The intraseasonal oscillation (ISO) is studied during the severe flood and drought years of the Changjiang-Huaihe River Basin with the NCEP/NCAR reanalysis data and the precipitation data in China. The results show th...The intraseasonal oscillation (ISO) is studied during the severe flood and drought years of the Changjiang-Huaihe River Basin with the NCEP/NCAR reanalysis data and the precipitation data in China. The results show that the upper-level (200 hPa) ISO pattern for severe flood (drought) is characterized by an anticyclonic (cyclonic) circulation over the southern Tibetan Plateau and a cyclonic (anti-cyclonic) circulation over the northern Tibetan Plateau. The lower-level (850 hPa) ISO pattern is characterized by an anticyclonic (cyclonic) circulation over the area south of the Changjiang River, the South China Sea, and the Western Pacific, and a cyclonic (anticyclonic) circulation from the area north of the Changjiang River to Japan. These low-level ISO circulation patterns are the first modes of the ISO wind field according to the vector EOF expansion with stronger amplitude of the EOF1 time coefficient in severe flood years than in severe drought years. The analyses also reveal that at 500 hPa and 200 hPa, the atmospheric ISO activity over the Changjiang-Huaihe River basin, North China, and the middle-high latitudes north of China is stronger for severe flood than for severe drought. The ISO meridional wind over the middle-high latitude regions can propagate southwards and meet with the northward propagating ISO meridional wind from lower latitude regions over the Changjiang-Huaihe River Basin during severe flood years, but not during severe drought years.展开更多
By using the high-resolution GAME reanalysis data, the heat and moisture budgets during the period of HUBEX/GAME in the summer of 1998 are calculated for exploring the thermodynamic features of Meiyu over the Changjia...By using the high-resolution GAME reanalysis data, the heat and moisture budgets during the period of HUBEX/GAME in the summer of 1998 are calculated for exploring the thermodynamic features of Meiyu over the Changjiang-Huaihe (CH) valley. During the CH Meiyu period, an intensive vertically-integrated heat source and moisture sink are predominant over the heavy rainfall area of the CH valley, accompanied by strong upward motion at 500 hPa. The heat and moisture budgets show that the main diabatic heating component is condensation latent heat released by rainfall. As residual terms, the evaporation and sensible heating are relatively small. Based on the vertical distribution of the heat source and moisture sink, the nature of the rainfall is mixed, in which the convective rainfall is dominant with a considerable percentage of continuous stratiform rainfall. There are similar time evolutions of the main physical parameters (〈Q <SUB>1</SUB>〉, 〈Q <SUB>2</SUB>〉, and vertical motion ω at 500 hPa). The time variations of 〈Q <SUB>1</SUB>〉 and 〈Q <SUB>2</SUB>〉 are in phase with those of −ω <SUB>500</SUB>, and have their main peaks within the CH Meiyu period. This shows the influence of the heat source on the dynamic structure of the atmosphere. The wavelet analyses of those time series display similar multiple timescale characteristics. During the CH Meiyu period, both the synoptic scale(∼6 days) and mesoscale (∼2 days and ∼12 hours) increase obviously and cause heavy rainfall as well as the appearances of the maxima of the main physical parameters. Among them, the mesoscale systems are the main factors.展开更多
Based on the theory of Ertel potential vorticity,the isentropic potential vorticity maps and vertical pro- files of potential vorticity for two summer cyclones over the Changjiang-Huaihe Valley are analysed.After disc...Based on the theory of Ertel potential vorticity,the isentropic potential vorticity maps and vertical pro- files of potential vorticity for two summer cyclones over the Changjiang-Huaihe Valley are analysed.After discussing a possible mechanism for the genesis and development of such systems and their differences from typical extratropical cyclones,a conceptual model for their activities is proposed:A weak disturbance in the mid- level of troposphere originated from around the Qinghai-Xizang Plateau may cause heavy precipitation under favourable conditions and latent heat release in the mid-troposphere leads to downward extension of cyclonic circulation and a wave on the quasi-stationary front.This weak cyclone can develop substantially and become a typical extratropical cyclone only when air from the lower stratosphere flows downslope along isentropic sur- faces into the region of interest.展开更多
