The predictability of a coupled system composed of a coupled reduced-order extratropical ocean-atmosphere model forced by a low-order three-variable tropical recharge-discharge model is explored with emphasis on its l...The predictability of a coupled system composed of a coupled reduced-order extratropical ocean-atmosphere model forced by a low-order three-variable tropical recharge-discharge model is explored with emphasis on its long-term forecasting capabilities.Highly idealized ensemble forecasts are produced taking into account the uncertainties in the initial states of the system,with specific attention to the structure of the initial errors in the tropical model.Three main types of experiments are explored:with random perturbations along the three Lyapunov vectors of the tropical model;along the two dominant Lyapunov vectors;and along the first Lyapunov vector only.When perturbations are introduced along all vectors,forecasting biases develop even if in a perfect model framework and with known initial uncertainty properties.Theses biases are considerably reduced only when the perturbations are introduced along the dominant Lyapunov vector.Furthermore,this perturbation strategy allows a reduced mean square error to be obtained at long lead times of a few years,as well as reliable ensemble forecasts across the whole time range.These very counterintuitive findings further underline the importance of appropriately controlling the initial error structure in the tropics through data assimilation.展开更多
Using multi-source reanalysis data,this study examines the relationship between the tropical Pacific-Atlantic SST Dipole Mode(TPA-DM)and summer precipitation in North China(NCSP)on the interannual timescale during the...Using multi-source reanalysis data,this study examines the relationship between the tropical Pacific-Atlantic SST Dipole Mode(TPA-DM)and summer precipitation in North China(NCSP)on the interannual timescale during the period of 1979-2022.The results show that the TPA-DM,the dominant pattern of interannual variability in the tropical Pacific and Atlantic regions,exhibits a significant negative correlation with NCSP.The positive phase of TPA-DM induces subsidence over the Maritime Continent through a zonal circulation pattern,which initiates a Pacific-Japan-like wave train along the East Asian coast.The circulation anomalies lead to moisture deficits and convergence subsidence over North China,leading to below-normal rainfall.Further analysis reveals that cooler SST in the Southern Tropical Atlantic facilitates the persistence of the TPA-DM by stimulating the anomalous Walker circulation associated with wind-evaporation-SST-convection feedback.展开更多
As one of the strongest convection bands in the Southern Hemisphere,the South Pacific Convergence Zone(SPCZ)substantially influences the variabilities in the atmospheric circulation and Antarctic climate.In this study...As one of the strongest convection bands in the Southern Hemisphere,the South Pacific Convergence Zone(SPCZ)substantially influences the variabilities in the atmospheric circulation and Antarctic climate.In this study,it is revealed that the intensity of the SPCZ can change the characteristics of sea ice in the West Antarctica during austral autumn,which is significantly independent of the El Niño-Southern Oscillation(ENSO).Observational and numerical results suggest that a stronger-than-usual SPCZ can generate a poleward-propagating Rossby wave train along a great circular route and induce a weakening of the Amundsen Sea Low(ASL)near West Antarctica,which may somewhat offset the teleconnections exerted by ENSO.These changes in the strength and zonal extent of ASL is noticeable and robustly lead to a tripole response of sea-ice perturbations in the Ross,Amundsen,and Weddell Seas.We find that the wind-driven dynamical processes determine the local sea-ice changes,while the influence from thermodynamic processes is trivial.This research underscores the need to consider the SPCZ variability for a comprehensive understanding of sea-ice changes in West Antarctica on interannual timescales.展开更多
The winter temperature variability of the Antarctic Peninsula(AP)has been proven to be influenced by sea surface temperature(SST)anomalies over the Tasman Sea.Using outputs over an extended time period from historical...The winter temperature variability of the Antarctic Peninsula(AP)has been proven to be influenced by sea surface temperature(SST)anomalies over the Tasman Sea.Using outputs over an extended time period from historical experiments,the skills of CMIP6 models in simulating the atmospheric responses to Tasman Sea SST are evaluated in this study,with an emphasis on the relationships with AP temperatures.The spatial correlation coefficient and normalized standard deviation are used as the evaluation metrics.Corresponding results suggest that the majority of CMIP6 models can capture the basic spatial distributions of Tasman Sea-related teleconnections across the Southern Hemisphere extratropical region,featuring a Pacific–South America-like pattern.However,the overestimation of atmospheric interannual variability and the underestimation of oceanic interannual variability in CMIP6 models result in a considerable amplification of the atmospheric responses to SST anomalies.The model uncertainty in depicting the relationships between Tasman Sea SSTs and AP surface temperatures,as well as the associated teleconnections,can partially be attributed to variations in grid resolutions among models.Additionally,further analysis of the Antarctic sea ice shows that the Tasman Sea SST may contribute to the interannual variability of the Antarctic dipole in CMIP6.展开更多
Multi-angle statistical analysis of tropical cyclones(TCs)and their distant thermodynamic disturbances over Northwest Pacific from July to September during 2001-2020 was conducted.The results show that TCs could trigg...Multi-angle statistical analysis of tropical cyclones(TCs)and their distant thermodynamic disturbances over Northwest Pacific from July to September during 2001-2020 was conducted.The results show that TCs could trigger distant thermodynamic disturbances,which mainly caused an increase in air pressure and a rise in temperature in northern China.The distant thermodynamic disturbances triggered by TCs differed in spatial distribution and intensity in different months.In the same month,the spatial distribution of such disturbances triggered by high-intensity TCs was consistent with the overall pattern,and there was a significant increase in intensity and area.From the probability of TC activities and the significance test of variance of analysis under different levels of P-J index,it is found that TC activities could stimulate the increase of P-J teleconnection index.There was a significant positive correlation between them,which was accompanied by a step effect.展开更多
