This study explores the linkage between summertime temperature fluctuations over midlatitude Eurasia and the preceding Arctic sea ice concentration (SIC) by utilizing the squared norm of the temperature anomaly, the e...This study explores the linkage between summertime temperature fluctuations over midlatitude Eurasia and the preceding Arctic sea ice concentration (SIC) by utilizing the squared norm of the temperature anomaly, the essential part of local eddy available potential energy, as a metric to quantify the temperature fluctuations with weather patterns on various timescales. By comparing groups of singular value decomposition (SVD) analysis, we suggest a significant linkage between strong (weak) August 10-to-30-day temperature fluctuations over mid-west Asia and enhanced (decreased) Barents-Kara Sea ice in the previous February. We find that when the February SIC increases in the Barents-Kara Sea, a zonal dipolar pattern of SST anomalies appears in the Atlantic subpolar region and lasts from February into the summer months. Evidence suggests that in such a background state, the atmospheric circulation changes evidently from July to August, so that the August is characterized by an amplified meridional circulation over Eurasia, weakened westerlies, and high- pressure anomalies along the Arctic coast. Moreover, the 10-to-30-day wave becomes more active in the North Atlantic-Barents-Kara Sea-Central Asia regions and manifests a more evident southward propagation from the Barents- Kara Sea into the Ural region, which is responsible for the enhanced 10-to-30-day wave activity and temperature fluctuations in the region.展开更多
The summertime anticyclonic circulation mode(SACM)is related to recent substantial loss of sea ice in the Arctic.This review outlines the potential causes of the SACM and considers its influence on sea ice depletion.L...The summertime anticyclonic circulation mode(SACM)is related to recent substantial loss of sea ice in the Arctic.This review outlines the potential causes of the SACM and considers its influence on sea ice depletion.Local triggers(i.e.,sea ice loss and sea surface temperature(SST)variation)and spatiotemporal teleconnections(i.e.,extratropical cyclone intrusion,tropical and mid-latitude SST anomalies,and winter atmospheric circulation preconditions)are discussed.The influence of the SACM on the dramatic loss of sea ice is emphasized through inspection of relevant dynamic(i.e.,Ekman drift and export)and thermodynamic(i.e.,moisture content,cloudiness,and associated changes in radiation)mechanisms.Moreover,the motivation for investigation of the underlying physical mechanisms of the SACM in response to the recent substantial sea ice depletionis also clarified through an attempt to better understand the shifting ice-atmosphere interaction in the Arctic during summer.Therecord low extent of sea ice in September 2012 could be reset in the near future if the SACM-like scenario continues to exist during summer in the Arctic troposphere.展开更多
An intercomparison of summertime （JJA）subtropical geopotential heights from the ERA-40 and NCEP/NCAR reanalysis is specifically conducted over East Eurasia and the western North Pacific. The NCEP/NCAR is obviously l...An intercomparison of summertime （JJA）subtropical geopotential heights from the ERA-40 and NCEP/NCAR reanalysis is specifically conducted over East Eurasia and the western North Pacific. The NCEP/NCAR is obviously lower than the ERA-40 in the mid-to-lower troposphere in most regions of East Eurasia before the mid-1970s, but becomes higher than the ERA-40 after the mid-1970s and thus demonstrates stronger increased trends during the period of 1958-2001. Both reanalyses are lower than the observations in most regions of China. The NCEP/NCAR especially shows tremendously systematic lower values before the mid-1960s and displays abrupt changes before the 1970s. Several indices of the western North Pacific subtropical high （WNPSH）, calculated from both reanalyzed summer geopotential heights, also reveal that the variation trend of the NCEP/NCAR is stronger than that of the ERA-40 in the mid-to-lower troposphere from 1958 to 2001. Through singular value decomposition （SVD） analysis, the summer geopotential heights at 500 hPa from the ERA-40 are better than the NCEP/NCAR counterparts at interacting with the precipitation over the East Asian monsoon region. The results indicate that the NCEP/NCAR in the mid-and-lower troposphere may overestimate interdecadal changes and should be used cautiously to study the relationship between the WNPSH and precipitation ove ther East Asia Monsoon region before the mid-1970s.展开更多
