This study concerns atmospheric responses to the North Pacific subtropical front (NPSTF) in boreal spring over the period 1982-2014. Statistical results show that a strong NPSTF in spring can significantly enhance t...This study concerns atmospheric responses to the North Pacific subtropical front (NPSTF) in boreal spring over the period 1982-2014. Statistical results show that a strong NPSTF in spring can significantly enhance the East Asian jet stream (EAJS). Both transient eddy activity and the atmospheric heat source play important roles in this process. The enhanced atmospheric temperature gradient due to a strong NPSTF increases atmospheric baroclinicity, resulting in an intensification of transient eddy and convection activities. On the one hand, the enhanced transient eddy activities can excite an anomalous cyclonic circulation with a quasi-baraotropical structure in the troposphere to the north of the NPSTF. Accordingly, the related westerly wind anomalies around 30°N can intensify the component of the EAJS over the Northeast Pacific. On the other hand, an enhanced atmospheric heat source over the NPSTF, which is related to increased rainfall, acts to excite an anomalous cyclonic circulation system in the troposphere to the northwest of the NPSTF, which can explain the enhanced component of the EAJS over the Northwest Pacific. The two mechanisms may combine to enhance the EAJS.展开更多
Previous studies have shown that meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) dominates interannual variability of the EAJS in the summer months.This study investigates the tropical P...Previous studies have shown that meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) dominates interannual variability of the EAJS in the summer months.This study investigates the tropical Pacific sea surface temperature (SST) anomalies associated with meridional displacement of the monthly EAJS during the summer.The meridional displacement of the EAJS in June is significantly associated with the tropical central Pacific SST anomaly in the winter of previous years,while displacements in July and August are related to tropical eastern Pacific SST anomalies in the late spring and concurrent summer.The EAJS tends to shift southward in the following June (July and August) corresponding to a warm SST anomaly in the central (eastern) Pacific in the winter (late spring-summer).The westerly anomaly south of the Asian jet stream is a result of tropical central Pacific warm SST anomaly-related warming in the tropical troposphere,which is proposed as a possible reason for southward displacement of the EAJS in June.The late spring-summer warm SST anomaly in the tropical eastern Pacific,however,may be linked to southward displacement of the EAJS in July and August through a meridional teleconnection over the western North Pacific (WNP) and East Asia.展开更多
On the interannual timescale, the meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) is significantly associated with the rainfall anomalies in East Asia in summer. In this study, using the...On the interannual timescale, the meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) is significantly associated with the rainfall anomalies in East Asia in summer. In this study, using the data from the National Centers for Environmental Prediction-Department of Energy (NCEP/DOE) reanalysis-2 from 1979 to 2002, the authors investigate the interannual variations of the EAJS's meridional displacement in summer and their associations with the variations of the South Asian high (SAH) and the western North Pacific subtropical high (WNPSH), which are dominant circulation features in the upper and lower troposhere, respectively. The result from an EOF analysis shows that the meridional displacement is the most remarkable feature of the interannual variations of the EAJS in each month of summer and in summer as a whole. A composite analysis indicates that the summer (June-July-August, JJA) EAJS index, which is intended to depict the interannual meridional displacement of the EAJS, is not appropriate because the anomalies of the zonal wind at 200 hPa (U200) in July and August only, rather than in June, significantly contribute to the summer EAJS index. Thus, the index for each month in summer is defined according to the location of the EAJS core in each month. Composite analyses based on the monthly indexes show that corresponding to the monthly equatorward displacement of the EAJS, the South Asian high (SAH) extends southeastward clearly in July and August, and the western North Pacific subtropical high (WNPSH) withdraws southward in June and August.展开更多
The present study validated the capability of the AM2.1,a model developed at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL),in reproducing the fundamental features of the East Asian Subtropical Westerly Jet S...The present study validated the capability of the AM2.1,a model developed at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL),in reproducing the fundamental features of the East Asian Subtropical Westerly Jet Stream (EASWJ).The main behaviors of the EASWJ are also investigated through the reanalysis of observational NCEP/NCAR data.The mean state of the EASWJ,including its intensity,location,structure,and seasonal evolution is generally well-portrayed in the model.Compared with the observation,the model tends to reproduce a weaker jet center.And,during summer,the simulated jet center is northward-situated.Results also demonstrate the model captures the variability of EASWJ during summer well.The results of the empirical orthogonal function (EOF) applied on the zonal wind at 200 hPa (U200) over East Asia for both the observation and simulation indicate an inter-decadal shift around the late 1970s.The correlation coefficient between the corresponding principle components is as great as 0.42 with significance at the 99% confidence level.展开更多
