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1.
以2018年盛夏一次典型的热带气旋群发(Multiple Tropical Cyclogenesis,MTC)事件为例,分析了多尺度环流(包括大尺度环流、季节内振荡及热带波动等)对MTC的影响,并探讨了MTC群发期和间歇期整层大气垂直扰动场的差异。结果表明:1)2018年盛夏西北太平洋经历了一次持续时间长达16 d有8个TC相继生成的MTC群发期和紧接着长达19 d仅1个TC生成的MTC间歇期;2)MTC群发期越赤道气流增强,季风槽加强东伸,南海和西北太平洋上空低层辐合高层辐散的环流配置有利于TC生成;3)夏季东亚-西北太平洋季节内振荡北传对MTC次季节变化具有显著的调制作用,MTC群发期(间歇期)南海和西北太平洋正好处于一次较强的季节内振荡(Intraeasonal Oscillation,ISO)北传湿(干)位相上;4)群发期内8个TC的生成皆与热带波动有关,其中5个同时受两种热带波动的影响,热带波动通过改变局地热动力状况为TC生成提供触发条件;5)多尺度环流的共同影响最终导致MTC群发期和间歇期在温压扰动场配置、垂直运动扰动和比湿扰动的垂直结构特征上表现出显著的差异,扰动分析法的应用为MTC生成的延伸期预报提供了一个新的思路。 相似文献
2.
利用中国气象局热带气旋（TC）资料、NCEP/NCAR 再分析资料和美国 NOAA 向外长波辐射（OLR）等资料,分析了2010年西北太平洋（WNP）及南海（SCS）热带气旋活动异常的可能成因,讨论了同期大气环流配置和海温外强迫对TC生成和登陆的动力和热力条件的影响。结果表明,2010年生成TC频数明显偏少,生成源地显著偏西,而登陆TC频数与常年持平。导致7～10月TC频数明显偏少的大尺度环境场特征为：副热带高压较常年异常偏强、西伸脊点偏西,季风槽位置异常偏西,弱垂直风切变带位置也较常年偏西且范围偏小,南亚高压异常偏强,贝加尔湖附近对流层低高层均为反气旋距平环流,这些关键环流因子的特征和配置都不利于 TC 在WNP的东部生成。影响TC活动的外强迫场特征为：2010年热带太平洋经历了El Ni?o事件于春末夏初消亡、La Ni?a事件于7月形成的转换;7～10月,WNP海表温度维持正距平,140°E以东为负距平且对流活动受到抑制;暖池次表层海温异常偏暖,对应上空850 hPa为东风距平,有利于季风槽偏西和TC在WNP的西北侧海域生成。WNP海表温度和暖池次表层海温的特征是2010年TC生成频数偏少、生成源地异常偏西的重要外强迫信号。有利于7～10月热带气旋西行和登陆的500 hPa风场特征为：北太平洋为反气旋环流距平,其南侧为东风异常,该东风异常南缘可到25°N,并向西扩展至中国大陆地区;南海和西北太平洋地区15°N以南的低纬也为东风异常;在这样的风场分布型下,TC容易受偏东气流引导西行并登陆我国沿海地区。这是2010年生成TC偏少但登陆TC并不少的重要环流条件。 相似文献
3.
利用ERA-Interim再分析资料分析了夏秋季西北太平洋季风槽的气候特征以及季节和年际变化特征及其对西北太平洋热带气旋和台风(TCs)生成大尺度环境因子的影响。研究结果表明了西北太平洋季风槽有很明显的季节变化,在6~7月,季风槽和强对流活动区在5°N~15°N的南海和西北太平洋西侧上空,并逐渐东伸;到了8~9月,季风槽和强对流活动区向北移动、并向东扩展,一般位于10°N~20°N的南海和西北太平洋西侧、中部上空,有的年份可东伸到西北太平洋东侧,强度加强;到了10~11月,季风槽迅速减弱,并成为涡旋,强对流活动区也向南移和向西收缩。同时,研究还表明了西北太平洋季风槽有明显的年际变化。在季风槽强的年份,季风槽和强对流活动区可以从南海经西北太平洋西侧和中部东伸到西北太平洋的东侧上空;而在季风槽弱的年份,季风槽和强对流活动区主要位于南海和西北太平洋西侧和中部上空,季风槽强度的年际变化对它的季节变化也有重要影响。此外,研究还表明了随着季风槽的季节和年际变化,西北太平洋TCs生成的大尺度环境因子分布也发生很明显的变化。 相似文献
4.
