Recent Advances in Understanding Multi-scale Climate Variability of the Asian Monsoon

Studies of the multi-scale climate variability of the Asian monsoon are essential to an advanced understanding of the physical processes of the global climate system.In this paper,the progress achieved in this field is systematically reviewed,with a focus on the past several years.The achievements are summarized into the following topics:(1)the onset of the South China Sea summer monsoon;(2)the East Asian summer monsoon;(3)the East Asian winter monsoon;and(4)the Indian summer monsoon.Specifically,new results are highlighted,including the advanced or delayed local monsoon onset tending to be synchronized over the Arabian Sea,Bay of Bengal,Indochina Peninsula,and South China Sea;the basic features of the record-breaking mei-yu in 2020,which have been extensively investigated with an emphasis on the role of multi-scale processes;the recovery of the East Asian winter monsoon intensity after the early 2000s in the presence of continuing greenhouse gas emissions,which is believed to have been dominated by internal climate variability(mostly the Arctic Oscillation);and the accelerated warming over South Asia,which exceeded the tropical Indian Ocean warming,is considered to be the main driver of the Indian summer monsoon rainfall recovery since 1999.A brief summary is provided in the final section along with some further discussion on future research directions regarding our understanding of the Asian monsoon variability.

Linkage between precipitation isotopes and water vapor sources in the monsoon margin:Evidence from arid areas of Northwest China

The isotope composition in precipitation has been widely considered as a tracer of monsoon activity.Compared with the coastal region,the monsoon margin usually has limited precipitation with large fluctuation and is usually sensitive to climate change.The water resource management in the monsoon margin should be better planned by understanding the composition of precipitation isotope and its influencing factors.In this study,the precipitation samples were collected at five sampling sites(Baiyin City,Kongtong District,Maqu County,Wudu District,and Yinchuan City)of the monsoon margin in the northwest of China in 2022 to analyze the characteristics of stable hydrogen(δD)and oxygen(δ18O)isotopes.We analyzed the impact of meteorological factors(temperature,precipitation,and relative humidity)on the composition of precipitation isotope at daily level by regression analysis,utilized the Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT)-based backward trajectory model to simulate the air mass trajectory of precipitation events,and adopted the potential source contribution function(PSCF)and concentration weighted trajectory(CWT)to analyze the water vapor sources.The results showed that compared with the global meteoric water line(GMWL),the slope of the local meteoric water line(LMWL;δD=7.34δ^(18)O-1.16)was lower,indicating the existence of strong regional evaporation in the study area.Temperature significantly contributed toδ18O value,while relative humidity had a significant negative effect onδ18O value.Through the backward trajectory analysis,we found eight primary locations that were responsible for the water vapor sources of precipitation in the study area,of which moisture from the Indian Ocean to South China Sea(ITSC)and the western continental(CW)had the greatest influence on precipitation in the study area.The hydrogen and oxygen isotopes in precipitation are significantly influenced by the sources and transportation paths of air mass.In addition,the results of PSCF and CWT analysis showed that the water vapor source areas were primarily distributed in the south and northwest direction of the study area.

Influence of Continental Atmospheric Forcing on the Decadal Variability of the West African Monsoon

The West African Monsoon (WAM) is characterized by strong decadal and multi-decadal variability and the impacts can be catastrophic for the local populations. One of the factors put forward to explain this variability involves the role of atmospheric dynamics, linked in particular to the Saharan Heat Low (SHL). This article addresses this question by comparing the sets of preindustrial control and historical simulation data from climate models carried out in the framework of the CMIP5 project and observations data over the 20th century. Through multivariate statistical analyses, it was established that decadal modes of ocean variability and decadal variability of Saharan atmospheric dynamics significantly influence decadal variability of monsoon precipitation. These results also suggest the existence of external anthropogenic forcing, which is superimposed on the decadal natural variability inducing an intensification of the signal in the historical simulations compared to preindustrial control simulations. We have also shown that decadal rainfall variability in the Sahel, once the influence of oceanic modes has been eliminated, appears to be driven mainly by the activity of the Arabian Heat Low (AHL) in the central Sahel, and by the structure of the meridional temperature gradient over the inter-tropical Atlantic in the western Sahel.

