atmospheric circulation linkages, although the roles of atmospheric CO2, ocean and vegetation feedbacks need further investigation. In future study, high-resolution independent dating, novel proxy indices and transient numerical simulations are still basic tools to understand the loess deposition and AM variations that require considerably more work. Issues such as reliable spatial comparison and regional linkages of records (dependent on precise and accurate numerical chronologies), and quantitative reconstruction of the AM variations, should be given priority in the study the past climate change in Asia, and low-latitude hydroclimate process.

There is a great need for the reconstruction of independent El Nino Southern Oscillation (ENSO) from different archives and locations to provide a robust understanding of its driving and feedback mechanisms on long time scales. Though tree-ring cellulose δ18O (δ18OTR) records from the East Asian monsoon (EAM) region of China have the potential to reconstruct ENSO on an annual time scale, δ18OTR ENSO signals may be masked by local climate effects since any individual δ18OTR record is influenced by both large-scale atmospheric circulation and local climate. Few attempts have been made to reduce the uncertainties of the reconstructed ENSO index by δ18OTR records from the EAM region of China by ensemble data analysis. In this study, twelve published δ18OTR records spanning over 100 years (1902–2003 CE) have been collected and processed using principal component analysis (PCA). The first principal component (PC1) extracted from the δ18OTR records shows a positive/negative relationship with the annual Nino 3.4 index/southern oscillation index (SOI), with correlation coefficients higher than those between single δ18OTR record and the Nino 3.4 index/SOI, suggesting the ENSO signal is improved by PCA. A 31-year running correlation on PC1- Nino 3.4 index/SOI reveals an increasingly stronger correlation between δ18OTR and ENSO since the last century, inferring that, in the EAM region, the δ18OTR-ENSO correlation may become much stronger under continuous global warming in the future. Spectrum and spatial correlation analysis further support the idea that PC1 responds to ENSO. The significant relationships between observational precipitation δ18O and Nino 3.4 SST anomaly and PC1 from 1973–2003 CE suggest that precipitation δ18O is a key link to connect δ18OTR with ENSO. This study shows the advantage of ensemble data analysis on δ18OTR records in EAM region of China, which could better extract ENSO signals and reduce the uncertainties of reconstructed ENSO variations by individual δ18OTR records from the EAM region of China. It provides an alternative independent annual indicator for ENSO reconstruction on long time scales when more δ18OTR records from this region are extended in the near future.

The midwinter suppression (MWS) of the North Pacific Storm Track (NPST) has been an active research topic for decades. Based on the daily-mean NCEP/NCAR reanalysis from 1948 to 2018, this study investigates the MWS-related atmospheric circulation characteristics in the Northern Hemisphere by regression analysis with respect to a new MWS index, which may shed more light on this difficult issue. The occurrence frequency of the MWS of the upper-tropospheric NPST is more than 0.8 after the mid-1980s. The MWS is accompanied by significantly positive sea-level pressure anomalies in Eurasia and negative anomalies over the North Pacific, which correspond to a strengthened East Asian winter monsoon. The intensified East Asian trough and atmospheric blocking in the North Pacific as well as the significantly negative low-level air temperature anomalies, lying upstream of the MNPST, are expected to be distinctly associated with the MWS. However, the relationship between the MWS and low-level atmospheric baroclinicity is somewhat puzzling. From the diagnostics of the eddy energy budget, it is identified that the inefficiency of the barotropic energy conversion related to the barotropic governor mechanism does not favor the occurrence of the MWS. In contrast, weakened baroclinic energy conversion, buoyancy conversion, and generation of eddy available potential energy by diabatic heating are conducive to the occurrence of the MWS. In addition, Ural blocking in the upstream region of the MNPST may be another candidate mechanism associated with the MWS.

There are significant differences in the way that researchers have defined “Etesian wind days”. An attempt is made here to establish common definitions of the various types of Etesian winds from the weather forecaster’s viewpoint. These definitions are based on objective criteria adopted from the frequency of atmospheric circulation features associated with the occurrence of the Etesian winds and their physical characteristics. The presence of fairly constant northerly winds over the Greek Seas in summer are called Etesian winds. When a new spell of Etesian winds is established with no diurnal variation of the wind direction for consecutive days (maximum of seven), these winds are called “type B” Etesian winds or “Etesian outbursts”. The atmospheric circulations associated with the occurrence, origin and evolution of the type B Etesian winds and the accompanying weather are revealed utilizing data for the period 1975-2015 and focusing on two case studies on July 21-22, 1983 and July 3-4, 2017. The presence of the Subtropical Jet Stream (SJS) over the Greek territory and its interaction with the Polar Jet Stream (PJS) are dominant factors. Large-scale atmospheric circulations are studied to identify simultaneous direct links to the Indian Summer Monsoon (ISM), El Niño-Southern Oscillation (ENSO), Madden-Julian Oscillation (JMO), deep convective activity in the Hadley circulation in the tropics, and West Africa Monsoon (WAM)

This study presents the daily atmospheric circulation patterns at surface and altitude related to the South Atlantic Convergence Zone (SACZ) events that occurred between 2007 and 2017. For this analysis, Principal Pattern Sequence Analysis (PPSA) and sea level pressure and geopotential height reanalysis were used. Four typical atmospheric circulation patterns associated with SACZ episodes were identified. Three of them are related to the propagation of a cold front toward southeastern Brazil with a post-frontal anticyclone moving over the Atlantic Ocean. The fourth pattern is associated with the presence of a cut-off low centered over the central-south region of Brazil that induces moisture transport from the Atlantic Ocean and from the Amazon basin to most of southeastern Brazil. Considering the first three patterns, they represent, respectively, a frontal wave, a classical cold front, and a slow-moving cold front. All of these patterns provide permanent northwesterly winds in the lower troposphere over southeastern Brazil from two days before the SACZ occurrence.

This study focuses on the strengthening of the maritime influence on the Balkan Peninsula in summer. The study uses mainly statistical methods such as trend analysis, multiple linear regression models, etc. The research period is 1979–2020. The results show that in the beginning of the twenty-first century in southeastern Europe there is a tendency of faster increase in the average August air temperatures compared to the increase in average July air temperatures. Thus, the temperature in August is already higher than that in July. The causes for these changes are changes in atmospheric circulation in summer. Over the last two decades, the transport of air masses from east and southeast has been strengthening, which for the Balkan Peninsula means a transport from water basins toward land. The intra-annual course of air temperature above a water basin, which has a maximum in August, is now becoming typical over land. This feature is not yet present in the entire studied region, but the trends from the measurements in meteorological stations show that very soon the temperatures in August could be higher than that in July over the entire territory of the Balkan Peninsula. On a more global scale, it is still unclear which mechanisms of atmospheric circulation influence the processes in southeastern Europe. Changes in ocean temperatures and atmospheric circulation in the North Atlantic are likely to have an impact. However, other factors (e.g. the increase in global temperatures, the expansion of Hadley cell) may also have an impact.