The relationship between the tropical intra-seasonal oscillation (ISO) and tropical cyclones (TCs) activities over the South China Sea (SCS) is investigated by utilizing the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) global reanalysis data and tropical cyclone best-track data from 1949 to 2009. The main conclusions are: (1) A new ISO index is designed to describe the tropical ISO activity over the SCS, which can simply express ISO for SCS. After examining the applicability of the index constructed by the Climate Prediction Center (CPC), we find that the convection spatial scale reflected by this index is too large to characterize the small-scale SCS and fails to divide the TCs activities over the SCS into active and inactive categories. Consequently, the CPC index can’t replace the function of the new ISO index; (2) The eastward spread process of tropical ISO is divided into eight phases using the new ISO index, the phase variation of which corresponds well with the TCs activities over the SCS. TCs generation and landing are significantly reduced during inactive period (phase 4-6) relative to that during active period (phase 7-3); (3) The composite analyses indicate distinct TCs activities over the SCS, which is consistent with the concomitant propagation of the ISO convective activity. During ISO active period, the weather situations are favorable for TCs development over the SCS, e.g., strong convection, cyclonic shear and weak subtropical high, and vice versa; (4) The condensation heating centers, strong convection and water vapor flux divergence are well collocated with each other during ISO active period. In addition, the vertical profile of condensation heat indicates strong ascending motion and middle-level heating over the SCS during active period, and vice versa. Thus, the eastward propagation of tropical ISO is capable to modulate TCs activities by affecting the heating configuration over the SCS. 相似文献
5.
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 总被引：12，自引：5，他引：12
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。 相似文献
6.
南海-西北太平洋地区大气准双周振荡对TC生成的调节作用 总被引：3，自引：1，他引：2
通过对南海-西北太平洋地区大气10～20 d准双周振荡(QBWO)不同位相的划分(A～D),研究了QBWO对南海-西北太平洋海域热带气旋(TC)生成的调节作用。将TC分为强热带风暴及以下级别(TS)和台风及以上级别(TY),并将QBWO分为干湿位相,发现南海海域生成的TS(TY)在干湿位相的比与西北太平洋海域生成的TS(TY)在干湿位相的比相等,这表明QBWO对TS(TY)生成的调节作用在南海和西太平洋地区可能相同。从A位相到C位相,南海和西北太平洋地区TC的生成频数均逐渐增多,D位相时期,TC生成最少,多数TC发生在QBWO的对流活动湿位相,少数TC发生在干位相。南海-西北太平洋海域TC的生成受到QBWO的明显调制。从位相A到位相C,低频对流和低频风场逐渐向西北方向移动,低频对流强度持续加强,低频风场逐渐由异常西风-东风-西风转为异常东风-西风-东风配置,西北太平洋地区季风槽加强,使得TC生成频数逐渐增多。此外,在QBWO活跃位相,非绝热加热增强和纬向风垂直切变减弱也有利于TC的生成。 相似文献
7.
