氣候與氣候變化研究進(jìn)展

Progress in Research on Climate and Climate Change

1 次季節(jié)至季節(jié)變化特征與機(jī)理

1 Features and mechanism of the subseasonal to seasonal variability

1.1 Extremely late onset of the 2018 South China Sea summer monsoon following a La Ni?a event:Effects of triple SST anomaly mode in the North Atlantic and a weaker Mongolian cyclone

The onset of South China Sea (SCS) summer monsoon (SCSSM) in June 2018 was extremely late following a La Ni?a event,indicating a breakdown in the traditional positive relationship between ENSO and SCSSM onset.Although the weaker western Pacific subtropical high in early May facilitated the SCSSM establishment,the persistent weaker Mongolian cyclone featured by an anomalous barotropic anticyclone over Northeast Asia during mid-late May dramatically postponed the SCSSM onset in 2018.This not only reduced upper-tropospheric divergence over the SCS,which suppressed monsoon convection by attenuating the South Asian High,but also cooled the mid-upper troposphere to decrease the in-situ vertical easterly shear.The convection over the Maritime Continent was therefore trapped in the tropics,which further delayed the SCSSM onset via an enhanced local Hadley cell.It suggests a potential effect of triple SSTA mode in North Atlantic on the SCSSM onset by changing the mid-latitudinal circulation.(Liu Boqi,Zhu Congwen)

1.2 Weak linkage of winter surface air temperature over Northeast Asia with East Asian winter monsoon during 1993–2003

A colder winter over Northeast Asia (NEA) has traditionally been attributed to the stronger East Asian winter monsoon (EAWM) on interannual timescale.However,the present work proposes this robust linkage becomes weak during 1993–2003,along with the changes of the underlying condition in the last three decades.During 1981–1992 and 2004–2016,the loss of autumn Arctic sea ice condensation (SIC) leads to the stratospheric warming and the polar vortex weakening,which results in the enhancement of the Siberian High (SH) and the colder surface air temperature (SAT) over NEA.In particular,the persisting anomalies of snow cover near the Mongolian Plateau from autumn to winter could amplify the influences of Arctic SIC on the EAWM during 1981–1992.However,during 1993–2003 both the EAWM and the SAT over NEA are modulated by the tropical SSTAs in the western Pacific warm pool,corresponding to a weak association between the EAWM and the SAT over NEA.These tropical warm SSTAs could excite a meridional teleconnection over East Asia to generate a barotropic anticyclonic anomaly in situ.It not only weakens the SH and EAWM but also decreases the SAT over NEA.Therefore,the predictor of winter SAT over NEA is altered from the cryosphere to the tropical SSTAs in this episode.The changes of interdecadal background may contribute to the distinct interannual relationship between EAWM and winter SAT over NEA.This will increase the uncertainty in seasonal forecast on the winter climate over East Asia.(Liu Boqi,Zhu Congwen)

1.3 Record-breaking northward shift of the western North Pacific subtropical high in July 2018

The northward shift of the western North Pacific subtropical high (WNPSH) in July 2018 broke the historical record since 1958 and resulted in extreme heat waves and casualties across Northeast Asia (NEA).In the present work,we associated this extreme WNPSH anomaly with the anomalies of barotropic anticyclone above NEA originating from the strongest positive tripole pattern of sea surface temperature anomaly (SSTA) in North Atlantic in July.Both data analysis and numerical experiments indicated that the positive tripole SSTA pattern could produce an upper-tropospheric wave source over Europe,which stimulated an eastward propagating wave train along the subpolar westerly jet over the Eurasian Continent.When its anticyclonic node reached NEA,the WNPSH started to shift northward.After the cyclonic node in the circulation anomaly encountered the Tibetan Plateau (TP),atmospheric diabatic heating was enhanced over the eastern TP,initiating another subtropical wave train,which furthered the northward shift of the WNPSH.Therefore,the wave source over Europe was critical for the northward shift of the WNPSH in July,connecting the tripole SSTA pattern in the North Atlantic with the WNPSH anomaly and maintaining the downstream effects of thermal forcing over the eastern TP on the East Asian summer monsoon.(Liu Boqi,Zhu Congwen,Su Jingzhi)

1.4 Subseasonal mode of cold and wet climate in South China during the cold season:A climatological view

The authors investigate the dominant mode of climatological intraseasonal oscillation (CISO) of surface air temperature (SAT) and rainfall in China,and discuss the linkage of cold and wet climate in South China (SC) with the Arctic circulation regime during the cold season (from November to March).Results show that a positive CISO displays a cold-dry climate in North China,whereas a cold-wet pattern prevails in SC with a quasi-30-day oscillation during the peak winter season.In SC,the intraseasonal variability of SAT plays a leading role,altering the cold-wet climate by the southward shift of a cold front.Evidence shows that the circulation regime related to the cold and wet climate in SC is mainly regulated by a pair of propagating ISO modes at the 500-hPa geopotential height in the negative phase of Arctic Oscillation.It is demonstrated that the local cyclonic wave activity enhances the southward movement of the Siberian high,favoring an unstable atmosphere and resulting in the cold-wet climate over SC.Therefore,the cold-air activity acts as a precursor for subseasonal rainfall forecasting in SC.(Yu Minjie,Zhu Congwen,Jiang Ning)

1.5 Asymmetry in the dominant co-variation mode of boreal summer monsoon rainfall regulated by the ENSO evolution

Interannual variability of boreal summer monsoon (BSM) rainfall exhibits a prominent co-variation mode,which affects the regions with the highest population density in the world.The mode intensity depends on the rainfall variation over the western North Pacific (WNP) and the North America (NAM) monsoon regions.This study suggests that relative importance of the WNP and NAM rainfall anomalies is asymmetric between strong positive (SP) and strong negative (SN) phases of this mode,which can be attributed to the distinct seasonal evolution of ENSO events.In the SP-phase,the suppressed summer rainfall over the WNP determines the mode following a decaying El Ni?o event.When the tropical Indian Ocean (TIO) warms and the eastern Equatorial Pacific (EEP) cools,the emanating Kelvin wave- and zonal SST difference-induced low-level WNP anticyclone thus gets enhanced to damp the local rainfall,which further affects the other members of the BSM.However,the SN-phase of this mode,showing closer association with anomalous NAM rainfall,appears with a developing El Ni?o event.The tropical North Atlantic (TNA) becomes colder from spring to summer,when the EEP warms due to the zonal circulation anomalies.A stronger zonal SST difference between warm EEP and cold TNA suppresses the NAM rainfall by strengthening the low-level anticyclone in situ.Such asymmetry in different phases of the BSM co-variation mode is validated by the pre-industrial control runs in a state-of-theart CGCM,indicating the roles of ENSO evolution in regulating the interaction between the BSM members.(Hao Yuqian,Liu Boqi,Zhu Congwen,He Bian)

1.6 Possible impact of North Atlantic warming on the decadal change in the dominant modes of winter Eurasian snow water equivalent

A west-east dipole mode of winter Eurasian snow water equivalent (SWE) is found during the period of 1979?2015.It accounts for about 23.4% of the total variance,and displays a significant decadal change in the early-2000s.The basin warming footprint of the North Atlantic possibly exerts an influence on this decadal change,and the observed evidence is reproduced by numerical experiments with the Community Atmosphere Model (CAM3.1).A basin-wide warming of North Atlantic sea surface temperature induces atmospheric anomalies by exciting a stationary Rossby wave train,which prorogates from the subtropical North Atlantic to the mid-to-high latitudes of the Eurasian continent.Along with the Rossby wave train,a blocking ridge occurs over the Ural Mountain,and an upper-level trough appears over the eastern Siberian Plateau,which promotes heavy snowfall over the eastern Siberian Plateau and light snowfall to its west.Thus,it is plausible that the North Atlantic warming plays a role in exciting the Rossby wave train to modulate the decadal change in the west-east dipole SWE mode of the extratropical Eurasian continent.The possible moisture transport paths associated with the decadal change in the dipole SWE mode are also discussed.(Sun Chenghu,Zhang Ruonan,Li Weijing,Zhu Jieshun,Yang Song)

1.7 Role of Eurasian snow cover in linking winter-spring Eurasian coldness to the autumn Arctic sea ice retreat

An anomalous“north-south”dipole mode of snow water equivalent (SWE) persisting from winter to spring is detected over the Eurasian mid-to-high latitudes in this study.We show that this mode plays a key role in modulating the prolonged winter-spring coldness in Eurasian mid-latitudes,and is linked closely to the declined November Arctic sea ice concentration (SIC) using observational datasets and numerical experiments of the Community Atmospheric Model 5.0.The declined SICs over the Barents-Laptev seas can induce a teleconnection pattern over the mid-to-high latitudes in the following winter,accompanied by an anomalous ridge over the Ural Mountains and an anomalous trough over Europe and East Asia,respectively.Such changes in the large-scale circulation further lead to increased cold surges and heavy snowfall in mid-latitudes and light snowfall in high-latitudes,forming an anomalous“north-south”dipole mode of SWE.Due to the seasonal memory,this SWE pattern can persist into the following spring and lead to occurrence of mid-latitude coldness in spring via both thermodynamic and dynamic processes.For the thermodynamic process,the anomalous SWE condition can lead to anomalous wet soil,reduced incoming surface solar radiation,and cooling air in mid-latitudes.This in turn induces an enhanced Siberian high and a deepened East Asian trough via the snow-Siberian high feedback mechanism,which favors a cold spring in the northern East Asia.Further analysis suggests that an empirical seasonal prediction model based on the SWE factor has a reasonably good prediction skill for East Asian spring temperature.(Zhang Ruonan,Sun Chenghu,Zhang Renhe,Li Weijing,Zuo Jinqing)