Using the daily data of temperature from China Meteorological Administration and the NCEP/NCAR reanalysis from 1960 to 2005, we have analyzed the relationships between the summertime high/low temperature events in the...Using the daily data of temperature from China Meteorological Administration and the NCEP/NCAR reanalysis from 1960 to 2005, we have analyzed the relationships between the summertime high/low temperature events in the middle and lower reaches of the Yangtze River （MLRYR） and the related circulation anomalies in the Eastern Hemisphere. Our results have demonstrated that a significantly increasing trend is observed in daily minimum temperature in the past 50 years. And in some regions in the Northern Hemisphere, the opposite scenarios are observed in circulation anomalies in lower and upper parts of the troposphere in the years when the temperatures are higher than normal, as compared to those in the years when the temperatures are lower than normal in the middle and lower reaches of the Yangtze River （MLRYR）. Additionally, the anomalous circulation structure in vertical direction in both the high and lower temperature years are barotropic. It is found that the emergence and maintenance of the aforementioned anomalous circulations are related to three kinds of wave train teleconnection patterns. Further more, influences of the long wave surface radiation on the air temperature are stronger in the nighttime than that in the daytime. While both the maximum and minimum temperatures have negative relationships with the sensible heat flux but positive relationships with the latent heat flux. To some extent, the anomalous dynamic heating （cooling） caused by the vertical thermal advection as well as the diabatic heating （cooling） caused by diabatic processes can explain the formation of the high （low） temperature events in the middle and lower reaches of the Yangtze River （MLRYR） in boreal summer.展开更多
On Page 119 of the printed edition （Issue 1, Vol. 26）, the paper title should be ＂Intercomparison of the Summertime Subtropical High from the ERA-40 and NCEP/NCAR Reanalysis over East Eurasia and the Western North ...On Page 119 of the printed edition （Issue 1, Vol. 26）, the paper title should be ＂Intercomparison of the Summertime Subtropical High from the ERA-40 and NCEP/NCAR Reanalysis over East Eurasia and the Western North Pacific＂. The editorial office and the authors are sincerely sorry for any inconvenience this may have caused.展开更多
Synthesis analysis and singular value decomposition (SVD) methods were used to study the impact of surface air temperature (SAT) over Asian-Pacific region on the summertime northeastern Asian blocking high (NABH) with...Synthesis analysis and singular value decomposition (SVD) methods were used to study the impact of surface air temperature (SAT) over Asian-Pacific region on the summertime northeastern Asian blocking high (NABH) with NCEP/NCAR Reanalysis Data.The results showed that 500 hPa geopotential height and SAT fields over Asian-Pacific region shared the similar pattern of East Asian Pacific (EAP) wave train;there was steady remote response relationship between the EAP wave train in summer and the '+-+' pattern of tropical SAT in zonal direction from former winter to summer;there were two relative negative(positive) Walker circulations over the tropical Indian Ocean and Pacific when being more(less) summertime NABH. The influence of sea surface temperature anomaly (SSTA) on the summertime NABH was possibly as follows.The special distribution of SSTA in tropical zonal direction continuously forced the tropical convection and zonal circulation from former winter to summer,and led them to act anomaly.Finally the abnormal conditions were transported to middle-high latitudes through EAP wave train and yielded the advantageous or disadvantageous atmospheric circulation background for the summertime NABH.展开更多
The Sichuan-Tibet Railway,mainly located in the southeastern Qinghai-Tibet Plateau,is affected by summertime extreme precipitation(SEP).Using daily rain-gauge observations and ERA5 reanalysis data for the summers of 1...The Sichuan-Tibet Railway,mainly located in the southeastern Qinghai-Tibet Plateau,is affected by summertime extreme precipitation(SEP).Using daily rain-gauge observations and ERA5 reanalysis data for the summers of 1979-2020,the spatiotemporal distribution characteristics of SEP in the key region of the Sichuan-Tibet Railway(28°-33°N,90°-105°E,hereafter KR)are revealed,and the mechanism for SEP amount(SEPA)variation in the KR is investigated.The results show that SEPA in the KR contributes nearly 30%to the total summer precipitation.Regional differences are evident in SEP,justifying thresholds higher in the plateau-dominated central-western KR(CWKR)and lower in the basindominated eastern KR(EKR).In