There is limited understanding regarding the formation of multiple tropical cyclones(MTCs).This study explores the environmental conditions conducive to MTC formation by objectively determining the atmospheric circula...There is limited understanding regarding the formation of multiple tropical cyclones(MTCs).This study explores the environmental conditions conducive to MTC formation by objectively determining the atmospheric circulation patterns favorable for MTC formation over the western North Pacific.Based on 199 MTC events occurring from June to October 1980–2020,four distinct circulation patterns are identified:the monsoon trough(MT)pattern,accounting for 40.3%of occurrences,the confluence zone(CON)pattern at 26.2%,the easterly wave(EW)pattern at 17.8%,and the monsoon gyre(MG)pattern at 15.7%.The MT pattern mainly arises from the interaction between the subtropical high and the monsoon trough,with MTCs forming along the monsoon trough and its flanks.The CON pattern is affected by the subtropical high,the South Asian high,and the monsoon trough,with MTCs emerging at the confluence zone where the prevailing southwesterly and southeasterly flows converge.The EW pattern is dominated by easterly flows,with MTCs developing along the easterly wave train.MTCs in the MG pattern arise within a monsoon vortex characterized by strong southwesterly flows.A quantitative analysis further indicates that MTC formation in the MT pattern is primarily governed by mid-level vertical velocity and low-level vorticity,while mid-level humidity and vertical velocity are significantly important in the other patterns.The meridional shear and convergence of zonal winds are essential in converting barotropic energy from the basic flows to disturbance kinetic energy,acting as the primary source for eddy kinetic energy growth.展开更多
Recent studies on tropical cyclone(TC)intensity change indicate that the development of a vertically aligned TC circulation is a key feature of its rapid intensification(RI),however,understanding how vortex alignment ...Recent studies on tropical cyclone(TC)intensity change indicate that the development of a vertically aligned TC circulation is a key feature of its rapid intensification(RI),however,understanding how vortex alignment occurs remains a challenging topic in TC intensity change research.Based on the simulation outputs of North Atlantic Hurricane Wilma(2005)and western North Pacific Typhoon Rammasun(2014),vortex track oscillations at different vertical levels and their associated role in vortex alignment are examined to improve our understanding of the vortex alignment during RI of TCs with initial hurricane intensity.It is found that vortex tracks at different vertical levels oscillate consistently in speed and direction during the RI of the two simulated TCs.While the consistent track oscillation reduces the oscillation tilt during RI,the reduction of vortex tilt results mainly from the mean track before RI.It is also found that the vortex tilt is primarily due to the mean vortex track before and after RI.The track oscillations are closely associated with wavenumber-1 vortex Rossby waves that are dominant wavenumber-1 circulations in the TC inner-core region.This study suggests that the dynamics of the wavenumber-1 vortex Rossby waves play an important role in the regulation of the physical processes associated with the track oscillation and vertical alignment of TCs.展开更多
Under global warming,understanding the long-term variation in different types of heatwaves is vital for China’s preparedness against escalating heat stress.This study investigates dry and wet heatwave shifts in easte...Under global warming,understanding the long-term variation in different types of heatwaves is vital for China’s preparedness against escalating heat stress.This study investigates dry and wet heatwave shifts in eastern China over recent decades.Spatial trend analysis displays pronounced warming in inland midlatitudes and the Yangtze River Valley,with increased humidity in coastal regions.EOF results indicate intensifying dry heatwaves in northern China,while the Yangtze River Valley sees more frequent dry heatwaves.On the other hand,Indochina and regions north of 25°N also experience intensified wet heatwaves,corresponding to regional humidity increases.Composite analysis is conducted based on different situations:strong,frequent dry or wet heatwaves.Strong dry heatwaves are influenced by anticyclonic circulations over northern China,accompanied by warming SST anomalies around the coastal midlatitudes of the western North Pacific(WNP).Frequent dry heatwaves are related to strong subsidence along with a strengthened subtropical high over the WNP.Strong and frequent wet heatwaves show an intensified Okhotsk high at higher latitudes in the lower troposphere,and a negative circumglobal teleconnection wave train pattern in the upper troposphere.Decaying El Niño SST patterns are observed in two kinds of wet heatwave and frequent dry heatwave years.Risk analysis indicates that El Niño events heighten the likelihood of these heatwaves in regions most at risk.As global warming continues,adapting and implementing mitigation strategies toward extreme heatwaves becomes crucial,especially for the aforementioned regions under significant heat stress.展开更多
