环境场对东海登陆热带气旋陆地路径的影响

采用合成分析的方法，对比分析了在华东南部沿海登陆，维持较短陆地路径和维持较长陆地路径的两类热带气旋的环境场变化，结果表明：环境场对登陆热带气旋的陆地路径的维持有重要影响。当西北太平洋副热带高压迅速加强西伸；中低层低压环流迅速减弱；中低层环境热力条件差，海洋水汽输送中断；高层水平流场呈纬向型，青藏高原反气旋环流相对较弱而西北太平洋副热带高压反气旋环流强大，中纬带西风急流强大时，环境场的配置使热带气旋周围的高层水平辐散弱并衰减，低层水平辐合弱并衰减，热带气旋的对流被抑制，仅能维持较短路径很快就减弱消亡。反之，当西北太平洋副热带高压减弱东退，西风槽南压；低层低压环流长时间维持；中低层环境热力条件好，海洋水汽输送通畅；高层水平流场呈经向型，青藏高原反气旋环流相对强大而西北太平洋副热带高压反气旋环流减弱东退，中纬带西风急流较弱，低空东南风急流强大时，环境场的配置使热带气旋周围高层水平辐散强并维持，低层水平辐合强并维持，热带气旋的对流通畅，能维持较长生命史和较长的路径。     

快速西行进入南海台风的统计特征

通过对快速西行进入南海的 1 3个台风快速西行期间西风带环流系统、副热带高压活动和台风环境流场的特征以及这些台风进一步的移向、移速进行统计分析 ,结果表明 ,台风快速西行进南海期间西风带的特点是中纬从中亚到东亚有高压脊或以纬向环流为主 ,西风槽偏北 ;西北太平洋副热带高压一直强大且呈带状分布或不断加强与西伸 ,造成副热带高压南侧与台风之间梯度加大 ,使偏东引导气流加强。研究还发现 ,如果台风南北两侧均为偏东环境流场 ,将使台风西行更快。     

"05.6"广东致洪暴雨过程的500 hPa环流场及低频特征

分析2005年6月15~25日广东出现的连续暴雨过程及结束期的500 hPa候平均环流场,并对4~9月暴雨中心区域的降水低频振荡特征进行了分析。结果表明:连续暴雨期欧亚中高纬度维持稳定的两槽一脊形势;中低纬度非洲与西太平洋副热带高压强大,西太平洋副高西伸到广东沿海,青藏高原为稳定的高压脊,高原下游为西风槽活动区,使冷空气沿着高原频繁扩散南下,并与西太平洋副高边缘的暖湿气流相遇,产生连续的暴雨过程。当巴尔喀什湖-贝加尔湖的高压脊东移而转为宽槽区,青藏高原高压脊减弱消失,高原以东为平直的西风环流,我国东北到日本为高压脊控制时,西北太平洋副热带高压加强北抬,华南降水减弱,连续暴雨过程结束。小波分析表明,连续暴雨期存在准20 d的周期振荡。     

东亚-太平洋地区环流场和热力场由冬向夏转换的过程特征及其可能机制

利用NCEP/NCAR逐日再分析资料和青藏高原逐日视热源资料,分析了东亚 太平洋地区对流层热力场和环流场的季节特征.结果表明,东亚-太平洋热力场上呈现出冬、夏半年反向的特征,冬半年热力格局为“西冷东暖”,夏半年则转为“西暖东冷”,冬半年向夏半年的过渡发生在3月底4月初,相应地,我国东部上空视热源也从冷却转为加热.热力场季节转换的同时,对流层各层环流形势也发生了调整:低层大陆冷高压减弱、东移,太平洋副热带高压显著西伸,形成东亚-西太平洋35°N以南一致的南风区;中层西风带发生了长波调整,由冬季“三槽型”向夏季“四槽型”过渡,西风急流减弱、北移;高层反气旋中心史替,我国上空偏南风由偏北风替代.环流的演变自低层向高层推进,下垫面感热加热的季节变化引起了低层环流的调整以及上升运动的发展,与上升运动相伴的凝结潜热释放则增强了东亚上空的热源,进一步加强了“西暖东冷”的热力格局,从而推进中高层环流的演变.环流调整的时间与东亚副热带季风雨带建立的时间一致,因此,由热力场季节变化引起的对流层环流形势的调整可看成是东亚副热带夏季风环流型的建立过程.     