The connection between rainfall over topographic regions and their downstream areas represents a phenomenon of great concern in atmospheric research.Focusing on the rainfall events of the past two decades,we analyzed ...The connection between rainfall over topographic regions and their downstream areas represents a phenomenon of great concern in atmospheric research.Focusing on the rainfall events of the past two decades,we analyzed the impact of rainfall over the Northeastern Slope of the Tibetan Plateau(NSTP)on rainfall in downstream areas.We discovered that rainfall followed two propagation routes,guided by two modes related to the three-dimensional circulation structure.In the first mode,dominated by cold(warm)anomalies along the west(east)direction,rainfall over the NSTP was concentrated between an upstream cyclonic and a downstream anti-cyclonic anomalous circulation(an upstream trough and a downstream ridge).This pattern was accompanied by upper-level divergence,low-level convergence,a deep moist layer,and a vertical updraft.As a consequence of the eastward movement of the trough-ridge system associated with the coldwarm anomalies,the rainfall over the NSTP moved eastward along 37°-40°N,reaching North China after about 36 h.In the second mode,the circulation structure was also dominated by cold-warm anomalies but rotated clockwise,introducing cold anomalies to the northeast and warm anomalies to the east of the plateau.Following the southeastward movement of the circulation structure,rainfall concentrated upstream of the anti-cyclonic circulation around the warm center before moving southeastward to the Sichuan Basin along the eastern edge of the plateau after 30-36 h.The findings of this study could broaden the understanding of rainfall-related teleconnection between two distant regions and offer helpful guidance for identifying early signals of rainfall disasters over the Chinese mainland.展开更多
The North Atlantic Oscillation(NAO),a crucial low-frequency variability mode in the atmospheric circulation of the Northern Hemisphere at mid-to-high latitudes,exhibits an unclear mechanism of influence on the Western...The North Atlantic Oscillation(NAO),a crucial low-frequency variability mode in the atmospheric circulation of the Northern Hemisphere at mid-to-high latitudes,exhibits an unclear mechanism of influence on the Western Tibetan Vortex(WTV).Based on ERA5 reanalysis data,this study elucidates the different impacts of NAO on WTV in summer versus winter.The results demonstrate that:(1)The impacts of the NAO on WTV are the strongest in summer,and stronger NAO events exert a heavier influence on the WTV.(2)The NAO modulates the WTV mainly through influencing the zonal winds north and south of the western Tibetan Plateau(TP):the positive(negative)strong NAO causes the enhanced westerlies(easterlies)on the northern flank and easterlies(westerlies)along the southern flank of the western TP,resulting in an anticyclonic(cyclonic)WTV.(3)The differences in wave energy propagation between summer and winter can explain the seasonal dependence of the impacts of the NAO on the WTV.In summer,wave energy propagates eastward along the westerly jet from the North Atlantic,reaching the western TP,generating anticyclonic/cyclonic circulation anomalies and altering the zonal winds along the western TP's northern and southern flanks,thereby modifying the WTV's circulation structure and intensity.In winter,however,the wave propagation associated with the NAO is stronger between middle and high latitudes in the North Atlantic sector,with less eastward propagation to the TP,resulting in limited influence on the WTV.This study verifies that high-latitude systems influence low-latitude climates through upstreamdownstream effects,providing a foundation for extended-range forecasting of plateau weather systems and responses to climate change.展开更多
Understanding the relationship between fire activity and climate variability is a major concern for the scientific community and is essential for reducing economic losses and life-threatening fire hazards.However,the ...Understanding the relationship between fire activity and climate variability is a major concern for the scientific community and is essential for reducing economic losses and life-threatening fire hazards.However,the drivers of fire activity and the influence of climate variability remain uncertain.Here,we show that the Madden–Julian Oscillation(MJO)—a dominant tropical subseasonal variability—influences fire activity by modulating local fire-supporting weather through atmospheric teleconnections.Our results show that midlatitude fire emissions exhibit significant subseasonal variability,with MJO-related weather influencing the fire intensity and contributing to large fire events.MJO-related fire events account for about 10%–20%of total midlatitude fire events,suggesting that if MJO teleconnections strengthen in the future,fire emissions and associated economic losses could worsen.展开更多
This study identified the relationship between tropical cyclone(TC)activity and extreme Pacific–Japan(PJ)teleconnection patterns in August and September.In the East China Sea(ECS)and Mariana Islands(MI)regions,where ...This study identified the relationship between tropical cyclone(TC)activity and extreme Pacific–Japan(PJ)teleconnection patterns in August and September.In the East China Sea(ECS)and Mariana Islands(MI)regions,where the edge of the western North Pacific subtropical high(WNPSH)is located,approximately 60%–75%of TCs migrate to Far East Asian countries.A significant positive correlation existed between the frequency of northward migration of TCs and PJ patterns,since the TC frequency in the ECS and MI regions was significantly higher in the positive compared with the negative phase.In the positive phase,the main reason for the large number of TCs occurring was the monsoon trough’s location and strength.The strong and northeastward-shifted monsoon trough in the positive phase leads to more TCs in the ECS and MI regions.Other large-scale environments associated with TC formation also favored TC genesis around the ECS and MI regions.The higher PDI(power dissipation index)during the positive PJ phase can potentially lead to significant impacts in the Far East Asian countries.These characteristics were particularly more notable in August compared with September.展开更多
The Yangtze River Valley(YRV) of China experienced record-breaking heatwaves in July and August 2022. The characteristics, causes, and impacts of this extreme event have been widely explored, but its seasonal predicta...The Yangtze River Valley(YRV) of China experienced record-breaking heatwaves in July and August 2022. The characteristics, causes, and impacts of this extreme event have been widely explored, but its seasonal predictability remains elusive. This study assessed the real-time one-month-lead prediction skill of the summer 2022 YRV heatwaves using 12operational seasonal forecast systems. Results indicate that most individual forecast systems and their multi-model ensemble(MME) mean exhibited limited skill in predicting the 2022 YRV heatwaves. Notably, after the removal of the linear trend, the predicted 2-m air temperature anomalies were generally negative in the YRV, except for the Met Office Glo Sea6 system, which captured a moderate warm anomaly. While the models successfully simulated the influence of La Ni?a on the East Asian–western North Pacific atmospheric circulation and associated YRV temperature anomalies, only Glo Sea6 reasonably captured the observed relationship between the YRV heatwaves and an atmospheric teleconnection extending from the North Atlantic to the Eurasian mid-to-high latitudes. Such an atmospheric teleconnection plays a crucial role in intensifying the YRV heatwaves. In contrast, other seasonal forecast systems and the MME predicted a distinctly different atmospheric circulation pattern, particularly over the Eurasian mid-to-high latitudes, and failed to reproduce the observed relationship between the YRV heatwaves and Eurasian mid-to-high latitude atmospheric circulation anomalies.These findings underscore the importance of accurately representing the Eurasian mid-to-high latitude atmospheric teleconnection for successful YRV heatwave prediction.展开更多