We investigated the abrupt alternation from flood to drought in southern China during summer 2019 using multiple datasets. Positive anomalies of precipitation occurred in southern China in the summer of 2019 and the daily precipitation in the Jiangnan area south of the mid and lower reaches of the Yangtze River valley showed an abrupt change from flood to drought conditions around mid-July. The highest precipitation in 39 years was recorded between 1 June and 14 July 2019. The circulation systems affecting this high precipitation included a persistent deepened East Asian trough, the southward location of the western Pacific subtropical high, an intensified East Asian subtropical jet, an anomalous low-level cyclone from southern Japan to southern China and extremely strong positive vorticity over the Jiangnan area. Completely different atmospheric circulation anomalies from 15 July to 31 August caused continuously high temperatures, below-normal precipitation and severe drought in Jiangnan. Further investigations showed that the sudden change in atmospheric circulation around mid-July started in the mid and lower troposphere and was influenced by the northward track of tropical cyclone Danas in the northwestern Pacific.

The human circulatory system is one of the admirable rhythms of nature. The heart and the vasculature are constitutive structures. The vasculature consists of arterial and venous appurtenances which are arranged in an idealized network capable of enhancing circulation. The crux of this study is the representation of the cardiovascular system as a network in which electrical constraints apply. As a network, the system is amenable to graph analytic treatment; as edge-nodal parameters ensue, topological constraints apply. In virtue of cardiac auto-rhythmicity, electrical impulses are driven through the vessels to the body cells. As a rule, the vessels must elicit a modicum of resistance. This work weaponized the elements of graph theory and electrical properties of the heart in elucidating the flow mechanism associated with the cardio-vascular system. The voltage drop across the connecting vessels (idealized as wires) was carefully depicted and analyzed by the method of matrices. When the cardiac function is within physiological definition a vascular compartment may be a liability in the event of poor circulation. Therefore the knowledge of vascular resistive capacities, which this work portrayed, is a sine-qua-non to the assessment of flow integrity of the system under consideration. MSC 2010 No.: 05C21, 92C42, 92B25. Keywords: Cardiovascular, Network, Matrices, Flow, Circuit, Edges and Nodes, Wave propagation, Bifurcation.

European climate is associated with variability and changes in the mid-latitude atmospheric circulation. In this study, we aim to investigate potential future change in circulation over Europe by using the EURO-CORDEX regional climate projections at 0.11° grid mesh. In particular, we analyze future change in 500-hPa geopotential height (Gph), 500-hPa wind speed and mean sea level pressure (MSLP) addressing different warming levels of 1 °C, 2 °C and 3 °C, respectively. Simple scaling with the global mean temperature change is applied to the regional climate projections for monthly mean 500-hPa Gph and 500-hPa wind speed. Results from the ensemble mean of individual models show a robust increase in 500-hPa Gph and MSLP in winter over Mediterranean and Central Europe, indicating an intensification of anticyclonic circulation. This circulation change emerges robustly in most simulations within the coming decade. There are also enhanced westerlies which transport warm and moist air to the Mediterranean and Central Europe in winter and spring. It is also clear that, models showing different responses to circulation depend very much on the global climate model ensemble member in which they are nested. For all seasons, particularly autumn, the ensemble mean is much more correlated with the end of the century than most of the individual models. In general, the emergence of a scaled pattern appears rather quickly. Tugba Ozturk was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under the programme TUBITAK 2219—International Postdoctoral Research Fellowship. This work also received support by the European Union under the Horizon 2020 Grant Agreement 776613, the EUCP project. Publisher's Version Q2 WOS:000722493100002

The variability of occurrence of snow cover and the impact of atmospheric circulation on the snow cover occurrence in the period 1966/1967–2019/2020 in Poznań (Poland) have been examined. The implementation of the primary study objective covers the comprehensive analysis of the winter snow and thermal conditions using various indicators. This paper is based on daily data from the years 1966–2020 concerning the winter period. Winters in Poznań are highly variable and differentiated, considering the duration of particular seasons, number of days with snow cover, mean snow cover thickness, winter snowiness coefficient, or winter severity index. Negative trends concerning days with snow cover total snow cover depth winter snowiness coefficient and winter severity index in Poznań prove statistically significant. A higher probability of occurrence of snow cover was determined during cyclonic than anticyclonic circulation. The westerly and northerly types especially favoured the occurrence of days with snow cover. The increase of snow cover was associated with the northerly inflow mainly. Westerly types of circulation caused the decrease of snow cover predominantly.

Extratropical cyclones play a major role in the atmospheric circulation and weather variability and can cause widespread damage and destruction. Extratropical cyclones in northern Europe, which is located at the end of the North Atlantic storm track, have been less studied than extratropical cyclones elsewhere. Our study investigates extratropical cyclones and windstorms in northern Europe (which in this study covers Norway; Sweden; Finland; Estonia; and parts of the Baltic, Norwegian, and Barents seas) by analysing their characteristics, spatial and temporal evolution, and precursors. We examine cold and warm seasons separately to determine seasonal differences. We track all extratropical cyclones in northern Europe, create cyclone composites, and use an ensemble sensitivity method to analyse the precursors. The ensemble sensitivity analysis is a novel method in cyclone studies where linear regression is used to statistically identify what variables possibly influence the subsequent evolution of extratropical cyclones. We investigate windstorm precursors for both the minimum mean sea level pressure (MSLP) and for the maximum 10 m wind gusts. The annual number of extratropical cyclones and windstorms has a large inter-annual variability and no significant linear trends during 1980–2019. Windstorms originate and occur over the Barents and Norwegian seas, whereas weaker extratropical cyclones originate and occur over land areas in northern Europe. During the windstorm evolution, the maximum wind gusts move from the warm sector to behind the cold front following the strongest pressure gradient. Windstorms in both seasons are located on the poleward side of the jet stream. The maximum wind gusts occur nearly at the same time as the minimum MSLP occurs. The cold-season windstorms have higher sensitivities and thus are potentially better predictable than warm-season windstorms, and the minimum MSLP has higher sensitivities than the maximum wind gusts. Of the four examined precursors, both the minimum MSLP and the maximum wind gusts are the most sensitive to the 850 hPa potential temperature anomaly, i.e. the temperature gradient. Hence, this parameter is likely important when predicting windstorms in northern Europe.

The Western Tibetan Vortex (WTV) is a large-scale circulation pattern identified from year-to-year circulation variability, which was used to understand the causal mechanisms for slowdown of the glacier melting over the western Tibetan Plateau (TP). A recent argument has suggested the WTV is the set of wind field anomalies resulting from variability in near-surface air temperatures over the western TP (above 1500 m), which, in turn, is likely driven by the surface net radiation. This study thereby evaluates the above putative thermal-direct mechanism. By conducting numerical sensitivity experiments using a global atmospheric circulation model, SAMIL, we find a WTV-like structure cannot be generated from a surface thermal forcing imposed on the western TP. A thermally-direct circulation generated by the surface or near surface heating is expect to cause upward motions and a baroclinic structure above it. In contrast, downward motions and a quasi-barotropic are observed in the vertical structure of the WTV. Besides, we find variability of the surface net radiation (sum of the surface shortwave and longwave net radiation) over the western TP can be traced back to the WTV variability based on ERA5 data. The anticyclonic (cyclonic) WTV reduces (increases) the cloudiness through the anomalous downward (upward) motions, causes more (less) input shortwave net radiation and thereby more (less) surface net radiations, resulting in the warmer (cooler) surface and near-surface air temperature over the western TP. The argument is constructive in encouraging examination of the radiative balance processes that complements previous studies.