Impacts of monsoon break events in the western North Pacific on the cross-equatorial flows over the Maritime Continent

本文利用ERA5逐日再分析资料,探讨了1979-2020年间西北太平洋季风中断事件对海洋性大陆越赤道气流的影响.合成结果表明,西北太平洋季风中断事件会造成高,低空越赤道气流减弱,即高层南风异常,低层北风异常,与此相关的环流异常表现为西北太平洋高层气旋,低层反气旋的斜压结构。特别的是,西北太平洋季风中断对高空越赤道气流的影响更为显著,92%的季风中断事件都导致高空越赤道气流减弱,而只有70%的事件造成低空越赤道气流减弱,这是由于低空越赤道气流同时还受到赤道中东太平洋海温异常的调控.

Monsoon Break over the South China Sea during Summer: Statistical Features and Associated Atmospheric Anomalies

This study identifies break events of the South China Sea(SCS)summer monsoon(SCSSM)based on 42 years of data from 1979 to 2020,and investigates their statistical characteristics and associated atmospheric anomalies.A total of 214 break events are identified by examining the convection evolution during each monsoon season.It is found that most events occur between June and September and show a roughly even distribution.Short-lived events(3–7 days)are more frequent,accounting for about two thirds of total events,with the residual one third for long-lived events(8–24 days).The SCSSM break is featured by drastic variations in various atmospheric variables.Particularly,the convection and precipitation change from anomalous enhancement in adjoining periods to a substantial suppression during the break,with the differences being more than 60 W m−2 for outgoing longwave radiation(OLR)and 10 mm d−1 for precipitation.This convection/precipitation suppression is accompanied by an anomalous anticyclone in the lower troposphere,corresponding to a remarkable westward retreat of the monsoon trough from the Philippine Sea to the Indochina Peninsula,which reduces the transportation of water vapor into the SCS.Besides,the pseudo-equivalent potential temperature()declines sharply,mainly attributable to the local specific humidity reduction caused by downward dry advection.Furthermore,it is found that the suppressed convection and anomalous anticyclone responsible for the monsoon break form near the equatorial western Pacific and then propagate northwestward to the SCS.

Recent Enhancement in Co-Variability of the Western North Pacific Summer Monsoon and the Equatorial Zonal Wind

The western North Pacific summer monsoon(WNPSM)is an important subcomponent of the Asian summer monsoon.The equatorial zonal wind(EZW)in the lower troposphere over the western Pacific may play a critical role in the evolution of the El Niño-Southern Oscillation(ENSO).The possible linkage between the EZW over the western Pacific and the offequatorial monsoonal winds associated with the WNPSM and its decadal changes have not yet been fully understood.Here,we find a non-stationary relationship between the WNPSM and the western Pacific EZW,significantly strengthening their correlation around the late 1980s/early 1990s.This observed shift in the WNPSM–EZW relationship could be explained by the changes in the related sea surface temperature(SST)configurations across the tropical oceans.The enhanced influence from the springtime tropical North Atlantic,summertime tropical central Pacific,and maritime continent SST anomalies may be working together in contributing to the recent intensified WNPSM–EZW co-variability.The observed recent strengthening of the WNPSM–EZW relationship may profoundly impact the climate system,including prompting more effective feedback from the WNPSM on subsequent ENSO evolution and bolstering a stronger biennial tendency of the WNPSM–ENSO coupled system.The results obtained herein imply that the WNPSM,EZW,ENSO,and the tropical North Atlantic SST may be closely linked within a unified climate system with a quasi-biennial rhythm occurring during recent decades,accompanied by a reinforcement of the WNPSM–ENSO interplay quite possibly triggered by enhanced tropical Pacific–Atlantic cross-basin interactions.These results highlight the importance of the tropical Atlantic cross-basin influences in shaping the spatial structure of WNPSM-related wind anomalies and the WNPSM–ENSO interaction.