1.8 Interannual relationship between intensity of rainfall intraseasonal oscillation and summer-mean rainfall over Yangtze River Basin in the eastern China

The analysis of observational rainfall shows that the intensity of rainfall intraseasonal oscillation (ISO) and the summer-mean rainfall over the middle-lower reaches of the Yangtze River Basin (YRB) exhibit a significant positive correlation during 1979–2007.A stronger (weaker) ISO variability is often associated with wet (dry) summer in the YRB.The composite ISOs in both the wet and dry summers are further analyzed.In the wet summers,the rainfall ISO in YRB is primarily associated with the northward propagation of a lowlevel cyclone-anticyclone pair from the tropics.Cyclonic vorticity and associated boundary layer convergence strengthen the rainfall in situ.In contrast,the rainfall ISO in YRB in the dry summers is primarily associated with the westward propagation of an anomalous anticyclone.Southerly flow to the west of the anomalous anticyclone enhances rainfall in YRB through anomalous moisture advection.In addition to the difference in ISO propagation,the background mean state also shows a marked difference.The diagnosis of water vapor flux budget shows that the convergence and advection of seasonal mean moisture play a critical role in maintenance of the intraseasonal rainfall in the YRB.A greater mean ascending motion and associated higher mean moisture in YRB in the wet summers favor greater intraseasonal rainfall variability in situ.The mean state difference is responsible for distinctive vertical structures of boundary layer vertical velocity.A possible feedback of the ISO to the summer-mean rainfall over the YRB is also discussed.(Qi Yanjun,Li Tim,Zhang Renhe)

1.9 Influence of intraseasonal oscillation on the asymmetric decays of El Ni?o and La Ni?a

Warm and cold phases of El Ni?o-Southern Oscillation (ENSO) exhibit a significant asymmetry in their decay speed.To explore the physical mechanism responsible for this asymmetric decay speed,the asymmetric features of anomalous sea surface temperature (SST) and atmospheric circulation over the tropical Western Pacific (WP) in El Ni?o and La Ni?a mature-to-decay phases are analyzed.It is found that the interannual standard deviations of outgoing longwave radiation and 850 hPa zonal wind anomalies over the equatorial WP during El Ni?o (La Ni?a) mature-to-decay phases are much stronger (weaker) than the intraseasonal standard deviations.It seems that the weakened (enhanced) intraseasonal oscillation during El Ni?o (La Ni?a) tends to favor a stronger (weaker) interannual variation of the atmospheric wind,resulting in asymmetric equatorial WP zonal wind anomalies in El Ni?o and La Ni?a decay phases.Numerical experiments demonstrate that such asymmetric zonal wind stress anomalies during El Ni?o and La Ni?a decay phases can lead to an asymmetric decay speed of SST anomalies in the central-eastern equatorial Pacific through stimulating different equatorial Kelvin waves.The largest negative anomaly over the Ni?o3 region caused by the zonal wind stress anomalies during El Ni?o can be threefold greater than the positive Ni?o3 SSTA anomalies during La Ni?a,indicating that the stronger zonal wind stress anomalies over the equatorial WP play an important role in the faster decay speed during El Ni?o.(Song Xiaomeng,Zhang Renhe,Rong Xinyao)

1.10 Why do we have El Ni?o:Quantifying a diabatic and nonlinear perspective using observations

El Ni?o,due to its global impact on weather patterns,ecosystems,agriculture and public health,has become as commonly known to the public as the recent global warming.But why we have El Ni?o is not yet as well answered as it may have been assumed.Linear theories have been successful in explaining the transition from the warm phase to the cold phase of the eastern tropical Pacific that results from the rise and fall of El Ni?o,but failed to explain the asymmetry between the two phases.A nonlinear theory for El Ni?o has suggested that there exist two equilibrium states for the tropical Pacific—one is zonally symmetric (or nearly so) with the warm-pool extending all the way to the eastern Pacific,and the other is strongly zonally asymmetric with the warm-pool confined to the western half of the tropical Pacific.Under this hypothesis,ENSO results from the fact that under the current radiative heating,both states are unstable,resulting in the apparent“wandering”behavior in between these two states as seen in the observations.To test this hypothesis,the authors have obtained the best approximations for the two equilibrium states empirically using updated ocean assimilation data,and quantified the stability of these two empirically obtained equilibrium states using two stability analysis methods.The results suggest that the two states are unstable,offering support for the nonlinear view of why we have El Ni?o.(Hua Lijuan,Sun Dezheng,Yu Yongqiang)

1.11 Possible causes of the flooding over South China during the 2015/2016 winter

Sequential heavy rainfall clusters and resultant severe winter flooding were observed over South China during the 2015/2016 super El Ni?o event.In the present,the intra-seasonal oscillations (ISOs) related with heavy rainfall over East Asia from late autumn to early winter in 2015/2016 were investigated using the daily in situ rainfall records and the NCEP-DOE reanalysis data set.Results suggested that the successive heavy winter rainfall events in 2015/2016 were contributed by the ISOs with significant periods of 10?25 and 30?45-days.The wet phase of 10?25-day ISO was jointly induced by the anomalous convergence of the low-level water vapor associated with the tropical-subtropical interaction and the upper-level divergence attributed to the eastwards propagating wave train.However in the wet phase of the 30?45-day ISO,the anomalous upperlevel divergence was possibly caused by the weaker East Asian trough and the stronger barotropic westerly in subtropics.The 30?45-day ISO can facilitate the eastwards propagation of the 10?25-day ISO by providing a benefit upper-level waveguide.Afterwards,the low-level southwesterly surrounding the Tibetan Plateau gets enhanced to bring more moisture into South China where the winter flooding was serious in 2015/2016.In contrast,the more-than-normal winter rainfall was weaker in the super El Ni?o of 1997/1998 due to the lack of the 30?45-day ISO.Therefore,the strongest winter rainfall anomaly over SC was ascribed to the superposition between the wet phases of 10-25 and 30?45-day ISOs in 2015/2016.(Guo Li,Zhu Congwen,Liu Boqi)

1.12 Interdecadal changes in the asymmetric impacts of ENSO on wintertime rainfall over China and atmospheric circulations over the western North Pacific

Based on data diagnoses,in this study the interdecadal changes in asymmetric impacts of ENSO on wintertime East Asian climate are investigated.It is found that the Pacific Decadal Oscillation (PDO) can significantly modulate the asymmetry in the responses of the East Asian climate to El Ni?o and La Ni?a events.In positive PDO phase the response is asymmetric with a strong anomalous anticyclone over the western North Pacific (WNP) and significant positive rainfall anomalies over the southern China during El Ni?o winters,but a weak anomalous cyclone over WNP and insignificant negative rainfall anomalies over the southern China during La Ni?a winters.However,such asymmetric responses do not appear in negative PDO phase,with comparable amplitudes of anomalous circulations over WNP and rainfall over the southern China in El Ni?o and La Ni?a winters.Further analyses reveal that the warm background of the tropical Pacific in positive PDO phase causes significant difference in the amplitudes of convection anomalies over the tropical western Pacific,resulting in asymmetric responses of the WNP circulation and rainfall over the southern China to El Ni?o and La Ni?a events.Nevertheless,the cold background in negative PDO phase reduces the amplitude difference between El Ni?o and La Ni?a winters.A comparable convection anomalies appear in the tropical western Pacific in El Ni?o and La Ni?a winters and the asymmetric responses do not occur.(Gao Ronglu,Zhang Renhe,Wen Min,Li Tianran)

1.13 The influence of wave trains in mid-high latitudes on persistent heavy rain during the first rainy season over South China

Based on daily precipitation data from the China Meteorological Administration and reanalysis data from the National Centers for Environmental Prediction-Department of Energy,the character of low-frequency precipitation variability during the first rainy season (April–June) over South China and its corresponding atmospheric circulations in the mid-high latitudes are investigated.The results show that the precipitation anomalies during this period exhibit obvious quasi-biweekly oscillation (QBWO) features,with a period of 8–24 days.The influence of wave trains in the mid-high latitudes on the low-frequency persistent heavy rain event (PHR-LF event,the 8–24-day filtered precipitation larger than one standard deviation of filtered time series and persisting at least three days over South China) is further discussed.During the first rainy season over South China,there are two low-frequency wave trains in the mid-high latitudes associated with the PHR-LF event—the wave train crossing the Eurasian continent and the wave train along the subtropical westerly jet.Analysis of wave activity flux indicates that the wave energy disperses toward the eastern China along these two lowfrequency wave trains from north to south and from west to east,and then propagates downward over South China.Accordingly,the disturbance of the relative vorticity of the cyclonic anomalies over the eastern China is strengthened,which enhances the meridional gradient of relative vorticity.Owing to the transport of lowfrequency relative vorticity and geostrophic vorticity by meridional wind,the ascending motion over South China intensifies and lasts for a long time,triggering a PHR-LF event.In addition,the tropical system is also a key factor to PHR-LF event.The QBWO of the convection over the South China Sea provides moisture for PHR-LF events,maintaining persistent rainfall and vertical ascending motion over South China.(Miao Rui,Wen Min,Zhang Renhe,Li Lun)