During the recent four decades since 1980,a series of modern climate satellites were launched,allowing for the measurement and record-keeping of multiple climate parameters,especially over the polar regions where trad...During the recent four decades since 1980,a series of modern climate satellites were launched,allowing for the measurement and record-keeping of multiple climate parameters,especially over the polar regions where traditional observations are difficult to obtain.China has been actively engaging in polar expeditions.Many observations were conducted during this period,accompanied by improved Earth climate models,leading to a series of insightful understandings concerning Arctic and Antarctic climate changes.Here,we review the recent progress China has made concerning Arctic and Antarctic climate change research over the past decade.The Arctic temperature increase is much higher than the global-mean warming rate,associated with a rapid decline in sea ice,a phenomenon called the Arctic Amplification.The Antarctic climate changes showed a zonally asymmetric pattern over the past four decades,with most of the fastest changes occurring over West Antarctica and the Antarctic Peninsula.The Arctic and Antarctic climate changes were driven by anthropogenic greenhouse gas emissions and ozone loss,while tropical-polar teleconnections play important roles in driving the regional climate changes and extreme events over the polar regions.Polar climate changes may also feedback to the entire Earth climate system.The adjustment of the circulation in both the troposphere and the stratosphere contributed to the interactions between the polar climate changes and lower latitudes.Climate change has also driven rapid Arctic and Southern ocean acidification.Chinese researchers have made a series of advances in understanding these processes,as reviewed in this paper.展开更多
The Lightning Imaging Sensor(LIS)and Radar Precipitation Feature(RPF)data are used to investigate the activities and properties of lightning and thunderstorms over a region including the Western Pacific,northern India...The Lightning Imaging Sensor(LIS)and Radar Precipitation Feature(RPF)data are used to investigate the activities and properties of lightning and thunderstorms over a region including the Western Pacific,northern Indian Ocean and the South China Sea along with their adjacent lands.The lands feature significantly more frequent lightning flashes and thunderstorms than the oceans,especially the open oceans.The highest densities of lightning and thunderstorm occur over the Strait of Malacca and the southern foothills of the Himalayas.Over the ocean regions,the Bay of Bengal and the South China Sea are characterized by relatively frequent lightning and thunderstorm activities.Larger average spatiotemporal size and optical radiance of flashes can be found over the oceans;specifically,the offshore area features the most significant flash duration,and the open ocean area is characterized by the greatest flash length and optical radiance.The smallest average values of flash properties can be found over and around the Tibetan Plateau(TP).The oceanic thunderstorms tend to have a significantly larger horizontal extent than the continental thunderstorms,with the former and latter having the average area of the regions with radar reflectivity larger than 20 dBZ,generally over 7000 km^(2) and commonly below 6000 km^(2),respectively.The TP thunderstorms show the smallest horizontal extent.Meanwhile,the oceanic thunderstorms exhibit greater 20 dBZ but smaller 40 dBZ top heights than the continental thunderstorms.The average flash frequency and density of the oceanic thunderstorms are typically less than 5 fl min^(-1) and 0.3 fl 100 km^(-2) min^(-1),respectively;in contrast,the corresponding values of continental thunderstorms are greater.It is explored that the regions associated with strong convective thunderstorms are more likely to feature small-horizontal-extent and low-radiance flashes.展开更多
The influence of Arctic sea ice concentration (SIC) on the subseasonal prediction of the North Atlantic Oscillation (NAO) event is investigated by utilizing the Community Atmospheric Model version 4. The optimal Arcti...The influence of Arctic sea ice concentration (SIC) on the subseasonal prediction of the North Atlantic Oscillation (NAO) event is investigated by utilizing the Community Atmospheric Model version 4. The optimal Arctic SIC perturbations which exert the greatest influence on the onset of an NAO event from a lead of three pentads (15 days) are obtained with a conditional nonlinear optimal perturbation approach. Numerical results show that there are two types of optimal Arctic SIC perturbations for each NAO event, with one weakening event (marked as type-1) and another strengthening event (marked as type-2). For positive NAO events, type-1 optimal SIC perturbations mainly show positive SIC anomalies in the Greenland, Barents, and Okhotsk Seas, while type-2 perturbations mainly feature negative SIC anomalies in these regions. For negative NAO events, the optimal SIC perturbations have almost opposite patterns to those in positive events, although there are some differences among these SIC perturbations due to different atmospheric initial conditions. Further diagnosis reveals that the optimal Arctic SIC perturbations first modify the surface turbulent heat flux and the temperature in the lower troposphere via diabatic processes. Afterward, the temperature in the low troposphere is mainly affected by dynamic advection. Finally, potential vorticity advection plays a crucial role in the 500-hPa geopotential height prediction in the northern North Atlantic sector during pentad 4, which influences NAO event prediction. These results highlight the importance of Arctic SIC on NAO event prediction and the spatial characteristics of the SIC perturbations may provide scientific support for target observations of SIC in improving NAO subseasonal predictions.展开更多