Abstract： Statistical classification of the intensification of different deepChangiang-Huaihe Cyclones （CHCs） over the East China and Yellow Seas （ECYSs）during 2008 to 2012 is studied using the FNL reanalysis dat...Abstract： Statistical classification of the intensification of different deepChangiang-Huaihe Cyclones （CHCs） over the East China and Yellow Seas （ECYSs）during 2008 to 2012 is studied using the FNL reanalysis data. Based on the penetrationdepth and the season of occurrence, the CHCs are divided into four categoriesincluding warm-season-deep （WSD）, warm-season-shallow （WSS）, winter-shallow（WTS） and early-spring-bottom （ESB）. Statistics show the CHCs take either aneastward or a northeastward path after entering ECYSs. After moving to the seas, theintensification of CHCs is more significant in cold season than that in warm season.They all have the reduction of the friction of the underlying surface and the increase ofthe near surface winds. The area of strong winds extends and migrates from the east tothe southeast of the CHCs. A significant increase of precipitation during the warmseasons is consistent with the penetration depth of the cyclones. While a slight increaseof precipitation in cold season cyclones and scattered precipitation is observed behindthe ESB cyclones in the early stage of spring. Synthetic diagnosis analysis of the CHCsover ECYSs shows that the latent heat release plays an important role in theamplification of cyclones during the warm season. The ESB cyclones are sensitive tothe dynamic and thermal effects from the underlying surface. The vertical stretching of the positive vorticity volume is much more significant in ESB cyclones than that in othercyclones. The height of maximum upper level divergence is proportional to thepenetration depth of the cyclone for all the categories. Diabatic heating from the underlying surface is more prominent in cold season cyclones. Downward transport ofthe kinetic energy from upper level jet and the reduced friction both have positivecontributions to intensification of the CHCs. Moist Potential Vorticity （MPV） has morecontribution to the intensification of warm season cyclones, especially WSD cyclones.The combined effects from iner展开更多
利用NCEP/NCAR多年逐日再分析资料、美国环境预报中心CMAP(NOAA NCEP Climate Prediction Center Merged Analysis of Precipitation)候平均降雨量资料以及全国740站逐日降水资料,对华南前汛期和江淮梅雨期大范围持续性暴雨过程中西太...利用NCEP/NCAR多年逐日再分析资料、美国环境预报中心CMAP(NOAA NCEP Climate Prediction Center Merged Analysis of Precipitation)候平均降雨量资料以及全国740站逐日降水资料,对华南前汛期和江淮梅雨期大范围持续性暴雨过程中西太平洋副高短期位置变异的异同及其可能成因进行了分析。结果表明:华南和江淮大范围持续性暴雨期间,西太平洋副高位置均比同期气候平均值异常偏南偏西,且强度偏强。华南暴雨期间,副高西北侧华南地区以及西侧孟加拉湾地区存在异常强烈的视热源和视水汽汇;江淮暴雨期间,副高北侧江淮流域及西侧孟加拉湾地区也存在异常强烈的视热源和视水汽汇。运用全型垂直涡度倾向方程理论,研究非绝热加热对西太平洋副高短期位置变异的影响,结果表明:副高位置的短期变异与非绝热加热场及其配置有密切联系。华南暴雨期间,副高西北侧边缘的华南地区加热场可在短期内迫使副高东撤南退;江淮暴雨期间,副高北侧江淮流域加热场的存在不利于副高北进,而西侧较远处孟加拉湾热源会诱导副高西伸,两者的共同作用导致副高在江淮以南维持,且会明显西伸。展开更多
文摘The intraseasonal oscillation (ISO) is studied during the severe flood and drought years of the Changjiang-Huaihe River Basin with the NCEP/NCAR reanalysis data and the precipitation data in China. The results show that the upper-level (200 hPa) ISO pattern for severe flood (drought) is characterized by an anticyclonic (cyclonic) circulation over the southern Tibetan Plateau and a cyclonic (anti-cyclonic) circulation over the northern Tibetan Plateau. The lower-level (850 hPa) ISO pattern is characterized by an anticyclonic (cyclonic) circulation over the area south of the Changjiang River, the South China Sea, and the Western Pacific, and a cyclonic (anticyclonic) circulation from the area north of the Changjiang River to Japan. These low-level ISO circulation patterns are the first modes of the ISO wind field according to the vector EOF expansion with stronger amplitude of the EOF1 time coefficient in severe flood years than in severe drought years. The analyses also reveal that at 500 hPa and 200 hPa, the atmospheric ISO activity over the Changjiang-Huaihe River basin, North China, and the middle-high latitudes north of China is stronger for severe flood than for severe drought. The ISO meridional wind over the middle-high latitude regions can propagate southwards and meet with the northward propagating ISO meridional wind from lower latitude regions over the Changjiang-Huaihe River Basin during severe flood years, but not during severe drought years.
基金This work was supported by the National Natural Science Foundation of China under Grant No. 497914030.
文摘By using the high-resolution GAME reanalysis data, the heat and moisture budgets during the period of HUBEX/GAME in the summer of 1998 are calculated for exploring the thermodynamic features of Meiyu over the Changjiang-Huaihe (CH) valley. During the CH Meiyu period, an intensive vertically-integrated heat source and moisture sink are predominant over the heavy rainfall area of the CH valley, accompanied by strong upward motion at 500 hPa. The heat and moisture budgets show that the main diabatic heating component is condensation latent heat released by rainfall. As residual terms, the evaporation and sensible heating are relatively small. Based on the vertical distribution of the heat source and moisture sink, the nature of the rainfall is mixed, in which the convective rainfall is dominant with a considerable percentage of continuous stratiform rainfall. There are similar time evolutions of the main physical parameters (〈Q <SUB>1</SUB>〉, 〈Q <SUB>2</SUB>〉, and vertical motion ω at 500 hPa). The time variations of 〈Q <SUB>1</SUB>〉 and 〈Q <SUB>2</SUB>〉 are in phase with those of −ω <SUB>500</SUB>, and have their main peaks within the CH Meiyu period. This shows the influence of the heat source on the dynamic structure of the atmosphere. The wavelet analyses of those time series display similar multiple timescale characteristics. During the CH Meiyu period, both the synoptic scale(∼6 days) and mesoscale (∼2 days and ∼12 hours) increase obviously and cause heavy rainfall as well as the appearances of the maxima of the main physical parameters. Among them, the mesoscale systems are the main factors.