1951—2010年西太平洋副热带高压脊线季节性变化特征分析

文章通过对1951—2010年NECP/NCAR再分析逐日资料的分析,发现西太平洋副热带高压存在明显的季节性变化。夏季,副热带高压(以下简称副高)脊线出现两次显著的北跳,而且均伴随着副高强度指数的降低和西伸脊点的东退。脊线北跳过程也影响着东亚大气环流系统,南亚高压与西风急流在副高北跳后均同时减弱。但两次北跳过程仍然存在各自的特点:第一次副高脊线北跳时受到高纬地区纬向型环流调整与中低纬环流变化的共同影响,而第二次副高脊线北跳则主要受中低纬环流调整(太平洋负EAP事件)的影响。     

热带东太平洋关键区海温与中国东北地区气温的关系

近三十年我国东北地区夏季异常低温与赤道东太平洋埃尔尼诺现象的出现遥相呼应.本文对此遥相关现象进行了分析,认为在埃尔尼诺现象发生时期低层海温异常影响到大尺度环流的异常。并把信息传到中纬度地区,从而产生处于中纬度的我国东北地区的气温异常.在这时期,沃克环流东移,热带中部和西部太平洋对流层高层东风增强,反气旋环流增强;相反,南亚高压弱而偏南,亚洲沿岸西风带偏南,冷空气活动频繁,出现大范围低温现象.     

应用模糊识别确定天气阶段

我们过去的工作指出,冬半年西风带存在着具有20天左右生命史的大型高值环流系统,我们称之为主导环流系统。它制约着某一地区天气的发展和变化。在主导环流系统影响的时段内,本地区的天气演变趋势保持相对稳定,形成了天气阶段。不同的主导环流系统所形成的天气阶段,其类型也不同。我们将西风带欧亚地区500毫巴主导环流系统分成高压脊类和阻塞高压类,并按主导环流系统出现的地理位置将高压脊类分成三     

陕西夏季旱涝的主要环流特征

利用1961—2008年NCEP／NCAR再分析资料以及陕西地面月降水资料,采用EOF分解、合成分析等方法,分析了陕西夏季旱涝的时空分布特征以及前期气候系统的异常信号特征。结果表明：陕西夏季多雨年乌拉尔山高压脊和鄂霍次克海高压偏强,贝加尔湖低槽偏深,西太平洋副热带高压偏强,西伸脊点偏西。并且前期冬季中高纬度中亚长波脊偏强偏西,西太平洋副热带高压偏强,印缅槽偏弱,700hPa西北地区东部至华北偏北风异常偏强,赤道东太平洋出现暖水位相,西风漂流区海温偏低,印度洋海温偏高,陕西夏季易多雨;而陕西夏季少雨年西太平洋副热带高压偏弱,西伸脊点偏东,陕西主要受中亚高脊前西北气流控制。前期冬季中高纬度欧洲西北部低槽偏强,中亚长波脊偏弱,西太平洋副热带高压偏弱,印缅槽偏强,700hPa西北地区东部至华北偏南风异常偏强,赤道东太平洋出现冷水位相,西风漂流区海温偏高,印度洋海温偏低,陕西夏季易少雨。     

2009/2010年冬季云南严重干旱的原因分析

2009/2010年冬季我国云南省出现严重干旱,这次大范围严重干旱是较长时期降水稀少所造成的。首先讨论云南省冬季降水偏多和偏少时大气环流和海温的统计特征,基于它们的统计关系,再对2009/2010年冬季我国云南省的严重干旱进行个例对比分析。研究表明西风带环流系统异常是造成这次干旱灾害的主要成因。贝加尔湖为高度负距平,东亚沿海为高度正距平,从贝加尔湖以西到东亚中高纬度西风带较平直,冬季冷空气偏弱,很难影响西南地区。尤其是副热带中东急流减弱,从欧洲东部到里海为高压脊控制,西风带的扰动系统不易东移到东亚上空;青藏高原上空为稳定的高压脊,孟加拉湾南支槽减弱,云南省受异常西北气流控制。对太平洋和印度洋海温的分析表明,虽然海温异常可以影响冬季的云南降水,但海温异常并不是2009/2010年冬季云南省降水偏少的最重要原因。     

PDO对西太平洋副热带高压年代际东退的可能贡献

以往的研究已证实,西太平洋副热带高压(副高)在1970s后期减弱东退.基于大气模式(CAM4)的理想型海温强迫试验,结果表明:副高的东退可能是大气对于正位相太平洋年代际振荡(PDO)的相应.伴随着PDO转变为正位相,西太平洋至印度半岛以及热带东太平洋的对流加热增强,大气表现为Gill型响应,在亚洲大陆至西太平洋上空低层产生气旋性异常,有利于副高东退.同时,高层产生反气旋异常,使得东亚西风急流加强和向南扩展,进而调节西太平洋上空的次级环流,进一步有利于副高东退.     

