This research analyzes the variations of the South Asian Summer Monsoon Rainfall Anomaly(SASMRA)between the first development year(Y0)and the following year(Y1)of all multi-year La Ni?a events from 1958 to 2022.During...This research analyzes the variations of the South Asian Summer Monsoon Rainfall Anomaly(SASMRA)between the first development year(Y0)and the following year(Y1)of all multi-year La Ni?a events from 1958 to 2022.During Y0,monsoon precipitation surpasses climatological values,presenting a tripole spatial pattern,whereas Y1 is characterized by below-normal precipitation with a dipole pattern.In certain regions,the difference in precipitation between Y0 and Y1 reaches up to 3 mm day–1.This work provides further insight into the key tropical ocean regions driving the precipitation distinction,and elucidates their coupling mechanisms with large-scale atmospheric circulation anomalies.Influenced by the development of earlier ocean-atmosphere anomaly patterns,the Tropical Indian Ocean and Western Pacific(TIO-WP)warming(cooling)is significant during the summer of Y0(Y1).The elevated sea surface temperature(SST)in Y0 supports an anomalous Western North Pacific(WNP)anticyclone via a Kelvin-wave-induced Ekman divergence mechanism.This anomalous anticyclone intensifies the suppressed convection over the WNP,which results in increased divergence in the upper-level troposphere over the Indian Ocean and South Asian regions,thereby boosting convection.Simultaneously,the easterly winds associated with the strengthened equatorial latitude SST anomaly(SSTA)gradient and the anomalous anticyclone intensified,transporting a large amount of water vapor to the west.The combined moisture and dynamic conditions support the enhanced precipitation in the South Asian region.展开更多
We evaluate the performance of GAMILI.1.1 in a 27-year forced simulation of the summer intraseasonal oscillation （ISO） over East Asia （EA）-western North Pacific （WNP）. The assessment is based on two mea- sures：...We evaluate the performance of GAMILI.1.1 in a 27-year forced simulation of the summer intraseasonal oscillation （ISO） over East Asia （EA）-western North Pacific （WNP）. The assessment is based on two mea- sures： climatological ISO （CISO） and transient ISO （TISO）. CISO is the ISO component that is phase-locked to the annual cycle and describes seasonal march. TISO is the ISO component that varies year by year. The model reasonably captures many observed features of the ISO, including the stepwise northward advance of the rain belt of CISO, the dominant periodicities of TISO in both the South China Sea-Philippine Sea （SCS-PS） and the Yangtze River Basin （YRB）, the northward propagation of 30-50-day TISO and the westward propagation of the 12-25-day TISO mode over the SCS-PS, and the zonal propagating features of three major TISO modes over the YRB. However, the model has notable deficiencies. These include the early onset of the South China Sea monsoon associated with CISO, too fast northward propagation of CISO from 20°N to 40°N and the absence of the CISO signal south of 10°N, the deficient eastward propagation of the 30-50-day TISO mode and the absence of a southward propagation in the YRB TISO modes. The authors found that the deficiencies in the ISO simulation are closely related to the model＇s biases in the mean states, suggesting that the improvement of the model mean state is crucial for realistic simulation of the intraseasonal variation.展开更多
Storm surges in the Western North Pacific cause significant economic damage and loss of life,highlighting the need for accurate storm surge predictions.This study evaluated four storm surge models:the Global Tide and ...Storm surges in the Western North Pacific cause significant economic damage and loss of life,highlighting the need for accurate storm surge predictions.This study evaluated four storm surge models:the Global Tide and Surge Model(GTSMv3.0),ERA20C neural network(ERA20C_nn),ERA20C multiple linear regression(ERA20C_ml),and 20th Century Reanalysis multiple linear regression(20CR_ml),using data from 160 tidal stations.The results show that the ERA20C_nn model outperformed others,with the highest correlation to tide-gauge observations.The GTSMv3.0 model follows closely,although slightly less accurate.The ERA20C_ml and 20CR_ml models were less effective,especially in predicting extreme surges.The ERA20C_nn model also provided more reliable estimates for 100-year return surge levels,outperforming other models.These findings suggest that neural network-based models,particularly ERA20C_nn,are better suited for assessing coastal flood risks in the region.展开更多