Utilizing the Community Atmosphere Model,version 4,the influence of Arctic sea-ice concentration(SIC)on the extended-range prediction of three simulated cold events(CEs)in East Asia is investigated.Numerical results s...Utilizing the Community Atmosphere Model,version 4,the influence of Arctic sea-ice concentration(SIC)on the extended-range prediction of three simulated cold events(CEs)in East Asia is investigated.Numerical results show that the Arctic SIC is crucial for the extended-range prediction of CEs in East Asia.The conditional nonlinear optimal perturbation approach is adopted to identify the optimal Arctic SIC perturbations with the largest influence on CE prediction on the extended-range time scale.It shows that the optimal SIC perturbations are more inclined to weaken the CEs and cause large prediction errors in the fourth pentad,as compared with random SIC perturbations under the same constraint.Further diagnosis reveals that the optimal SIC perturbations first modulate the local temperature through the diabatic process,and then influence the remote temperature by horizontal advection and vertical convection terms.Consequently,the optimal SIC perturbations trigger a warming center in East Asia through the propagation of Rossby wave trains,leading to the largest prediction uncertainty of the CEs in the fourth pentad.These results may provide scientific support for targeted observation of Arctic SIC to improve the extended-range CE prediction skill.展开更多
As "the third pole", the Tibetan Plateau(TP) is sensitive to climate forcing and has experienced rapid warming in recent decades. This study analyzes annual and seasonal near-surface air temperature changes ...As "the third pole", the Tibetan Plateau(TP) is sensitive to climate forcing and has experienced rapid warming in recent decades. This study analyzes annual and seasonal near-surface air temperature changes on the TP in response to transient and stabilized 2.0℃/1.5℃ global warming targets based on simulations of the Community Earth System Model(CESM). Elevation-dependent warming(EDW) with faster warming at higher elevations is predicted. A surface energy budget analysis is adopted to uncover the mechanisms responsible for the temperature changes. Our results indicate a clear amplified warming on the TP with positive EDW in 2.0℃/1.5℃ warmer futures, especially in the cold season. Mean TP warming relative to the reference period(1961–90) is dominated by an enhanced downward longwave radiation flux, while the variations in surface albedo shape the detailed pattern of EDW. For the same global warming level, the temperature changes under transient scenarios are ~0.2℃ higher than those under stabilized scenarios, and the characteristics of EDW are broadly similar for both scenarios. These differences can be primarily attributed to the combined effects of differential downward longwave radiation, cloud radiative forcing, and surface sensible and latent heat fluxes. These findings contribute to a more detailed understanding of regional climate on the TP in response to the long-term climate goals of the Paris Agreement and highlight the differences between transient and stabilized warming scenarios.展开更多
Drying soil has been conducive to a high frequency of extreme high-temperature events over many regions worldwide in recent decades.However,changes in the intraseasonal variability of soil moisture can also influence ...Drying soil has been conducive to a high frequency of extreme high-temperature events over many regions worldwide in recent decades.However,changes in the intraseasonal variability of soil moisture can also influence the likelihood of extremely high temperatures.Although previous investigators have examined the association between extremely high temperatures and large-scale atmospheric circulation variability,the role of land-atmosphere coupling dominated by soil moisture variability in extremely high temperatures,particularly over the Eurasian continent,is not well understood.In this study,on the basis of the Land Surface,Snow,and Soil Moisture Model Intercomparison Project,we found that land-atmosphere feedback amplified the variability of soil moisture in most regions of Eurasia during summer from 1980 to 2014.This amplification of soil moisture variability is closely correlated with more intensive intraseasonal variability of surface air temperature and more frequent occurrences of extreme high-temperature events,particularly in Europe,Siberia,Northeast Asia,and the Indochina Peninsula.This correlation implies that increasing the intraseasonal variability of soil moisture results in a high likelihood of heat extremes during summer in most parts of Eurasia except Asian desert areas.On the intraseasonal timescale,the land-atmosphere coupling increases the variability of surface sensible heat flux and net long-wave radiation heating the atmosphere by intensifying the soil moisture variability,thus amplifying the variability of surface air temperature and enhancing the extreme high-temperature days.This finding demonstrates the importance of changes in intraseasonal soil moisture variability for the increasing likelihood of heat extremes in summer.展开更多
Based on modern observations,historical proxy data,and climate model simulations,this paper provides a comprehensive overview of the past,present and future evolution characteristics of the Atlantic Meridional Overtur...Based on modern observations,historical proxy data,and climate model simulations,this paper provides a comprehensive overview of the past,present and future evolution characteristics of the Atlantic Meridional Overturning Circulation(AMOC),as well as its impact on the surface air temperature(SAT)at regional and hemispherical scales.The reconstruction results based on the proxy data indicate that the AMOC has weakened since the late 19th century and experienced overall weakening throughout the 20th century with low confidence.Direct observations show that the AMOC weakened during 2004–2016,but it is not possible to distinguish between its decadal variability and long-term trend.Climate models predict that if greenhouse gas emissions continue to