再论夏季西太平洋副热带高压的西伸北跳

利用NCEP/NCAR再分析资料, 选择了1998年、2003年和2005年夏季我国东部雨带位置变化过程进行诊断分析。研究表明:夏季我国东部暴雨带位置的变动, 受西太平洋副热带高压西伸北跳 (南撤东退) 的调节。当副热带高压西伸北跳 (南撤东退) 时, 暴雨带向北 (向南) 移动。在副热带高压西伸北跳持续时期, 长江流域中下游地区出现高温酷暑天气。副热带高压西伸北跳是由于欧亚大陆上空存在静止Rossby波列, 波的能量沿着高空副热带急流向东传播到我国沿海海岸 (115°~130°E) 时, 在该地区激发出一个长波脊。这个长波脊的建立, 使得副热带高压和对流层上部的青藏高压都朝长波脊方向伸展, 表现为“相向”而行。而当在沿海海岸上空激发出一个长波槽时, 副热带高压南撤东退而青藏高压退回到高原上空。当夏季沿海海岸上空的长波脊持续维持时, 长江中下游会出现持久的高温酷暑天气。根据夏季天气预报的经验, 欧洲中期数值预报中心发布的预报对副热带高压的西伸北跳有较好的可预报性。     

1999年东亚夏季风异常活动的物理机制研究

文中从海-气相互作用的角度探讨了1999年东亚夏季风及与其相联系的雨带异常活动的物理机制。结果表明,由于1998年春季至1999年南海-热带西太平洋出现了近20 a最强的异常暧海温,该地强异常海-气相互作用的维持使得这种局地的热力强迫成为1999年东亚夏季风和降水异常的最主要外强迫机制,并使得1999年的季风活动和降水分布有别于一般的统计情形。从1998年秋到1999年,由于热带大气对南海-西太平洋暧海温所诱发的局地强加热的响应,热带西太平洋地区所出现的Gill模态的异常环流分布从冬季一直发展到夏季,并因此在海洋和大气之间形成了局地的强烈正反馈,不仅使得异常环流得以持续发展,而且也使得暖海温得以维持,成为影响1999年环流异常的最强前期信号。随着从冬到夏的季节演变,大气基本态对上述持续性异常环流的影响导致了冬、夏异常环流呈现出不同的纬向非对称,诱发了盛夏期间东亚到北美沿岸的遥相关波列。在东亚沿岸异常气旋性环流的影响下,大尺度异常东风在东亚沿岸的维持形成了极不利于季风西风在南海北部转向的条件,导致了季风在中国东部北进的异常偏弱和低纬西风转向位置的异常偏东。     

Subseasonal Zonal Oscillation of the Western Pacific Subtropical High during Early Summer

This study examines the features and dynamical processes of subseasonal zonal oscillation of the western Pacific subtropical high (WPSH) during early summer, by performing a multivariate empirical orthogonal function (MVEOF) analysis on daily winds and a diagnosis on potential vorticity (PV) at 500 hPa for the period 1979–2016. The first MV-EOF mode is characterized by an anticyclonic anomaly occupying southeastern China to subtropical western North Pacific regions. It has a period of 10–25 days and represents zonal shift of the WPSH. When the WPSH stretches more westward, the South Asian high (SAH) extends more eastward. Above-normal precipitation is observed over the Yangtze–Huaihe River (YHR) basin. Suppressed convection with anomalous descending motion is located over the subtropical western North Pacific. The relative zonal movement of the SAH and the WPSH helps to establish an anomalous local vertical circulation of ascending motion with upper-level divergence over the YHR basin and descending motion with upper-level convergence over the subtropical western Pacific. The above local vertical circulation provides a dynamic condition for persistent rainfall over the YHR basin. An enhanced southwest flow over the WPSH’s western edge transports more moisture to eastern China, providing a necessary water vapor condition for the persistent rainfall over the YHR basin. A potential vorticity diagnosis reveals that anomalous diabatic heating is a main source for PV generation. The anomalous cooling over the subtropical western Pacific produces a local negative PV center at 500 hPa. The anomalous heating over the YHR basin generates a local positive PV center. The above south–north dipolar structure of PV anomaly along with the climatological southerly flow leads to northward advection of negative PV. These two processes are conducive to the WPSH’s westward extension. The vertical advection process is unfavorable to the westward extension but contributes to the eastward retreat of the WPSH.     