Based on monthly mean sea level pressure and 500 hPa height data for a 20-year period simulated by IAP 2L AGCM, teleconnection patterns in the Northern Hemisphere appearing in the model are identified and compared wit...Based on monthly mean sea level pressure and 500 hPa height data for a 20-year period simulated by IAP 2L AGCM, teleconnection patterns in the Northern Hemisphere appearing in the model are identified and compared with observations. The results show that almost all of the observed teleconnection patterns in the Northern winter can be reproduced by the model, thus these patterns exist in the atmosphere without any external anomalies. On the other hand, the simulated teleconnection patterns are more dependent on each other than the observed, i.e., they are lack of spatial orthogonality among them, therefore, it is possible that more complex patterns will appear under the action of anomalous external factors. Besides, the simulated teleconnection patterns in summer are greatly different from those in winter, in particular, its scale in summer is much less than that in winter.展开更多
Recent advances in studies of the structural characteristics and temporal-spatial variations of the East Asian monsoon （EAM） system and the impact of this system on severe climate disasters in China are reviewed. Pr...Recent advances in studies of the structural characteristics and temporal-spatial variations of the East Asian monsoon （EAM） system and the impact of this system on severe climate disasters in China are reviewed. Previous studies have improved our understanding of the basic characteristics of horizontal and vertical structures and the annual cycle of the EAM system and the water vapor transports in the EAM region. Many studies have shown that the EAM system is a relatively independent subsystem of the Asian- Australian monsoon system, and that there exists an obvious quasi-biennial oscillation with a meridional tripole pattern distribution in the interannual variations of the EAM system. Further analyses of the basic physical processes, both internal and external, that influence the variability of the EAM system indicate that the EAM system may be viewed as an atmosphere-ocean-land coupled system, referred to the EAM climate system in this paper. Further, the paper discusses how the interaction and relationships among various components of this system can be described through the East Asia Pacific （EAP） teleconnection pattern and the teleconnection pattern of meridional upper-tropospheric wind anomalies along the westerly jet over East Asia. Such reasoning suggests that the occurrence of severe floods in the Yangtze and Hualhe River valleys and prolonged droughts in North China are linked, respectively~ to the background interannual and interdecadal variability of the EAM climate system. Besides, outstanding scientific issues related to the EAM system and its impact on climate disasters in China are also discussed.展开更多
Recent advances in the study of the characteristics, processes, and causes of spatio-temporal variabilities of the East Asian monsoon （EAM） system are reviewed in this paper. The understanding of the EAM system has ...Recent advances in the study of the characteristics, processes, and causes of spatio-temporal variabilities of the East Asian monsoon （EAM） system are reviewed in this paper. The understanding of the EAM system has improved in many aspects： the basic characteristics of horizontal and vertical structures, the annual cycle of the East Asian summer monsoon （EASM） system and the East Asian winter monsoon （EAWM） system, the characteristics of the spatio-temporal variabilities of the EASM system and the EAWM system, and especially the multiple modes of the EAM system and their spatio-temporal variabilities. Some new results have also been achieved in understanding the atmosphere-ocean interaction and atmosphere-land interaction processes that affect the variability of the EAM system. Based on recent studies, the EAM system can be seen as more than a circulation system, it can be viewed as an atmosphere-ocean-land coupled system, namely, the EAM climate system. In addition, further progress has been made in diagnosing the internal physical mechanisms of EAM climate system variability, especially regarding the characteristics and properties of the East Asia-Pacific （EAP） teleconnection over East Asia and the North Pacific, the ＂Silk Road＂ teleconnection along the westerly jet stream in the upper troposphere over the Asian continent, and the dynamical effects of quasi-stationary planetary wave activity on EAM system variability. At the end of the paper, some scientific problems regarding understanding the EAM system variability are proposed for further study.展开更多
In this study, the relationship between El Nifio-Southern Oscillation （ENSO） and winter rainfall over Southeast China （SC） is demonstrated based on instrumental and reanalysis data. The results show that ENSO and ...In this study, the relationship between El Nifio-Southern Oscillation （ENSO） and winter rainfall over Southeast China （SC） is demonstrated based on instrumental and reanalysis data. The results show that ENSO and SC winter rainfall （ENSO-SC rainfall） are highly correlated and intimately coupled through an anomalous high pressure over the northwestern Pacific. In mature phase, El Nifio （La Nina） events can cause more （less） rainfall over SC in winter. Due to the persistence and spring barrier of ENSO, SC winter rainfall has potential predictability of about half a year ahead with ENSO as a predictor.展开更多
Using the latest daily observational rainfall datasets for the period 1961–2008, the present study investigates the interannual variability of June–September （JJAS） mean rainfall in northern China. The regional ch...Using the latest daily observational rainfall datasets for the period 1961–2008, the present study investigates the interannual variability of June–September （JJAS） mean rainfall in northern China. The regional characteristics of JJAS mean rainfall are revealed by a rotated empirical orthogonal function （REOF） analysis. The analysis identifies three regions of large interannual variability of JJAS rainfall： North China （NC）, Northeast China （NEC）, and the Taklimakan Desert in Northwest China （TDNWC）. Summer rainfall over NC is shown to have displayed a remarkable dry period from the late 1990s; while over NEC, decadal-scale variation with a significant decreasing trend in the last two decades is found, and over TDNWC, evidence of large interannual variability is revealed. Results also show that the interannual variability of JJAS rainfall in northern China is closely associated with the Northern Hemisphere circumglobal teleconnection （CGT）. Correlation coefficients between the CGT index and regional-averaged JJAS mean rainfall over NC and NEC were calculated, revealing values of up to 0.50 and 0.53, respectively, both of which exceeded the 99% confidence level.展开更多
In this study, the teleconnection between Indian Ocean sea surface temperature anomalies （SSTAs） and the frequency of high temperature extremes （HTEs） across the southern Yangtze River valley （YRV） was investiga...In this study, the teleconnection between Indian Ocean sea surface temperature anomalies （SSTAs） and the frequency of high temperature extremes （HTEs） across the southern Yangtze River valley （YRV） was investigated. The results indicate that the frequency of HTEs across the southern YRV in August is remotely influenced by the Indian Ocean basin mode （IOBM） SSTAs. Corresponding to June-July-August （JJA） IOBM warming condition, the number of HTEs was above normal, and corresponding to IOBM cooling conditions, the number of HTEs was below normal across the southern YRV in August. The results of this study indicate that the tropical IOBM warming triggered low-level anomalous anticyclonic circulation in the subtropical northwestern Pacific Ocean and southern China by emanating a warm Kelvin wave in August. In the southern YRV, the reduced rainfall and downward vertical motion associated with the anomalous low-level anticyclonic circulation led to the increase of HTE frequency in August.展开更多