Influences of MJO-induced Tropical Cyclones on the Circulation-Convection Inconsistency for the 2021 South China Sea Summer Monsoon Onset

The South China Sea Summer Monsoon(SCSSM)onset is characterized by an apparent seasonal conversion of circulation and convection.Accordingly,various indices have been introduced to identify the SCSSM onset date.However,the onset dates as determined by various indices can be very inconsistent.It not only limits the determination of onset dates but also misleads the assessment of prediction skills.In 2021,the onset time as identified by the circulation criteria was 20 May,which is 12 days earlier than that deduced by also considering the convection criteria.The present study mainly ascribes such circulation-convection inconsistency to the activities of tropical cyclones(TCs)modulated by the Madden-Julian Oscillation(MJO).The convection of TC“Yaas”(2021)acted as an upper-level diabatic heat source to the north of the SCS,facilitating the circulation transition.Afterward,TC“Choi-wan”(2021)over the western Pacific aided the westerlies to persist at lower levels while simultaneously suppressing moist convection over the SCS.Accurate predictions using the ECMWF S2S forecast system were obtained only after the MJO formation.The skillful prediction of the MJO during late spring may provide an opportunity to accurately predict the establishment of the SCSSM several weeks in advance.

Correlation Between the Arabian Sea Surface Temperature and the Onset Period of South Asian Summer Monsoon with Trend Analysis on the Intensity

The long-term trend of the Arabian Sea surface temperature(ASST)during the formation of the South Asian summer monsoon(SASM)is discussed in this manuscript.From April to June,ASST changed from a meridional gradual distribution to a spatially uniform distribution and then to a zonal gradual distribution.The South Asian summer monsoon intensity(SASMI)and South Asian summer monsoon direction(SASMD)indicate that the variation of the ASST is highly related to the formation of the SASM during the summer monsoon period and can contribute to the spread of the SASM from the Southwest Arabian Sea throughout all of South Asia.Results of the correlation between the ASST and SASMI for the same month and its adjacent months were the same,and the areas of the positive correlation between the ASST and SASMI significantly increased from May–June as compared to April–May.The maximum correlation coefficient was 0.86.The results of the ASST and SASMD for the same month and its adjacent months were substantially different.However,the ASST and SASMD for May and April also showed a high positive correlation with a maximum correlation coefficient of 0.61 in the southwestern Arabian Sea.Existence of the ASST had a spatially consistent and significant upward trend with a mean increase of 0.6℃during the summer monsoon period from 1980 to 2020(between April and September),whereas the SASMI had a strengthening trend along the western and southwestern regions of the Arabian Sea and the southeastern region of the Arabian Peninsula.Meanwhile,the rest of the study regions showed a declining trend.Overall,the entire study region showed a slight downward trend,and the average value decreased by 0.02ms^(−1).

Future Changes in the Relationship Between the South and East Asian Summer Monsoons in CMIP6 Models

The future changes in the relationship between the South Asian summer monsoon(SASM)and the East Asian summer monsoon(EASM)are investigated by using the high-emissions Shared Socioeconomic Pathway 5-8.5(SSP5-8.5)experiments from 26 coupled models that participated in the phase 6 of the Coupled Model Intercomparison Project(CMIP6).Six models,selected based on their best performance in simulating the upper-and lower-level pathways related to the SASM-EASM teleconnection in the historical run,can capture the positive relationship between the SASM and the rainfall over northern China.In the future scenario,the upper-level teleconnection wave pattern connecting the SASM and the EASM exhibits a significant weakening trend,due to the rainfall anomalies decrease over the northern Indian Peninsula in the future.At the lower level,the western North Pacific anticyclone is projected to strengthen in the warming climate.The positive(negative)rainfall anomalies associated with positive(negative)SASM rainfall anomalies are anticipated to extend southward from northern China to the Yangtze-Huai River valley,the Korea Peninsula,and southern Japan.The connection in the lower-level pathway may be strengthened in the future.