increase,AMOC will weaken in the future,but there will not be a sudden collapse before 2100.For the thermodynamic effects of AMOC,the increased surface heat flux release and meridional heat transport(MHT)over the North Atlantic associated with the strong AMOC cause an increase in the hemispherical SAT.At the millennial scale,climate cooling(warming)periods correspond to a weakened(strengthened)AMOC.The enhanced MHT of a strong AMOC can affect Arctic warming and thus influence regional SAT anomalies and SAT extremes through mutual feedback between Arctic sea ice and AMOC.In terms of dynamic effects,a strong AMOC modulates the Rossby wave trains originating from the North Atlantic and spreading across mid-to-high latitudes in the Northern Hemisphere and causes an increase in the variabilities in the circulation anomalies over the Ural and Siberian regions.Ultimately,a strong AMOC significantly affects the frequencies of extreme cold and warm events in the mid-to-high latitude regions over Eurasia.In addition,AMOC can also influence regional and global SAT anomalies through its dynamic adjustment of planetary-scale circulation.Decadal variation in AMOC is closely related to the Atlantic Multidecadal Oscillation(AMO).During positive phases of AMO and AMOC,enhanced surface heat fluxes over the North Atlantic lead to abnormal warming in the Northern Hemisphere,while during negative phases,the reverse case occurs.Under high emission scenarios in the future,the possibility of AMOC collapse increases due to freshwater forcing.However,most advanced climate models underestimate the strength of the AMOC and its impact on the AMO and relevant climate change,which presents a major challenge for future understanding and prediction of the AMOC and its climate effects.展开更多
It has been said,arguably,that causality analysis should pave a promising way to interpretable deep learning and generalization.Incorporation of causality into artificial intelligence algorithms,however,is challenged ...It has been said,arguably,that causality analysis should pave a promising way to interpretable deep learning and generalization.Incorporation of causality into artificial intelligence algorithms,however,is challenged with its vagueness,nonquantitativeness,computational inefficiency,etc.During the past 18 years,these challenges have been essentially resolved,with the establishment of a rigorous formalism of causality analysis initially motivated from atmospheric predictability.This not only opens a new field in the atmosphere-ocean science,namely,information flow,but also has led to scientific discoveries in other disciplines,such as quantum mechanics,neuroscience,financial economics,etc.,through various applications.This note provides a brief review of the decade-long effort,including a list of major theoretical results,a sketch of the causal deep learning framework,and some representative real-world applications pertaining to this journal,such as those on the anthropogenic cause of global warming,the decadal prediction of El Niño Modoki,the forecasting of an extreme drought in China,among others.展开更多
Oceanic observation design is of considerable significance and has made remarkable progress during the past several decades.This study addresses the critical role of numerical modeling in oceanic observation design.Fo...Oceanic observation design is of considerable significance and has made remarkable progress during the past several decades.This study addresses the critical role of numerical modeling in oceanic observation design.Following a brief introduction of the characteristics of existing oceanic observation design studies,we present the advantages of the model-based observation design strategy and further review its decisive contribution.To demonstrate the effectiveness of this strategy,the targeted observation applications using the conditional nonlinear optimal perturbation(CNOP)approach for improving the Kuroshio predictions are introduced.Finally,the authors present their consideration for correcting model errors by targeted observations of sensitive model parameters and mitigating the model-dependency problem by utilizing multiple modeling systems.Suggestions on using observing system simulation experiments to validate the designed observations and extending the model-based observation design strategy into observing oceanic climatological mean states are also discussed.展开更多
The conditional nonlinear optimal perturbation(CNOP for short) approach is a powerful tool for predictability and targeted observation studies in atmosphere-ocean sciences. By fully considering nonlinearity under appr...The conditional nonlinear optimal perturbation(CNOP for short) approach is a powerful tool for predictability and targeted observation studies in atmosphere-ocean sciences. By fully considering nonlinearity under appropriate physical constraints, the CNOP approach can reveal the optimal perturbations of initial conditions, boundary conditions, model parameters, and model tendencies that cause the largest simulation or prediction uncertainties. This paper reviews the progress of applying the CNOP approach to atmosphere-ocean sciences during the past five years. Following an introduction of the CNOP approach, the algorithm developments for solving the CNOP are discussed.Then, recent CNOP applications, including predictability studies of some high-impact ocean-atmospheric environmental events, ensemble forecast, parameter sensitivity analysis, uncertainty estimation caused by errors of model tendency or boundary condition, are reviewed. Finally, a summary and discussion on future applications and challenges of the CNOP approach are presented.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.42075015)the Science and Technology Commission of Shanghai Municipality,China(23DZ1204703).