The interannual variations of summer surface air temperature over Northeast China （NEC） were investigated through a month-to-month analysis from May to August. The results suggested that the warmer temperature over ...The interannual variations of summer surface air temperature over Northeast China （NEC） were investigated through a month-to-month analysis from May to August. The results suggested that the warmer temperature over NEC is related to a local positive 500-hPa geopotential height anomaly for all four months. However, the teleconnection patterns of atmospheric circulation anomalies associated with the monthly surface air temperature over NEC behave as a distinguished subseasonal variation, although the local positive height anomaly is common from month to month. In May and June, the teleconnection pattern is characterized by a wave train in the upper and middle troposphere from the Indian Peninsula to NEC. This wave train is stronger in June than in May, possibly due to the positive feedback between the wave train and the South Asian rainfall anomaly in June, when the South Asian summer monsoon has been established. In July and August, however, the teleconnection pattern associated with the NEC temperature anomalies is characterized by an East Asia/Pacific （EAP） or Pacific/Japan （PJ） pattern, with the existence of precipitation anomalies over the Philippine Sea and the South China Sea. This pattern is much clearer in July corresponding to the stronger convection over the Philippine Sea compared to that in August.展开更多
In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key r...In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-ice variability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnection mechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strong near-surface thermal forcing, which further triggers a meridional overturning wave-like pattern extending to midlatitudes.Anomalous downward motion therefore forms over the Caspian Sea, which in turn induces zonally oriented overturning circulation along the subtropical jet stream, exhibiting the east–west Rossby wave train known as the Silk Road pattern. It is suggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due to the eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Bonin high anomaly ultimately triggers a meridional overturning, establishing the Pacific–Japan pattern. This in turn induces an anomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented over East Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experiments using version 5 of the Community Atmosphere Model support the interpretation of this chain of events.展开更多
The variation of the East Asian jet stream （EAJS） associated with the Eurasian （EU） teleconnection pattern is investigated using 60-yr NCEP-NCAR daily reanalysis data over the period 1951-2010.The EAJS consists of...The variation of the East Asian jet stream （EAJS） associated with the Eurasian （EU） teleconnection pattern is investigated using 60-yr NCEP-NCAR daily reanalysis data over the period 1951-2010.The EAJS consists of three components：the polar front jet （PFJ）; the plateau subtropical jet （PSJ）; and the ocean subtropical jet （OSJ）.Of these three jets over East Asia,the EU pattern exhibits a significant influence on the PFJ and OSJ.There is a simultaneous negative correlation between the EU pattern and the PFJ.A significant positive correlation is found between the EU pattern and the OSJ when the EU pattern leads the OSJ by about 5 days.There is no obvious correlation between the EU pattern and the PSJ.The positive EU phase is accompanied by a weakened and poleward-shifted PFJ,which coincides with an intensified OSJ.A possible mechanism for the variation of the EAJS during different EU phases is explored via analyzing the effects of 10-day high-and low-frequency eddy forcing.The zonal wind tendency due to high-frequency eddy forcing contributes to the simultaneous negative correlation between the EU pattern and the PFJ,as well as the northward/southward shift of the PFJ.High-and low-frequency eddy forcing are both responsible for the positive correlation between the EU pattern and the OSJ,but only high-frequency eddy forcing contributes to the lagged variation of the OSJ relative to the EU pattern.The negative correlation between the EU pattern and winter temperature and precipitation anomalies in China is maintained only when the PFJ and OSJ are out of phase with each other.Thus,the EAJS plays an important role in transmitting the EU signal to winter temperature and precipitation anomalies in China.展开更多
The aim of the paper is to analyze a possible teleconnection of Quasi-Biennial Oscillation （QBO）, Southern Oscillation （SO）, North Atlantic Oscillation （NAO）, and Arctic Oscillation （AO） phenomena with longter...The aim of the paper is to analyze a possible teleconnection of Quasi-Biennial Oscillation （QBO）, Southern Oscillation （SO）, North Atlantic Oscillation （NAO）, and Arctic Oscillation （AO） phenomena with longterm streamflow fluctuation of the Bela River （1895-2004） and Cierny Hron River （1931-2004） （central Slovakia）. Homogeneity, long-term trends, as well as inter-annual dry and wet cycles were analyzed for the entire 1895-2004 time series of the Bela River and for the 1931-2004 time series of the Cierny Hron River. Inter-annual fluctuation of the wet and dry periods was identified using spectral analysis. The most significant period is that of 3.6 years. Other significant periods are those of 2.35 years, 13.5 years, and 21 years. Since these periods were found in other rivers of the world, as well as in SO, NAO, and AO phenomena, they can be considered as relating to the general regularity of the Earth.展开更多
基金supported by the National Key R&D Program of China(Grant No.2023YFF0805100)。
文摘The predictability of a coupled system composed of a coupled reduced-order extratropical ocean-atmosphere model forced by a low-order three-variable tropical recharge-discharge model is explored with emphasis on its long-term forecasting capabilities.Highly idealized ensemble forecasts are produced taking into account the uncertainties in the initial states of the system,with specific attention to the structure of the initial errors in the tropical model.Three main types of experiments are explored:with random perturbations along the three Lyapunov vectors of the tropical model;along the two dominant Lyapunov vectors;and along the first Lyapunov vector only.When perturbations are introduced along all vectors,forecasting biases develop even if in a perfect model framework and with known initial uncertainty properties.Theses biases are considerably reduced only when the perturbations are introduced along the dominant Lyapunov vector.Furthermore,this perturbation strategy allows a reduced mean square error to be obtained at long lead times of a few years,as well as reliable ensemble forecasts across the whole time range.These very counterintuitive findings further underline the importance of appropriately controlling the initial error structure in the tropics through data assimilation.