Modulation of Western North Pacific Tropical Cyclone Genesis by
Intraseasonal Oscillation of the ITCZ: A Statistical Analysis 总被引：1，自引：0，他引：1
The present study investigates modulation of western North Pacific(WNP) tropical cyclone(TC) genesis in relation to different phases of the intraseasonal oscillation(ISO) of ITCZ convection during May to October in the period 1979-2008.The phases of the ITCZ ISO were determined based on 30-80-day filtered OLR anomalies averaged over the region(5-20 N,120-150 E).The number of TCs during the active phases was nearly three times more than during the inactive phases.The active(inactive) phases of ISO were characterized by low-level cyclonic(anticyclonic) circulation anomalies,higher(lower) midlevel relative humidity anomalies,and larger(smaller) vertical gradient anomalies of relative vorticity associated with enhanced(weakened) ITCZ convection anomalies.During the active phases,TCs tended to form in the center of the ITCZ region.Barotropic conversion from the low-level mean flow is suggested to be the major energy source for TC formation.The energy conversion mainly depended on the zonal and meridional gradients of the zonal flow during the active phases.However,barotropic conversion weakened greatly during the inactive phases.The relationship between the meridional gradient of absolute vorticity and low-level zonal flow indicates that the sign of the absolute vorticity gradient tends to be reversed during the two phases,whereas the same sign between zonal flow and the absolute vorticity gradient is more easily satisfied in the active phases.Thus,the barotropic instability of low-level zonal flow might be an important mechanism for TC formation over the WNP during the active phases of ISO. 相似文献
8.
应用NOAA气候预测中心提供的热带大气季节内振荡(MJO)客观业务指数及中国气象局上海台风研究所提供的西北太平洋热带气旋(TC)最佳路径资料集,定量统计榆验了MJO对夏季西北太平洋TC活动的调制作用.结果表明:MJO对TC的生成、强度、路径和登陆活动都有显著的调节作用.当高空辐合中心位于120°E～160°E(MJO位相3～5)时,西北太平洋TC生成偏少,且生成位置偏北;而当高空辐合中心位于10°W～70°E(MJO位相8～10)时,西北太平洋TC生成偏多,且生成位置偏南;随着TC强度加强,能达到显著调节作用的MJO位相逐渐减少,当高空辐合辐散中心位于70°E(MJO位相10)时,对TC强度调制最显著.在路径调节方面,MJO位相1～4和10时,TC活跃于菲律宾以东的西北太平洋上,主要路径为西北偏北行,可能登陆华东、华北;而位相5～8时,TC主要活跃在菲律宾附近及以西到南海,以偏西行路径为主,可能登陆华南.MJO对登陆华南TC也有显著影响.该定量统计检验结果可为TC活动季节内预测提供依据. 相似文献
9.
西北太平洋与南海热带气旋活动季节变化的差异及可能原因 总被引：1，自引：0，他引：1
利用1945~2011年美国联合台风预警中心(JTWC)西北太平洋热带气旋资料,研究了南海(5°N~25°N,110°E~120°E)与西北太平洋(5°N~25°N,120°E~180°)热带气旋生成位置、生成频数、强度和持续时间的季节变化差异及其成因。从热带气旋路径穿越经度带频数的角度,探讨了ENSO对气旋活动年际变化的影响。结果表明,南海热带气旋活动显著地受季风调控。在南海冬季风作用下,1~4月热带气旋生成于10°N以南且频数较少、强度较弱,这主要是低层气旋式相对涡度和弱东风切变区偏南造成的。相反,受夏季风影响,6~9月是热带气旋生成最多、最频繁的季节,大都生成于南海北部17°N附近。在5月(10月)的季节转换期,生成位置大幅度北进(南撤)且生成频数显著增加(减少),取决于风速垂直切变及中层的相对湿度的急剧转变。11、12月两海域热带气旋生成于10°N以南主要归因于其上空中层大气相对湿度较北部偏大。在西北太平洋,热带气旋生成的季节变化没有南海显著,只在7月有一次明显的变化,7~10月是热带气旋活动的"盛期"。在强度上,西北太平洋大部分区域全年均为弱东风切变,因此热带气旋以台风为主且持续时间长;但南海多为热带风暴。ENSO事件使得不同季节热带气旋生成区域和气旋路径地理位置发生显著变化。在El Nio事件期间,穿越南海所在经度带路径频数为负距平,而西北太平洋经度带为正距平;在La Nia事件期间,情况相反。 相似文献
10.