1.14 Development and eastward movement mechanisms of the Tibetan Plateau vortices moving off the Tibetan Plateau

Based on the final operational global analysis (FNL) data from the Global Forecasting System of the National Centers for Environment Prediction (NCEP) and the radiosonde data,the development and eastward movement mechanisms of fifteen Tibetan Plateau vortices (TPVs) after they move off the plateau are investigated.The results show that the convergence to the east of the TPVs at 500 hPa,the divergence associated with the westerly jet stream at 200 hPa,as well as the corresponding ascending motion,provide favorable conditions for the development and eastward movement of the TPVs.The spatial structures of the atmospheric apparent heat source (Q1) and the apparent moisture sink (Q2) are studied,showing that the heating centers of Q1at 400 hPa mainly sourced from the condensation latent heat are beneficial to the eastward movement of the TPVs,while the horizontal distribution of Q1at 500 hPa goes against that.The development and eastward movement mechanisms of the TPVs after they move off the plateau are further discussed through diagnosing the potential vorticity (PV) tendency equation.It is revealed that the horizontal PV flux convergence to the east of the TPVs related to the convergence at 500 hPa plays the dominant role,exerting positive contribution to the PV tendency.Meanwhile,the heating fields induce feeble PV tendency,indicating more important effect of the dynamic factor.The development and eastward movement mechanisms of the TPVs after they move off the plateau are different from those before the TPVs move off,and the dynamic effect is vital in the former stage while the effect of Q1is revealed as the dominant influencing factor in the latter.(Li Lun,Zhang Renhe,Wen Min)

1.15 Large-scale backgrounds and crucial factors modulating the eastward moving speed of vortices moving off the Tibetan Plateau

Tibetan Plateau vortices (TPVs) are major rain producer over the Tibetan Plateau,which trigger heavy rainfall in the southwestern and eastern China when moving off the plateau.In this work,two groups of TPVs moving off the plateau are selected according to their eastward moving speeds.The features of the atmospheric dynamic and thermodynamic fields associated with the two groups of TPVs are compared,based on the final (FNL) operational global analysis data from the Global Forecasting System of the National Centers for Environment Prediction (NCEP).The results show that the large-scale circulations and heating fields have a close relationship with the moving speed of the TPVs.The TPVs move eastward faster when wider and stronger convergence at 500 hPa,divergence at 200 hPa and the related ascending motion are observed to the east of TPVs.In addition,the stronger and further eastward stretching unstable stratification and water vapor convergence,as well as the more intensive heating field above 500 hPa to the east of TPVs,correspond to larger eastward moving speed of TPVs.Furthermore,the crucial factors modulating the moving speed of TPVs are explored through potential vorticity (PV) budget analyses,in which the physical variables are partitioned into zonal means and disturbances.The convergence of the mean zonal winds and disturbance winds at 500 hPa,as well as the vertical distribution of disturbance heating to the east of TPVs are the crucial factors influencing the eastward moving speed of TPVs,among which the vertical distribution of disturbance heating is the most dominant.(Li Lun,Zhang Renhe,Wen Min)

1.16 Characteristics of the Tibetan Plateau vortices and the related large-scale circulations causing different precipitation intensity

Tibetan Plateau vortices (TPVs) are important synoptic systems generated over the Tibetan Plateau,triggering heavy rainfall over southwestern and eastern China when they move off the plateau.In the present work,the precipitation associated with the moving-off TPVs is explored,and two groups of TPVs are selected according to the precipitation intensity related to the TPVs (PI).The characteristics of these two groups of TPVs and the large-scale circulations during the period after the TPVs move off the plateau are compared.The results show that the impact of TPVs is mainly found in the region to the west of 115°E between 30°?36°N,becoming weaker along with the longitude.Sichuan Basin is the area with the greatest influence from the TPVs.PI is attributed to both the TPVs and the large-scale background.The TPVs related to high (low) PI are stronger (weaker) and travel further eastward (travel shorter distance),and the ascending motion associated with the TPVs is stronger (weaker) and deeper (shallower).The Western Pacific subtropical high (WPSH),southwesterlies to the south of TPVs in middle and lower troposphere,the South Asia High (SAH) and upperlevel jet stream are crucial systems influencing the PI.Stronger and northwestward stretching WPSH,more intensive southwesterlies and the associated water vapor transportation to the south of TPVs,stronger upperlevel jet stream,as well as the more powerful and eastward extending SAH,correspond to higher PI,and vice versa.(Li Lun,Zhang Renhe,Wen Min)

1.17 Effects of the atmospheric dynamic and thermodynamic fields on the eastward propagation of Tibetan Plateau vortices

Tibetan Plateau vortices (TPVs) are major rain-producing systems over the Tibetan Plateau.Some TPVs can move off the plateau under certain conditions,and impact rainfall over the eastern China.Accordingly,the eastward propagation distances of the TPVs moving off the plateau (EPDs) are closely related to the areas of rainfall associated with TPVs.In this study,the moving-off TPVs during May?August of 1998?2015 are classified into two groups according to their EPDs,and the circulations and heating fields at the times when the TPVs move off the plateau (i.e.,moving-off times) are investigated based on reanalysis data.The dynamic and thermodynamic conditions to the east of the Tibetan Plateau are found to significantly impact the EPDs.In the middle and lower troposphere,the zonal ranges of negative geopotential height anomalies to the east of the Tibetan Plateau are in accordance with the EPDs of the TPVs,indicating that anomalous lows play a favorable role in the eastward movement of TPVs.In addition,the anomalous highs to the northeast of the Tibetan Plateau and over Southeastern China also benefit the maintenance of cyclonic circulation to the east of the plateau.Meanwhile,in the upper troposphere,the jet stream over Northeast Asia is beneficial for divergence at 200 hPa.Accordingly,ascending motion associated with the upper-level divergence and lowerlevel convergence is observed,with the zonal extent corresponding well to the EPDs in the two situations.The atmospheric thermodynamic factors also show a remarkable effect on the EPDs.The TPVs move farther away when the unstable stratification and water vapor convergence extend further eastward.The heating ranges above 500 hPa coincide with the EPDs of TPVs,implying a close relationship between the heating fields and the EPDs.These results benefit prediction on EPDs and further on rainfall to the east of the Tibetan Plateau.(Li Lun,Zhang Renhe,Wen Min,Duan Jianping,Qi Yanjun)

1.18 東亞夏季風(fēng)次季節(jié)變化研究進(jìn)展

東亞夏季風(fēng)次季節(jié)（10～90 d）變化是中國(guó)夏季持續(xù)性強(qiáng)降水、高溫?zé)崂说雀哂绊懱鞖馐录闹匾h(huán)流載體，處于天氣預(yù)報(bào)上限和氣候季節(jié)預(yù)測(cè)下限之間的預(yù)報(bào)過渡區(qū)。研究表明：東亞夏季風(fēng)次季節(jié)變化是東亞夏季風(fēng)的固有物理特征，它和季節(jié)進(jìn)程之間的時(shí)間鎖相關(guān)系是東亞夏季風(fēng)次季節(jié)變化潛在可預(yù)報(bào)性的重要來源。東亞夏季風(fēng)次季節(jié)變化與Madden-Julian振蕩（MJO）存在顯著差異，試圖通過MJO來預(yù)測(cè)東亞夏季風(fēng)次季節(jié)變化不確定性較大。東亞夏季風(fēng)次季節(jié)預(yù)測(cè)的另一重要來源是下墊面外強(qiáng)迫，包括歐亞大陸春季積雪、 中國(guó)東部春季土壤濕度和厄爾尼諾-南方濤動(dòng)（ENSO）事件。此外，去趨勢(shì)偏交叉相關(guān)分析統(tǒng)計(jì)方法能夠分析東亞夏季風(fēng)多因子和多時(shí)間尺度問題。目前，亟需解決的科學(xué)問題包括：東亞夏季風(fēng)次季節(jié)模態(tài)的客觀定量描述、 造成東亞夏季風(fēng)次季節(jié)模態(tài)年際變化的關(guān)鍵物理過程、不同外強(qiáng)迫因子對(duì)東亞夏季風(fēng)次季節(jié)模態(tài)的共同影響。（祝從文，劉伯奇，左志燕，袁乃明，劉舸）

1.19 全球變化背景下北半球冬季MJO 傳播的年代際變化

利用1979—2013年實(shí)時(shí)多要素MJO（Madden-Julian Oscillation）監(jiān)測(cè)（RMM）指數(shù)、美國(guó)NOAA逐日長(zhǎng)波輻射資料和NCEP/NCAR再分析資料等，分析了全球變化背景下北半球冬季MJO傳播的年代際變化特征。從全球平均氣溫快速增暖期（1985—1997年）到變暖趨緩期（2000—2012年），MJO 2～4位相頻次減少，5～7位相頻次增多，即MJO對(duì)流活躍區(qū)在熱帶印度洋地區(qū)停留時(shí)間縮短、傳播速度加快，而在熱帶西太平洋停留時(shí)間加長(zhǎng)、傳播明顯減緩。進(jìn)一步分析發(fā)現(xiàn)，以上MJO的年代際變化特征與全球變化年代際波動(dòng)有關(guān)。當(dāng)太平洋年代際濤動(dòng)（PDO）處于負(fù)位相時(shí)，全球變暖趨緩，熱帶東印度洋—西太平洋海溫異常偏暖，使其上空對(duì)流加強(qiáng)，垂直上升運(yùn)動(dòng)加強(qiáng)，對(duì)流層低層輻合，大氣中的水汽含量增多，該區(qū)域的濕靜力能（MSE）為正異常。當(dāng)MJO對(duì)流活躍區(qū)位于熱帶印度洋地區(qū)時(shí)，MJO異常環(huán)流對(duì)季節(jié)平均MSE的輸送在強(qiáng)對(duì)流中心東側(cè)為正、西側(cè)為負(fù)，有利于東側(cè)MSE擾動(dòng)增加，使得MJO對(duì)流擾動(dòng)?xùn)|移加快；而當(dāng)MJO對(duì)流活躍區(qū)在熱帶西太平洋地區(qū)，MJO異常環(huán)流對(duì)平均MSE 的輸送形成東負(fù)西正的形勢(shì)，東側(cè)MSE擾動(dòng)減小，不利于MJO快速東傳。因此，全球變化背景下PDO引起的大氣中水汽含量及MSE的變化可能是MJO傳播年代際變化的重要原因。（修軍藝，溫敏，王遵婭，張人禾）