The central China summer precipitation (CCSP) is of great importance to the people’s livelihood of this densely populated region, including the agriculture, ecosystems, water resources, economies, and health. Based on the observed precipitation, sea surface temperature (SST), and atmospheric reanalysis datasets, the present study investigates the effects of El Nino in the developing stage on the CCSP during 1960–2014. The results show that the CCSP anomalies exhibit significant negative correlations with the El Nino-related SST anomalies in both the simultaneous summer and the following winter, implying that the developing El Nino is important for modulating the CCSP. However, this climatic teleconnection of El Nino is unstable, with an obvious interdecadal change around the late 1980s. Specifically, the negative correlation is not statistically significant in the previous epoch before the late 1980s (1960–1988), but dramatically strengthens since the late 1980s (the post epoch for 1989–2014). Such an interdecadal change is closely associated with the change of the El Nino-related SST anomaly pattern. Compared to the previous epoch, the central Pacific El Nino occurs more frequently in the post epoch, leading to an interdecadal shift of the maximum warm SST anomalies from the eastern Pacific to the central Pacific. The resultant westward extension of the atmospheric circulation responses induces an anomalous low-level cyclone covering South China in the post epoch. It would prevent the southwest monsoon from delivering the moisture to the north and hence reduce the CCSP. While, in the previous epoch, the anomalous cyclone locates east of South China, exerting insignificant influence on the CCSP. This work highlights a strengthening effect of El Nino on the CCSP since the late 1980s, with great implications for the regional seasonal climate prediction.

The El Nino–Southern Oscillation (ENSO) significantly affects the formation of precipitation anomalies over Japan, with more (less) and less (more) winter precipitation over the Pacific and Sea of Japan during El Nino (La Nina), respectively. In this study, the effect of ENSO on winter precipitation in Japan was investigated using a large ensemble of regional climate simulations that capture the meridional contrast of precipitation anomalies between areas facing the Sea of Japan and the Pacific along the Japanese Archipelago during ENSO. Self-organizing maps (SOMs) of the surface atmospheric circulation were applied to explore the effect of ENSO forcing on weather patterns (WPs) and associated changes in precipitation including snowfall. The results suggest that ENSO-related spatial variations in precipitation can be attributed to differences in WP frequency such as extratropical cyclone events and WP precipitation in the ENSO-modulated seasonal background state. The former and latter can be interpreted as dynamical and thermodynamic effects of ENSO, respectively. Atmospheric circulation analogs reveal that thermodynamic and dynamic effects account for approximately one-third and two-thirds of the precipitation differences between ENSO phases, respectively. ENSO–precipitation relationships in Japan are more pronounced in the negative phase of the Pacific Decadal Oscillation.

Air pollution is one of the main environmental problems in the metropolitan area of Sao Paulo (MASP) in Brazil, with frequent exceedances of air quality standards. Occasionally, the exceedance events last many days, resulting in continuous exposure to concentrations above the standards, with impacts to human health. In this air pollution long-term study, a method was developed to identify persistent exceedance events (PEE) of particulate matter (PM10) and ozone (O3) and associated surface weather patterns. Between 2005 and 2017, 119 PEE were identified, with exceedances occurring simultaneously in at least 50% of monitoring stations along 3 to 14 consecutive days. Median PM10 and O3 concentrations increased by 60% during the events. Mean fields of sea level pressure from global reanalysis data revealed the influence of high-pressure systems and pre-frontal conditions. PM10 events were frequent in austral winter and mostly driven by anomalous atmospheric circulation with a wind change to northwest. On the other hand, O3 events were common in the spring, associated with higher positive anomalies of temperature and solar radiation. Overall, results show that PEE span a regional scale, differing from ordinary exceedance events that can be driven by local conditions. Policy makers should be aware of the frequency of PEE in the development of mitigation measures against the exposure to harmful levels of air pollutants. The concept of PEE can be applied to other metropolitan areas and may support the development of data-driven air quality predictive models based on current or forecasted weather conditions.

The response of atmospheric circulation to sea surface temperature anomaly (SSTA) of different scales in extratropical oceans has always been a popular issue in air-sea interactions, especially regarding the influence of widely active, small-scale ocean eddies on the atmosphere. Based on the regional climate model RegCM4.6, three sets of ensemble experiments with different initial values were designed, and the response of atmospheric circulation and possible mechanisms to Kuroshio Extension Decadal Variability SSTA with different scales (KEDV-induced SSTA) during winter were discussed. The response of atmospheric circulation to the KEDV-induced mesoscale SSTA presents a broadly tripolar pattern, while the response to the KEDV-induced large-scale SSTA presents a baroclinic structure in the central Pacific and a dipole-type response with a barotropic structure in the eastern Pacific. Further diagnostic analysis shows that under the influence of mesoscale SSTA, transient eddy activity is strengthened, and feedback of transient eddy plays a major role in the large-scale circulation anomaly in the central-eastern Pacific. The associated barotropic energy conversion also plays an important role in maintaining the large-scale circulation anomaly in the northwestern Pacific Ocean. Under the influence of large-scale SSTA, diabatic heating is stronger, and the feedback of diabatic heating plays a major role in the large-scale circulation anomaly.

Vegetation phenology is one of the key agroclimatic indices that is sensitive to climate change. Analyzing the variation in plant phenology under a changing environment can provide reference information to assess the impact of climate change on ecosystems and agricultural management. In this study, we focused on the thermal growth season, an important phenology index. We defined four growing season indices based on the surface temperature to quantify the changes in thermal growth season and analyze their association with atmospheric circulation in China. The results showed that the start date of the growing season exhibited a significant advanced trend (P

Atmospheric diabatic heating, a major driving force of atmospheric circulation over the tropics, is strongly confined to the tropical western North Pacific (TWNP) region, with the global warmest sea surface temperature (SST). The changes in diabatic heating over the TWNP, which exert great impacts on the global climate system, have recently exhibited a noticeable seasonal dependence with a remarkable increase in boreal spring. In this study, we applied observations, reanalysis data, and numerical experiments to investigate the causes of the seasonality in heating changes. Results show that in boreal spring convection is more sensitive to the TWNP SST, leading to a more significant enhancement of deep convection, although the increase in the SST is nearly the same as that in the other seasons. In the non-spring seasons, the enhanced convection due to increased local SST is suppressed by the anomalous anticyclonic wind shear over the TWNP, generated by the easterly wind anomalies induced by the tropical Indian Ocean (TIO) warming via the Kevin waves. However, the TIO warming does not show any suppressing effect in spring because it is much weaker than that in the other seasons and thus the warming itself cannot induce sufficient convective heating anomalies to excite the Kelvin waves.

The flows of international students are like the currents of the oceans, not only affecting the individuals adrift in them but the global circulation of policy, economics and academics as a whole, bearing pros and cons for each country or region along the way. To date, there has not been a detailed and elaborate description of the fluxes of international students over decades. In light of the research gap, the article utilises the chord diagram to draw threads between each pair of origin and destination of international students in the last 20 years and divides the periods into four main phases. With each phase exhibiting its specific features, we have tentatively concluded that the global student mobility structure has evolved from Arterial (1999–2003), Breakthrough (2004–2008) to Catch-Up (2009–2013), and lastly, Diversification (2014–2018). Corresponding reasons underpinning each change of the migration flows are also discussed briefly in the article.