The Relationship between Model Biases in East Asian Summer Monsoon Rainfall and Land Evaporation

The East Asian Summer Monsoon(EASM)provides the majority of annual rainfall to countries in East Asia.Although state-of-the-art models broadly project increased EASM rainfall,the spread of projections is large and simulations of present-day rainfall show significant climatological biases.Systematic evapotranspiration biases occur locally over East Asia,and globally over land,in simulations both with and without a coupled ocean.This study explores the relationship between evapotranspiration and EASM precipitation biases.First,idealized model simulations are presented in which the parameterization of land evaporation is modified,while sea surface temperature is fixed.The results suggest a feedback whereby excessive evapotranspiration over East Asia results in cooling of land,a weakened monsoon low,and a shift of rainfall from the Philippine Sea to China,further fueling evapotranspiration.Cross-model regressions against evapotranspiration over China indicate a similar pattern of behavior in Atmospheric Model Intercomparison Project(AMIP)simulations.Possible causes of this pattern are investigated.The feedback is not explained by an overly intense global hydrological cycle or by differences in radiative processes.Analysis of land-only simulations indicates that evapotranspiration biases are present even when models are forced with prescribed rainfall.These are strengthened when coupled to the atmosphere,suggesting a role for land-model errors in driving atmospheric biases.Coupled atmosphere-ocean models are shown to have similar evapotranspiration biases to those in AMIP over China,but different precipitation biases,including a northward shift in the ITCZ over the Pacific and Atlantic Oceans.

Dynamical Predictability of Leading Interannual Variability Modes of the Asian-Australian Monsoon in Climate Models

The dynamical prediction of the Asian-Australian monsoon(AAM)has been an important and long-standing issue in climate science.In this study,the predictability of the first two leading modes of the AAM is studied using retrospective prediction datasets from the seasonal forecasting models in four operational centers worldwide.Results show that the model predictability of the leading AAM modes is sensitive to how they are defined in different seasonal sequences,especially for the second mode.The first AAM mode,from various seasonal sequences,coincides with the El Niño phase transition in the eastern-central Pacific.The second mode,initialized from boreal summer and autumn,leads El Niño by about one year but can exist during the decay phase of El Niño when initialized from boreal winter and spring.Our findings hint that ENSO,as an early signal,is conducive to better performance of model predictions in capturing the spatiotemporal variations of the leading AAM modes.Still,the persistence barrier of ENSO in spring leads to poor forecasting skills of spatial features.The multimodel ensemble(MME)mean shows some advantage in capturing the spatiotemporal variations of the AAM modes but does not provide a significant improvement in predicting its temporal features compared to the best individual models in predicting its temporal features.The BCC_CSM1.1M shows promising skill in predicting the two AAM indices associated with two leading AAM modes.The predictability demonstrated in this study is potentially useful for AAM prediction in operational and climate services.

Seasonal Prediction Skill and Biases in GloSea5 Relating to the East Asia Winter Monsoon

The simulation and prediction of the climatology and interannual variability of the East Asia winter monsoon(EAWM),as well as the associated atmospheric circulation,was investigated using the hindcast data from Global Seasonal Forecast System version 5(GloSea5),with a focus on the evolution of model bias among different forecast lead times.While GloSea5 reproduces the climatological means of large-scale circulation systems related to the EAWM well,systematic biases exist,including a cold bias for most of China’s mainland,especially for North and Northeast China.GloSea5 shows robust skill in predicting the EAWM intensity index two months ahead,which can be attributed to the performance in representing the leading modes of surface air temperature and associated background circulation.GloSea5 realistically reproduces the synergistic effect of El Niño–Southern Oscillation(ENSO)and the Arctic Oscillation(AO)on the EAWM,especially for the western North Pacific anticyclone(WNPAC).Compared with the North Pacific and North America,the representation of circulation anomalies over Eurasia is poor,especially for sea level pressure(SLP),which limits the prediction skill for surface air temperature over East Asia.The representation of SLP anomalies might be associated with the model performance in simulating the interaction between atmospheric circulations and underlying surface conditions.