1.20 歐亞大陸上環(huán)球遙相關(guān)波列與絲綢之路波列的關(guān)系

分析了北半球夏季歐亞大陸上空CGT和SRP之間的聯(lián)系與區(qū)別，結(jié)果表明這兩種遙相關(guān)波列的空間分布形態(tài)高度相似，在時(shí)間變化上也顯著關(guān)聯(lián)。采用偏相關(guān)分析方法討論了這兩種遙相關(guān)波列的相對(duì)獨(dú)立性，研究發(fā)現(xiàn)去除SRP的影響后，CGT在歐亞大陸上的波列狀結(jié)構(gòu)消失；而去除CGT的影響后，SRP在歐亞大陸上依然能維持自身的結(jié)構(gòu)。這說明在歐亞大陸上SRP相對(duì)獨(dú)立于CGT，而CGT依賴與SRP而存在，是SRP的一部分。（周馥荔，張人禾，韓晉平）

1.21 2018/2019年冬季江南超長(zhǎng)連陰雨天氣特征及其成因

2018/2019年冬季，我國(guó)長(zhǎng)江以南（簡(jiǎn)稱江南）地區(qū)發(fā)生了超長(zhǎng)連陰雨天氣。區(qū)域平均有效降水日數(shù)長(zhǎng)達(dá)51天，打破了1981年以來的最高紀(jì)錄，造成了極大的社會(huì)影響。本研究利用JRA55再分析資料，通過診斷分析，指出2018/2019年冬季中部型El Ni?o導(dǎo)致的江南地區(qū)異常低空水汽輻合和東亞冬季風(fēng)次季節(jié)變化異?；钴S，是造成此次江南地區(qū)超長(zhǎng)連陰雨天氣的主要原因。一方面，受此次中部型El Ni?o影響，西太平洋副熱帶高壓異常偏強(qiáng)西伸，為江南地區(qū)的持續(xù)性降水異常提供了穩(wěn)定的異常暖濕背景。另一方面，東亞冬季風(fēng)準(zhǔn)雙周活動(dòng)的異常偏強(qiáng)是江南地區(qū)超長(zhǎng)連陰雨天氣的維持條件。當(dāng)冬季風(fēng)偏強(qiáng)時(shí)，中、高緯度冷空氣向南輸送至江南地區(qū)，觸發(fā)了局地強(qiáng)降水過程; 而當(dāng)冬季風(fēng)偏弱時(shí)，副熱帶地區(qū)的大氣東傳低頻波列活躍，當(dāng)該波列到達(dá)青藏高原后，在高原大地形的機(jī)械阻擋作用下，加強(qiáng)了江南地區(qū)上空的動(dòng)力抬升，并引發(fā)弱降水過程。與歷史事件相比，2018/2019年冬季江南地區(qū)的低空水汽輻合最強(qiáng)，東亞冬季風(fēng)次季節(jié)顯著周期最長(zhǎng)，兩者均達(dá)自1981年以來的極值。因此，江南地區(qū)次季節(jié)強(qiáng)、弱降水過程交替出現(xiàn)，最終造成了此次當(dāng)?shù)爻L(zhǎng)連陰雨天氣。（郭莉，劉伯奇，祝從文）

1.22 東亞夏季環(huán)流多齒輪耦合特征及其對(duì)中國(guó)夏季降水異常的影響分析

東亞夏季風(fēng)成員的相互作用，構(gòu)成了東亞夏季風(fēng)高、低層環(huán)流的“多齒輪耦合”形態(tài)。本文利用多變量主成分分析（MV-EOF）等方法診斷分析了東亞夏季風(fēng)多齒輪耦合的變化特征、耦合機(jī)制、時(shí)間穩(wěn)定性、空間穩(wěn)定特征及其對(duì)中國(guó)夏季降水的影響機(jī)制，并在此基礎(chǔ)上構(gòu)建了典型多齒輪耦合形態(tài)影響夏季降水的概念模型。結(jié)果表明，多齒輪耦合受到垂直溫、壓場(chǎng)的強(qiáng)迫和青藏高原大地形的影響，主要表現(xiàn)在年際變化上（周期為2～6年）。其前兩個(gè)模態(tài)穩(wěn)定地反映了東亞夏季風(fēng)成員典型聯(lián)動(dòng)作用。在第一模態(tài)中，北方氣旋、南亞高壓和西太平洋副熱帶高壓為主要耦合系統(tǒng)。其中北方氣旋為正壓結(jié)構(gòu)，在高層通過南側(cè)偏西氣流與南亞高壓耦合，南亞高壓則通過中緯東部地區(qū)下沉輻散氣流與西太平洋副熱帶高壓聯(lián)動(dòng)。當(dāng)該耦合模態(tài)增強(qiáng)時(shí)，有利于中國(guó)夏季降水呈自北向南“＋－＋－”分布。第二模態(tài)主要反映中高緯氣旋、東亞副熱帶西風(fēng)氣流、南亞高壓、西北太平洋反氣旋系統(tǒng)和西太平洋副熱帶高壓耦合特征。其中，中高緯氣旋和西北太平洋反氣旋為正壓系統(tǒng)，兩者通過其間的東南氣流聯(lián)動(dòng)。氣旋系統(tǒng)在高層通過南側(cè)西風(fēng)與東亞副熱帶西風(fēng)急流和南亞高壓聯(lián)動(dòng)。反氣旋在中低層通過南側(cè)的偏東氣流影響副熱帶高壓強(qiáng)度和面積。當(dāng)該耦合模態(tài)增強(qiáng)時(shí)，中國(guó)黃河以北及河套地區(qū)降水偏多，黃河以南降水偏少。（龐軼舒，祝從文，馬振峰，秦寧生）

1.23 動(dòng)力和統(tǒng)計(jì)預(yù)測(cè)信息融合預(yù)測(cè)方法及對(duì)我國(guó)夏季降水預(yù)測(cè)的檢驗(yàn)

短期氣候預(yù)測(cè)中如何將氣候模式和統(tǒng)計(jì)方法的預(yù)測(cè)結(jié)果科學(xué)、客觀的集成起來，一直是非常重要的問題。本文針對(duì)動(dòng)力模式和統(tǒng)計(jì)方法預(yù)測(cè)結(jié)果相結(jié)合的問題，引入資料同化中信息融合的思想，采用最優(yōu)內(nèi)插同化方法，實(shí)現(xiàn)了動(dòng)力模式和統(tǒng)計(jì)季節(jié)降水預(yù)測(cè)結(jié)果的融合。檢驗(yàn)表明，對(duì)1982—2015年我國(guó)夏季降水百分率的回報(bào)，融合預(yù)測(cè)結(jié)果與觀測(cè)的平均空間相關(guān)系數(shù)可達(dá)0.44，也分別較統(tǒng)計(jì)預(yù)測(cè)和CFSv2模式統(tǒng)計(jì)降尺度訂正的技巧提高了0.1左右，而均方根誤差較兩者可以降低5%～20%?？梢?，該方法可以進(jìn)一步提升對(duì)我國(guó)夏季降水的預(yù)測(cè)技巧，具有顯著的業(yè)務(wù)應(yīng)用價(jià)值。（孫丞虎，崔童，李維京，左金清）

1.24 次季節(jié)至季節(jié)氣候預(yù)測(cè)業(yè)務(wù)支撐與決策服務(wù)

在季節(jié)預(yù)測(cè)方面，氣候所次季節(jié)至季節(jié)研究團(tuán)隊(duì)（S2S團(tuán)隊(duì)）積極參加汛期氣候預(yù)測(cè)，為決策部門提供預(yù)測(cè)意見。我們先后參加了5次不同部委組織的國(guó)家級(jí)氣候會(huì)商，包括：（1）2019年3月，國(guó)家海洋局海洋環(huán)境預(yù)報(bào)中心的ENSO季節(jié)預(yù)測(cè)會(huì)商會(huì)；（2）2019年3月，國(guó)家氣候中心汛期氣候預(yù)測(cè)全國(guó)會(huì)商會(huì)；（3）2019年5月，水利部黃河水利委員會(huì)的汛期黃海河流域氣候預(yù)測(cè)會(huì)商會(huì)；（4）2019年5月，國(guó)家氣候中心汛期氣候預(yù)測(cè)滾動(dòng)訂正會(huì)商（全國(guó)電視電話會(huì)議）；（5）2019年6月，國(guó)家氣候中心盛夏氣候預(yù)測(cè)會(huì)商（全國(guó)電視電話會(huì)議）。在春季成功地預(yù)測(cè)出2018/19年的厄爾尼諾事件將持續(xù)到今年夏季，基于“氣科院東亞季風(fēng)統(tǒng)計(jì)預(yù)測(cè)自動(dòng)化系統(tǒng)”成功地預(yù)測(cè)出今年夏季我國(guó)東北地區(qū)降水異常偏多的情況，為決策部門提供了重要的預(yù)報(bào)信息。