文摘There is limited understanding regarding the formation of multiple tropical cyclones(MTCs).This study explores the environmental conditions conducive to MTC formation by objectively determining the atmospheric circulation patterns favorable for MTC formation over the western North Pacific.Based on 199 MTC events occurring from June to October 1980–2020,four distinct circulation patterns are identified:the monsoon trough(MT)pattern,accounting for 40.3%of occurrences,the confluence zone(CON)pattern at 26.2%,the easterly wave(EW)pattern at 17.8%,and the monsoon gyre(MG)pattern at 15.7%.The MT pattern mainly arises from the interaction between the subtropical high and the monsoon trough,with MTCs forming along the monsoon trough and its flanks.The CON pattern is affected by the subtropical high,the South Asian high,and the monsoon trough,with MTCs emerging at the confluence zone where the prevailing southwesterly and southeasterly flows converge.The EW pattern is dominated by easterly flows,with MTCs developing along the easterly wave train.MTCs in the MG pattern arise within a monsoon vortex characterized by strong southwesterly flows.A quantitative analysis further indicates that MTC formation in the MT pattern is primarily governed by mid-level vertical velocity and low-level vorticity,while mid-level humidity and vertical velocity are significantly important in the other patterns.The meridional shear and convergence of zonal winds are essential in converting barotropic energy from the basic flows to disturbance kinetic energy,acting as the primary source for eddy kinetic energy growth.
基金National Natural Science Foundation of China(Grant Nos:42150710531,42192551,61827901)supported this study.
文摘Recent studies on tropical cyclone(TC)intensity change indicate that the development of a vertically aligned TC circulation is a key feature of its rapid intensification(RI),however,understanding how vortex alignment occurs remains a challenging topic in TC intensity change research.Based on the simulation outputs of North Atlantic Hurricane Wilma(2005)and western North Pacific Typhoon Rammasun(2014),vortex track oscillations at different vertical levels and their associated role in vortex alignment are examined to improve our understanding of the vortex alignment during RI of TCs with initial hurricane intensity.It is found that vortex tracks at different vertical levels oscillate consistently in speed and direction during the RI of the two simulated TCs.While the consistent track oscillation reduces the oscillation tilt during RI,the reduction of vortex tilt results mainly from the mean track before RI.It is also found that the vortex tilt is primarily due to the mean vortex track before and after RI.The track oscillations are closely associated with wavenumber-1 vortex Rossby waves that are dominant wavenumber-1 circulations in the TC inner-core region.This study suggests that the dynamics of the wavenumber-1 vortex Rossby waves play an important role in the regulation of the physical processes associated with the track oscillation and vertical alignment of TCs.
基金supported by the National Natural Science Foundation of China(Grant Nos.42120104001,42192563 and 42005010)the Hong Kong RGC General Research Fund 11300920.
文摘Under global warming,understanding the long-term variation in different types of heatwaves is vital for China’s preparedness against escalating heat stress.This study investigates dry and wet heatwave shifts in eastern China over recent decades.Spatial trend analysis displays pronounced warming in inland midlatitudes and the Yangtze River Valley,with increased humidity in coastal regions.EOF results indicate intensifying dry heatwaves in northern China,while the Yangtze River Valley sees more frequent dry heatwaves.On the other hand,Indochina and regions north of 25°N also experience intensified wet heatwaves,corresponding to regional humidity increases.Composite analysis is conducted based on different situations:strong,frequent dry or wet heatwaves.Strong dry heatwaves are influenced by anticyclonic circulations over northern China,accompanied by warming SST anomalies around the coastal midlatitudes of the western North Pacific(WNP).Frequent dry heatwaves are related to strong subsidence along with a strengthened subtropical high over the WNP.Strong and frequent wet heatwaves show an intensified Okhotsk high at higher latitudes in the lower troposphere,and a negative circumglobal teleconnection wave train pattern in the upper troposphere.Decaying El Niño SST patterns are observed in two kinds of wet heatwave and frequent dry heatwave years.Risk analysis indicates that El Niño events heighten the likelihood of these heatwaves in regions most at risk.As global warming continues,adapting and implementing mitigation strategies toward extreme heatwaves becomes crucial,especially for the aforementioned regions under significant heat stress.
基金supported by the National Key Research and Development Program of China(2018YFA 0605703)the National Natural Science Foundation of China(No.41976193 and No.42176243)+8 种基金X.CHEN was supported by the National Key Research and Development Program of China(2019YFC1509100)the National Science Foundation of China(No.41825012)B.WU was supported by the Major Program of the National Natural Science Foundation of China(41790472)the National Key Basic Research Project of China(2019YFA0607002)the National Natural Science Foundation of China(41730959)X.CHENG was funded by the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant No.311021008)M.DING was supported by the National Natural Science Foundation of China(42122047 and 42105036)the Basic Research Fund of the Chinese Academy of Meteorological Sciences(2021Y021 and 2021Z006)Q.SUN was supported by the National Key R&D Program of China(No.2022YFE0106300).