Interdecadal Enhancement in the Relationship between the Western North Pacific Summer Monsoon and Sea Surface Temperature in the Tropical Central-Western Pacific after the Early 1990s

This study reveals the strengthened interdecadal relationship between the western North Pacific summer monsoon(WNPSM)and tropical central-western Pacific sea surface temperature anomaly(SSTA)in summer after the early 1990s.In the first period(1979–91,P1),the WNPSM-related precipitation anomaly and horizontal wind anomaly present themselves as an analogous Pacific-Japan(PJ)-like pattern,generally considered to be related to the Niño-3 index in the preceding winter.During the subsequent period(1994–2019,P2),the WNPSM-related precipitation anomaly presents a zonal dipole pattern,correlated significantly with the concurrent SSTA in the Niño-4 and tropical western Pacific regions.The negative(positive)SSTA in the tropical western Pacific and positive(negative)SSTA in the Niño-4 region,could work together to influence the WNPSM,noting that the two types of anomalous SSTA configurations enhance(weaken)the WNPSM by the positive(negative)phase PJ-like wave and Gill response,respectively,with an anomalous cyclone(anticyclone)located in the WNPSM,which shows obvious symmetry about the anomalous circulation.Specifically,the SSTA in Niño-4 impacts the WNPSM by an atmospheric Gill response,with a stronger(weaker)WNPSM along with a positive(negative)SSTA in the Niño-4 region.Furthermore,the SSTA in the tropical western Pacific exerts an influence on the WNPSM by a PJ-like wave,with a stronger(weaker)WNPSM along with a negative(positive)SSTA in the tropical western Pacific.In general,SSTAs in the tropical western Pacific and Niño-4 areas could work together to exert influence on the WNPSM,with the effect most likely to occur in the El Niño(La Niña)developing year in P2.However,the SSTAs in the tropical western Pacific worked alone to exert an influence on the WNPSM mainly in 2013,2014,2016,and 2017,and the SSTAs in the Niño-4 region worked alone to exert an influence on the WNPSM mainly in Central Pacific(CP)La Niña developing years.The sensitivity experiments also can reproduce the PJ-like wave/Gill response associated with SSTA in the tropical western Pacific/Niño-4 regions.Therefore,the respective and synergistic impacts from the Niño-4 region and the tropical western Pacific on the WNPSM have been revealed,which helps us to acquire a better understanding of the interdecadal variations of the WNPSM and its associated climate influences.

Ecological and hydrologic evolution history in the sensitive zone of both East Asian summer monsoon and Westerly since the Last Glacial Maximum

The Qilian Mountains,located in the northeastern Qinghai-Tibet Plateau,is a sensitive zone of both East Asian summer monsoon(EASM)and westerly winds(WW).The evolution history and driving mechanism of the ecosystem and hydrologic cycle in this region on long-term timescales have not yet been clarified.In this study,we comprehensively study the hydrologic and ecological evolution history in the sensitive zone since the Last Glacial Maximum(LGM)by integrating surface sediments,paleoclimate records,TraCE-21ka transient simulations,and PMIP3-CMIP5 multi-model simulation.Results show that hydrologic and ecological proxies from surface sediments are significantly different from west to east and mainly divided into three sections:the monsoonaffected region in the eastern Qilian Mountains,the intersection region in the central Qilian Mountains,and the westerly-affected region in the western Qilian Mountains.Meanwhile,paleo-ecological and paleohydrologic reconstructions from the surroundings uncover a synchronous climate evolution that the EASM mainly controls the eastern Qilian Mountains and penetrates the central Qilian Mountains in monsoon intensity maximum,while the WW dominates the central and western Qilian Mountains on both glacial-interglacial and millennial timescales.The simulation results further bear out the glacial humid climate in the central and western Qilian Mountains caused by the enhanced WW,and the humidity maximum in the eastern Qilian Mountains controlled by the strong mid-Holocene monsoon.In general,east-west differences in climate pattern and response for the EASM and the WW are integrally stable on both short-term and long-term timescales.