Based on 10 years precipitation data from Tropical Rainfall Measurement Mission （TRMM） Multi-satellite Precipitation Analysis （TMPA） 3B42 and the best track data from China Meteorological Administration （CMA）, t...Based on 10 years precipitation data from Tropical Rainfall Measurement Mission （TRMM） Multi-satellite Precipitation Analysis （TMPA） 3B42 and the best track data from China Meteorological Administration （CMA）, the seasonal, monthly and annual contribution of tropical cyclone （TC） precipitation to the total rainfall are analyzed over the Western North Pacific （WNP） during 1998 to 2007 from May to December. The results show that： （1） TC seasonal rainfall contribution ranges from 4% in inland regions to above 40% in ocean-regions of 15°N-25°N. TCs at higher categories contribute much more to the total precipitation. （2） On monthly scale, TCs contribute 60% to the total rainfall regionally during whole TC season, which is the maximum contribution. The peak contribution of TC rainfall averaged in multi-months of the ten years occurs in August （28%） over the whole ocean impacted by TC and in December （23%） over the whole land impacted by TC, respectively. （3） On annual scale, the maximum contribution of TC precipitation to the total rainfall are in 2004 （-30%） over ocean and in 1998 （-20%） over land, respectively. （4） The contribution of TC precipitation to the total rainfall increases 6% （decreases 6%） in El Nino （La Nifia） years compared with neutral years.展开更多
In summer 2018,a total of 18 tropical cyclones(TCs)formed in the western North Pacific(WNP)and South China Sea(SCS),among which 8 TCs landed in China,ranking respectively the second and the first highest since 1951.Mo...In summer 2018,a total of 18 tropical cyclones(TCs)formed in the western North Pacific(WNP)and South China Sea(SCS),among which 8 TCs landed in China,ranking respectively the second and the first highest since 1951.Most of these TCs travelled northwest to northward,bringing in heavy rainfall and strong winds in eastern China and Japan.The present study investigates the impacts of decaying La Nina and intraseasonal oscillation(ISO)on the extremely active TCs over the WNP and SCS in summer 2018 by use of correlation and composite analyses.It is found that the La Nina episode from October 2017 to March 2018 led to above-normal sea surface temperature(SST)over central–western Pacific,lower sea level pressure and 500-hPa geopotential height over WNP,and abnormally strong convective activities over the western Pacific in summer 2018.These preceding oceanic thermal conditions and their effects on circulation anomalies are favorable to TC genesis in summer.Detailed examination reveals that the monsoon trough was located further north and east,inducing more TCs in northern and eastern WNP;and the more eastward WNP subtropical high as well as the significant wave train with a"-+-+"height anomaly pattern over the midlatitude Eurasia–North Pacific region facilitated the northwest to northward TC tracks.Further analyses reveal that two successively active periods of Madden–Julian Oscillation(MJO)occurred in summer 2018 and the boreal summer intraseasonal oscillation(BSISO)was also active over WNP,propagating northward significantly,corresponding to the more northward TC tracks.The MJO was stagnant over the Maritime Continent to western Pacific,leading to notably enhanced convection in the lower troposphere and divergence in the upper troposphere,conducive to TC occurrences.In a word,the extremely active TC activities over the WNP and SCS in summer 2018 are closely linked with the decaying La Nina,and the MJO and BSISO;their joint effects result in increased TC occurrences and the TC tracks being shifted more northwest to northward than normal.展开更多
This study demonstrates the main physical mechanism for the maintenance of the western North Pacific(WNP)anomalous anticyclone(WNPAC)during the El Niño decaying summer by analyzing the respective effects of the c...This study demonstrates the main physical mechanism for the maintenance of the western North Pacific(WNP)anomalous anticyclone(WNPAC)during the El Niño decaying summer by analyzing the respective effects of the cold sea surface temperature(SST)anomalies in the WNP,the warm SST anomalies in the Indian Ocean(IO),and the El Niño and Southern Oscillation(ENSO)combination mode.We find that the WNPAC is usually accompanied by significant cold WNP SST anomalies in the El Niño mature winter and following spring,which almost disappear in the decaying summer and cannot explain the maintenance of the WNPAC in summer.The influence of the IO warm SST anomalies on the WNPAC exhibits conspicuous decadal differences.Before the 2000 s,the IO warm SST anomalies played a role in the WNPAC maintenance through the response of the baroclinic atmospheric Kelvin wave;however,this effect cannot be evidently detected after the 2000 s.This decadal difference may be related to changes in the decaying speed of ENSO events.In contrast to El Niño events before the 2000 s,El Niño events after the 2000 s decay more rapidly,and the associated tropical central-eastern Pacific SST features a La Ni?a-like condition in the El Niño decaying summer.Concomitantly,no significant warm SST anomalies appear over the tropical Indian Ocean,exerting a weak influence on the WNPAC.Relative to the cold WNP SSTanomalies and warm IO SST anomalies,the ENSO combination mode,originating from the nonlinear interaction between ENSO and the annual cycle,has a relatively stable relationship with the WNPAC during the El Niño decaying summer,which exhibits a crucial role in the maintenance of the WNPAC.Considering the persistence of the ENSO combination mode,the WNPAC and associated climate variability during the El Niño decaying summer can be skillfully predicted at least one season in advance based on the ENSO combination mode.展开更多