文摘During the recent four decades since 1980,a series of modern climate satellites were launched,allowing for the measurement and record-keeping of multiple climate parameters,especially over the polar regions where traditional observations are difficult to obtain.China has been actively engaging in polar expeditions.Many observations were conducted during this period,accompanied by improved Earth climate models,leading to a series of insightful understandings concerning Arctic and Antarctic climate changes.Here,we review the recent progress China has made concerning Arctic and Antarctic climate change research over the past decade.The Arctic temperature increase is much higher than the global-mean warming rate,associated with a rapid decline in sea ice,a phenomenon called the Arctic Amplification.The Antarctic climate changes showed a zonally asymmetric pattern over the past four decades,with most of the fastest changes occurring over West Antarctica and the Antarctic Peninsula.The Arctic and Antarctic climate changes were driven by anthropogenic greenhouse gas emissions and ozone loss,while tropical-polar teleconnections play important roles in driving the regional climate changes and extreme events over the polar regions.Polar climate changes may also feedback to the entire Earth climate system.The adjustment of the circulation in both the troposphere and the stratosphere contributed to the interactions between the polar climate changes and lower latitudes.Climate change has also driven rapid Arctic and Southern ocean acidification.Chinese researchers have made a series of advances in understanding these processes,as reviewed in this paper.
基金supported by the National Natural Science Foundation of China [grant numbers 42030601 and 42205019]supported by a project funded by the China Postdoctoral Science Foundation [grant number 2022M710715]
基金National Key Research and Development Program of China(2019YFC1510103)the Second Tibetan Plateau Scientific Expedition and Research(STEP)Program(2019QZKK0104)。
文摘The Lightning Imaging Sensor(LIS)and Radar Precipitation Feature(RPF)data are used to investigate the activities and properties of lightning and thunderstorms over a region including the Western Pacific,northern Indian Ocean and the South China Sea along with their adjacent lands.The lands feature significantly more frequent lightning flashes and thunderstorms than the oceans,especially the open oceans.The highest densities of lightning and thunderstorm occur over the Strait of Malacca and the southern foothills of the Himalayas.Over the ocean regions,the Bay of Bengal and the South China Sea are characterized by relatively frequent lightning and thunderstorm activities.Larger average spatiotemporal size and optical radiance of flashes can be found over the oceans;specifically,the offshore area features the most significant flash duration,and the open ocean area is characterized by the greatest flash length and optical radiance.The smallest average values of flash properties can be found over and around the Tibetan Plateau(TP).The oceanic thunderstorms tend to have a significantly larger horizontal extent than the continental thunderstorms,with the former and latter having the average area of the regions with radar reflectivity larger than 20 dBZ,generally over 7000 km^(2) and commonly below 6000 km^(2),respectively.The TP thunderstorms show the smallest horizontal extent.Meanwhile,the oceanic thunderstorms exhibit greater 20 dBZ but smaller 40 dBZ top heights than the continental thunderstorms.The average flash frequency and density of the oceanic thunderstorms are typically less than 5 fl min^(-1) and 0.3 fl 100 km^(-2) min^(-1),respectively;in contrast,the corresponding values of continental thunderstorms are greater.It is explored that the regions associated with strong convective thunderstorms are more likely to feature small-horizontal-extent and low-radiance flashes.
基金the National Natural Science Foundation of China(Grant Nos.42288101,41790475,42005046,and 41775001).
文摘The influence of Arctic sea ice concentration (SIC) on the subseasonal prediction of the North Atlantic Oscillation (NAO) event is investigated by utilizing the Community Atmospheric Model version 4. The optimal Arctic SIC perturbations which exert the greatest influence on the onset of an NAO event from a lead of three pentads (15 days) are obtained with a conditional nonlinear optimal perturbation approach. Numerical results show that there are two types of optimal Arctic SIC perturbations for each NAO event, with one weakening event (marked as type-1) and another strengthening event (marked as type-2). For positive NAO events, type-1 optimal SIC perturbations mainly show positive SIC anomalies in the Greenland, Barents, and Okhotsk Seas, while type-2 perturbations mainly feature negative SIC anomalies in these regions. For negative NAO events, the optimal SIC perturbations have almost opposite patterns to those in positive events, although there are some differences among these SIC perturbations due to different atmospheric initial conditions. Further diagnosis reveals that the optimal Arctic SIC perturbations first modify the surface turbulent heat flux and the temperature in the lower troposphere via diabatic processes. Afterward, the temperature in the low troposphere is mainly affected by dynamic advection. Finally, potential vorticity advection plays a crucial role in the 500-hPa geopotential height prediction in the northern North Atlantic sector during pentad 4, which influences NAO event prediction. These results highlight the importance of Arctic SIC on NAO event prediction and the spatial characteristics of the SIC perturbations may provide scientific support for target observations of SIC in improving NAO subseasonal predictions.