Interannual variability of landfalling tropical cyclones(TCs) in China during 1960-2010 is investigated.By using the method of partial least squares regression(PLS-regression),canonical ENSO and ENSO Modoki are identified to be the factors that contribute to the interannual variability of landfalling TCs.El Ni o Modoki years are associated with a greater-than-average frequency of landfalling TCs in China,but reversed in canonical El Ni o years.Significant difference in genesis locations of landfalling TCs in China for the two kinds of El Ni o phases occurs dominantly in the northern tropical western North Pacific(WNP).The patterns of low-level circulation anomalies and outgoing longwave radiation(OLR) anomalies associated with landfalling TC genesis with different types of El Ni o phases are examined.During canonical El Ni o years,a broad zonal band of positive OLR anomalies dominates the tropical WNP,while the circulation anomalies exhibit a meridionally symmetrical dipole pattern with an anticyclonic anomaly in the subtropics and a cyclonic anomaly near the tropics.In El Ni o Modoki years,a vast region of negative OLR anomalies,roughly to the south of 25°N with a strong large-scale cyclonic anomaly over the tropical WNP,provides a more favorable condition for landfalling TC genesis compared to its counterpart during canonical El Ni o years.For more landfalling TCs formed in the northern tropical WNP in El Ni o Modoki years,there are more TCs making landfall on the northern coast of China in El Ni o Modoki years than in canonical El Ni o years.The number of landfalling TCs is slightly above normal in canonical La Ni a years.Enhanced convection is found in the South China Sea(SCS) and the west of the tropical WNP,which results in landfalling TCs forming more westward in canonical La Ni a years.During La Ni a Modoki years,the landfalling TC frequency are below normal,owing to an unfavorable condition for TC genesis persisting in a broad zonal band from 5°N to 25°N.Since the western North Pacific subtropical high(WNPSH) in La Ni a Modoki years is located in the westernmost region,TCs mainly make landfall on the south coast of China. 相似文献
11.
The influence of intraseasonal oscillation (ISO) on TC genesis over the northwestern Pacific is studied through comparing analyses of the more and less TC years from 1979 to 2006. It is indicated that the ISO strongly affects the TC genesis. In the years for more TC genesis, the ISO is weak and propagates insignificantly in the area to the west of the Philippines, but the ISO is strong in the area to the east of the Philippines and propagates significantly northwestward. In this situation, the Walker cell shifts gradually westward from the tropical western Pacific to the tropical eastern Indian Ocean. Convergent winds appear in the lower atmosphere while divergent winds in the upper atmosphere, suggesting the presence of enhanced ascending flow over the 140-160°E region and a favorable condition for TC genesis. Moreover, in the years for less TC genesis, the ISO gradually becomes stronger in the area to the west of the Philippines and significant eastward propagation prevails from the eastern Indian Ocean to the area around 120°E; the ISO is weak in the area to the east of the Philippines. During these years, the Walker circulation gradually moved eastward, with convergent winds in the upper troposphere and divergent winds in the lower troposphere. Sinking motion was significant, unfavorable for the TC genesis over the Northwestern Pacific. 相似文献
12.