FSS-based Evaluation on Monsoon Precipitation Forecasts in South China from Regional Models with Different Resolution

This study evaluated the forecast skill of CMA-GD 3 km and CMA-GD 1 km with hourly Rapid Update Cycle(RUC)for five monsoon precipitation events in South China from 2018 to 2020,using the fraction skill score(FSS)of the neighborhood spatial verification method.The results revealed that,among the 24-lead-hour forecasts in CMA-GD 3 km,the FSS for the 0.1 mm precipitation threshold increased linearly with the lead time from 3 to 1 hour,while there was no significant improvement in other lead times.For the 5 mm precipitation threshold,the forecast skill was highest for the latest 1-hour lead time,while the FSS showed slight variation between lead times of 24 hours and 8 hours.The FSS for 10 mm and 20 mm precipitation thresholds were similar to that of 5 mm,with the difference that the best score occurred at the 2-hour lead time.Among the 6-lead-hour forecasts in CMA-GD 1 km,the forecasts of the latest 1-hour lead time were the best choices for four precipitation thresholds.When comparing CMA-GD 3 km and CMA-GD 1 km,it was found that CMA-GD 3 km had better skill for forecasts of 0.1 mm and 5 mm precipitation at 2-hour and 1-hour lead times,while CMA-GD 1 km had better skill for all other forecasts,including the forecast of 20 mm precipitation nearly all lead hours(including 3-to 6-hour,and 1-hour lead times).The results suggest that the increased resolution of the model may be beneficial for precipitation forecasts in South China,especially for short-duration heavy precipitation over a longer lead hours.However,the limited sample size of this study calls for further evaluation using more cases to validate the results′generality.

Contrasting Regional Responses of Indian Summer Monsoon Rainfall to Exhausted Spring and Concurrently Emerging Summer El Nino Events

The inverse relationship between the warm phase of the El Nino Southern Oscillation(ENSO)and the Indian Summer Monsoon Rainfall(ISMR)is well established.Yet,some El Nino events that occur in the early months of the year(boreal spring)transform into a neutral phase before the start of summer,whereas others begin in the boreal summer and persist in a positive phase throughout the summer monsoon season.This study investigates the distinct influences of an exhausted spring El Nino(springtime)and emerging summer El Nino(summertime)on the regional variability of ISMR.The two ENSO categories were formulated based on the time of occurrence of positive SST anomalies over the Nino-3.4 region in the Pacific.The ISMR’s dynamical and thermodynamical responses to such events were investigated using standard metrics such as the Walker and Hadley circulations,vertically integrated moisture flux convergence(VIMFC),wind shear,and upper atmospheric circulation.The monsoon circulation features are remarkably different in response to the exhausted spring El Nino and emerging summer El Nino phases,which distinctly dictate regional rainfall variability.The dynamic and thermodynamic responses reveal that exhausted spring El Nino events favor excess monsoon rainfall over eastern peninsular India and deficit rainfall over the core monsoon regions of central India.In contrast,emerging summer El Nino events negatively impact the seasonal rainfall over the country,except for a few regions along the west coast and northeast India.

An Extreme Monsoonal Heavy Rainfall Event over Inland South China in June 2022: A Synoptic Causes Analysis

An extreme monsoonal heavy rainfall event lasted for nine days and recurred in the interior of northern south China from June 13 to 21, 2022. Using regional meteorological stations and ERA5 reanalysis data, the causes of this extreme monsoonal rainfall event in south China were analyzed and diagnosed. The results are shown as follows. A dominant South Asian high tended to be stable near the Qinghai-Tibet Plateau, providing favorable upper-level dispersion conditions for the occurrence of heavy rainfall in south China. A western Pacific subtropical high dominated the eastern part of the South China Sea, favoring stronger and more northward transport of water vapor to the northern part of south China at lower latitudes than normal. The continuous heavy precipitation event can be divided into two stages. The first stage(June 13-15) was the frontal heavy rainfall caused by cold air(brought by an East Asian trough)from the mid-latitudes that converged with a monsoonal airflow. The heavy rains occurred mostly in the area near a shear in front of the center of a synoptic-system-related low-level jet(SLLJ), and the jet stream and precipitation were strongest in the daytime. The second stage(June 16-21) was the warm-sector heavy rainfall caused by a South China Sea monsoonal low-level jet penetrating inland. The heavy rainfall occurred on the windward slope of the Nanling Mountains and in the northern part of a boundary layer jet(BLJ). The BLJ experienced five nighttime enhancements, corresponding well with the enhancement of the rainfall center, showing significant nighttime heavy rainfall characteristics. Finally, a conceptual diagram of inland-type warm-sector heavy rainfall in south China is summarized.