addition,SEP in the CWKR is less intense but more frequent than SEP in the EKR.During 1979-2020,the SEPA in the KR increased slightly while the SEPA in the CWKR increased significantly and peaked in the last decade.When anticyclonic circulation(AC)anomalies dominate the 500 hPa pattern over the Bay of Bengal and Mongolia,the southerly flow and cyclonic shear over the southeastern plateau will be strengthened,favoring more SEPA in the CWKR.When an AC anomaly dominates the 500 hPa pattern over the Bohai Sea,the low-level easterly wind over the basin will be strengthened,favoring more SEPA in the EKR.The strengthening of the ascent,water vapor convergence,and convective instability is conducive to more SEPA in the KR.Our results deepen the understanding of the characteristics and the physical mechanisms responsible for extreme precipitation in the KR.展开更多
M 2 tide and density residual currents in the Bohai Sea were examined using the Blumberg and Mellor 3D nonlinear numerical coastal circulation model incorporating Mellor and Yamada level 2.5 turbulent closure model. T...M 2 tide and density residual currents in the Bohai Sea were examined using the Blumberg and Mellor 3D nonlinear numerical coastal circulation model incorporating Mellor and Yamada level 2.5 turbulent closure model. The tidal results showed good agreement with previous work. The model results indicated that the density residual currents are robust in summer; and that at the transition zone between well-mixed and stratified water, the horizontal velocity is high and the vertical velocity is positive.展开更多
The origin of the Tsushima Warm Current Water(TWCW) in summer is studied mainly on the basis of the CTD data and the observations of satellite-traced surface drifters of Coastal Ocean Process Experiment of the East Ch...The origin of the Tsushima Warm Current Water(TWCW) in summer is studied mainly on the basis of the CTD data and the observations of satellite-traced surface drifters of Coastal Ocean Process Experiment of the East China Sea(COPEX-ECS) conducted by Korea Ocean Research and Development Institute. The main results are as follows: (1) The structures of the TWCW show obvious regional varitaions. The TWCW can be divided into three layers in the northern Okinawa Trough west of Kyushu and into two layers on the continental shelf and in the Tsushima/Korea Strait. (2) The surface TWCW, charactered by a sub-high salinity (33. 5～ 34. 10), comes mainly from the coastal water composed largely of the Changjiang Diluted Water, the surface Kuroshio water and the shelf water in the area south of the East China Sea (ECS). (3) The middle TWCW is sub-grouped into two parts: the water of salinity (S) larger than 34. 50 located below the thermocline originates from the climbed sub-surface Kuroshio water;the TWCW lying in the thermocline is a mixture of the Kuroshio water and the shelf water with low salinity. (4) In the strait, the water from the source area is denatured obviously due to mixing unceasingly wth the shelf water and coastal water. The high salinity water of S >34. 5 appears only in the bottom layer with depths>50m.展开更多
The present study investigates the persistence of summer sea surface temperature anomalies（SSTAs） in the midlatitude North Pacific and its interdecadal variability. Summer SSTAs can persist for a long time（approxim...The present study investigates the persistence of summer sea surface temperature anomalies（SSTAs） in the midlatitude North Pacific and its interdecadal variability. Summer SSTAs can persist for a long time（approximately 8–14 months）around the Kuroshio Extension（KE） region. This long persistence may be strongly related to atmospheric forcing because the mixed layer is too shallow in the summer to be influenced by the anomalies at depths in the ocean. Changes in atmospheric circulation, latent heat flux, and longwave radiation flux all contribute to the long persistence of summer SSTAs. Among these factors, the longwave radiation flux has a dominant influence. The effects of sensible heat flux and shortwave radiation flux anomalies are not significant. The persistence of summer SSTAs displays pronounced interdecadal variability around the KE region, and the variability is very weak during 1950–82 but becomes stronger during 1983–2016. The changes in atmospheric circulation, latent heat flux, and longwave radiation flux are also responsible for this interdecadal variability because their forcings on the summer SSTAs are sustained for much longer after 1982.展开更多
基金the National Key Research and Development Program under Grant 2022YFE0106900the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant XDA2010030804the National Natural Science Foundation of China under Grant No.41621005.