基金the National Natural Science Foundation of China(Grant Nos.42288101,41790475,42175051,and 42005046)the State Key Laboratory of Tropical Oceanography(South China Sea Institute of Oceanology,Chinese Academy of Sciences+1 种基金Grant No.LTO2109)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2021A1515011868).
文摘Utilizing the Community Atmosphere Model,version 4,the influence of Arctic sea-ice concentration(SIC)on the extended-range prediction of three simulated cold events(CEs)in East Asia is investigated.Numerical results show that the Arctic SIC is crucial for the extended-range prediction of CEs in East Asia.The conditional nonlinear optimal perturbation approach is adopted to identify the optimal Arctic SIC perturbations with the largest influence on CE prediction on the extended-range time scale.It shows that the optimal SIC perturbations are more inclined to weaken the CEs and cause large prediction errors in the fourth pentad,as compared with random SIC perturbations under the same constraint.Further diagnosis reveals that the optimal SIC perturbations first modulate the local temperature through the diabatic process,and then influence the remote temperature by horizontal advection and vertical convection terms.Consequently,the optimal SIC perturbations trigger a warming center in East Asia through the propagation of Rossby wave trains,leading to the largest prediction uncertainty of the CEs in the fourth pentad.These results may provide scientific support for targeted observation of Arctic SIC to improve the extended-range CE prediction skill.
基金the National Natural Science Foundation of China(Grant Nos.41971072,41771069).
文摘As "the third pole", the Tibetan Plateau(TP) is sensitive to climate forcing and has experienced rapid warming in recent decades. This study analyzes annual and seasonal near-surface air temperature changes on the TP in response to transient and stabilized 2.0℃/1.5℃ global warming targets based on simulations of the Community Earth System Model(CESM). Elevation-dependent warming(EDW) with faster warming at higher elevations is predicted. A surface energy budget analysis is adopted to uncover the mechanisms responsible for the temperature changes. Our results indicate a clear amplified warming on the TP with positive EDW in 2.0℃/1.5℃ warmer futures, especially in the cold season. Mean TP warming relative to the reference period(1961–90) is dominated by an enhanced downward longwave radiation flux, while the variations in surface albedo shape the detailed pattern of EDW. For the same global warming level, the temperature changes under transient scenarios are ~0.2℃ higher than those under stabilized scenarios, and the characteristics of EDW are broadly similar for both scenarios. These differences can be primarily attributed to the combined effects of differential downward longwave radiation, cloud radiative forcing, and surface sensible and latent heat fluxes. These findings contribute to a more detailed understanding of regional climate on the TP in response to the long-term climate goals of the Paris Agreement and highlight the differences between transient and stabilized warming scenarios.
基金supported by the National Key Research and Development Program of China (2022YFF0801703)the National Natural Science Foundation of China (42175053 and 41822503).
文摘Drying soil has been conducive to a high frequency of extreme high-temperature events over many regions worldwide in recent decades.However,changes in the intraseasonal variability of soil moisture can also influence the likelihood of extremely high temperatures.Although previous investigators have examined the association between extremely high temperatures and large-scale atmospheric circulation variability,the role of land-atmosphere coupling dominated by soil moisture variability in extremely high temperatures,particularly over the Eurasian continent,is not well understood.In this study,on the basis of the Land Surface,Snow,and Soil Moisture Model Intercomparison Project,we found that land-atmosphere feedback amplified the variability of soil moisture in most regions of Eurasia during summer from 1980 to 2014.This amplification of soil moisture variability is closely correlated with more intensive intraseasonal variability of surface air temperature and more frequent occurrences of extreme high-temperature events,particularly in Europe,Siberia,Northeast Asia,and the Indochina Peninsula.This correlation implies that increasing the intraseasonal variability of soil moisture results in a high likelihood of heat extremes during summer in most parts of Eurasia except Asian desert areas.On the intraseasonal timescale,the land-atmosphere coupling increases the variability of surface sensible heat flux and net long-wave radiation heating the atmosphere by intensifying the soil moisture variability,thus amplifying the variability of surface air temperature and enhancing the extreme high-temperature days.This finding demonstrates the importance of changes in intraseasonal soil moisture variability for the increasing likelihood of heat extremes in summer.
基金supported by the National Natural Science Foundation of China(Grant Nos.41822503 and 42175053)the National Key Research and Development Program(Grant No.2016YFA0601502).