Interdecadal Change in the Interannual Variability of South China Sea Summer Monsoon Intensity

The interdecadal change in the interannual variability of the South China Sea summer monsoon(SCSSM)intensity and its mechanism are investigated in this study.The interannual variability of the low-level circulation of the SCSSM has experienced a significant interdecadal enhancement around the end of the 1980s,which may be attributed to the interdecadal changes in the evolution of the tropical Indo-Pacific sea surface temperature(SST)anomalies and their impacts on the SCSSM.From 1961 to 1989,the low-level circulation over the South China Sea is primarily affected by the SST anomalies in the tropical Indian Ocean via the mechanism of Kelvin-wave-induced Ekman divergence.While in 1990 to 2020,the impacts of the summer SST anomalies in the Maritime Continent and the equatorial central to eastern Pacific on the SCSSM are enhanced,via anomalous meridional circulation and Mastuno-Gill type Rossby wave atmospheric response,respectively.The above interdecadal changes are closely associated with the interdecadal changes in the evolution of El Niño–Southern Oscillation(ENSO)events.The interdecadal variation of the summer SST anomalies in the developing and decaying phases of ENSO events enhances the influence of the tropical Indo-Pacific SST on the SCSSM,resulting in the interdecadal change in the interannual variability of the SCSSM.

Enhancement of East African Monsoon Long Rainfall (March to May) Variability from Weekly to Annual Scale by Climatic Extremes

As global warming increasingly affects vulnerable regions such as Central East Africa, it is crucial to understand future changes in rainfall variability to reduce vulnerability. Despite the importance of rainfall variability, it has received less attention compared to changes in mean and extreme rainfall. This study evaluates the amplification of synoptic (weekly) to annual variability of East African Monsoon (EAM) Long Rainfall (March to May) by climatic extremes. Using band-pass filtered daily rainfall data, we found that EAM rainfall variability is anticipated to increase by 20% - 60% across the region under global warming conditions. The majority of the intermodal variability in Long Rain EAM rainfall forecasting is explained by differences in mean rainfall. Our results show that the synoptic variability of Long Rain for EAM rainfall is likely to amplify, resulting in more extreme rainfall events and longer dry spells under global warming. This amplification is attributed to the warming of the Indian Ocean and the associated changes in atmospheric circulation patterns. The projected increase in synoptic to annual variability of Long Rain for EAM rainfall has significant implications for water resources management and agriculture in the region, challenging policymakers to develop adaptive strategies that can mitigate the impacts of these extreme events. This study emphasizes the potential impacts of projected climate changes in rainfall variability on the East African region at all periods and underscores the need for effective adaptation strategies to ensure sustainable development.

Strength of the North African monsoon in the Last Interglacial and under future warming

与人为强迫引起的全球变暖相比,末次间冰期是轨道强迫引起的过去80万年来最暖的一个间冰期,但鲜有人研究末次间冰期中北非季风的响应.因此,本文基于CMIP6多模式模拟结果对比研究了末次间冰期和SSP5-8.5情景下北非季风的响应,发现末次间冰期下北非季风平均降水及其降水变率均远大于SSP5-8.5情景下的结果.轨道强迫导致的北大西洋暖于南大西洋增加了北非季风环流和平均降水,同时,南北大西洋海温梯度变化通过增强热带北大西洋的海气相互作用增大了海温梯度和撒哈拉低压的变率,从而增强了北非季风降水变率.