The East Asian upper-tropospheric jet stream (EAJS) typically jumps north of 45~N in midsummer. These annual northward jumps are mostly classified into two dominant types: the first type corresponds to the enhanced...The East Asian upper-tropospheric jet stream (EAJS) typically jumps north of 45~N in midsummer. These annual northward jumps are mostly classified into two dominant types: the first type corresponds to the enhanced westerly to the north of the EAJS's axis (type A), while the second type is related to the weakened westerly within the EAJS's axis (type B). In this study, the impacts of these two types of northward jumps on rainfall in eastern China are investigated. Our results show that rainfall significantly increases in northern Northeast China and decreases in the Yellow River-Huaihe River valleys, as well as in North China, during the type A jump. As a result of the type B jump, rainfall is enhanced in North China and suppressed in the Yangtze River valley. The changes in rainfall in eastern China during these two types of northward jumps are mainly caused by the northward shifts of the ascending air flow that is directly related to the EAJS. Concurrent with the type A (B) jump, the EAJS-related ascending branch moves from the Yangtze-Huai River valley to northern Northeast (North) China when the EAJS's axis jumps from 40~N to 55~N (50~N). Meanwhile, the type A jump also strengthens the Northeast Asian low in the lower troposphere, leading to more moisture transport to northern Northeast China. The type B jump, however, induces a northwestward extension of the lower-tropospheric western North Pacific subtropical high and more moisture transport to North China.展开更多
A 600-year integration performed with the Bergen Climate Model and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data were used to investigate the impa...A 600-year integration performed with the Bergen Climate Model and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data were used to investigate the impact of strong tropical volcanic eruptions on the East Asian summer monsoon (EASM) and EASM rainfall.Both the simulation and NCEP/NCAR reanalysis data show a weakening of the EASM in strong eruption years.The model simulation suggests that North and South China experience droughts and the Yangtze-Huaihe River Valley experiences floods during eruption years.In response to strong tropical volcanic eruptions,the meridional air temperature gradient in the upper troposphere is enhanced,which leads to a southward shift and an increase of the East Asian subtropical westerly jet stream (EASWJ).At the same time,the land-sea thermal contrast between the Asian land mass and Northwest Pacific Ocean is weakened.The southward shift and increase of the EASWJ and reduction of the land-sea thermal contrast all contribute to a weakening of the EASM and EASM rainfall anomaly.展开更多
The surface and upper-level features associated with a sharp drop ofwintertime daily temperature over South Korea is investigated in this study. This sharp drop indaily temperature is called a cold surge and is one of...The surface and upper-level features associated with a sharp drop ofwintertime daily temperature over South Korea is investigated in this study. This sharp drop indaily temperature is called a cold surge and is one of the most hazardous weather phenomena in EastAsian winters. An upper-level baroclinic wave of 60° wavelength propagating eastward at a phasespeed of 12° longitude per day across the continent of northern China from the west of Lake Baikaltoward the eastern coast of China causes the outbreak of cold air over South Korea. The coolingassociated with the upper-level baroclinic jvave is found at all altitudes under the geopotentialheight-fall center near the tropopause. The development in the ridge seems to derive the earlyevolution of the eastward-propagating sinusoidal wave, whereas the trough is connected directly withthe tropospheric temperature-drop. An enhancement of the wintertime East Asian jet stream after theoutbreak of a cold surge is a response to the steep temperature gradient associated with thedeveloping baroclinic wave.展开更多
基金jointly supported by the Ministry of Science and Technology of China,through the National Basic Research Program of China(Grant No.2012CB955602)the National Natural Science Foundation of China(Grant Nos.41575077,41490643 and 41275094)+1 种基金a project funded by the PAPD(Priority Academic Program Development of Jiangsu Higher Education Institutions)supported by the Innovation Project for Graduate Student of Jiangsu Province(Grant No.KYLX15-0860)
文摘This study concerns atmospheric responses to the North Pacific subtropical front (NPSTF) in boreal spring over the period 1982-2014. Statistical results show that a strong NPSTF in spring can significantly enhance the East Asian jet stream (EAJS). Both transient eddy activity and the atmospheric heat source play important roles in this process. The enhanced atmospheric temperature gradient due to a strong NPSTF increases atmospheric baroclinicity, resulting in an intensification of transient eddy and convection activities. On the one hand, the enhanced transient eddy activities can excite an anomalous cyclonic circulation with a quasi-baraotropical structure in the troposphere to the north of the NPSTF. Accordingly, the related westerly wind anomalies around 30°N can intensify the component of the EAJS over the Northeast Pacific. On the other hand, an enhanced atmospheric heat source over the NPSTF, which is related to increased rainfall, acts to excite an anomalous cyclonic circulation system in the troposphere to the northwest of the NPSTF, which can explain the enhanced component of the EAJS over the Northwest Pacific. The two mechanisms may combine to enhance the EAJS.