文摘This study explores the linkage between summertime temperature fluctuations over midlatitude Eurasia and the preceding Arctic sea ice concentration (SIC) by utilizing the squared norm of the temperature anomaly, the essential part of local eddy available potential energy, as a metric to quantify the temperature fluctuations with weather patterns on various timescales. By comparing groups of singular value decomposition (SVD) analysis, we suggest a significant linkage between strong (weak) August 10-to-30-day temperature fluctuations over mid-west Asia and enhanced (decreased) Barents-Kara Sea ice in the previous February. We find that when the February SIC increases in the Barents-Kara Sea, a zonal dipolar pattern of SST anomalies appears in the Atlantic subpolar region and lasts from February into the summer months. Evidence suggests that in such a background state, the atmospheric circulation changes evidently from July to August, so that the August is characterized by an amplified meridional circulation over Eurasia, weakened westerlies, and high- pressure anomalies along the Arctic coast. Moreover, the 10-to-30-day wave becomes more active in the North Atlantic-Barents-Kara Sea-Central Asia regions and manifests a more evident southward propagation from the Barents- Kara Sea into the Ural region, which is responsible for the enhanced 10-to-30-day wave activity and temperature fluctuations in the region.
基金This work is financially supported by Laoshan Laboratory(Grant no.LSKJ202203003)National Natural Science Foundation of China(Grant nos.42276250,41976221)General Project of Natural Science Foundation of Shandong Province(Grant no.ZR2020MD100).
文摘The summertime anticyclonic circulation mode(SACM)is related to recent substantial loss of sea ice in the Arctic.This review outlines the potential causes of the SACM and considers its influence on sea ice depletion.Local triggers(i.e.,sea ice loss and sea surface temperature(SST)variation)and spatiotemporal teleconnections(i.e.,extratropical cyclone intrusion,tropical and mid-latitude SST anomalies,and winter atmospheric circulation preconditions)are discussed.The influence of the SACM on the dramatic loss of sea ice is emphasized through inspection of relevant dynamic(i.e.,Ekman drift and export)and thermodynamic(i.e.,moisture content,cloudiness,and associated changes in radiation)mechanisms.Moreover,the motivation for investigation of the underlying physical mechanisms of the SACM in response to the recent substantial sea ice depletionis also clarified through an attempt to better understand the shifting ice-atmosphere interaction in the Arctic during summer.Therecord low extent of sea ice in September 2012 could be reset in the near future if the SACM-like scenario continues to exist during summer in the Arctic troposphere.
基金supported by the National Key Basic Research Program of China (Grant No. 2006CB400502 and 2009CB723904)the National Natural Science Foundation of China (Grant No.40805032)IAP/CAS Knowledge Innovation Project(IAP07405)
文摘An intercomparison of summertime （JJA）subtropical geopotential heights from the ERA-40 and NCEP/NCAR reanalysis is specifically conducted over East Eurasia and the western North Pacific. The NCEP/NCAR is obviously lower than the ERA-40 in the mid-to-lower troposphere in most regions of East Eurasia before the mid-1970s, but becomes higher than the ERA-40 after the mid-1970s and thus demonstrates stronger increased trends during the period of 1958-2001. Both reanalyses are lower than the observations in most regions of China. The NCEP/NCAR especially shows tremendously systematic lower values before the mid-1960s and displays abrupt changes before the 1970s. Several indices of the western North Pacific subtropical high （WNPSH）, calculated from both reanalyzed summer geopotential heights, also reveal that the variation trend of the NCEP/NCAR is stronger than that of the ERA-40 in the mid-to-lower troposphere from 1958 to 2001. Through singular value decomposition （SVD） analysis, the summer geopotential heights at 500 hPa from the ERA-40 are better than the NCEP/NCAR counterparts at interacting with the precipitation over the East Asian monsoon region. The results indicate that the NCEP/NCAR in the mid-and-lower troposphere may overestimate interdecadal changes and should be used cautiously to study the relationship between the WNPSH and precipitation ove ther East Asia Monsoon region before the mid-1970s.