Explaining the relationship between atmospheric circulation patterns and precipitation over a given area is one of the key problems in predicting climate variables for monthly and seasonal leadtime. We investigated the influence of atmospheric circulation indices on winter precipitation over the northern part of the Korean Peninsula (WP-NPKP) during the period 1949-�2020. Data from 37 weather stations were used to calculate the correlation coefficients between WP-NPKP and the Siberian High (SH) and the Aleutian Low (AL), which are thought to dominate the winter weather systems over the study area. We chose those atmospheric circulation indices which are closely connected with the interannual variability of WP-NPKP and explained their possible mechanisms. To identify circulation patterns which most strongly correlated with WP-NPKP, one-point simultaneous correlation maps were created using Pearson correlation analysis, and their monotonic trends were tested with the Mann-Kendall method. We found that interannual variability of WP-NPKP had a closer connection with the difference in area-averaged climate variable anomalies over any 2 areas than with the anomalies themselves. Increased AL index minus decreased SH index had some correlation with winter rainfall; higher sea level pressure over the ocean, rather than that over land, was favorable for the transport of moisture toward the study area. Also, the indices which describe differences in air temperature anomalies at lower and middle latitudes had a relatively high correlation with WP-NPKP, and the difference indices of area-averaged zonal and meridional wind anomalies indicated a considerable linkage with winter precipitation over the study area. Their possible mechanisms, which we discuss in comparison to other studies of winter climate over East Asia, are very useful in selecting the predictors for monthly and seasonal prediction of climate variables over the study area.

A two-zone model of the atmospheric circulation over a hemisphere is considered. The latitude φ of the boundary between the zone of the Rossby circulation regime at mid and high latitudes and the zone of the Hadley circulation regime at low latitudes serves as a model variable. The principle of maximum of the (information) entropy of the eddy regime within the Rossby regime zone is used to determine a statistical (climatic) equilibrium value of φ. Based on the proposed model, the question of atmospheric blocking action over the hemisphere is addressed. An attempt has been made to represent a blocking phenomenon as a necessary attribute of the atmospheric circulation in statistical equilibrium. The model suggests that long-term climate change related either to the (significant) global warming or to the (significant) global cooling, both respective to the current climate state, and quantified in terms of changes in latitude φ, leads to an increase in the probability of blocking action.

The effect of soil moisture (SM) on precipitation is an important issue in the land–atmosphere interaction and shows largely regional differences. In this study, the SM of the ERA-Interim reanalysis and precipitation data of the weather stations were used to investigate their relationship over eastern China during July and August. Moreover, the WRF model was applied to further validate the effect of SM on rainfall. In the observations, a significantly negative relationship was found that, when the soil over southern China is wet (dry) in July, the rainfall decreases (increases) over the Huang–Huai–River basin (hereafter HHR) in August. In the model results, the soil can “memorize” its wet anomaly over southern China from July to August. In August, the wet soil increases the latent heat flux at surface and the air moisture at lower levels of the atmosphere, which is generally unstable due to the summer monsoon. Thus, upward motion is prevailing over southern China in August, and the increased surface air moisture is transported upwards. After that, the condensation of water vapor is enhanced at the middle and upper levels, increasing the release of latent heat in the atmosphere. The heat release forms a cyclonic circulation at the lower levels over eastern China, and induces the transport and convergence of water vapor increased over southern China in August. This further strengthens the upward motion over southern China and the cyclonic circulation at the lower levels. Therefore, positive feedback appears between water vapor transport and atmospheric circulation. Meanwhile, the cyclonic circulation over southern China results in a response of water vapor divergence and a downward motion over HHR. Consequently, the negative anomalies of precipitation occur over HHR in August. When the July soil is dry over southern China, the opposite results can be found through the similar mechanism.

Snow in the earth-atmosphere system contains high impact, but its correlation with meteorological factors at multi-time components has not been fully addressed over the warming Tibetan Plateau (TP). Here, the correlations between snow cover and six meteorological factors were examined at inter-annual, annual, and intra-seasonal components (2003–2018) reconstructed by the ensemble empirical mode decomposition method. Firstly, inter-annual snow cover area with significant decreases in summer (− 0.076% per year) and autumn (− 0.318% per year) shows strong correlations with air temperature (r 0.57 in summer and winter), and shortwave radiation (r < − 0.45 in summer and winter). Moreover, a maximum lead-lag correlation coefficient (MLLCC) was proposed to derive the lead-lag correlations at the two remaining components. In annual components representing the annual cycle of the original time series, shortwave radiation leads snow cover variations by 50 days, and that snow cover leads wind speed variations by 42 days due to the influence of snow on the atmospheric circulation. In the high-frequency intra-seasonal component associated with the event scale, precipitation, shortwave radiation, and air humidity lead snow cover variation by 2 to 6 days. Meanwhile, snow cover leads longwave radiation variations by 3 to 5 days due to the surface albedo being changed by snow. Specifically, intra-seasonal correlations are more significant in winter-spring due to larger snow cover variability. Additionally, with climate warming, the correlations of snow cover with temperature and radiations have been enhanced with increases of the MLLCCs by 0.05–0.29. However, its correlation with precipitation has been weakened with the decrease of MLLCCs by 0.09–0.22. The results of this study will help to deepen our understandings of hydroclimatic dynamics under climate warming in the TP.

Northeast China (NEC) is an important crop production base in East Asia. The monthly evolution of precipitation during spring sowing from April to May is of significance for agricultural activity and production over NEC. This study first investigates the predominant modes of April-to-May precipitation evolution over NEC and then explores their connections with North Atlantic sea surface temperature (SST) anomalies during 1979–2016. The first mode obtained using a multivariate empirical orthogonal function (MV-EOF1) shows an out-of-phase change in NEC precipitation anomalies from April to May, but the second mode (MV-EOF2) shows an in-phase change. Further analysis indicates that SST variability over mid-latitude North Atlantic (MNA) is related to MV-EOF1 by exciting a wave train from MNA to Eurasia. The wave train position is located more westward in May relative to April, leading to reverse atmospheric circulation and precipitation anomalies over NEC between April and May. The changes in position of circulations may be related to the westward shift of the North Atlantic storm track from April to May. MV-EOF2 is related to SST variability over northern tropical Atlantic (NTA). In April, NTA SST anomalies impact NEC precipitation through mid-latitude Eurasian wave train and Walker-like circulation anomalies between the Atlantic and Pacific Oceans. In May, the mid-latitude pathway is effective; however, the tropical pathway is significantly weakened, which may be related to the weakened intensity of NTA SST-induced tropical diabatic heating. Numerical simulations can reproduce the linkage between the North Atlantic SSTs and the pronounced atmospheric circulation anomalies in the observation, further confirming the impacts of North Atlantic SSTs on NEC April-to-May precipitation evolution.