基金supported by the National Natural Science Foundation of China (Grant No. 40810059005)
文摘Previous studies have shown that meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) dominates interannual variability of the EAJS in the summer months.This study investigates the tropical Pacific sea surface temperature (SST) anomalies associated with meridional displacement of the monthly EAJS during the summer.The meridional displacement of the EAJS in June is significantly associated with the tropical central Pacific SST anomaly in the winter of previous years,while displacements in July and August are related to tropical eastern Pacific SST anomalies in the late spring and concurrent summer.The EAJS tends to shift southward in the following June (July and August) corresponding to a warm SST anomaly in the central (eastern) Pacific in the winter (late spring-summer).The westerly anomaly south of the Asian jet stream is a result of tropical central Pacific warm SST anomaly-related warming in the tropical troposphere,which is proposed as a possible reason for southward displacement of the EAJS in June.The late spring-summer warm SST anomaly in the tropical eastern Pacific,however,may be linked to southward displacement of the EAJS in July and August through a meridional teleconnection over the western North Pacific (WNP) and East Asia.
基金This work was supported by the Chinese Academy of Sciences(Grant No.KZCX3 SW-221)the National Natural Science Foundation of China under Grant No.40221503.
文摘On the interannual timescale, the meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) is significantly associated with the rainfall anomalies in East Asia in summer. In this study, using the data from the National Centers for Environmental Prediction-Department of Energy (NCEP/DOE) reanalysis-2 from 1979 to 2002, the authors investigate the interannual variations of the EAJS's meridional displacement in summer and their associations with the variations of the South Asian high (SAH) and the western North Pacific subtropical high (WNPSH), which are dominant circulation features in the upper and lower troposhere, respectively. The result from an EOF analysis shows that the meridional displacement is the most remarkable feature of the interannual variations of the EAJS in each month of summer and in summer as a whole. A composite analysis indicates that the summer (June-July-August, JJA) EAJS index, which is intended to depict the interannual meridional displacement of the EAJS, is not appropriate because the anomalies of the zonal wind at 200 hPa (U200) in July and August only, rather than in June, significantly contribute to the summer EAJS index. Thus, the index for each month in summer is defined according to the location of the EAJS core in each month. Composite analyses based on the monthly indexes show that corresponding to the monthly equatorward displacement of the EAJS, the South Asian high (SAH) extends southeastward clearly in July and August, and the western North Pacific subtropical high (WNPSH) withdraws southward in June and August.
基金supported by the National Basic Research Program of China (973 Program) under Grant 2011CB309704the National Special Scientific Research Project for Public Interest under Grant 201006021the National Natural Science Foundation of China under Grants 40890155,U0733002,and 40810059005
文摘The present study validated the capability of the AM2.1,a model developed at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL),in reproducing the fundamental features of the East Asian Subtropical Westerly Jet Stream (EASWJ).The main behaviors of the EASWJ are also investigated through the reanalysis of observational NCEP/NCAR data.The mean state of the EASWJ,including its intensity,location,structure,and seasonal evolution is generally well-portrayed in the model.Compared with the observation,the model tends to reproduce a weaker jet center.And,during summer,the simulated jet center is northward-situated.Results also demonstrate the model captures the variability of EASWJ during summer well.The results of the empirical orthogonal function (EOF) applied on the zonal wind at 200 hPa (U200) over East Asia for both the observation and simulation indicate an inter-decadal shift around the late 1970s.The correlation coefficient between the corresponding principle components is as great as 0.42 with significance at the 99% confidence level.