基金Guangdong Major Project of Basic and Applied Basic Research(2020B0301030004)National Key Research and Development Program of China(2023YFF0805300)Civilian Space Programme of China(D040305)。
文摘This research analyzes the variations of the South Asian Summer Monsoon Rainfall Anomaly(SASMRA)between the first development year(Y0)and the following year(Y1)of all multi-year La Ni?a events from 1958 to 2022.During Y0,monsoon precipitation surpasses climatological values,presenting a tripole spatial pattern,whereas Y1 is characterized by below-normal precipitation with a dipole pattern.In certain regions,the difference in precipitation between Y0 and Y1 reaches up to 3 mm day–1.This work provides further insight into the key tropical ocean regions driving the precipitation distinction,and elucidates their coupling mechanisms with large-scale atmospheric circulation anomalies.Influenced by the development of earlier ocean-atmosphere anomaly patterns,the Tropical Indian Ocean and Western Pacific(TIO-WP)warming(cooling)is significant during the summer of Y0(Y1).The elevated sea surface temperature(SST)in Y0 supports an anomalous Western North Pacific(WNP)anticyclone via a Kelvin-wave-induced Ekman divergence mechanism.This anomalous anticyclone intensifies the suppressed convection over the WNP,which results in increased divergence in the upper-level troposphere over the Indian Ocean and South Asian regions,thereby boosting convection.Simultaneously,the easterly winds associated with the strengthened equatorial latitude SST anomaly(SSTA)gradient and the anomalous anticyclone intensified,transporting a large amount of water vapor to the west.The combined moisture and dynamic conditions support the enhanced precipitation in the South Asian region.
基金supported by the Innovative Research Group Funds (Grant No. 408210921)the CAS International Partnership Project+1 种基金the 973 Project(Grant Nos. 2005CB321703 and 2006CB403602)fund from State Key Laboratory of Earth Surface Processes and Resource Ecology (No. 070205) in Beijing Normal University
文摘We evaluate the performance of GAMILI.1.1 in a 27-year forced simulation of the summer intraseasonal oscillation （ISO） over East Asia （EA）-western North Pacific （WNP）. The assessment is based on two mea- sures： climatological ISO （CISO） and transient ISO （TISO）. CISO is the ISO component that is phase-locked to the annual cycle and describes seasonal march. TISO is the ISO component that varies year by year. The model reasonably captures many observed features of the ISO, including the stepwise northward advance of the rain belt of CISO, the dominant periodicities of TISO in both the South China Sea-Philippine Sea （SCS-PS） and the Yangtze River Basin （YRB）, the northward propagation of 30-50-day TISO and the westward propagation of the 12-25-day TISO mode over the SCS-PS, and the zonal propagating features of three major TISO modes over the YRB. However, the model has notable deficiencies. These include the early onset of the South China Sea monsoon associated with CISO, too fast northward propagation of CISO from 20°N to 40°N and the absence of the CISO signal south of 10°N, the deficient eastward propagation of the 30-50-day TISO mode and the absence of a southward propagation in the YRB TISO modes. The authors found that the deficiencies in the ISO simulation are closely related to the model＇s biases in the mean states, suggesting that the improvement of the model mean state is crucial for realistic simulation of the intraseasonal variation.
基金supported by the National Natural Science Foundation of China(Grant Nos.42176198,42176203)the National Key Research and Development Program of China(Grant No.2023YFC3008200)funding from the Taishan Scholars Program(tsqn202211252)。
文摘Storm surges in the Western North Pacific cause significant economic damage and loss of life,highlighting the need for accurate storm surge predictions.This study evaluated four storm surge models:the Global Tide and Surge Model(GTSMv3.0),ERA20C neural network(ERA20C_nn),ERA20C multiple linear regression(ERA20C_ml),and 20th Century Reanalysis multiple linear regression(20CR_ml),using data from 160 tidal stations.The results show that the ERA20C_nn model outperformed others,with the highest correlation to tide-gauge observations.The GTSMv3.0 model follows closely,although slightly less accurate.The ERA20C_ml and 20CR_ml models were less effective,especially in predicting extreme surges.The ERA20C_nn model also provided more reliable estimates for 100-year return surge levels,outperforming other models.These findings suggest that neural network-based models,particularly ERA20C_nn,are better suited for assessing coastal flood risks in the region.