The present study investigated the long-term change in the interannual relationship between the boreal winter Arctic Oscillation (AO) and tropical Indian Ocean (TIO) climate during 1979–2019 and found that their linkage experienced a decadal change in 2001/2002. The 19-yr sliding correlation coefficient between the January–February–March (JFM) AO index and central TIO (0–10°S, 65°–80°E) precipitation was significant, with values of approximately 0.50–0.75 during 1979–2001, but abruptly decreased to 0.35 in 2002 and 0.10 in 2010. Meanwhile, the spatial patterns of the AO-related atmospheric circulation anomalies also displayed different features before and after 2001. During 2002–2019, the anomalous anticyclone in the middle troposphere over the Arabian Sea moved northwestward and strengthened, and the JFM AO was more closely correlated to the anticyclone, with correlation coefficient changed from −0.38 before 2001 to −0.63 after 2001; correspondingly, strong cross-equator air flows were observed over the western TIO (40°–50°E), but no significant anomalies of precipitation in the central TIO were observed. During 1979–2001, however, significant southward cross-equator air flows appeared over the central TIO (65°–75°E), which enhanced the intertropical convergence zone and upward air motions, leading to more precipitation in central TIO. An analysis shows that the AO may modulate the Arabian anticyclone through two Rossby wave paths in the upper troposphere: a midlatitude (50°–60°N) path during 1979–2001 from North Atlantic southeastward to the Middle East and the neighboring Arabian Sea; and a subtropical (20°–30°N) path during 2002–2019 from North Atlantic eastward to the Middle East and Arabian Sea. Large wave activity fluxes induced by AO were concentrated along the two paths before and after 2001, and the location of the cross-equator flows depends on thelocation of the anticyclone. Causes of the decadal changes in the AO-associated wave trains need further investigation.

Terrestrial ecosystems are fully coupled with the climate. The planet has been greening owing to the increased vegetation growth in response to the changing atmosphere, which in turn has feedback on the climate. Greening has slowed down the rise in global land-surface air temperature mainly through a coincident increase of evapotranspiration and precipitation in wet regions. In dry regions, greening intensifies the decrease in soil moisture induced by greening-enhanced transpiration. Uncertain, however, is how the climate effects of greening in semi-arid lands might differ for variable wet and dry conditions. Here, we focus on the biosphere–atmosphere interactions in Australia by modeling the perturbation of vegetation changes under various states of sea surface temperature (SST), including the climatology mean, El Niño, and La Niña conditions. For the dry conditions of El Niño, greening exacerbates water stress and largely depletes the soil moisture, while for the wet conditions of La Niña, greening-enhanced evapotranspiration and precipitation resupply the soil moisture. For the normal conditions using the climatology mean SST, a small decrease in soil moisture occurs but with large spatial contrast because of heterogeneous changes of evapotranspiration and precipitation induced by greening. We emphasize that the alternating dry and wet conditions modulated by the large-scale climate variability are vital to understanding the response of climate to greening. Furthermore, vegetation-based warming mitigation policies need to be cautious when inferring distinct climate effects associated with greening.

Important discrepancies in the large-scale summer climate change projections were recently detected between the global and regional climate models (RCM/GCM) in the EURO-CORDEX ensemble for several variables including surface temperature, total precipitation, and surface solar radiation. In this study, we use a new experimental framework inspired by the Big-Brother-Little-Brother protocol to explore the mechanisms responsible for generating large-scale discrepancies in future projections between GCM/RCM pairs over Europe in summer. Starting from past and future simulations with a perfect GCM/RCM pair (same resolution, same physics, same forcings), we then disentangle the role of potential sources of GCM/RCM inconsistency by carrying out targeted sensitivity studies. We show that by following such a perfect approach, it is possible to obtain a GCM/RCM pair without statistically significant inconsistencies in projected climate change. Such discrepancies are mainly generated by differences in aerosols representation and atmospheric physics. The role of plant physiology is limited and unlikely to be the dominant factor in the detected discrepancies. Finally, it is unlikely that the discrepancies in the EURO-CORDEX ensemble projections are a result of the upscaled added value, as we show that the effect of increased resolution is not strong enough and mostly limited to areas with complex topography. These findings raise important questions about the current practices in regional climate modelling. In the short term, implementing RCM external forcings consistent with the driving GCM can significantly improve the situation at low cost. In the long term, adopting a seamless strategy in developing the GCM/RCM models should be questioned.

This study examined the characteristics of the diurnal variations of heavy rainfall (⩾110 mm in 12 hours) in Korea and the related atmospheric circulation for July from 1980–2020. During the analysis period, two dominant pattens of diurnal variation of the heavy rainfall emerged: all-day heavy rainfall (AD) and morning only heavy rainfall (MO) types. For the AD-type, the heavy rainfall is caused by abundant moisture content in conjunction with active convection in the morning (0000–1200, LST; LST = UTC + 9) and the afternoon hours (1200–2400 LST). These systems are related to the enhanced moisture inflow and upward motion induced by the strengthening of the western North Pacific subtropical high and upper-tropospheric jet. For the MO-type, heavy rainfall occurs mostly in the morning hours; the associated atmospheric patterns are similar to the climatology. We find that the atmospheric pattern related to severe heavy rainfalls in 2020 corresponds to a typical AD-type and resembles the 1991 heavy-rainfall system in its overall synoptic/mesoscale circulations. The present results imply that extremely heavy rainfall episodes in Korea during the 2020 summer may occur again in the future associated with the recurring atmospheric phenomenon related to the heavy rainfall.

This work presents the influence of atmospheric circulation on the occurrence of dry and wet periods in the central Polish region of Kujawy. The material on which the authors relied encompassed monthly totals of precipitation obtained from 10 weather stations in the period 1954–2018. Both dry and wet periods have been identified on the basis of monthly values of the Standardised Precipitation Index (SPI). Additionally, the calendar of circulation types over Central Poland was used to determine the atmospheric circulation indices: western (W), southern (S) and cyclonicity (C). The analyses have indicated that the region concerned experiences low precipitation totals in comparison with the rest of Poland. According to the circulation indices W, S and C, for Central Poland, the air mass advection from the West prevails over that from the East. Moreover, a slightly more frequent inflow of air from the South than from the North has been observed. The frequency of anticyclonic situations is higher than that of the cyclonic types in this part of Europe. Drought spells occurred in the study area at a clear dominance of anticyclonic circulation, with the inflow of air mostly from the North and with increased westerly circulation. On the other hand, the occurrence of wet periods was mainly influenced by cyclonic circulation during the advection of the masses from the South and West. Dry and wet periods accounted for 28% and 27% of the study period, respectively.

The terrestrial biosphere plays a pivotal role in removing carbon from the atmosphere. The removal processes are primarily affected by the presence of extreme temperature in the atmosphere. Little information is available on carbon removal response by the terrestrial biosphere during extreme temperature events over the Indian region. India has witnessed frequent and intense heatwaves in the recent past, and future projections about the frequency of heatwave occurrence suggest a further increase in the changing climate scenario. This study used surface CO2 flux observations and satellite retrieved columnar and mid-tropospheric CO2 concentrations to understand atmospheric CO2 variability and its transport patterns with anomalously high-temperature events such as heatwave conditions over India. Intensification of temperature up to 32 °C has increased the atmosphere-biosphere CO2 fluxes (carbon sink). But further intensification in temperature (> 32–33 °C), like those observed during heatwaves, tends to drive the ecosystem to act as a CO2 source into the atmosphere due to reduced ability to absorb atmospheric CO2. Such excess CO2 fluxes may lead to change in the atmospheric CO2 concentration via atmospheric circulation or the vertical transport of the air masses from the near-surface to the upper levels in the atmosphere. The satellite observed CO2 concentration is elevated by 2–3 ppm during the heatwave conditions over India. The impact of extreme temperature on the biospheric sink capability in the carbon cycle, leading to an increase in the atmospheric CO2 concentration, is one of the significant outcomes of this study.