基金supported by the National Natural Science Foundation of China (Grant No. 40905025)GYHY201006019, and GYHY200906017
文摘The East Asian upper-tropospheric jet stream (EAJS) typically jumps north of 45~N in midsummer. These annual northward jumps are mostly classified into two dominant types: the first type corresponds to the enhanced westerly to the north of the EAJS's axis (type A), while the second type is related to the weakened westerly within the EAJS's axis (type B). In this study, the impacts of these two types of northward jumps on rainfall in eastern China are investigated. Our results show that rainfall significantly increases in northern Northeast China and decreases in the Yellow River-Huaihe River valleys, as well as in North China, during the type A jump. As a result of the type B jump, rainfall is enhanced in North China and suppressed in the Yangtze River valley. The changes in rainfall in eastern China during these two types of northward jumps are mainly caused by the northward shifts of the ascending air flow that is directly related to the EAJS. Concurrent with the type A (B) jump, the EAJS-related ascending branch moves from the Yangtze-Huai River valley to northern Northeast (North) China when the EAJS's axis jumps from 40~N to 55~N (50~N). Meanwhile, the type A jump also strengthens the Northeast Asian low in the lower troposphere, leading to more moisture transport to northern Northeast China. The type B jump, however, induces a northwestward extension of the lower-tropospheric western North Pacific subtropical high and more moisture transport to North China.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences [grant number XDA17010105-02]Key Research Program of Frontier Sciences,CAS [grant number QYZDY-SSW-DQC018]the National Natural Science Foundation of China [grant numbers91437105,41430533,and 41575041]
基金supported by the Strategic Priority Research Program(Grant No.XDA05110203) of the Chinese Academy of Sciencesthe Research Council of Norway through the India-Clim projectthe National Basic Research Program of China(Grant Nos.2012CB955401 and 2010CB951802)
文摘A 600-year integration performed with the Bergen Climate Model and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data were used to investigate the impact of strong tropical volcanic eruptions on the East Asian summer monsoon (EASM) and EASM rainfall.Both the simulation and NCEP/NCAR reanalysis data show a weakening of the EASM in strong eruption years.The model simulation suggests that North and South China experience droughts and the Yangtze-Huaihe River Valley experiences floods during eruption years.In response to strong tropical volcanic eruptions,the meridional air temperature gradient in the upper troposphere is enhanced,which leads to a southward shift and an increase of the East Asian subtropical westerly jet stream (EASWJ).At the same time,the land-sea thermal contrast between the Asian land mass and Northwest Pacific Ocean is weakened.The southward shift and increase of the EASWJ and reduction of the land-sea thermal contrast all contribute to a weakening of the EASM and EASM rainfall anomaly.
基金supported by the National Natural Science Foundation of China [grant number 41991281]the National Key R&D Program of China [grant number 2018YFA0606403]the National Natural Science Foundation of China [grant number 41790472]。
文摘The surface and upper-level features associated with a sharp drop ofwintertime daily temperature over South Korea is investigated in this study. This sharp drop indaily temperature is called a cold surge and is one of the most hazardous weather phenomena in EastAsian winters. An upper-level baroclinic wave of 60° wavelength propagating eastward at a phasespeed of 12° longitude per day across the continent of northern China from the west of Lake Baikaltoward the eastern coast of China causes the outbreak of cold air over South Korea. The coolingassociated with the upper-level baroclinic jvave is found at all altitudes under the geopotentialheight-fall center near the tropopause. The development in the ridge seems to derive the earlyevolution of the eastward-propagating sinusoidal wave, whereas the trough is connected directly withthe tropospheric temperature-drop. An enhancement of the wintertime East Asian jet stream after theoutbreak of a cold surge is a response to the steep temperature gradient associated with thedeveloping baroclinic wave.