基金jointly supported by the Second Tibetan Plateau Scientific Expedition and Research Program[grant number-ber 2019QZKK0103]the National Natural Science Foundation of China[grant number 42293294]the China Meteorological Admin-istration Climate Change Special Program[grant number QBZ202303]。
文摘Using multi-source reanalysis data,this study examines the relationship between the tropical Pacific-Atlantic SST Dipole Mode(TPA-DM)and summer precipitation in North China(NCSP)on the interannual timescale during the period of 1979-2022.The results show that the TPA-DM,the dominant pattern of interannual variability in the tropical Pacific and Atlantic regions,exhibits a significant negative correlation with NCSP.The positive phase of TPA-DM induces subsidence over the Maritime Continent through a zonal circulation pattern,which initiates a Pacific-Japan-like wave train along the East Asian coast.The circulation anomalies lead to moisture deficits and convergence subsidence over North China,leading to below-normal rainfall.Further analysis reveals that cooler SST in the Southern Tropical Atlantic facilitates the persistence of the TPA-DM by stimulating the anomalous Walker circulation associated with wind-evaporation-SST-convection feedback.
基金supported by the National Natural Science Foundation of China(Grant No.42375024).
文摘As one of the strongest convection bands in the Southern Hemisphere,the South Pacific Convergence Zone(SPCZ)substantially influences the variabilities in the atmospheric circulation and Antarctic climate.In this study,it is revealed that the intensity of the SPCZ can change the characteristics of sea ice in the West Antarctica during austral autumn,which is significantly independent of the El Niño-Southern Oscillation(ENSO).Observational and numerical results suggest that a stronger-than-usual SPCZ can generate a poleward-propagating Rossby wave train along a great circular route and induce a weakening of the Amundsen Sea Low(ASL)near West Antarctica,which may somewhat offset the teleconnections exerted by ENSO.These changes in the strength and zonal extent of ASL is noticeable and robustly lead to a tripole response of sea-ice perturbations in the Ross,Amundsen,and Weddell Seas.We find that the wind-driven dynamical processes determine the local sea-ice changes,while the influence from thermodynamic processes is trivial.This research underscores the need to consider the SPCZ variability for a comprehensive understanding of sea-ice changes in West Antarctica on interannual timescales.
基金jointly supported by the National Natural Science Foundation of China(Grant No.42375027)the Natural Science Foundation of Guangdong Province(Grant No.2023A1515010889)。
文摘The winter temperature variability of the Antarctic Peninsula(AP)has been proven to be influenced by sea surface temperature(SST)anomalies over the Tasman Sea.Using outputs over an extended time period from historical experiments,the skills of CMIP6 models in simulating the atmospheric responses to Tasman Sea SST are evaluated in this study,with an emphasis on the relationships with AP temperatures.The spatial correlation coefficient and normalized standard deviation are used as the evaluation metrics.Corresponding results suggest that the majority of CMIP6 models can capture the basic spatial distributions of Tasman Sea-related teleconnections across the Southern Hemisphere extratropical region,featuring a Pacific–South America-like pattern.However,the overestimation of atmospheric interannual variability and the underestimation of oceanic interannual variability in CMIP6 models result in a considerable amplification of the atmospheric responses to SST anomalies.The model uncertainty in depicting the relationships between Tasman Sea SSTs and AP surface temperatures,as well as the associated teleconnections,can partially be attributed to variations in grid resolutions among models.Additionally,further analysis of the Antarctic sea ice shows that the Tasman Sea SST may contribute to the interannual variability of the Antarctic dipole in CMIP6.
基金the National Natural Science Foundation of China(42305011).
文摘Multi-angle statistical analysis of tropical cyclones(TCs)and their distant thermodynamic disturbances over Northwest Pacific from July to September during 2001-2020 was conducted.The results show that TCs could trigger distant thermodynamic disturbances,which mainly caused an increase in air pressure and a rise in temperature in northern China.The distant thermodynamic disturbances triggered by TCs differed in spatial distribution and intensity in different months.In the same month,the spatial distribution of such disturbances triggered by high-intensity TCs was consistent with the overall pattern,and there was a significant increase in intensity and area.From the probability of TC activities and the significance test of variance of analysis under different levels of P-J index,it is found that TC activities could stimulate the increase of P-J teleconnection index.There was a significant positive correlation between them,which was accompanied by a step effect.
基金supported by the National Natural Science Foundation of China(Grant No.U2142204 and 42475013)the Beijing Nova Program(Z211100002121100)+1 种基金the National Key Research and Development Program of China(2023YFC3007504)the Science&Technology Development Fund of Chinese Academy of Meteorological Sciences(CAMS)(2022KJ007)。
文摘The connection between rainfall over topographic regions and their downstream areas represents a phenomenon of great concern in atmospheric research.Focusing on the rainfall events of the past two decades,we analyzed the impact of rainfall over the Northeastern Slope of the Tibetan Plateau(NSTP)on rainfall in downstream areas.We discovered that rainfall followed two propagation routes,guided by two modes related to the three-dimensional circulation structure.In the first mode,dominated by cold(warm)anomalies along the west(east)direction,rainfall over the NSTP was concentrated between an upstream cyclonic and a downstream anti-cyclonic anomalous circulation(an upstream trough and a downstream ridge).This pattern was accompanied by upper-level divergence,low-level convergence,a deep moist layer,and a vertical updraft.As a consequence of the eastward movement of the trough-ridge system associated with the coldwarm anomalies,the rainfall over the NSTP moved eastward along 37°-40°N,reaching North China after about 36 h.In the second mode,the circulation structure was also dominated by cold-warm anomalies but rotated clockwise,introducing cold anomalies to the northeast and warm anomalies to the east of the plateau.Following the southeastward movement of the circulation structure,rainfall concentrated upstream of the anti-cyclonic circulation around the warm center before moving southeastward to the Sichuan Basin along the eastern edge of the plateau after 30-36 h.The findings of this study could broaden the understanding of rainfall-related teleconnection between two distant regions and offer helpful guidance for identifying early signals of rainfall disasters over the Chinese mainland.