GFDL_RegCM对21世纪西北太平洋热带气旋活动的情景预估 总被引：1，自引：0，他引：1
首先评估了GFDL模式对西北太平洋热带气旋(TC)环境热力及动力因子的模拟性能,再利用夏威夷大学国际太平洋研究中心高分辨率区域气候模式( IPRC-RegCM),进行降尺度研究西北太平洋TC活动特征,在此基础上预估21世纪全球变暖背景下(A1B)西北太平洋TC活动的主要特点.结果显示,在西北太平洋TC活动区,GFDL控制试验的海平面温度(SST)比ERSST偏低.与NCEP/NCAR再分析资料相比,GFDL模拟的1980-1999年大尺度环流平均场表现为:副高脊线平均位置近乎一致,西伸脊点偏东,强度偏弱,面积偏小;季风槽槽线的范围偏小,强度偏弱;水平风垂直切变值在南海及菲律宾群岛海域偏小,而在160°E～170°W的20°N以南偏强.与NCEP/NCAR强迫的模拟结果相比,GFDL强迫得到的TC源地频数在南海偏少,菲律宾群岛以东海域偏多,两者的季节及年际变化特征相似.路径频数在南海北部和我国华南沿岸显著偏多.AlB情景下,西北太平洋TC生成数目将增加一倍,生成源地偏北且同时向东部洋而扩展,路径频数增多主要发生在20°N以北的中东部洋面上,移经西北太平洋西部的TC频数减少,由此影响我国的TC将减少.TC频数的季节分布发生较大变化,最多的月份在10月.TC平均强度增强,最大强度在10月增加最多,这与10月SST的增加和环境风切变的减小均为最大值有密切的关系. 相似文献
13.
孟加拉湾西南季风与南海热带季风季节内振荡特征的比较 总被引：4，自引：2，他引：2
采用美国国家环境预报中心的向外长波辐射和风场资料及日本气象厅的降水资料,用30-60d滤波后的夏季风指数在孟加拉湾和南海的区域平均值分别代表孟加拉湾西南季风和南海热带季风季节内振荡,对两支季风的季节内振荡特征进行比较分析,发现孟加拉湾西南季风的季节内振荡和南海热带季风的季节内振荡在夏季风期间(5-10月)都有约3次半的波动.夏季风期间,在阿拉伯海-西太平洋纬带上,夏季风的季节内振荡有4次从阿拉伯海的东传和3次从西太平洋的西传,其中7月后东传可直达西太平洋.孟加拉湾和南海在夏季风期间都有4次季节内振荡的经向传播,但孟加拉湾在约15°N以南为季节内振荡从热带东印度洋的北传,在约15°N以北则为副热带季风季节内振荡的南传;而在南海则是4次季节内振荡从热带的北传.在以孟加拉湾西南季风季节内振荡和南海热带季风季节内振荡分别划分的6个位相中,都存在1-3位相和4-6位相中低频对流、环流形势相反的特征,这是由热带东印度洋季节内振荡的东传和北传所致.热带印度洋季节内振荡沿西南-东北向经过约14d传到孟加拉湾,激发了孟加拉湾西南季风季节内振荡的东传,经过约6d到达南海,激发了南海热带季风季节内振荡的北传,经过约25d到达华南,形成热带印度洋季节内振荡向华南的经纬向接力传播(45d).孟加拉湾西南季风季节内振荡所影响的降水主要是在20°N以南的热带雨带随低频对流的东移而东移;而南海热带季风季节内振荡所影响的降水除了这种热带雨带随低频对流的东移外,还有在20°N以北的东亚副热带地区存在雨带随南海低频对流的北移而北移. 相似文献
14.
The influence of the interannual variation of cross-equatorial flow(CEF) on tropical cyclogenesis over the western North Pacific(WNP) is examined in this paper by using the tropical cyclone(TC) best track data from the Joint Typhoon Warning Center and the JRA-25 reanalysis dataset. The results showed that the number of TCs forming to the east of 140°E over the southeastern part of the western North Pacific(WNP) is in highly positive correlation with the variation of the CEF near 125° E and 150° E, i.e., the number of tropical cyclogeneses increases when the cross-equatorial flows are strong. Composite analyses showed that during the years of strong CEF, the variations of OLR, vertical wind shear between 200-850 h Pa, 850 h Pa relative vorticity and 200 h Pa divergence are favorable for tropical cyclogenesis to the east of 140°E over the tropical WNP, and vice versa. Moreover, it is also discussed from the view of barotropic energy conversion that during the years of strong CEF, an eastward-extended monsoon trough leads to the rapid growth of eddy kinetic energy over the eastern part of WNP, which is favorable for tropical cyclogenesis;but during the years of weak CEF, the monsoon trough is located westward in the western part of the WNP, consistent with the growth area of eddy kinetic energy. As a result, there are fewer TC geneses over the eastern part of WNP.Besides, the abrupt strengthening of a close-by CEF 2-4 days before tropical cyclogenesis may be the one of its triggers. 相似文献
15.