在次季節(jié)預(yù)測(cè)方面，S2S團(tuán)隊(duì)積極參與2022年北京冬奧會(huì)氣候預(yù)測(cè)保障，圍繞冬奧會(huì)賽區(qū)溫度的次季節(jié)至季節(jié)溫度預(yù)測(cè)開展基礎(chǔ)研究。針對(duì)泛冬奧會(huì)地區(qū)（東北亞）冬季氣溫的年際變化開展了專項(xiàng)研究，揭示了冬季西伯利亞高壓影響東北亞冬季氣溫的多樣性特征，并將氣候變化背景引入冬奧會(huì)氣溫預(yù)測(cè)研究中，指出不同氣候背景下影響東北亞地區(qū)冬季氣溫的前兆信號(hào)存在明顯差異。此外，我們還揭示了影響賽區(qū)關(guān)鍵區(qū)的最高和最低極端溫度變化特征和中緯度波列結(jié)構(gòu)，為進(jìn)一步開展冬奧會(huì)的次季節(jié)尺度溫度波動(dòng)預(yù)測(cè)工作奠定了科學(xué)依據(jù)。同時(shí)，團(tuán)隊(duì)成員代表氣科院先后參加了數(shù)次由北京市氣象局組織的2020年冬奧會(huì)測(cè)試賽專題會(huì)商，建立了針對(duì)賽區(qū)氣溫異常的次季節(jié)統(tǒng)計(jì)預(yù)測(cè)模型。

在決策氣象服務(wù)方面，S2S團(tuán)隊(duì)針對(duì)2018年冬季以來我國(guó)長(zhǎng)江以南地區(qū)的連陰雨天氣成因、春季云南地區(qū)的持續(xù)性干旱成因和未來發(fā)展趨勢(shì)、在全球變暖背景下近5年?yáng)|北地區(qū)的6月持續(xù)低溫現(xiàn)象及其對(duì)農(nóng)業(yè)的潛在影響，我們基于研究，分別撰寫了3份決策服務(wù)材料上報(bào)給中國(guó)氣象局。在決策服務(wù)材料的基礎(chǔ)上，我們進(jìn)一步加強(qiáng)科學(xué)研究，撰寫研究論文。其中對(duì)我國(guó)江南地區(qū)冬季連陰雨天氣的分析已在今年的《科學(xué)通報(bào)》上發(fā)表，針對(duì)春季云南干旱的分析投稿《中國(guó)科學(xué)：地球科學(xué)》，關(guān)于東北地區(qū)冷夏的決策服務(wù)材料被局應(yīng)急辦選送上報(bào)“兩辦”（《 全球變暖給東北地區(qū)帶來更頻繁持久異常冷夏專家建議關(guān)注冷夏對(duì)區(qū)域糧食產(chǎn)量的不利影響》）。（劉伯奇，祝從文，馬雙梅，蔣寧，蘇京志）

2 氣候特征與氣候變化

2 Climate characteristics and climate change

2.1 Half-a-degree matters for reducing and delaying global land exposure to combined daytimenighttime hot extremes

The Paris Agreement has motivated rapid analysis differentiating changes in frequency/intensity of weather and climate extremes in 1.5 versus 2 warmer worlds.However,implications of these global warming levels on locations,spatial scales and emergence timings of hotspots to extremes are more relevant to policy-making,but remain strikingly under-addressed.Based on a bivariate definitional framework,we show that compared to 2 ,the 1.5 target could avoid a transition of prevailing type of summertime hot extremes from daytime-/nighttime-only events to combined daytime-nighttime hot extremes in approximately 18% of global continents,and protect 14%?26% of land areas from seeing over three-to-tenfold increases in occurrence of combined hot extremes.This half-a-degree reduction also matters for around 21% of global lands,mostly within the tropics,in constraining historically-unprecedented combined hot extremes from becoming the new norm within just 1?3 decades ahead.By contrast,previous analyses based on univariatedefined hot days substantially underestimate the magnitude,areal extent,and emergence rate of 0.5 -caused aggravation of summertime hot extremes.These projected changes of bivariate-classified hot extremes,therefore,underline not only the imperative but also the urgency of striving for the lower Paris target.(Chen Yang,Zhou Baiquan,Zhai Panmao,Wilfran Moufouma-Okia)

2.2 Anthropogenic warming has substantially increased the likelihood of July 2017-like heat waves over the central eastern China

Heat waves in the central eastern China like the record-breaking July 2017 event were rare in natural worlds but have now become approximately 1-in-5-year events due to anthropogenic forcings.(Chen Yang,Chen Wei,Su Qin,Luo Feifei,Sarah Sparrow,Tian Fangxing,Dong Buwen,Simon F B Tett,Fraser C Lott,David Wallom)

2.3 Coincidence of increasingly volatile winters in China with Arctic sea-ice loss during 1980—2018

Despite intense discussions on the recent boom of mid-latitude wintertime cold extremes,co-variations of warm and cold extremes,i.e.winter temperature volatility,garnered substantially less attention.Apart from using temperature extremes’ frequency and intensity,we also define“temperature whiplash”,which depicts rapid switches between warm and cold extremes,to measure winter temperature volatility in China.Results show that Northeast-,Northwest-,Southwest-,Southeast-China and the Yangtze River Valley have experienced increasingly volatile winters after 1980,co-occurring with precipitous decline in Arctic sea-ice.This enhanced volatility has a strong expression in significant increases in temperature whiplash events,with some hotspots also seeing both warm and cold extremes more frequent and/or intense.An observation-based detection analysis highlights the dominance of intrinsic atmospheric variability over both anthropogenic warming and sea-ice decline during 1980?2018 in driving winters in China more volatile over this period.(Chen Yang,Liao Zhen,Zhai Panmao)

2.4 Extreme cold wave over East Asia in January 2016:A possible response to the larger internal atmospheric variability induced by Arctic warming

It is argued that anthropogenic global warming may decrease the global occurrence of cold waves.However,a historical record-extreme cold wave,popularly called the“boss-level”cold wave,attacked East Asia in January 2016,which gives rise to the discussion of why this“boss-level”cold wave occurred during the winter with the warmest recorded global mean surface air temperature (SAT).To explore the impacts of human-induced global warming and natural internal atmosphere variability,we investigated the cold waverelated circulation regime (i.e.,the large-scale atmospheric circulation pattern) and compared the observation with the large ensemble simulations of the MIROC5 model.Our results showed that this East Asian extreme cold wave-related atmospheric circulation regime mainly exhibited an extremely strong anomaly of the Ural blocking high (UBH) and a record-breaking anomaly of the surface Siberian high (SH),and it largely originated from the natural internal atmosphere variability.However,due to the dynamic effect of Arctic amplification,anthropogenic global warming may increase the likelihood of extreme cold waves through shifting the responsible natural atmospheric circulation regime towards a stronger amplitude.The probability of occurrence of extreme anomalies of UBH,SH,and the East Asia area-mean SAT have been increased by 58%,57%,and 32%,respectively,as a consequence of anthropogenic global warming.Therefore,extreme cold waves in East Asia,such as the one in January 2016,may be an enhanced response to the larger internal atmospheric variability modulated by human-induced global warming.(Ma Shuangmei,Zhu Congwen)

2.5 Persistent precipitation extremes in the Yangtze River Valley prolonged by opportune configuration among atmospheric teleconnections

This study investigates whether and how three synoptic-scale teleconnections,i.e.,East Asia/Pacific teleconnection (EAP),Silk-road teleconnection (SR) and Eurasia teleconnection (EU),induce persistent precipitation extremes (PPEs) in the Yangtze River Valley.Results show that only the EAP teleconnection has the potential of independently incurring PPEs; while the other two teleconnections’ influences on PPEs need to be exerted via their liaison with the EAP pattern.Cases are accordingly grouped into two subsets,i.e.,single EAP-PPEs and three teleconnection-PPEs.In both groups,the EAP teleconnection evolves following a similar pathway that poleward energy dispersion dynamically links a westward-extended subtropical high,a deepened mid-latitude trough and the Okhotsk blocking.EAP-induced circulation anomalies enhance low-level convergences and upper-level divergences,convey exceptionally abundant moisture,and hence give birth to a quasi-stationary front leading to PPEs in the Yangtze River Valley.Despite similarities,PPEs last noticeably longer in the three-teleconnection context.The EU teleconnection-related downstream energy dispersion at higher latitudes favors both earlier establishment and latter decay of the Okhotsk blocking.Constructed meridional flows at mid-high latitudes continuously steer migratory disturbances southeastward into the EAP trough.The SR plays a bigger role during the latter half of PPE lifespan (3 days after onset) via stimulating new cyclonic disturbances that largely overlap with the EAP trough spatially.Moreover,EU- and SR-excited disturbances could effectively extract baroclinic and barotropic energies from local mean flows to replenish components of the EAP tripole pattern,which therefore survives longer and prolongs PPEs by several days.(Chen Yang,Zhai Panmao,Liao Zhen,Li Lei)