The northeastern United States (NEUS) and the adjacent Northwest Atlantic Shelf (NWS) have emerged as warming hotspots, but the connection between them remains unexplored. Here we use gridded observational and reanalysis datasets to show that the twentieth-century surface air temperature increase along the coastal NEUS is exceptional on the continental and hemispheric scale and is induced by a combination of two factors: the sea surface temperature (SST) increase in the NWS associated with a weakening Atlantic Meridional Overturning Circulation (AMOC), and atmospheric circulation changes associated with a more persistent positive North Atlantic Oscillation. These connections are important because AMOC slowdown and NWS warming are projected to continue. A survey of climate model simulations indicates that realistic SST representation at high spatial resolution might be a minimum requirement to capture the observed pattern of coastal warming, suggesting that prior projection-based assessments may not have captured key features in this populous region. The coastal northeastern United States is a warming hotspot, and observations identify a slower Atlantic overturning circulation and a positive North Atlantic Oscillation phase as drivers. Analysis suggests that low horizontal resolution probably hampers models’ ability to capture the spatial pattern of enhanced warming.

The current work examines the impact of the snow cover extent (SCE) of the Tibetan Plateau (TP) on the interannual variation in the summer (June-July-August) surface air temperature (SAT) over Central Asia (CA) (SAT_CA) during the 1979–2019 period. The leading mode of the summer SAT_CA features a same-sign temperature anomalies in CA and explains 62% of the total variance in SAT_CA. The atmospheric circulation associated with a warming SAT_CA is characterized by a pronounced high-pressure system dominating CA. The high-pressure system is accompanied by warm advection as well as descending motion over CA, favoring the warming of the SAT_CA. Analysis shows that the interannual variation in the summer SAT_CA is significantly positively correlated with the April SCE over the central-eastern TP. In April, higher than normal SCE over the central-eastern TP has a pronounced cooling effect on the column of the atmosphere above the TP and can persist until the following early summer. Negative and positive height anomalies appear above and to the west of the TP. In the following months, the perturbation forcing generated by the TP SCE anomalies lies near the western center of the Asian subtropical westerly jet (SWJ), which promotes atmospheric waves in the zonal direction guided by the Asian SWJ. Associated with this atmospheric wave, in the following summer, a significant high-pressure system dominates CA, which is a favorable condition for a warm summer SAT_CA.

Synoptic weather and larger scale circulation patterns are closely coupled and have a major influence on regional weather and extreme events. This study examines the role of regional circulations on meteorology and extreme events for the present and future years over Asia with the WRF model driven by HadGEM2 global model boundary conditions that includes RCP4.5 scenarios based bicentennial transient simulation. The regional scale analysis was based on boundary conditions derived from 40 years of global model outputs spanning periods of 1995-2005, 2015-2025, 2025-2035 and 2045-2055. For brevity these periods are labelled as 2000, 2020, 2030, 2050 and 'represent' decadal periods centered around the named years. Model results were compared and validated (using a number of skill metrics) against observations for the present period showing that the model is able to delineate the observed features within 95% confidence level compared to the annual mean. To characterise and quantify the changes in the circulation patterns, an Empirical Orthogonal Function (EOF) based analysis was conducted. Results indicate that wintertime minimum temperatures are projected to increase by 3-4 0 C over Asia by 2050 compared to reference period of 2000. Furthermore, anti-cyclonic activity associated with low PV anomalies and high positive temperature anomalies may be a key driver that influence the increase in frequency and duration of heat waves and droughts over SA, SEA, EA and NA regions of Asia. Overall, the modelling results suggest that regional meteorology and circulation patterns may significantly influence extremes over Asia in the future. Such impacts will have major implications for weather patterns as well as for air pollution over the region both of which will require policy responses to adjust to a changing regional climate.

Three sets of model experiments are performed with the Community Earth System Model to study the role of soil moisture anomalies as a boundary forcing for the formation of upper-level Rossby wave patterns during Southern Hemisphere summer. In the experiments, soil moisture over Australia is set to ±1STD of an ERA-Interim reanalysis derived soil moisture reconstruction for the years 2009 to 2016 and 50 ensemble members are run. The local response is a positive heating anomaly in the dry simulations that results in a thermal low-like circulation anomaly with an anomalous surface low and upper-level anticyclone. Significant differences in convective rainfall over Australia are related to differences in convective instability and associated with changes in near surface moisture and moisture advection patterns. A circum-hemispheric flow response is identified both in the upper-level flow and in the surface storm tracks that overall resembles a positive Southern Annular Mode-like flow anomaly in the dry simulations. The structure of this atmospheric response strongly depends on the background flow. The results point to a modulation of the hemispheric flow response to the forcing over Australia by the El Niño Southern Oscillation. Significant changes of precipitation over the Maritime continent and South Africa are found and significant differences in the frequency of surface cyclones are present all along the storm tracks.

During strong El Niño events, below-average rainfall is expected in large parts of southern Africa. The 1992 El Niño season was associated with one of the worst drought episodes in large parts of South Africa. Using reanalysis data set from NCEP-NCAR, this study examined circulation types (CTs) in Africa south of the equator that are statistically related to the El Niño signal in the southwest Indian Ocean and the implication of this relationship during the 1992 drought episode in South Africa. A statistically significant correlation was found between the above-average Nino 3.4 index and a CT that features widespread cyclonic activity in the tropical southwest Indian Ocean, coupled with a weaker state of the south Indian Ocean high-pressure. During the analysis period, it was found that the El Niño signal enhanced the amplitude of the aforementioned CT. The impacts of the El Niño signal on CTs in southern Africa, which could have contributed to the 1992 severe drought episode in South Africa, were reflected in (i) robust decrease in the frequency of occurrence of the austral summer climatology pattern of atmospheric circulation that favors southeasterly moisture fluxes, advected by the South Indian Ocean high-pressure; (ii) modulation of easterly moisture fluxes, advected by the South Atlantic Ocean high-pressure, ridging south of South Africa; (iii) and enhancement of the amplitude of CTs that both enhances subsidence over South Africa, and associated with the dominance of westerlies across the Agulhas current. Under the ssp585 scenario, the analyzed climate models suggested that the impact of radiative heating on the CT significantly related to El Niño might result in an anomalous increase in surface pressure at the eastern parts of South Africa.

Based on historical observations daily data for 1981–2016 from 130 meteorological stations over and around the Tibetan Plateau (TP), the trends of sensible heat flux (SH) and their elevation dependence were investigated. Results indicate that the SH over and around the TP experienced apparent trends’ shift in approximately 2000, demonstrating noticeable reductions during 1981–2000 and pronounced recovery during 2001–2016 for the four seasons. The relation between elevations and trends in SH over and around TP has shown a feature known as “elevation amplification.” Pronounced elevation-dependent reductions in SH can be discovered for the four seasons except winter during 1981–2000, and a substantially more significant enhance in SH was found in the higher elevation plateau compared to the lower elevation plateau during 2001–2016. The elevation-dependent trends of surface wind speed (V0) influenced by the atmospheric circulation anomalies were the dominant factor driving the elevation-dependent trends of SH whenever during 1981–2000 and 2001–2016. During 1981–2000 (2001–2016), the areas to the north of TP warmed more strengthened (weaker) than the areas to the south of TP. It led to the anomalous temperature gradient and geopotential height gradient from the south (north) of TP to the north (south) of TP and resulted in decreasing (increasing) trends of the 500hPa subtropical westerlies over and around the TP. Furthermore, it caused the rate of reduction (increases) in V0 amplified with elevation, because the higher altitude areas responded more strongly to the changes of atmosphere wind speed. As a result of the elevation-dependent reductions (increases) of V0, the positive correlation between the subdued (enhanced) SH and elevation occurred in TP during 1981–2000 (2001–2016). The difference in ground-air temperature (Ts-Ta) was another factor influencing elevation dependence of SH trends during 2001–2016, which needs further investigations.