Anomalous Western Pacific Subtropical High during Late Summer in Weak La Nia Years: Contrast between 1981 and 2013

Both 1981 and 2013 were weak La Niña years with a similar sea surface temperature (SST) anomaly in the tropical Pacific, yet the western Pacific subtropical high (WPSH) during August exhibited an opposite anomaly in the two years. A comparison indicates that, in the absence of a strong SST anomaly in the tropics, the cold advection from Eurasian high latitudes and the convection of the western Pacific warm pool play important roles in influencing the strength and position of the WPSH in August. In August 1981, the spatial pattern of 500 hPa geopotential height was characterized by a meridional circulation with a strong ridge in the Ural Mountains and a deep trough in Siberia, which provided favorable conditions for cold air invading into the lower latitudes. Accordingly, the geopotential height to the north of the WPSH was reduced by the cold advection anomaly from high latitudes, resulting in an eastward retreat of the WPSH. Moreover, an anomalous cyclonic circulation in the subtropical western Pacific, excited by enhanced warm pool convection, also contributed to the eastward retreat of the WPSH. By contrast, the influence from high latitudes was relatively weak in August 2013 due to a zonal circulation pattern over Eurasia, and the anomalous anticyclonic circulation induced by suppressed warm pool convection also facilitated the westward extension of the WPSH. Therefore, the combined effects of the high latitude and tropical circulations may contribute a persistent anomaly of the WPSH in late summer, despite the tropical SST anomaly being weak.     

CHARACTERISTICS OF SEASONAL VARIATION OF RAINFALL OVER THE TIBETAN PLATEAU DURING SUMMER 1998 AND ITS IMPACT ON EAST ASIAN WEATHER

The seasonal variation of rainy season over the Tibetan Plateau in summer 1998 is analyzed byusing daily observational rainfall data for Lhasa from 1955 to 1996,and rainfall data at 70 stationsfrom January to August of 1998 over the Tibetan Plateau (TP) and adjacent regions,as well asTBB data from May to August of 1998.The onset date of rainy season for Lhasa is climatologically6 June.Among the analyzed years,the earliest onset date is 6 May,while the latest may delay to2 July.The obvious inter-decadal variation can be found in the series of onset date.The onset dateof summer 1998 over middle TP (onset date of Lhasa) is 24 June,which is relatively later than thenormal case.The onset for rainy season of 1998 started over southeast and northeast parts of TP and thenpropagated westward and northward.The convection over east and west parts of TP shows thatthere is a quasi 12-15 day oscillation.In June,the convection over middle and lower reaches ofYangtze River is formed by the westward propagation of convection over subtropical westernPacific.while in July.it is formed by the eastward propagation of convection over TP.Besides,it is also found that there exists good negative and obvious advance and lagcorrelation between the convection over the middle and western TP and that over the subtropicalwestern Pacific and southern China.Therefore it can be inferred that a feedback zonal circulationwith a quasi two-three week oscillation exists between the ascending region of TP and descendingregion of subtropical western Pacific,i.e.the convection over TP may affect the subtropical highover western Pacific and vice versa.     

CHARACTERISTICS OF SEASONAL VARIATION OF RAINFALL OVER THE TIBETAN PLATEAU DURING SUMMER 1998 AND ITS IMPACT ON EAST ASIAN WEATHER*

