1998年南海夏季风低频振荡特征分析

利用NCEP/NCAR1998年再分析资料和SST资料，研究了南海夏季风的低频振荡特征。结果表明，南海夏季风的低频振荡对南海夏季风的爆发具有加强的作用；南海低频低层辐合（散）区对应低频降水正（负）值区；南海地区的大气低频振荡以向北、向东传播为主，南海地区低频散度在垂直方向呈现出相互补偿的特征。     

基于改进综合气象干旱指数的2011年和2013年长江中下游干旱低频振荡特征分析

利用NCEP/NCAR逐日再分析资料和地面观测资料,基于改进的综合气象干旱指数（I_C）对长江中下游地区2011年春季和2013年夏季干旱过程的低频振荡特征进行了分析。结果表明：2011年春季干旱过程的主要低频I_C周期为30~60 d,西太平洋500 hPa正异常低频高度场系统的西移、南支锋区上游500 hPa正异常低频高度场系统的东移和北扩、西北地区东部低层低频反气旋的向南移动可能是低频I_C传播变化特征的重要原因。2013年夏季干旱过程的主要低频I_C周期也为30~60 d,西亚和西北太平洋500 hPa正异常低频高度场向我国南方地区移动、孟加拉湾和西北太平洋的低层低频反气旋向西和向北移动与低频I_C传播变化特征有重要联系。     

VARIATIONS OF 30—60 DAY OSCILLATION IN ATMOSPHERE BEFORE AND DURING 1982 EL NINO*

By using the upper-wind data from July 1980 to June 1983,the variations of the low-frequency oscillation(LFO) in the atmosphere before and during 1982 El Nino have been investigated.Before the El Nino,the LFO propagates from west to east over the equator of the Eastern Hemisphere and from east to west over 20°N.The eastward propagating LFO over the equator consists of zonal wavenumber 1 propagating eastward and zonal wavenumber 2 with a character of stationary wave.The oscillation of zonal wavenumber 2 can modulate the oscillation strength.After the onset of the El Nino,the propagating directions of the LFO over the equator and 20°N of the Eastern Hemisphere change to be westward and eastward,respectively.The LFO over the western Pacific weakens rapidly and one coming from middle and high latitudes propagates to the equator.From the phase compositions of streamline fields for the zonal wavenumber 1 of equatorial westward propagatirg LFO,it is found that the atmospheric heat source in the equator of the eastern Pacific(EEP)excites a series of the equatorial cyclones and anticyclones which move northward and westward and form the westward propagating LFO over the equator.With the wavelength of 20000km,this kind of equatorial wave is similar to the mixing Rossby-gravity wave.In its westward and northward movement,the circulation in East Asia is modified.This may be the mechanism of the influence of El Nino on the climate of China.     

青藏高原大气低频振荡的源、汇特征分析

使用1998年美国NCAR再分析的逐日资料，研究了1998年夏季青藏高原大气低频振荡的源、汇特征。青藏高原对于纬向风的低频波来说，有时是低频振荡的源区，有时是汇区。通过计算低频涡度的通量散度，进一步研究了低频涡源、涡汇特征。青藏高原在不同时间和不同部位，低频涡源、涡汇具有不同的分布特征，传播特征也不尽相同，青藏高原上空100hPa低频涡源、涡汇受到了南亚高压的很大影响。     

1998年我国东部大陆夏季风特征研究

利用NCEP／NCAR再分析资料和OLR资料，研究了1998年我国东部大陆夏季风的特征。结果指出，1998年夏季副高脊线的平均位置偏南，华南地区和长江流域的夏季风较强，强对流维持时间长；华北地区的夏季风较弱，对流比常年偏弱；我国东部大陆夏季风存在明显的低频振荡现象。     

Main features of regional circulation variation during onset of the south china sea monsoon in 1998

1.IntroductionTheAsiansummermonsoonconsistsoftwosystems,i.e.,theSouthAsianmonsoonandtheEastAsianmonsoon.TheSouthChinaSea(SCS)monsoonisoneoftheimportantsubsystemsoftheEastAsianmonsoon.IthaslongbeenconcernedabouttherelationshipoftheSCSmonsoonwithchangesofthegeneralcirculationandweatherpatternsinadjacentregions.TaoandChen(1987)suggestedthattheonsetoftheAsiansummermonsoonstartsfirstinthenorthernSCSusuallyinmid--May,thenpropagatesnorthwardtothemainlandofChinaandthewesternPacificsouthofJap…     

1998年青藏高原大气低频振荡的结构特征分析

使用ＮＣＥＰ／ＮＣＡＲ再分析的逐日资料,研究了１９９８年夏季青藏高原大气低频振荡的结构特征。结果表明：不同低频频率的遥相关水平结构既有相似的波列结构,也存在相异的特征。高原主体的低频振荡为相当正压结构,低频降水一般位于低频气旋性环流及低频气流辐合带内,利用高原低频降水可提前预测江南及高原南部的低频降水活动,高原和长江中下游及东北地区的低频水存在同时加强和同时减弱的关系。     

CISK, EVAPORATION-WIND FEEDBACK MECHANISM AND 30-60 DAY OSCILLATIONS IN THE TROPICAL ATMOSPHERE*

A baroclinic semi-geostrophic model with evaporation-wind feedback mechanism(EWFM) and CISK is established,two non-dimensional parameters a and η are introduced to represent EWFM and CISK,respectively.Analytic solutions of the model system are obtained,dynamics analyses and the model atmosphere calculations further confirm that EWFM and CISK are very important physical processes in leading to the low-frequency oscillations in the tropics.     

东亚冬季风三维环流的低频振荡特征

利用ＥＣＭＷＦ／ＷＭＯ逐日客观分析格点资料，采用带通滤波分析了冬季风环流的低频振荡特征，结果表明冬季风水平环流和垂直环流都表现出显著的准４０天振荡特征，高低层水平环流的低频变化主要受热带西太平洋和澳大利亚附近的低频涡旋系统的影响，纬向环流的低频变化表现为Ｗａｌｋｅｒ环流的加强和减弱。经向环流则表现为局地振荡特征，它的低频振荡起着联接南北半球和高低层季风环流低频振荡的作用。     

VARIATIONS OF 30—60 DAY OSCILLATION IN ATMOSPHERE BEFORE AND DURING 1982 EL NINO

By using the upper-wind data from July 1980 to June 1983,the variations of the low-frequency oscillation(LFO)in the atmosphere before and during 1982 El Nino have been investigated.Before the El Nino,the LFOpropagates from west to east over the equator of the Eastern Hemisphere and from east to west over 20°N.The eastward propagating LFO over the equator consists of zonal wavenumber 1 propagating eastward andzonal wavenumber 2 with a character of stationary wave.The oscillation of zonal wavenumber 2 can modulatethe oscillation strength.After the onset of the El Nino,the propagating directions of the LFO over the equatorand 20°N of the Eastern Hemisphere change to be westward and eastward,respectively.The LFO over thewestern Pacific weakens rapidly and one coming from middle and high latitudes propagates to the equator.From the phase compositions of streamline fields for the zonal wavenumber 1 of equatorial westward propa-gatirg LFO,it is found that the atmospheric heat source in the equator of the eastern Pacific(EEP)excites aseries of the equatorial cyclones and anticyclones which move northward and westward and form the westwardpropagating LFO over the equator.With the wavelength of 20000km,this kind of equatorial wave is similarto the mixing Rossby-gravity wave.In its westward and northward movement,the circulation in East Asiais modified.This may be the mechanism of the influence of El Nino on the climate of China.