基金National Natural Science Foundation of China(42088101,42175026,42175080,42475036)the Innovation Group of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(SML2023SP209)Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies(2023B1212060019)。
文摘The North Atlantic Oscillation(NAO),a crucial low-frequency variability mode in the atmospheric circulation of the Northern Hemisphere at mid-to-high latitudes,exhibits an unclear mechanism of influence on the Western Tibetan Vortex(WTV).Based on ERA5 reanalysis data,this study elucidates the different impacts of NAO on WTV in summer versus winter.The results demonstrate that:(1)The impacts of the NAO on WTV are the strongest in summer,and stronger NAO events exert a heavier influence on the WTV.(2)The NAO modulates the WTV mainly through influencing the zonal winds north and south of the western Tibetan Plateau(TP):the positive(negative)strong NAO causes the enhanced westerlies(easterlies)on the northern flank and easterlies(westerlies)along the southern flank of the western TP,resulting in an anticyclonic(cyclonic)WTV.(3)The differences in wave energy propagation between summer and winter can explain the seasonal dependence of the impacts of the NAO on the WTV.In summer,wave energy propagates eastward along the westerly jet from the North Atlantic,reaching the western TP,generating anticyclonic/cyclonic circulation anomalies and altering the zonal winds along the western TP's northern and southern flanks,thereby modifying the WTV's circulation structure and intensity.In winter,however,the wave propagation associated with the NAO is stronger between middle and high latitudes in the North Atlantic sector,with less eastward propagation to the TP,resulting in limited influence on the WTV.This study verifies that high-latitude systems influence low-latitude climates through upstreamdownstream effects,providing a foundation for extended-range forecasting of plateau weather systems and responses to climate change.
基金supported by the National Science Foundation of China(Grant No.42088101)by a National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(Grant Nos.RS-2024-00416848 and NRF-2022R1A2C1013296)。
文摘Understanding the relationship between fire activity and climate variability is a major concern for the scientific community and is essential for reducing economic losses and life-threatening fire hazards.However,the drivers of fire activity and the influence of climate variability remain uncertain.Here,we show that the Madden–Julian Oscillation(MJO)—a dominant tropical subseasonal variability—influences fire activity by modulating local fire-supporting weather through atmospheric teleconnections.Our results show that midlatitude fire emissions exhibit significant subseasonal variability,with MJO-related weather influencing the fire intensity and contributing to large fire events.MJO-related fire events account for about 10%–20%of total midlatitude fire events,suggesting that if MJO teleconnections strengthen in the future,fire emissions and associated economic losses could worsen.
基金the Korea Meteorological Administration Research and Development Program under Grant KMI(Grant No.RS-2023-00241809)conducted under the framework of the research and development program of the Korea Institute of Energy Research(C5-2422).
文摘This study identified the relationship between tropical cyclone(TC)activity and extreme Pacific–Japan(PJ)teleconnection patterns in August and September.In the East China Sea(ECS)and Mariana Islands(MI)regions,where the edge of the western North Pacific subtropical high(WNPSH)is located,approximately 60%–75%of TCs migrate to Far East Asian countries.A significant positive correlation existed between the frequency of northward migration of TCs and PJ patterns,since the TC frequency in the ECS and MI regions was significantly higher in the positive compared with the negative phase.In the positive phase,the main reason for the large number of TCs occurring was the monsoon trough’s location and strength.The strong and northeastward-shifted monsoon trough in the positive phase leads to more TCs in the ECS and MI regions.Other large-scale environments associated with TC formation also favored TC genesis around the ECS and MI regions.The higher PDI(power dissipation index)during the positive PJ phase can potentially lead to significant impacts in the Far East Asian countries.These characteristics were particularly more notable in August compared with September.
基金jointly supported by the National Key Research and Development Program of China (2023YFC3007503)the Joint Research Project for Meteorological Capacity Improvement (22NLTSZ002)+4 种基金the National Natural Science Foundations of China (Grant Nos.42375064, 41975102, 41730964, 42175047)the China Meteorological Administration Key Innovation Team for Climate Prediction (CMA2023ZD03)the Met Office Climate Science for Service Partnership (CSSP) China project under the International Science Partnerships Fund (ISPF)the Special Project of Innovation and Development of China Meteorological Administration (CXFZ2024J004)the China Yangtze Power Co.,Ltd.Research Project (Grant No.2423020054)。
文摘The Yangtze River Valley(YRV) of China experienced record-breaking heatwaves in July and August 2022. The characteristics, causes, and impacts of this extreme event have been widely explored, but its seasonal predictability remains elusive. This study assessed the real-time one-month-lead prediction skill of the summer 2022 YRV heatwaves using 12operational seasonal forecast systems. Results indicate that most individual forecast systems and their multi-model ensemble(MME) mean exhibited limited skill in predicting the 2022 YRV heatwaves. Notably, after the removal of the linear trend, the predicted 2-m air temperature anomalies were generally negative in the YRV, except for the Met Office Glo Sea6 system, which captured a moderate warm anomaly. While the models successfully simulated the influence of La Ni?a on the East Asian–western North Pacific atmospheric circulation and associated YRV temperature anomalies, only Glo Sea6 reasonably captured the observed relationship between the YRV heatwaves and an atmospheric teleconnection extending from the North Atlantic to the Eurasian mid-to-high latitudes. Such an atmospheric teleconnection plays a crucial role in intensifying the YRV heatwaves. In contrast, other seasonal forecast systems and the MME predicted a distinctly different atmospheric circulation pattern, particularly over the Eurasian mid-to-high latitudes, and failed to reproduce the observed relationship between the YRV heatwaves and Eurasian mid-to-high latitude atmospheric circulation anomalies.These findings underscore the importance of accurately representing the Eurasian mid-to-high latitude atmospheric teleconnection for successful YRV heatwave prediction.