2.6 Diurnal variations of summer precipitation over the Qilian Mountains in Northwest China

Based on the high-density hourly rain-gauge data from 265 stations over the Qilian Mountains in Northwest China,climatic mean diurnal variations of summer rainfall over different topographies of this area are investigated.Influences of the gauge elevations on the diurnal variation of rainfall are also revealed.Distinct regional features of diurnal variations in rainfall are observed over the Qilian Mountains.Rainfall over the Qinghai Lake area shows a single nocturnal peak.A dominant,late-afternoon peak of rainfall occurs over the mountain tops.Over the northeastern and southeastern slopes,a dominant diurnal peak appears in the late afternoon,and an evident second peak is found in the early morning,respectively.The strengths of the earlymorning peaks in the rainfall frequency are closely related to the rainfall events with different durations over the two slopes.The early-morning peak is dominant across plains with low elevations.From the mountain tops to the plains,the diurnal peaks of rainfall gradually vary from the dominant late-afternoon peak to the dominant early-morning peak with the enhanced early-morning peak in concurrent with the decreasing gauge elevation over the northeastern and southeastern slopes.Further examination indicates that the rainfall at higher elevations over the northeastern and southeastern slopes occurs more readily in the afternoon,compared to the lower elevations.This phenomenon corresponds to the result that the proportion of the rainfall frequency occurring during the early-morning period decreases with increasing elevations over the two slopes.(Li Liangliang,Li Jian,Chen Haoming,Yu Rucong)

2.7 Regional differences in hourly precipitation characteristics along the western coast of South China

The regional differences in hourly precipitation characteristics along the western coast of South China are investigated.The coastal area can be divided into three regions:two regions with large precipitation amounts to the west and east of the Leizhou Peninsula and another region with less precipitation over the Leizhou Peninsula.The precipitation center west of the Leizhou Peninsula (Dongxing station) is dominated by heavy precipitation,which frequently peaks in the early morning and has a long duration.The precipitation center east of the Leizhou Peninsula (Yangjiang station) has a high frequency of weak precipitation.There are two kinds of precipitation that occur at Yangjiang:short-duration precipitation in the afternoon and longlasting precipitation in the morning.Over the Leizhou Peninsula (Zhanjiang station),precipitation mainly occurs over a short duration in the afternoon.The possible reasons for the different precipitation features are discussed.The morning precipitation at Dongxing is usually caused by deep convection.A large proportion of the morning precipitation events are locally generated events,which are closely related to the southerly winds and topographic barriers.Among the many possible factors affecting the morning precipitation at Yangjiang,the convergence between the land breeze and prevailing onshore airflow is an important one.The afternoon precipitation events affecting Yangjiang mostly originate over the mountains northwest of Yangjiang.Influenced by the curvature of the coastline and the relatively flat terrain over the Leizhou Peninsula,there is no convergence and less convection in the morning.However,the Leizhou Peninsula is prone to being influenced by daytime thermal forcings,which trigger afternoon precipitation.(Li Jian,Li Nina,Yu Rucong)

2.8 Differences in the rainfall characteristics between Mount Tai and its surrounding areas

As a typical small-scale,isolated topography,Mount Tai exhibits great differences in precipitation characteristics from the surrounding areas.It is found that the amount of rainfall occurring over Mount Tai is significantly larger than what observed in the surrounding areas.Based on hourly rain gauge records for the warm season (May to September) of 1996–2015,differences between Mount Tai and its surrounding areas were further revealed in terms of rainfall diurnal variation,spatial scale,and evolution process.The diurnal variation of the enhancement on rainfall amount exhibit“dual peaks”occurring in the early morning and afternoon,and the dual peaks are mainly attributable to rainfall frequency.The diurnal phase of the rainfall amount in the surrounding areas lags 1 h behind that over Mount Tai.Regarding differences in rainfall spatial scale,compared to those of surrounding areas,precipitation over Mount Tai is characterized by a smaller coverage,especially in the early morning.Mount Tai also tends to have a kind of unique,small-scale rainfall in the afternoon and at night.Based on statistical analysis of precipitation events,differences in rainfall evolution process were identified as well.Rainfall over Mount Tai often starts earlier in the afternoon and ends later at night than it does in the surrounding areas.Furthermore,nocturnal rainfall events over Mount Tai are prone to peaking over a shorter period and enduring for a longer period after reaching their maximum intensity,compared with nocturnal rainfall events occurring in the surrounding areas.Rainfall events over Mount Tai always last longer,especially those occurring in the early morning.In general,Mount Tai has a large enhancement effect on rainfall.(Gan Yuting,Li Nina,Li Jian)

2.9 The relationship between heavy precipitation in the eastern region of China and atmospheric heating anomalies over the Tibetan Plateau and its surrounding areas

The relationships among heavy precipitation in the eastern region of China,the atmospheric heat source over the Tibetan Plateau and its surrounding areas,and atmospheric circulation in East Asia were investigated using the multi-variate empirical orthogonal function (MV-EOF) method and synthetic analysis on daily meteorological data from May through August 2010,which were compared with data from 2013.The MVEOF decomposition results revealed that the atmospheric heating over the eastern region of the Tibetan Plateau and the Bay of Bengal exhibited opposite trends when heavy precipitation events occurred in South China,West China,and the middle and lower reaches of the Yangtze River.These results indicated that the landsea thermal contrast between the eastern region of the Tibetan Plateau and the Bay of Bengal was likely one of the key factors leading to the occurrence of heavy precipitation events in the eastern region of China.The results of the synthetic analysis revealed a possible physical mechanism:When the atmospheric heating was weak over the Tibetan Plateau and strong over the Bay of Bengal,there was a strong ascending motion over the Bay of Bengal and its surrounding areas,which was conducive to maintaining the South Asian high and the western Pacific subtropical high (WPSH) in southerly positions.This also resulted in weak water vapor transport in the southwest,thus forming continuous heavy precipitation in South China.After the increase in atmospheric heating over the Tibetan Plateau,the convergence and ascending motion of the lower atmosphere were strengthened,and the South Asian high moved northward to the plateau,with a strengthened eastward extension.The WPSH then lifted northward,and the airflow around it conveyed more water vapor to West China and the middle and lower reaches of the Yangtze River,resulting in heavy precipitation in these regions.(Shi Xiaohui,Chen Jinqiu,Wen Min)

2.10 Climatic characteristics of East Asian tropical monsoon depressions

The climatic characteristics of 260 East Asian tropical monsoon depressions (EAMDs) are investigated using the ERA-Interim reanalysis dataset and a tracking dataset of global monsoon low-pressure systems.Most EAMDs form over the South China Sea (SCS) and the western tropical Pacific Ocean in July–October and have an average lifetime of 10 days.The vertical structures of EAMDs are usually upright or tilt slightly westward with height.The warm-over-cold thermal structure is a distinctive characteristic of EAMDs and two potential vorticity (PV) centers are related to the warm core in the upper level and the specific humidity center in the lower level,respectively.We divided the EAMDs into four groups:eastward-moving,westward-moving,turning,and northwestward-moving EAMDs.Most of the eastward-moving EAMDs form over the SCS in May and June,whereas the westward-moving EAMDs form over both the SCS and the western Pacific Ocean in July–October.The turning and northwestward-moving EAMDs are mainly generated over the western Pacific Ocean and have longer lifetimes.The structures of the eastward-moving and turning EAMDs show common characteristics in each stage.Their vertical structures change from upright in the developing and peak stages to northeast tilting with height in the attenuating stage,especially for the specific humidity.By contrast,the structures of westward- and northwestward-moving EAMDs show little change during their lifetime.They are symmetrical relative to the vertical axis of the EAMDs over their whole lifetime and only vary in strength.(Hu Yi,Wen Min,Li Lun,Zhang Renhe)

2.11 氣候變化和城市可持續(xù)發(fā)展

越來越多的研究表明，城市受到全球氣候變化以及城市化本身引起的局地氣候變化的多重影響，使得高溫?zé)崂?、?qiáng)降水和嚴(yán)重污染天氣更加頻繁和嚴(yán)重。加之城市在密集的空間內(nèi)容納了全世界55%的人口，集聚了人類大部分的資產(chǎn)和經(jīng)濟(jì)活動(dòng)，很容易受到氣候變化所帶來的負(fù)面影響。同時(shí)，城市又是化石能源利用的中心，二氧化碳和污染物排放占比很大。未來全世界城市將進(jìn)一步擴(kuò)展，城市人口也將進(jìn)一步增加，這意味著未來城市所面臨的氣候變化風(fēng)險(xiǎn)形勢(shì)可能會(huì)更為嚴(yán)峻。由此，從氣候變化應(yīng)對(duì)角度來看，城市具有舉足輕重的地位。顯然，氣候變化與未來城市可持續(xù)發(fā)展將是目前人類面臨的重大研究課題之一。政府間氣候變化委員會(huì)（IPCC）從第6次評(píng)估報(bào)告（AR6）開始，將更加關(guān)注氣候變化的區(qū)域問題; 并會(huì)結(jié)合巴黎協(xié)定、聯(lián)合國(guó)2030年可持續(xù)發(fā)展目標(biāo)（SDGs）等，來更多地關(guān)注氣候變化和城市可持續(xù)發(fā)展問題。IPCC計(jì)劃將在2023年第7次氣候變化評(píng)估報(bào)告期內(nèi)開展“氣候變化與城市”特別報(bào)告的編寫。2018年4月，IPCC與其他相關(guān)國(guó)際組織在加拿大Edmond市召開了城市與氣候變化大會(huì)，會(huì)議評(píng)估了全球城市與氣候變化有關(guān)科學(xué)、政策和應(yīng)用等方面的現(xiàn)狀，發(fā)現(xiàn)了有關(guān)研究方面的不足。本文在簡(jiǎn)要回顧國(guó)際上城市氣候變化及其應(yīng)對(duì)有關(guān)研究進(jìn)展和活動(dòng)的最新動(dòng)態(tài)基礎(chǔ)上，分析中國(guó)城市氣候變化有關(guān)風(fēng)險(xiǎn)的嚴(yán)峻形勢(shì)，并闡述城市應(yīng)對(duì)氣候變化與可持續(xù)發(fā)展的密切關(guān)系，圍繞對(duì)我國(guó)城市氣候變化問題的科學(xué)認(rèn)識(shí)和應(yīng)對(duì)行動(dòng)，梳理出中國(guó)針對(duì)城市應(yīng)對(duì)氣候變化問題上值得關(guān)注的幾個(gè)關(guān)鍵科學(xué)問題。（翟盤茂，袁宇鋒，余榮）