The most expedient means of analysing global climate change is to analyse the precipitation along with major components of the global atmospheric circulation. Like other Coastal areas, Coastal Andhra is also vulnerable to extreme weather events. So, in this study, the trend and pattern of the precipitation of the Coastal Andhra have been analyzed using daily and monthly rainfall data of 36 years (1983–2018). The standardized precipitation index, rainfall anomaly index and Mann–Kendall tests have been used to analyse the trend and pattern of precipitation. The result showed that the average annual rainfall was 161 cm in 1983 which first declined to 147 cm in 1991 but increased to 181 cm in 2001 and again declined rapidly to 91 cm in 2018. Apart from this normalized difference vegetation index (NDVI) has been used for the years 1983, 1991, 2001, 2011 and 2018 for the validation of dryness and wetness. The statistical analysis shows that rainfall in the study area shows a declining trend at the rate of − 1.27 cm per year as per the result obtained by the Sen, slope. Further, the association between mean annual rainfall and NDVI is found to be very strong with a higher positive value of the coefficient of determination.

We investigate the spatio-temporal characteristics of the austral spring Ross Ice Shelf Polynya (RISP) and its relationship with atmospheric circulation anomalies based on the sea ice concentration data from the National Snow and Ice Data Center (NSIDC) and the ERA5 reanalysis data. The RISP area series is derived by choosing 25% sea ice concentration as the threshold. Then the principal spatial patterns of the RISP are acquired by using the empirical orthogonal function (EOF) analysis. The leading EOF (EOF1) has a spatial distribution of a strong negative core in the northeastern RISP with a weak positive core near the Cape Adare, explaining 48.1% of the variance. This mode matches the wind pattern of the northwesterly on the western Ross Sea while southwesterly on the eastern Ross Sea, which reflects the zonal variation of the RISP. There is also a strong positive correlation between the RISP area and the PC1. The EOF2 explains 27.4% of the variance, and is mainly characterized by a large region of low values in the northwestern Ross Sea with a small region of high value near Cape Colbeck. Matching the strong southerly over the western Ross Sea, the EOF2 partly depicts the meridional variation of the RISP. We further explored the connections between the RISP and sea level pressure, and found that a deeper and more eastward Amundsen Sea Low (ASL) in November often coincides with a larger and more eastward RISP in December. This lagged response is partly generated through the influence of the ASL on the RISP in November.

In recent decades, a greening tendency due to increased vegetation has been noted around the Taklimakan Desert (TD), but the impact of such a change on the local hydrological cycle remains uncertain. Here, we investigate the response of the local hydrological cycle and atmospheric circulation to a green TD in summer using a pair of global climate model (Community Earth System Model version 1.2.1) simulations. With enough irrigation to support vegetation growth in the TD, the modeling suggests first, that significant increases in local precipitation are attributed to enhanced local recycling of water, and second, that there is a corresponding decrease of local surface temperatures. On the other hand, irrigation and vegetation growth in this low-lying desert have negligible impacts on the large-scale circulation and thus the moisture convergence for enhanced precipitation. It is also found that the green TD can only be sustained by a large amount of irrigation water supply since only about one-third of the deployed water can be “recycled” locally. Considering this, devising a way to encapsulate the irrigated water within the desert to ensure more efficient water recycling is key for maintaining a sustainable, greening TD.

During the last ice age, the Northern Hemisphere experienced a series of abrupt millennial-scale climatic changes linked to variations in the strength of the Atlantic Meridional Overturning Circulation and sea-ice extent. However, our understanding of their impacts on decadal-scale climate variability in central Europe has been limited by the lack of high-resolution continental archives. Here, we present a near annual-resolution climate proxy record of central European temperature reconstructed from the Eifel maar lakes of Holzmaar and Auel in Germany, spanning the past 60,000 years. The lake sediments reveal a series of previously undocumented multidecadal climate cycles of around 20 to 150 years that persisted through the last glacial cycle. The periodicity of these cycles suggests that they are related to the Atlantic multidecadal climate oscillations found in the instrumental record and in other climate archives during the Holocene. Our record shows that multidecadal variability in central Europe was strong during all warm interstadials, but was substantially muted during all cold stadial periods. We suggest that this decrease in multidecadal variability was the result of the atmospheric circulation changes associated with the weakening of the Atlantic Meridional Overturning Circulation and the expansion of North Atlantic sea-ice cover during the coldest parts of the last ice age. Central European multidecadal climate variability was subdued during cold stadials through the last glacial cycle due to atmospheric and oceanic circulation shifts, according to almost annual-resolution terrestrial climate proxy records from varved maar lakes in Germany.

An unprecedented cold event occurred in Central and eastern Eurasia during the 2020/21 winter, including five episodes of consecutive cold spells (EP1–5). Through analysis of both observational and simulations, we show that the concurrent Arctic sea-ice loss and extratropical Pacific decadal oscillation (EPDO) warming are potential drivers for the cold event. Their relative contributions to the intraseasonal evolutions of atmospheric circulation and concomitant cold surges are thoroughly investigated. The circulation anomalies highlight the gradual development of the negative Arctic oscillation, accompanied by strengthened Siberian high and deepened Aleutian low. Stratospheric pathways were integrally involved in the dynamical response and the timing of episodes. Our results suggest that the sea-ice, irrespective of seasonality, and autumn EPDO experiments can generally capture the spatial patterns of atmospheric circulation and temperature in observation, albeit weaker in magnitude. Autumn (winter) sea-ice loss led to the EP1–3 (EP2–3) cold spells, and autumn EPDO led to the EP1–3 cold surges; whereas the EP4–5 cold spells induced by autumn SIC and PDO were not statistically robust. The Eurasian cooling response to winter PDO is weak due to the extensive warming over southern China and Eurasian highlatitudes that offsets the midlatitude cooling. The largest coolings were found in SIC and EPDO combined experiments, suggesting their synergic importance in driving such cold events. Our results have implications for the potential predictability of winter extreme events over Eurasia in the context of ongoing sea-ice decline and a recent shift to the positive PDO phase.

Understanding the devastating nature of drought, this work has assessed the variability in the Severity-Area-Frequency (SAF) curve using Standardised Precipitation Evapotranspiration Index (SPEI) as meteorological drought indicator over Maharashtra, India. The future meteorological outputs from 19 Global Circulation Models (GCMs) of the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) under two Representative Concentration Pathway (RCP) 4.5 and 8.5 are used. The SAF curves are developed for five different seasons namely pre-monsoon, monsoon, post-monsoon, Kharif and Rabi. The uncertainty associated with GCMs and scenarios is assessed using possibility theory. The results reveal that the precipitation magnitude is expected to increase in pre-monsoon, monsoon, and Kharif seasons over most of the areas in Maharashtra. However, the temperature is likely to increase during all the seasons in future. The frequency of extreme drought condition during post-monsoon, pre-monsoon, and Rabi seasons shows an increment as compared to historical period. The Rabi season drought is noticed to be most pronounced and likely to affect significant portions of Maharashtra during all return periods. The SAF curve reveals that, in most of the cases, the percentage of drought affected area is expected to increase for high magnitude of severity.