基金The key technology R&D program of China, No.2007BAC29B02Project of Jiangsu Key Laboratory of Meteorological Disaster, No.KLME060101
文摘Using the daily data of temperature from China Meteorological Administration and the NCEP/NCAR reanalysis from 1960 to 2005, we have analyzed the relationships between the summertime high/low temperature events in the middle and lower reaches of the Yangtze River （MLRYR） and the related circulation anomalies in the Eastern Hemisphere. Our results have demonstrated that a significantly increasing trend is observed in daily minimum temperature in the past 50 years. And in some regions in the Northern Hemisphere, the opposite scenarios are observed in circulation anomalies in lower and upper parts of the troposphere in the years when the temperatures are higher than normal, as compared to those in the years when the temperatures are lower than normal in the middle and lower reaches of the Yangtze River （MLRYR）. Additionally, the anomalous circulation structure in vertical direction in both the high and lower temperature years are barotropic. It is found that the emergence and maintenance of the aforementioned anomalous circulations are related to three kinds of wave train teleconnection patterns. Further more, influences of the long wave surface radiation on the air temperature are stronger in the nighttime than that in the daytime. While both the maximum and minimum temperatures have negative relationships with the sensible heat flux but positive relationships with the latent heat flux. To some extent, the anomalous dynamic heating （cooling） caused by the vertical thermal advection as well as the diabatic heating （cooling） caused by diabatic processes can explain the formation of the high （low） temperature events in the middle and lower reaches of the Yangtze River （MLRYR） in boreal summer.
文摘On Page 119 of the printed edition （Issue 1, Vol. 26）, the paper title should be ＂Intercomparison of the Summertime Subtropical High from the ERA-40 and NCEP/NCAR Reanalysis over East Eurasia and the Western North Pacific＂. The editorial office and the authors are sincerely sorry for any inconvenience this may have caused.
基金supported by the National Natural Science Foundation of China under Grant of No.40233033 and No.40475040
文摘Synthesis analysis and singular value decomposition (SVD) methods were used to study the impact of surface air temperature (SAT) over Asian-Pacific region on the summertime northeastern Asian blocking high (NABH) with NCEP/NCAR Reanalysis Data.The results showed that 500 hPa geopotential height and SAT fields over Asian-Pacific region shared the similar pattern of East Asian Pacific (EAP) wave train;there was steady remote response relationship between the EAP wave train in summer and the '+-+' pattern of tropical SAT in zonal direction from former winter to summer;there were two relative negative(positive) Walker circulations over the tropical Indian Ocean and Pacific when being more(less) summertime NABH. The influence of sea surface temperature anomaly (SSTA) on the summertime NABH was possibly as follows.The special distribution of SSTA in tropical zonal direction continuously forced the tropical convection and zonal circulation from former winter to summer,and led them to act anomaly.Finally the abnormal conditions were transported to middle-high latitudes through EAP wave train and yielded the advantageous or disadvantageous atmospheric circulation background for the summertime NABH.