2.12 2018年7月北半球極端天氣氣候事件及環(huán)流特征分析

2018年7月北半球天氣氣候顯著異常，極端事件高發(fā)。歐洲、北非、東亞以及北美的大部分地區(qū)均遭受嚴(yán)重的高溫?zé)崂饲忠u;印度、東南亞、中國(guó)西南部以及日本西部等地出現(xiàn)極端降水;西太平洋臺(tái)風(fēng)活動(dòng)異?；钴S，移動(dòng)路徑偏北。初步診斷表明，北半球中高緯度，由低層到高層穩(wěn)定維持的異常高壓系統(tǒng)是導(dǎo)致北半球中高緯度大部分地區(qū)高溫?zé)崂顺掷m(xù)發(fā)生的直接原因。其中異常偏強(qiáng)、偏北的副熱帶高壓，以及增強(qiáng)、東伸的南亞高壓與東亞地區(qū)持續(xù)高溫和極端降水事件直接相關(guān);低層菲律賓周圍異?；钴S的對(duì)流活動(dòng)和強(qiáng)盛的西南水汽輸送共同導(dǎo)致南亞、東南亞地區(qū)極端降水發(fā)生。熱帶太平洋大部分地區(qū)偏暖的海溫條件和菲律賓附近異常氣旋性環(huán)流則與異?；钴S的臺(tái)風(fēng)活動(dòng)有關(guān)。更需要關(guān)注的是，北半球尤其是東亞地區(qū)大氣環(huán)流的異常主要受海洋表面熱力狀況以及其他區(qū)域大氣環(huán)流遙相關(guān)的影響。（王倩，翟盤茂，余榮）

3 氣候模式研發(fā)

3 Climate model development

3.1 Recent progress in numerical atmospheric modeling in China

This review summarizes the scientific and technical progress in atmospheric modeling in China since 2011,including the dynamical core,model physics,data assimilation,ensemble forecasting,and model evaluation strategies.In terms of the dynamical core,important efforts have been made in the improvement of the existing model formulations and in exploring new modeling approaches that can better adapt to massive parallel computers and global multiscale modeling.With regard to model physics,various achievements in physical representations have been made,especially a trend toward scale-aware parameterization for accommodating the increase of model resolution.In the field of data assimilation,a 4D-Var system has been developed and is operationally used by the National Meteorological Center of China,and its performance is promising.Furthermore,ensemble forecasting has played a more important role in operational forecast systems and progressed in many fundamental techniques.Model evaluation strategies,including key performance metrics and standardized experimental protocols,have been proposed and widely applied to better understand the strengths and weaknesses of the systems,offering key routes for model improvement.The paper concludes with a concise summary of the status quo and a brief outlook in terms of future development.(Yu Rucong,Zhang Yi,Wang Jianjie,Li Jian,Chen Haoming,Gong Jiandong,Chen Jing)

3.2 A layer-averaged nonhydrostatic dynamical framework on an unstructured mesh for global and regional atmospheric modeling:Model description,baseline evaluation and sensitivity exploration

This paper describes the development and evaluation of a new nonhydrostatic dynamical framework for global and regional atmospheric modeling,with an emphasis on the numerical performance of dry dynamics.The model is formulated in a layer-averaged manner using a generalized hybrid sigma-mass vertical coordinate and an unstructured mesh.The mass-based equations allow a flexible and effective switch between the hydrostatic and nonhydrostatic solvers.The unstructured mesh treats the conventional icosahedral grid and the more general Voronoi polygon in a consistent manner,allowing a flexible switch between quasi-uniform and variable-resolution modeling.The horizontal and vertical discretization is formulated in an explicit Eulerian approach,while those terms describing the vertically propagating fast waves are solved implicitly.The model is equipped with physically based Smagorinsky diffusion as a tuning tool.A suite of multiscale test cases from hydrostatic to nonhydrostatic regimes is used to assess the model performance.The general strategies for evaluation focus on two aspects:(i) the nonhydrostatic solver should behave similarly to its hydrostatic counterpart under the hydrostatic regime; and (ii) the nonhydrostatic solver should produce unique nonhydrostatic responses under the nonhydrostatic regime.In the context of model evaluation,model sensitivity to numerical configurations is further explored to understand the impact of isolated components,helping to identify appropriate configurations for realistic modeling applications.The present framework is a prototype towards a Global-Regional Integrated forecast SysTem (GRIST).(Zhang Yi,Li Jian,Yu Rucong,Zhang Shixun,Liu Zhuang,Huang Jiahao,Zhou Yihui)

3.3 Understanding the performance of an unstructured-mesh global shallow water model on kinetic energy spectra and nonlinear vorticity dynamics

A strategy for evaluating global shallow water model based on aspects of kinetic energy spectra and nonlinear vorticity dynamics is proposed in this study.The kinetic energy spectra and nonlinear vorticity dynamics of a recently developed global shallow water model on an unstructured mesh are evaluated,and are compared against the benchmark solutions from a global high-resolution spectral model.The kinetic energy spectra,the rotational and divergent components,the stationary and transient components,and the nonlinear spectral fluxes of the shallow water model are studied.Results show that the developed model agrees well with those results generated by the reference model.The influence of different flux operators for transporting the potential vorticity is assessed in detail.It is shown that the second-order flux operator leads to a spurious increase in the kinetic energy at the tail of the spectrum,whereas the upwind third-order flux operator does not support this behavior owing to implicit numerical diffusion.The nonlinear vorticity dynamics is studied using colliding modons.The grid-point model maintains the symmetrical pattern of vortices,and generates similar kinetic energy spectra and nonlinear spectral fluxes to the reference model.The evaluation provides a reference for evaluating the shallow water model in terms of nonlinear dynamics,and the developed global shallow water model presents a good example.(Wang Lei,Zhang Yi,Li Jian,Liu Zhuang,Zhou Yihui)

3.4 Boreal summer intraseasonal oscillation in the Asian-Pacific monsoon region simulated in CAMS-CSM

The simulation of boreal summer intraseasonal oscillation (BSISO) by the climate system model (CSM) developed at Chinese Academy of Meteorological Sciences (CAMS) is used in this study.The results indicate that this new model is able to simulate reasonable annual cycle and seasonal mean of the precipitation,as well as the vertical shear of large-scale zonal wind in tropics.The model reproduces the eastward- and northward-propagating signals similar to those found in observations.The simulation of BSISO is generally in agreement with the observations in terms of variance center,periodicity and propagation,with the exception that the magnitude of BSISO anomalous convections are underestimated in both eastward propagation along the equator and northward propagation over the Asian-Pacific summer monsoon domain.Our preliminary evaluation of the simulated BSISO by CAMS-CSM suggests that this new model has the capability,to a certain extent,in representing BSISO features,including its zonal propagation along the equator and meridional propagation over the Asian-Pacific summer monsoon domain.(Qi Yanjun,Zhang Renhe,Rong Xinyao,Li Jian,Li lun)

3.5 ENSO asymmetry in the CAMS-CSM

This study presents an overview of El Ni?o-Southern Oscillation (ENSO) asymmetry using the Chinese Academy of Meteorological Sciences climate system model (CAMS-CSM).We discover that the coupled run of the CAMS-CSM has an obvious bias of ENSO opposite-sign asymmetry compared to observation,mainly in the eastern Pacific.Further analysis shows that the spatial distributions of sea surface temperature anomalies (SSTA) during both phases of the ENSO present individual biases,consisting of a warmer field during the warm phase and a colder field during the cold phase,in comparison with observation.The bias of ENSO asymmetry during both phases is partly due to the unrealistic simulation of shortwave (SW) radiation flux and the corresponding total cloud cover (TCC).The Atmospheric Model Intercomparison Project (AMIP) run demonstrates that biases of the SW radiation flux and the associated TCC originate in the atmospheric component of the model,which could be attributed to its unrealistic cloud microphysical scheme.Through air-sea interaction,these biases are amplified significantly during both ENSO phases of the coupled run.Moreover,another cause for the bias of ENSO asymmetry during the warm phase is the relatively slow decay of the ENSO in the simulation,with the thermocline anomalies propagating eastward more slowly.The bias of ENSO asymmetry in the cold phase is attributed to oceanic internal dynamic advection,mainly associated with zonal and meridional terms.Further analysis also highlights the essential role of reasonably representing the climatological mean state in ENSO model simulation.(Hua Lijuan,Chen Lin)