文摘Based on monthly mean sea level pressure and 500 hPa height data for a 20-year period simulated by IAP 2L AGCM, teleconnection patterns in the Northern Hemisphere appearing in the model are identified and compared with observations. The results show that almost all of the observed teleconnection patterns in the Northern winter can be reproduced by the model, thus these patterns exist in the atmosphere without any external anomalies. On the other hand, the simulated teleconnection patterns are more dependent on each other than the observed, i.e., they are lack of spatial orthogonality among them, therefore, it is possible that more complex patterns will appear under the action of anomalous external factors. Besides, the simulated teleconnection patterns in summer are greatly different from those in winter, in particular, its scale in summer is much less than that in winter.
基金This paper was supported by the ＂National Key Programme for Developing Basic Sciences＂ under Grant No. G2006CB403600Knowledge Innovation for the 3rd Period,Chinese Academy of Sciences under Grant No. KZCX2-YW-220the National Natural Science Foundation of China under Grant Nos. 40730952, 40575026, 40775051 respectively.
文摘Recent advances in studies of the structural characteristics and temporal-spatial variations of the East Asian monsoon （EAM） system and the impact of this system on severe climate disasters in China are reviewed. Previous studies have improved our understanding of the basic characteristics of horizontal and vertical structures and the annual cycle of the EAM system and the water vapor transports in the EAM region. Many studies have shown that the EAM system is a relatively independent subsystem of the Asian- Australian monsoon system, and that there exists an obvious quasi-biennial oscillation with a meridional tripole pattern distribution in the interannual variations of the EAM system. Further analyses of the basic physical processes, both internal and external, that influence the variability of the EAM system indicate that the EAM system may be viewed as an atmosphere-ocean-land coupled system, referred to the EAM climate system in this paper. Further, the paper discusses how the interaction and relationships among various components of this system can be described through the East Asia Pacific （EAP） teleconnection pattern and the teleconnection pattern of meridional upper-tropospheric wind anomalies along the westerly jet over East Asia. Such reasoning suggests that the occurrence of severe floods in the Yangtze and Hualhe River valleys and prolonged droughts in North China are linked, respectively~ to the background interannual and interdecadal variability of the EAM climate system. Besides, outstanding scientific issues related to the EAM system and its impact on climate disasters in China are also discussed.
基金supported jointly by the National Basic Research Program of China 973 Projects (Grant No. 2010CB950403)the National Special Scientific Research Project for Public Interest (Meteorology) (Grant No. GYHY201006021)+1 种基金the Chinese Academy of Sciences(Grant No. KZCX2-EW-QN204)the National Natural Science Foundation of China (Grant No. 40975046)
文摘Recent advances in the study of the characteristics, processes, and causes of spatio-temporal variabilities of the East Asian monsoon （EAM） system are reviewed in this paper. The understanding of the EAM system has improved in many aspects： the basic characteristics of horizontal and vertical structures, the annual cycle of the East Asian summer monsoon （EASM） system and the East Asian winter monsoon （EAWM） system, the characteristics of the spatio-temporal variabilities of the EASM system and the EAWM system, and especially the multiple modes of the EAM system and their spatio-temporal variabilities. Some new results have also been achieved in understanding the atmosphere-ocean interaction and atmosphere-land interaction processes that affect the variability of the EAM system. Based on recent studies, the EAM system can be seen as more than a circulation system, it can be viewed as an atmosphere-ocean-land coupled system, namely, the EAM climate system. In addition, further progress has been made in diagnosing the internal physical mechanisms of EAM climate system variability, especially regarding the characteristics and properties of the East Asia-Pacific （EAP） teleconnection over East Asia and the North Pacific, the ＂Silk Road＂ teleconnection along the westerly jet stream in the upper troposphere over the Asian continent, and the dynamical effects of quasi-stationary planetary wave activity on EAM system variability. At the end of the paper, some scientific problems regarding understanding the EAM system variability are proposed for further study.
基金supported by the National Natural Science Foundation of China(NSFC) (Grant Nos.40906003 and 40830106)the National Basic Research Program of China(Grant No.2012CB 955603)
文摘In this study, the relationship between El Nifio-Southern Oscillation （ENSO） and winter rainfall over Southeast China （SC） is demonstrated based on instrumental and reanalysis data. The results show that ENSO and SC winter rainfall （ENSO-SC rainfall） are highly correlated and intimately coupled through an anomalous high pressure over the northwestern Pacific. In mature phase, El Nifio （La Nina） events can cause more （less） rainfall over SC in winter. Due to the persistence and spring barrier of ENSO, SC winter rainfall has potential predictability of about half a year ahead with ENSO as a predictor.
基金supported by the CAS Innovation Key Program (Grant No. KZCX2-YW-BR-14)National Basic Research Program of China (2011CB309704)+1 种基金Special Scientific Research Project for Public Interest (GrantNo. GYHY201006021)the National Natural Science Foundation of China (Grant Nos. 40890155, 40775051,U0733002)
文摘Using the latest daily observational rainfall datasets for the period 1961–2008, the present study investigates the interannual variability of June–September （JJAS） mean rainfall in northern China. The regional characteristics of JJAS mean rainfall are revealed by a rotated empirical orthogonal function （REOF） analysis. The analysis identifies three regions of large interannual variability of JJAS rainfall： North China （NC）, Northeast China （NEC）, and the Taklimakan Desert in Northwest China （TDNWC）. Summer rainfall over NC is shown to have displayed a remarkable dry period from the late 1990s; while over NEC, decadal-scale variation with a significant decreasing trend in the last two decades is found, and over TDNWC, evidence of large interannual variability is revealed. Results also show that the interannual variability of JJAS rainfall in northern China is closely associated with the Northern Hemisphere circumglobal teleconnection （CGT）. Correlation coefficients between the CGT index and regional-averaged JJAS mean rainfall over NC and NEC were calculated, revealing values of up to 0.50 and 0.53, respectively, both of which exceeded the 99% confidence level.