Three striking and impactful extreme cold weather events successively occurred across East Asia and North America during the mid-winter of 2020/21. These events open a new window to detect possible underlying physical processes. The analysis here indicates that the occurrences of the three events resulted from integrated effects of a concurrence of anomalous thermal conditions in three oceans and interactive Arctic-lower latitude atmospheric circulation processes, which were linked and influenced by one major sudden stratospheric warming (SSW). The North Atlantic warm blob initiated an increased poleward transient eddy heat flux, reducing the Barents-Kara seas sea ice over a warmed ocean and disrupting the stratospheric polar vortex (SPV) to induce the major SSW. The Rossby wave trains excited by the North Atlantic warm blob and the tropical Pacific La Nina interacted with the Arctic tropospheric circulation anomalies or the tropospheric polar vortex to provide dynamic settings, steering cold polar air outbreaks. The long memory of the retreated sea ice with the underlying warm ocean and the amplified tropospheric blocking highs from the midlatitudes to the Arctic intermittently fueled the increased transient eddy heat flux to sustain the SSW over a long time period. The displaced or split SPV centers associated with the SSW played crucial roles in substantially intensifying the tropospheric circulation anomalies and moving the jet stream to the far south to cause cold air outbreaks to a rarely observed extreme state. The results have significant implications for increasing prediction skill and improving policy decision making to enhance resilience in “One Health, One Future”.

Our confidence in future climate projection depends on the ability of climate models to simulate the current climate, and model performance in simulating atmospheric circulation affects its ability of simulating extreme events. In this study, the self-organizing map (SOM) method is used to evaluate the frequency, persistence, and transition characteristics of models in the Coupled Model Intercomparison Project Phase 6 (CMIP6) for different ensembles of daily 500 hPa geopotential height (Z500) in Asia, and then all ensembles are ranked according to a comprehensive ranking metric (MR). Our results show that the SOM method is a powerful tool for assessing the daily-scale circulation simulation skills in Asia, and the results will not be significantly affected by different map sizes. Positive associations between each two of the performance in frequency, persistence and transition were found, indicating that a good ensemble of simulation for one metric is good for the others. The r10i1p1f1 ensemble of CanESM5 best simulates Z500 in Asia comprehensively, and it is also the best of simulating frequency characteristics. The MR simulation of the highest 10 ensembles for the Western North Pacific Subtropical High (WNPSH) and the South Asia High (SAH) are far better than those of the lowest 10. Such differences may lead to errors in the simulation of extreme events. This study will help future studies in the choice of ensembles with better circulation simulation skills to improve the credibility of their conclusions.

Jupiter’s upper atmosphere is considerably hotter than expected from the amount of sunlight that it receives1–3. Processes that couple the magnetosphere to the atmosphere give rise to intense auroral emissions and enormous deposition of energy in the magnetic polar regions, so it has been presumed that redistribution of this energy could heat the rest of the planet4–6. Instead, most thermospheric global circulation models demonstrate that auroral energy is trapped at high latitudes by the strong winds on this rapidly rotating planet3,5,7–10. Consequently, other possible heat sources have continued to be studied, such as heating by gravity waves and acoustic waves emanating from the lower atmosphere2,11–13. Each mechanism would imprint a unique signature on the global Jovian temperature gradients, thus revealing the dominant heat source, but a lack of planet-wide, high-resolution data has meant that these gradients have not been determined. Here we report infrared spectroscopy of Jupiter with a spatial resolution of 2 degrees in longitude and latitude, extending from pole to equator. We find that temperatures decrease steadily from the auroral polar regions to the equator. Furthermore, during a period of enhanced activity possibly driven by a solar wind compression, a high-temperature planetary-scale structure was observed that may be propagating from the aurora. These observations indicate that Jupiter’s upper atmosphere is predominantly heated by the redistribution of auroral energy., High-resolution observations confirm that Jupiter’s global upper atmosphere is heated by transport of energy from the polar aurora.

Based on the NCEP/NCAR reanalysis data, the COBE sea surface temperature (SST) and the GPCC precipitation, the influences of El Nino-South Oscillation (ENSO) on the variability of winter rainfall anomalies in Southeast China is analyzed under the synergistic effect of Indian Ocean Dipole (IOD). Winter precipitation and atmospheric circulation of the years of IOD concurring with ENSO are compared with single IOD or ENSO, to reveal the mechanism of synergistic effects on the variability of winter rainfall anomalies in Southeast China. The results show that the correlation between IOD/ENSO and the winter precipitation in Southeast China has increased since 1980s. These correlations were significant in years of IOD and ENSO co-occurrence compared to years of IOD or ENSO only, which is mainly due to the lagged atmospheric thermal and dynamic responses to an IOD forcing in synergy with ENSO. The positive IOD (PIOD) events can trigger and modify the anticyclone to the east of India, which transports moisture from the tropical Indian Ocean to Southeast China. In addition, El Nino events can strengthen the abnormal anticyclone over Philippines in winter, which is conducive to maintain the water vapor channel from the tropical western Pacific to Southeast China. Information flow analysis shows that the causalities between IOD and ENSO were enhanced after 1980s, causing the significant increase in the frequency of winter abnormal precipitation in the years of IOD and ENSO concurrence. Furthermore, the higher frequency of PIOD with El Nino (compared to negative IOD with La Nina) attained a ratio of 2:1 after the 1980s, enhancing the Southeast China winter precipitation events associated with IOD and ENSO and the generation of interdecadal variability. This study is helpful to understand the mechanisms of winter precipitation changes in Southeast China, and to improve the forecast accuracy of winter extreme precipitation events.

The build-up of pollutants to harmful levels can occur when meteorological conditions favour their production or accumulation near the surface. Such conditions can arise when a region experiences air stagnation. The link between European air stagnation, air pollution and the synoptic- to large-scale circulation is investigated in this article across all seasons and the 1979–2018 period. Dynamical indices identifying atmospheric blocking, Rossby wave breaking, subtropical ridges, and the North Atlantic eddy-driven and subtropical jets are used to describe the synoptic- to large-scale circulation as predictors in statistical models of air stagnation and pollutant variability. It is found that the large-scale circulation can explain approximately 60 % of the variance in monthly air stagnation, ozone and wintertime particulate matter (PM) in five distinct regions within Europe. The variance explained by the model does not vary strongly across regions and seasons, apart from for PM when the skill is highest in winter. However, the dynamical indices most related to air stagnation do depend on region and season. The blocking and Rossby wave breaking predictors tend to be the most important for describing air stagnation and pollutant variability in northern regions, whereas ridges and the subtropical jet are more important to the south. The demonstrated correspondence between air stagnation, pollution and the large-scale circulation can be used to assess the representation of stagnation in climate models, which is key for understanding how air stagnation and its associated climatic impacts may change in the future.