印度洋海盆增暖及ENSO对西北太平洋热带气旋活动的影响 总被引：2，自引：1，他引：1
本文主要分析1950～2010年间印度洋海盆增暖和西北太平洋热带气旋(TC)活动的关系, 并与ENSO对西北太平洋TC活动的影响相比较, 结果表明:印度洋海盆异常增暖与西北太平洋地区总TC生成年频数尤其是弱TC相关较好, 印度洋海盆异常增暖, 西北太平洋地区为异常的反气旋, 对流抑制, 降水偏少, 不利于TC的生成, 反之亦然。而ENSO对西北太平洋热带气旋的影响, 主要体现在对强TC的年生成频数的影响, El Ni?o 发展年, 季风槽加深东伸, TC生成位置偏东, 由于TC在海洋上的生命史较长, TC的平均强度偏强, 因而强TC年生成频数偏多;La Ni?a发展年, 季风槽较浅, TC生成位置偏西, TC的平均强度偏弱, 强TC年生成频数偏少。但是ENSO指数与强TC年频数的相关有着年代际的变化, 在1950～1969年和1990～2009年间, ENSO指数和强TC年频数相关很好, 分别为0.532和0.687, 而在1970～1989这二十年间, 两者相关很弱, 只有0.081。 相似文献
16.
IMPACT OF TROPICAL INTRASEASONAL OSCILLATION ON THE TRACKS OF TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC 总被引：1，自引：1，他引：0
In this work,an index of tropical 20-90 d oscillation(intra-seasonal oscillation;ISO)in the western North Pacific(WNP)was determined via the combined empirical orthogonal function(EOF)method using daily outgoing longwave radiation(OLR)field data from the National Oceanic and Atmospheric Administration(NOAA),daily wind field data(at 850 hPa)from the European Centre for Medium-Range Weather Forecasts(ECMWF)and referencing the Madden-Julian oscillation(MJO)index proposed by Wheeler and Hendon.An in-depth investigation was conducted to examine the impact of the ISO on changes in tropical cyclone(TC)tracks in the WNP during different ISO phases.The research results indicate that during the easterly phase of the ISO,under the impact of the northeastern airflow of anti-cyclonic ISO circulation,the easterly airflow south of the western Pacific subtropical high is relatively weak,and TCs generated in the subtropical high tend to change their tracks east of 140°E;during the westerly phase,there is a relatively high probability that TCs change their tracks west of 140°E.This work also analyzed the ISO flow field situation in cases of typhoons and determined that the track of a tropical cyclone will experience a sudden right turn when the center of the ISO cyclonic(anti-cyclonic)circulation coincides with that of the cyclone. 相似文献
17.
根据热带西太平洋（１３０°－１６０°Ｅ,１０°－２０°Ｎ）上空对流的年际变化,对表面温度、向外长波幅射、８５０ ｈＰａ纬向风进行了合成分析。合成分析结果表明,热带西太平洋上空的弱（强）对流对应着前冬和春季厄尔尼诺（拉尼娜）型的海温异常。与以前的研究结果进行了比较,说明上述海温异常的时空分布也与热带西太平洋和南海季风的爆发早晚相关联。合成分析结果还表明,热带西太平洋上空的弱（强）对流对应着从热带西太平洋向西伸展到盂加拉湾的东风（西风）异常。数值模拟也得到类似的结果。此外,在对流弱（强）的夏季,热带西太平洋上空的对流和南海低层纬向风均表现出弱（强）的季节演变特征。 相似文献
18.