文摘Based on modern observations,historical proxy data,and climate model simulations,this paper provides a comprehensive overview of the past,present and future evolution characteristics of the Atlantic Meridional Overturning Circulation(AMOC),as well as its impact on the surface air temperature(SAT)at regional and hemispherical scales.The reconstruction results based on the proxy data indicate that the AMOC has weakened since the late 19th century and experienced overall weakening throughout the 20th century with low confidence.Direct observations show that the AMOC weakened during 2004–2016,but it is not possible to distinguish between its decadal variability and long-term trend.Climate models predict that if greenhouse gas emissions continue to increase,AMOC will weaken in the future,but there will not be a sudden collapse before 2100.For the thermodynamic effects of AMOC,the increased surface heat flux release and meridional heat transport(MHT)over the North Atlantic associated with the strong AMOC cause an increase in the hemispherical SAT.At the millennial scale,climate cooling(warming)periods correspond to a weakened(strengthened)AMOC.The enhanced MHT of a strong AMOC can affect Arctic warming and thus influence regional SAT anomalies and SAT extremes through mutual feedback between Arctic sea ice and AMOC.In terms of dynamic effects,a strong AMOC modulates the Rossby wave trains originating from the North Atlantic and spreading across mid-to-high latitudes in the Northern Hemisphere and causes an increase in the variabilities in the circulation anomalies over the Ural and Siberian regions.Ultimately,a strong AMOC significantly affects the frequencies of extreme cold and warm events in the mid-to-high latitude regions over Eurasia.In addition,AMOC can also influence regional and global SAT anomalies through its dynamic adjustment of planetary-scale circulation.Decadal variation in AMOC is closely related to the Atlantic Multidecadal Oscillation(AMO).During positive phases of AMO and AMOC,enhanced surface heat fluxes over the North Atlantic lead to abnormal warming in the Northern Hemisphere,while during negative phases,the reverse case occurs.Under high emission scenarios in the future,the possibility of AMOC collapse increases due to freshwater forcing.However,most advanced climate models underestimate the strength of the AMOC and its impact on the AMO and relevant climate change,which presents a major challenge for future understanding and prediction of the AMOC and its climate effects.
基金supported by National Science Foundation of China(grant#42230105)Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(#313022005 and#SML2023SP203)+2 种基金Fudan University(#IDH2318009Y)Shanghai B&R Joint Laboratory Project(#222-30750300)Shanghai International Science and Technology Partnership Project(#21230780200).
文摘It has been said,arguably,that causality analysis should pave a promising way to interpretable deep learning and generalization.Incorporation of causality into artificial intelligence algorithms,however,is challenged with its vagueness,nonquantitativeness,computational inefficiency,etc.During the past 18 years,these challenges have been essentially resolved,with the establishment of a rigorous formalism of causality analysis initially motivated from atmospheric predictability.This not only opens a new field in the atmosphere-ocean science,namely,information flow,but also has led to scientific discoveries in other disciplines,such as quantum mechanics,neuroscience,financial economics,etc.,through various applications.This note provides a brief review of the decade-long effort,including a list of major theoretical results,a sketch of the causal deep learning framework,and some representative real-world applications pertaining to this journal,such as those on the anthropogenic cause of global warming,the decadal prediction of El Niño Modoki,the forecasting of an extreme drought in China,among others.
基金supported by the National Natural Science Foundation of China(Grant Nos.41806013,41790475)the China Postdoctoral Science Foundation(Grant No.2017M622290)+1 种基金the NSFC Innovative Group Grant(Grant No.41421005)the NSFCShandong Joint Fund for Marine Science Research Centers(Grant No.U1406401)。
文摘Oceanic observation design is of considerable significance and has made remarkable progress during the past several decades.This study addresses the critical role of numerical modeling in oceanic observation design.Following a brief introduction of the characteristics of existing oceanic observation design studies,we present the advantages of the model-based observation design strategy and further review its decisive contribution.To demonstrate the effectiveness of this strategy,the targeted observation applications using the conditional nonlinear optimal perturbation(CNOP)approach for improving the Kuroshio predictions are introduced.Finally,the authors present their consideration for correcting model errors by targeted observations of sensitive model parameters and mitigating the model-dependency problem by utilizing multiple modeling systems.Suggestions on using observing system simulation experiments to validate the designed observations and extending the model-based observation design strategy into observing oceanic climatological mean states are also discussed.
基金supported by the National Natural Science Foundation of China (Nos. 41790475,92158202, 42076017, 41576015)Guangdong Major Project of Basic and Applied Basic Research(No. 2020B0301030004)。
文摘The conditional nonlinear optimal perturbation(CNOP for short) approach is a powerful tool for predictability and targeted observation studies in atmosphere-ocean sciences. By fully considering nonlinearity under appropriate physical constraints, the CNOP approach can reveal the optimal perturbations of initial conditions, boundary conditions, model parameters, and model tendencies that cause the largest simulation or prediction uncertainties. This paper reviews the progress of applying the CNOP approach to atmosphere-ocean sciences during the past five years. Following an introduction of the CNOP approach, the algorithm developments for solving the CNOP are discussed.Then, recent CNOP applications, including predictability studies of some high-impact ocean-atmospheric environmental events, ensemble forecast, parameter sensitivity analysis, uncertainty estimation caused by errors of model tendency or boundary condition, are reviewed. Finally, a summary and discussion on future applications and challenges of the CNOP approach are presented.