基金supported by the National Basic Research Program of China 973 Projects(Grants Nos. 2012CB955604 and 2010CB950403)the Chinese Academy of Sciences (Grant No. XDA05090402)+1 种基金the National Special Scientific Research Project for Public Interest under Grant 20106021the National Natural Science Foundation of China (Grant Nos. 40890155,U0733002,40730952,and 40810059005)
文摘In this study, the teleconnection between Indian Ocean sea surface temperature anomalies （SSTAs） and the frequency of high temperature extremes （HTEs） across the southern Yangtze River valley （YRV） was investigated. The results indicate that the frequency of HTEs across the southern YRV in August is remotely influenced by the Indian Ocean basin mode （IOBM） SSTAs. Corresponding to June-July-August （JJA） IOBM warming condition, the number of HTEs was above normal, and corresponding to IOBM cooling conditions, the number of HTEs was below normal across the southern YRV in August. The results of this study indicate that the tropical IOBM warming triggered low-level anomalous anticyclonic circulation in the subtropical northwestern Pacific Ocean and southern China by emanating a warm Kelvin wave in August. In the southern YRV, the reduced rainfall and downward vertical motion associated with the anomalous low-level anticyclonic circulation led to the increase of HTE frequency in August.
基金supported by the National Natural Science Foundation of China (Grant No. 41105046)
文摘The interannual variations of summer surface air temperature over Northeast China （NEC） were investigated through a month-to-month analysis from May to August. The results suggested that the warmer temperature over NEC is related to a local positive 500-hPa geopotential height anomaly for all four months. However, the teleconnection patterns of atmospheric circulation anomalies associated with the monthly surface air temperature over NEC behave as a distinguished subseasonal variation, although the local positive height anomaly is common from month to month. In May and June, the teleconnection pattern is characterized by a wave train in the upper and middle troposphere from the Indian Peninsula to NEC. This wave train is stronger in June than in May, possibly due to the positive feedback between the wave train and the South Asian rainfall anomaly in June, when the South Asian summer monsoon has been established. In July and August, however, the teleconnection pattern associated with the NEC temperature anomalies is characterized by an East Asia/Pacific （EAP） or Pacific/Japan （PJ） pattern, with the existence of precipitation anomalies over the Philippine Sea and the South China Sea. This pattern is much clearer in July corresponding to the stronger convection over the Philippine Sea compared to that in August.
基金supported by the National Key R&D Program of China(Grant No.2016YFA0600703)the National Natural Science Foundation of China(Grant Nos.41605059,41505073 and 41375083)+1 种基金the Young Talent Support Program of the China Association for Science and Technology(Grant No.2016QNRC001)the Research Council of Norway SNOWGLACE(244166/E10)project
文摘In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-ice variability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnection mechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strong near-surface thermal forcing, which further triggers a meridional overturning wave-like pattern extending to midlatitudes.Anomalous downward motion therefore forms over the Caspian Sea, which in turn induces zonally oriented overturning circulation along the subtropical jet stream, exhibiting the east–west Rossby wave train known as the Silk Road pattern. It is suggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due to the eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Bonin high anomaly ultimately triggers a meridional overturning, establishing the Pacific–Japan pattern. This in turn induces an anomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented over East Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experiments using version 5 of the Community Atmosphere Model support the interpretation of this chain of events.
基金supported by the National Natural Science Foundation of China (Grant No. 41130963)the National Basic Research Program of China (973 Program) (Grant No. 2012CB955901)the Jiangsu Collaborative Innovation Center for Climate Change
文摘The variation of the East Asian jet stream （EAJS） associated with the Eurasian （EU） teleconnection pattern is investigated using 60-yr NCEP-NCAR daily reanalysis data over the period 1951-2010.The EAJS consists of three components：the polar front jet （PFJ）; the plateau subtropical jet （PSJ）; and the ocean subtropical jet （OSJ）.Of these three jets over East Asia,the EU pattern exhibits a significant influence on the PFJ and OSJ.There is a simultaneous negative correlation between the EU pattern and the PFJ.A significant positive correlation is found between the EU pattern and the OSJ when the EU pattern leads the OSJ by about 5 days.There is no obvious correlation between the EU pattern and the PSJ.The positive EU phase is accompanied by a weakened and poleward-shifted PFJ,which coincides with an intensified OSJ.A possible mechanism for the variation of the EAJS during different EU phases is explored via analyzing the effects of 10-day high-and low-frequency eddy forcing.The zonal wind tendency due to high-frequency eddy forcing contributes to the simultaneous negative correlation between the EU pattern and the PFJ,as well as the northward/southward shift of the PFJ.High-and low-frequency eddy forcing are both responsible for the positive correlation between the EU pattern and the OSJ,but only high-frequency eddy forcing contributes to the lagged variation of the OSJ relative to the EU pattern.The negative correlation between the EU pattern and winter temperature and precipitation anomalies in China is maintained only when the PFJ and OSJ are out of phase with each other.Thus,the EAJS plays an important role in transmitting the EU signal to winter temperature and precipitation anomalies in China.
文摘The aim of the paper is to analyze a possible teleconnection of Quasi-Biennial Oscillation （QBO）, Southern Oscillation （SO）, North Atlantic Oscillation （NAO）, and Arctic Oscillation （AO） phenomena with longterm streamflow fluctuation of the Bela River （1895-2004） and Cierny Hron River （1931-2004） （central Slovakia）. Homogeneity, long-term trends, as well as inter-annual dry and wet cycles were analyzed for the entire 1895-2004 time series of the Bela River and for the 1931-2004 time series of the Cierny Hron River. Inter-annual fluctuation of the wet and dry periods was identified using spectral analysis. The most significant period is that of 3.6 years. Other significant periods are those of 2.35 years, 13.5 years, and 21 years. Since these periods were found in other rivers of the world, as well as in SO, NAO, and AO phenomena, they can be considered as relating to the general regularity of the Earth.