基金supported by the Key Program of the National Science Foundation of China(Grant No.42030611)the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(Grant No.2019QZKK0105)the Integration Project of the Major Research Program of the National Natural Science Foundation of China(Grant No.91937301)。
文摘The Sichuan-Tibet Railway,mainly located in the southeastern Qinghai-Tibet Plateau,is affected by summertime extreme precipitation(SEP).Using daily rain-gauge observations and ERA5 reanalysis data for the summers of 1979-2020,the spatiotemporal distribution characteristics of SEP in the key region of the Sichuan-Tibet Railway(28°-33°N,90°-105°E,hereafter KR)are revealed,and the mechanism for SEP amount(SEPA)variation in the KR is investigated.The results show that SEPA in the KR contributes nearly 30%to the total summer precipitation.Regional differences are evident in SEP,justifying thresholds higher in the plateau-dominated central-western KR(CWKR)and lower in the basindominated eastern KR(EKR).In addition,SEP in the CWKR is less intense but more frequent than SEP in the EKR.During 1979-2020,the SEPA in the KR increased slightly while the SEPA in the CWKR increased significantly and peaked in the last decade.When anticyclonic circulation(AC)anomalies dominate the 500 hPa pattern over the Bay of Bengal and Mongolia,the southerly flow and cyclonic shear over the southeastern plateau will be strengthened,favoring more SEPA in the CWKR.When an AC anomaly dominates the 500 hPa pattern over the Bohai Sea,the low-level easterly wind over the basin will be strengthened,favoring more SEPA in the EKR.The strengthening of the ascent,water vapor convergence,and convective instability is conducive to more SEPA in the KR.Our results deepen the understanding of the characteristics and the physical mechanisms responsible for extreme precipitation in the KR.
文摘M 2 tide and density residual currents in the Bohai Sea were examined using the Blumberg and Mellor 3D nonlinear numerical coastal circulation model incorporating Mellor and Yamada level 2.5 turbulent closure model. The tidal results showed good agreement with previous work. The model results indicated that the density residual currents are robust in summer; and that at the transition zone between well-mixed and stratified water, the horizontal velocity is high and the vertical velocity is positive.
文摘The origin of the Tsushima Warm Current Water(TWCW) in summer is studied mainly on the basis of the CTD data and the observations of satellite-traced surface drifters of Coastal Ocean Process Experiment of the East China Sea(COPEX-ECS) conducted by Korea Ocean Research and Development Institute. The main results are as follows: (1) The structures of the TWCW show obvious regional varitaions. The TWCW can be divided into three layers in the northern Okinawa Trough west of Kyushu and into two layers on the continental shelf and in the Tsushima/Korea Strait. (2) The surface TWCW, charactered by a sub-high salinity (33. 5～ 34. 10), comes mainly from the coastal water composed largely of the Changjiang Diluted Water, the surface Kuroshio water and the shelf water in the area south of the East China Sea (ECS). (3) The middle TWCW is sub-grouped into two parts: the water of salinity (S) larger than 34. 50 located below the thermocline originates from the climbed sub-surface Kuroshio water;the TWCW lying in the thermocline is a mixture of the Kuroshio water and the shelf water with low salinity. (4) In the strait, the water from the source area is denatured obviously due to mixing unceasingly wth the shelf water and coastal water. The high salinity water of S >34. 5 appears only in the bottom layer with depths>50m.
基金supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 41375094 and 41406028)the Basic Scientific Research Fund for National Public Institutes of China (Grant No. GY0215P04)+2 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA11010102)the NSFC–Shandong Joint Fund for Marine Science Research Centers (Grant No. U1406401)the Foundation for Innovative Research Groups of the NSFC (Grant No. 41421005)
文摘The present study investigates the persistence of summer sea surface temperature anomalies（SSTAs） in the midlatitude North Pacific and its interdecadal variability. Summer SSTAs can persist for a long time（approximately 8–14 months）around the Kuroshio Extension（KE） region. This long persistence may be strongly related to atmospheric forcing because the mixed layer is too shallow in the summer to be influenced by the anomalies at depths in the ocean. Changes in atmospheric circulation, latent heat flux, and longwave radiation flux all contribute to the long persistence of summer SSTAs. Among these factors, the longwave radiation flux has a dominant influence. The effects of sensible heat flux and shortwave radiation flux anomalies are not significant. The persistence of summer SSTAs displays pronounced interdecadal variability around the KE region, and the variability is very weak during 1950–82 but becomes stronger during 1983–2016. The changes in atmospheric circulation, latent heat flux, and longwave radiation flux are also responsible for this interdecadal variability because their forcings on the summer SSTAs are sustained for much longer after 1982.