基金This study is supported partially by National Natural Science Foundation of Chinapartially by the State Meteorological Administration Monsoon Research Funds.
文摘Based on the theory of Ertel potential vorticity,the isentropic potential vorticity maps and vertical pro- files of potential vorticity for two summer cyclones over the Changjiang-Huaihe Valley are analysed.After discussing a possible mechanism for the genesis and development of such systems and their differences from typical extratropical cyclones,a conceptual model for their activities is proposed:A weak disturbance in the mid- level of troposphere originated from around the Qinghai-Xizang Plateau may cause heavy precipitation under favourable conditions and latent heat release in the mid-troposphere leads to downward extension of cyclonic circulation and a wave on the quasi-stationary front.This weak cyclone can develop substantially and become a typical extratropical cyclone only when air from the lower stratosphere flows downslope along isentropic sur- faces into the region of interest.
基金supported by NSFC Grant No.41276033national science support program(2012BAH05B01)+3 种基金China Meteorological Administration Special Public Welfare Research Fund(201206068)CMA special fund on Jiangsu climate change(CSSF201318)Jiangsu science support program(BE2012774,BE2014729)funded by the Jiangsu university advantages subject of engineering discipline construction
文摘Abstract： Statistical classification of the intensification of different deepChangiang-Huaihe Cyclones （CHCs） over the East China and Yellow Seas （ECYSs）during 2008 to 2012 is studied using the FNL reanalysis data. Based on the penetrationdepth and the season of occurrence, the CHCs are divided into four categoriesincluding warm-season-deep （WSD）, warm-season-shallow （WSS）, winter-shallow（WTS） and early-spring-bottom （ESB）. Statistics show the CHCs take either aneastward or a northeastward path after entering ECYSs. After moving to the seas, theintensification of CHCs is more significant in cold season than that in warm season.They all have the reduction of the friction of the underlying surface and the increase ofthe near surface winds. The area of strong winds extends and migrates from the east tothe southeast of the CHCs. A significant increase of precipitation during the warmseasons is consistent with the penetration depth of the cyclones. While a slight increaseof precipitation in cold season cyclones and scattered precipitation is observed behindthe ESB cyclones in the early stage of spring. Synthetic diagnosis analysis of the CHCsover ECYSs shows that the latent heat release plays an important role in theamplification of cyclones during the warm season. The ESB cyclones are sensitive tothe dynamic and thermal effects from the underlying surface. The vertical stretching of the positive vorticity volume is much more significant in ESB cyclones than that in othercyclones. The height of maximum upper level divergence is proportional to thepenetration depth of the cyclone for all the categories. Diabatic heating from the underlying surface is more prominent in cold season cyclones. Downward transport ofthe kinetic energy from upper level jet and the reduced friction both have positivecontributions to intensification of the CHCs. Moist Potential Vorticity （MPV） has morecontribution to the intensification of warm season cyclones, especially WSD cyclones.The combined effects from iner
文摘利用NCEP/NCAR多年逐日再分析资料、美国环境预报中心CMAP(NOAA NCEP Climate Prediction Center Merged Analysis of Precipitation)候平均降雨量资料以及全国740站逐日降水资料,对华南前汛期和江淮梅雨期大范围持续性暴雨过程中西太平洋副高短期位置变异的异同及其可能成因进行了分析。结果表明:华南和江淮大范围持续性暴雨期间,西太平洋副高位置均比同期气候平均值异常偏南偏西,且强度偏强。华南暴雨期间,副高西北侧华南地区以及西侧孟加拉湾地区存在异常强烈的视热源和视水汽汇;江淮暴雨期间,副高北侧江淮流域及西侧孟加拉湾地区也存在异常强烈的视热源和视水汽汇。运用全型垂直涡度倾向方程理论,研究非绝热加热对西太平洋副高短期位置变异的影响,结果表明:副高位置的短期变异与非绝热加热场及其配置有密切联系。华南暴雨期间,副高西北侧边缘的华南地区加热场可在短期内迫使副高东撤南退;江淮暴雨期间,副高北侧江淮流域加热场的存在不利于副高北进,而西侧较远处孟加拉湾热源会诱导副高西伸,两者的共同作用导致副高在江淮以南维持,且会明显西伸。