The seasonal variation of rainy season over the Tibetan Plateau in summer 1998 is analyzed by using daily observational rainfall data for Lhasa from 1955 to 1996,and rainfall data at 70 stations from January to August of 1998 over the Tibetan Plateau (TP) and adjacent regions,as well as TBB data from May to August of 1998.The onset date of rainy season for Lhasa is climatologically 6 June.Among the analyzed years,the earliest onset date is 6 May,while the latest may delay to 2 July.The obvious inter-decadal variation can be found in the series of onset date.The onset date of summer 1998 over middle TP (onset date of Lhasa) is 24 June,which is relatively later than the normal case.The onset for rainy season of 1998 started over southeast and northeast parts of TP and then propagated westward and northward.The convection over east and west parts of TP shows that there is a quasi 12-15 day oscillation.In June,the convection over middle and lower reaches of Yangtze River is formed by the westward propagation of convection over subtropical western Pacific.while in July.it is formed by the eastward propagation of convection over TP.Besides,it is also found that there exists good negative and obvious advance and lag correlation between the convection over the middle and western TP and that over the subtropical western Pacific and southern China.Therefore it can be inferred that a feedback zonal circulation with a quasi two-three week oscillation exists between the ascending region of TP and descending region of subtropical western Pacific,i.e.the convection over TP may affect the subtropical high over western Pacific and vice versa.     

Interactions between the 30–60 day oscillation,the walker circulation and the convective activities in the tropical western pacific and their relations to the interannual oscillation

In this paper, interactions between the 30-60 day oscillation, the Walker circulation and the convective activities in the tropical western Pacific during the Northern Hemisphere summer are analyzed by using the observed data of wind fields and high-cloud amounts for the period from 1980 to 1989.The analyzed results show that the 30-60 day oscillation (hereafter called LFO) may be largely affected by the convective activities in the tropical western Pacific. The LFO in the tropical western Pacific during the strong convective activities around the Philippines stronger than those during the weak convective activities around the Philippines. Moreover, in the case of strong convective activities around the Philippines, the LFO in the tropical west-ern Pacific and tropical eastern Indian Ocean generally propagates westward, and it is intensified by the LFO with a westward propagating center of maximum oscillation from the east to 140oE. However, in the case of weak convective activities around the Philippines, the LFO gradually becomes stronger with a eastward propagating center of maximum oscillation from the eastern Indian Ocean to the tropical western Pacific.Corresponding to the 30-60 day oscillation, the Walker circulation is also in oscillation over the tropical Pacific and its circulation cell seems to shift gradually westward from the tropical western Pacific to the tropical eastern In-dian Ocean with strong convective activities around the Philippines. This may maintain the intensification of convective activities there. However, during the weak convective activities around the Philippines, the Walker circula-tion gradually moves eastward and an ascending flow may appear in the equatorial central Pacific. This may cause convective activities to be intensified over the equatorial central Pacific.The analyzed results also show that the LFO in the tropical western Pacific and East Asia may be associated with the interannual oscillation of the SST anomaly in the tropical western Pacific.     

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.     

南亚高压季节内变化与热带季节内振荡之间的关系

采用观测分析和数值试验等方法,分析夏季南亚高压与热带季节内振荡(ISO)之间的关系,并对两者之间的相互作用进行量化诊断,探讨其物理过程.主要结果表明:南亚高压ISO与热带ISO活动关系密切,当热带ISO处于印度洋位相(第1、2、3位相),则南亚高压东脊点位置偏西,当ISO处于太平洋位相(第5、6、7位相),则南亚高压东...     

1998和1999年西北太平洋热带气旋的异常特征及其大尺度条件

应用联合台风警报中心 (JTWC)的资料 ,研究了 1998和 1999年西北太平洋 (WNP)热带气旋 (TC)的活动 ,发现这两年具有较为相似的异常特征 :台风个数明显偏少 ,台风的生成源地显著偏西。对导致这种异常的大尺度条件场的分析表明 ,1998和 1999年的台风季季风槽、垂直风切变、海平面气压等因子的分布都不利于台风在WNP东部海域的生成 ,因此是导致这两年台风偏少和生成源地异常偏西的重要原因。其中 ,季风槽的异常偏西及在盛夏的异常偏北对TC的异常活动产生了主要影响。对低纬大气环流异常的进一步分析表明 ,WNP地区的环流异常是导致季风槽和垂直风切变场异常的主要原因 ,而 1999年异常环流的出现可能是由于低纬大气对印尼附近异常热源强迫的响应所致。由于该热源的存在 ,在其东侧 (WNP地区 )激发出东传的Kelvin波 ,而相应的异常风场则表现为低层盛行异常东风 ,而高层盛行异常西风 ,因此造成了WNP东部和西部海域垂直切变场的近乎相反的变化。同时 ,由于低层异常强的东风不利于季风西风的向东延伸 ,从而使季风槽明显偏西 ,未到达菲律宾以东的热带气旋频发区的位置。