基金supported by the Special Funds for Public Welfare of China(Grant No.GYHY201306077)CAS Strategic Priority Research Program(Grant No.XDA05100303)+1 种基金the National Natural Science Foundation of China(Grant Nos.41230419,91337213)the Jiangsu Provincial 2011 Program(Collaborative Innovation Center of Climate Change)
文摘Based on 10 years precipitation data from Tropical Rainfall Measurement Mission （TRMM） Multi-satellite Precipitation Analysis （TMPA） 3B42 and the best track data from China Meteorological Administration （CMA）, the seasonal, monthly and annual contribution of tropical cyclone （TC） precipitation to the total rainfall are analyzed over the Western North Pacific （WNP） during 1998 to 2007 from May to December. The results show that： （1） TC seasonal rainfall contribution ranges from 4% in inland regions to above 40% in ocean-regions of 15°N-25°N. TCs at higher categories contribute much more to the total precipitation. （2） On monthly scale, TCs contribute 60% to the total rainfall regionally during whole TC season, which is the maximum contribution. The peak contribution of TC rainfall averaged in multi-months of the ten years occurs in August （28%） over the whole ocean impacted by TC and in December （23%） over the whole land impacted by TC, respectively. （3） On annual scale, the maximum contribution of TC precipitation to the total rainfall are in 2004 （-30%） over ocean and in 1998 （-20%） over land, respectively. （4） The contribution of TC precipitation to the total rainfall increases 6% （decreases 6%） in El Nino （La Nifia） years compared with neutral years.
基金the National Key Research and Development Program of China(2018YFC1506001)National Basic Research(973)Program of China(2015CB453203)National Natural Science Foundation of China(41275073 and 41805067)
文摘In summer 2018,a total of 18 tropical cyclones(TCs)formed in the western North Pacific(WNP)and South China Sea(SCS),among which 8 TCs landed in China,ranking respectively the second and the first highest since 1951.Most of these TCs travelled northwest to northward,bringing in heavy rainfall and strong winds in eastern China and Japan.The present study investigates the impacts of decaying La Nina and intraseasonal oscillation(ISO)on the extremely active TCs over the WNP and SCS in summer 2018 by use of correlation and composite analyses.It is found that the La Nina episode from October 2017 to March 2018 led to above-normal sea surface temperature(SST)over central–western Pacific,lower sea level pressure and 500-hPa geopotential height over WNP,and abnormally strong convective activities over the western Pacific in summer 2018.These preceding oceanic thermal conditions and their effects on circulation anomalies are favorable to TC genesis in summer.Detailed examination reveals that the monsoon trough was located further north and east,inducing more TCs in northern and eastern WNP;and the more eastward WNP subtropical high as well as the significant wave train with a"-+-+"height anomaly pattern over the midlatitude Eurasia–North Pacific region facilitated the northwest to northward TC tracks.Further analyses reveal that two successively active periods of Madden–Julian Oscillation(MJO)occurred in summer 2018 and the boreal summer intraseasonal oscillation(BSISO)was also active over WNP,propagating northward significantly,corresponding to the more northward TC tracks.The MJO was stagnant over the Maritime Continent to western Pacific,leading to notably enhanced convection in the lower troposphere and divergence in the upper troposphere,conducive to TC occurrences.In a word,the extremely active TC activities over the WNP and SCS in summer 2018 are closely linked with the decaying La Nina,and the MJO and BSISO;their joint effects result in increased TC occurrences and the TC tracks being shifted more northwest to northward than normal.
基金supported by the National Natural Science Foundation of China(Grant Nos.42125501&42088101)。
文摘This study demonstrates the main physical mechanism for the maintenance of the western North Pacific(WNP)anomalous anticyclone(WNPAC)during the El Niño decaying summer by analyzing the respective effects of the cold sea surface temperature(SST)anomalies in the WNP,the warm SST anomalies in the Indian Ocean(IO),and the El Niño and Southern Oscillation(ENSO)combination mode.We find that the WNPAC is usually accompanied by significant cold WNP SST anomalies in the El Niño mature winter and following spring,which almost disappear in the decaying summer and cannot explain the maintenance of the WNPAC in summer.The influence of the IO warm SST anomalies on the WNPAC exhibits conspicuous decadal differences.Before the 2000 s,the IO warm SST anomalies played a role in the WNPAC maintenance through the response of the baroclinic atmospheric Kelvin wave;however,this effect cannot be evidently detected after the 2000 s.This decadal difference may be related to changes in the decaying speed of ENSO events.In contrast to El Niño events before the 2000 s,El Niño events after the 2000 s decay more rapidly,and the associated tropical central-eastern Pacific SST features a La Ni?a-like condition in the El Niño decaying summer.Concomitantly,no significant warm SST anomalies appear over the tropical Indian Ocean,exerting a weak influence on the WNPAC.Relative to the cold WNP SSTanomalies and warm IO SST anomalies,the ENSO combination mode,originating from the nonlinear interaction between ENSO and the annual cycle,has a relatively stable relationship with the WNPAC during the El Niño decaying summer,which exhibits a crucial role in the maintenance of the WNPAC.Considering the persistence of the ENSO combination mode,the WNPAC and associated climate variability during the El Niño decaying summer can be skillfully predicted at least one season in advance based on the ENSO combination mode.