3.6 An assessment of ENSO stability in CAMS climate system model simulations

We present an overview of the El Ni?o-Southern Oscillation (ENSO) stability simulation using the Chinese Academy of Meteorological Sciences climate system model (CAMS-CSM).The ENSO stability was quantified based on the Bjerknes (BJ) stability index.Generally speaking,CAMS-CSM has the capacity of reasonably representing the BJ index and ENSO-related air-sea feedback processes.The major simulation biases exist in the underestimated thermodynamic damping and thermocline feedbacks.Further diagnostic analysis reveals that the underestimated thermodynamic feedback is due to the underestimation of the shortwave radiation feedback,which arises from the cold bias in mean sea surface temperature (SST) over central-eastern equatorial Pacific (CEEP).The underestimated thermocline feedback is attributed to the weakened mean upwelling and weakened wind-SST feedback (μa) in the model simulation compared to observation.We found that the weakenedμais also due to the cold mean SST over the CEEP.The study highlights the essential role of reasonably representing the climatological mean state in ENSO simulations.(Hua Lijuan,Chen Lin,Rong Xinyao,Li Jian,Zhang Guo,Wang Lu)

3.7 Cloud radiative feedbacks during the ENSO cycle simulated by CAMS-CSM

This study evaluated the simulated cloud radiative feedbacks (CRF) during the El Ni?o-Southern Oscillation (ENSO) cycle in the latest version of the Chinese Academy of Meteorological Sciences climate system model (CAMS-CSM).We conducted two experimental model simulations:the Atmospheric Model Intercomparison Project (AMIP),forced by the observed sea surface temperature (SST); and the preindustrial control (PIcontrol),a coupled run without flux correction.Both the experiments generally reproduced the observed features of the shortwave and longwave cloud radiative forcing (SWCRF and LWCRF) feedbacks.The AMIP run exhibited better simulation performance in the magnitude and spatial distribution than the PIcontrol run.Furthermore,the simulation biases in SWCRF and LWCRF feedbacks were linked to the biases in the representation of the corresponding total cloud cover and precipitation feedbacks.It is interesting to further find that the simulation bias originating in the atmospheric component was amplified in the PIcontrol run,indicating that the coupling aggravated the simulation bias.Since the PIcontrol run exhibited an apparent mean SST cold bias over the cold tongue,the precipitation response to the SST anomaly (SSTA) changes during the ENSO cycle occurred towards the relatively warmer western equatorial Pacific.Thus,the corresponding cloud cover and CRF shifted westward and showed a weaker magnitude in the PIcontrol run versus observational data.In contrast,the AMIP run was forced by the observational SST,hence representing a more realistic CRF.Our results demonstrate the challenges of simulating CRF in coupled models.This study also underscores the necessity of realistically representing the climatological mean state when simulating CRF during the ENSO cycle.(Chen Lin,Hua Lijuan,Rong Xinyao,Li Jian,Wang Lu,Zhang Guo,Sun Ming,Ge Zi’an)

3.8 Performance of CAMS-CSM in simulating the shortwave cloud radiative effect over global stratus cloud regions:Baseline evaluation and sensitivity test

The ability of climate models to correctly reproduce clouds and the radiative effects of clouds is vitally important in climate simulations and projections.In this study,simulations of the shortwave cloud radiative effect (SWCRE) using the Chinese Academy of Meteorological Sciences climate system model (CAMSCSM) are evaluated.The relationships between SWCRE and dynamic-thermodynamic regimes are examined to understand whether the model can simulate realistic processes that are responsible for the generation and maintenance of stratus clouds.Over the eastern China,CAMS-CSM well simulates the SWCRE climatological state and stratus cloud distribution.The model captures the strong dependence of SWCRE on the dynamic conditions.Over the marine boundary layer regions,the simulated SWCRE magnitude is weaker than that in the observations due to the lack of low-level stratus clouds in the model.The model fails to simulate the close relationship between SWCRE and local stability over these regions.A sensitivity numerical experiment using a specifically designed parameterization scheme for the stratocumulus cloud cover confirms this assertion.Parameterization schemes that directly depict the relationship between the stratus cloud amount and stability are beneficial for improving the model performance.(Zhou Yihui,Zhang Yi,Rong Xinyao,Li Jian,Yu Rucong)

3.9 Robust nocturnal and early morning summer rainfall peaks over continental East Asia in a global multiscale modeling framework

The diurnal cycle of convection and precipitation is an important atmospheric feature.It also poses a great challenge to global numerical atmospheric modeling.Over continental East Asia,most global models cannot well capture the nocturnal and early morning peaks of summer rainfall.This problem may lead to dry biases and limit the modeling skills.This study investigates this problem using a global multiscale modeling framework (Super-Parameterized CAM5; SPCAM5).The nocturnal and early morning peaks,which are almost absent in CAM5 and a coarser-resolution SPCAM5,can be successfully captured by SPCAM5 with a moderate increase in the horizontal resolution.On the lee side of the Tibetan Plateau,SPCAM5 generates robust eastward propagating rainfall signals,which correspond to the moving convective systems,as revealed by the heating and drying profiles.Over the eastern plain of China,the early morning peaks become more evident,corresponding to a stratiform-type heating structure in the midlevel.A sensitivity experiment with altered gridscale forcing also suggests the important preconditioning role of the vertical moisture advection in regulating the early morning peaks.These results highlight the added value of representing multiscale processes to the successful simulation of the diurnal cycle over continental East Asia.(Zhang Yi,Chen Haoming,Wang Dan)

3.10 Revisiting the impact of stochastic multicloud model on the MJO using low-resolution ECHAM6.3 atmosphere model

Based on the preceding work,the influence of the stochastic multicloud model (SMCM) on the Madden-Julian oscillation (MJO) in the state-of-the-art ECHAM6.3 atmospheric general circulation model (AGCM) is further evaluated.The evaluation presented here is based on six recently proposed dynamics-oriented diagnostic metrics.Lag-longitude correlation maps of surface precipitation in the eastern Indian Ocean and West Pacific Ocean confirm the previously discovered improved representation of the MJO in the modified ECHAM6.3 model compared with the standard configuration.In fact,the modified ECHAM6.3 outperforms the default ECHAM6.3 in five of the six MJO-related diagnostics evaluated here.In detail,the modified ECHAM6.3 (1) successfully models the eastward propagation of boundary layer moisture convergence (BLMC); (2) captures the rearward-tilted structure of equivalent potential temperature (EPT) in the lower troposphere and forward-tilted structure of EPT in the upper troposphere; (3) exhibits the rearward-tilted structure of equatorial diabatic heating in the lower troposphere; (4) adequately simulates the MJO-related horizontal circulation at 850 and 200 hPa and the 300 hPa diabatic heating structure.These evaluations confirm the crucial role of convective-parameterization formulation on GCM-simulated MJO dynamics and support the further application and exploration of the SMCM concept in full-complexity GCMs.(Ma Libin,Karsten Peters,Wang Bin,Li Juan)

3.11 Prediction of heavy precipitation in the eastern China flooding events of 2016:Added value of convection-permitting simulations

During the period from 30th June to 6th July 2016,a heavy rainfall event affected the middle and lower reaches of the Yangtze River Valley in the eastern China.The event was characterized by high-intensity,longduration (lasted more than 6 days) precipitation and huge amounts (over 600.0 mm) of rainfall.The rainfall moved eastward from the Sichuan Basin to the middle Yangtze River valley during the first two days,and then entered a“quasi-stationary”(Mei-yu front) phase.During the second-phase,successive heavy rainfall systems occurred repeatedly over the same areas along the front,leading to widespread and catastrophic flooding.In this study,limited-area convection-permitting models (CPMs) covering all of eastern China,and globalmodel simulations from the Met Office Unified Model are compared to investigate the added values of CPMs on the veracity of short-range forecasts of the heavy rainfall event.The results show that all the models can successfully simulate the accumulated amount and the evolution of this heavy rainfall event.However,the global model produces too much light rainfall (10.0 mm day?1),fails to simulate the small-scale features of both atmospheric circulations and precipitation,and tends to generate steady heavy rainfall over the mountainous region.Afternoon precipitation is also excessively suppressed in the global model.By comparison,the CPMs add some value in reproducing the spatial distribution of precipitation,the smaller-scale disturbances within the rain-bands,and the diurnal cycle of precipitation and also reduce the spurious topographical rainfall,although there is a tendency for heavy rainfall to be too intense in CPMs.(Li Puxi,Guo Zhun,Kalli Furtado,Chen Haoming,Li Jian,Sean Milton,Paul R Field,Zhou Tianjun)

3.12 CAMS-CSM模式及其參與CMIP6的方案

世界氣候研究計(jì)劃(WCRP)組織開展的耦合模式比較計(jì)劃已實(shí)施到第6階段（CMIP6），中國(guó)氣象科學(xué)研究院發(fā)展的氣候系統(tǒng)模式CAMS-CSM是注冊(cè)參加CMIP6的模式之一。除CMIP6要求的氣候診斷、評(píng)估和描述試驗(yàn)（DECK）以及歷史氣候模擬試驗(yàn)（Historical）外，CAMS-CSM還計(jì)劃參加情景模式比較計(jì)劃（ScenarioMIP）、云反饋模式比較計(jì)劃（CFMIP）、全球季風(fēng)模式比較計(jì)劃（GMMIP）和高分辨率模式比較計(jì)劃（HighResMIP）這4個(gè)模式比較子計(jì)劃（MIPs）。文中通過介紹CAMS-CSM的基本情況和模擬性能，以及計(jì)劃參加的CMIP6試驗(yàn)及MIPs計(jì)劃，為模式試驗(yàn)數(shù)據(jù)使用者提供參考。（容新堯，李建，陳昊明，辛羽飛，蘇京志，華莉娟，張正秋）