Distinct quasi-biweekly features of the subtropical East Asian monsoon during early and late summers 总被引：2，自引：0，他引：2
Jing Yang Qing Bao Bin Wang Dao-Yi Gong Haozhe He Miao-Ni Gao 《Climate Dynamics》2014,42(5-6):1469-1486
Using Global Precipitation Climatology Project daily rainfall and ERA interim reanalysis data, we investigate the distinct characteristic of quasi-biweekly variation (QBV: 12–20 days) over East Asia (EA) during early (June 10–July 20) and late (July 21–August 31) summer. The QBV maximum variance is found over the core region of EA (30°–40°N, 110°–130°E), which includes eastern China (lower reaches of the Yellow, Huaihe, and Yangtze rivers) and the Korean Peninsula. At both its peak wet and dry phases, QBV over the core region has a baroclinic structure, but with different spatial distributions, different lower-level prevalent wind anomalies, and different upper-level major circulation anomalies in the two subseasons. Meanwhile, the two subseasons have different propagating tracks prior to reaching the peak phase, and different precursors associated with the local genesis of QBV. Furthermore, during the transition from the peak dry to peak wet phase of QBV, the major monsoon circulations have different behaviors that tropical monsoon trough extends eastward in early summer but retreats westward in late summer and the South Asia high (SAH) and western North Pacific (WNP) subtropical high move toward (away from) each other in early (late) summer. The abrupt change of mean state in mid to late July, which includes the northward migration of westerly jet, SAH and WNP, and the weakening and broken of westerly jet, is considered the root cause of the change in behavior of QBV. Finally, we indicate that the tropical monsoon trough and midlatitude westerly jet are possible sources of QBV over subtropical EA in both subseasons and provide useful guidance for 2–3 week predictions over EA. 相似文献
19.
The climatological summer monsoon onset displays a distinct step wise northeastward movement over the South China Sea and
the western North Pacific (WNP) (110°–160°E, 10°–20°N). Monsoon rain commences over the South China Sea-Philippines region
in mid-May, extends abruptly to the southwestern Philippine Sea in early to mid-June, and finally penetrates to the northeastern
part of the domain around mid-July. In association, three abrupt changes are identified in the atmospheric circulation. Specifically,
the WNP subtropical high displays a sudden eastward retreat or quick northward displacement and the monsoon trough pushes
abruptly eastward or northeastward at the onset of the three stages. The step wise movement of the onset results from the
slow northeastward seasonal evolution of large-scale circulation and the phase-locked intraseasonal oscillation (ISO). The
seasonal evolution establishes a large-scale background for the development of convection and the ISO triggers deep convection.
The ISO over the WNP has a dominant period of about 20–30 days. This determines up the time interval between the consecutive
stages of the monsoon onset. From the atmospheric perspective, the seasonal sea surface temperature (SST) change in the WNP
plays a critical role in the northeastward advance of the onset. The seasonal northeastward march of the warmest SST tongue
(SST exceeding 29.5 °C) favors the northeastward movement of the monsoon trough and the high convective instability region.
The seasonal SST change, in turn, is affected by the monsoon through cloud-radiation and wind-evaporation feedbacks.
Received: 19 October 1999 / Accepted: 5 June 2000 相似文献
20.
热带印度洋MJO活动对孟加拉湾西南夏季风季节内振荡的影响 总被引：1，自引：0，他引：1
通过对1979—2008年热带太平洋30—60 d振荡(Madden-Julian Oscillation,MJO)指数、美国国家环境预报中心再分析资料和日本气象厅降水资料的分析,发现热带东印度洋MJO强度和传播状况影响孟加拉湾西南夏季风季节内振荡及相关低频环流、对流和降水分布。当热带东印度洋MJO在春末夏初较活跃时,孟加拉湾西南季风季节内振荡活动在4—8月比其不活跃时提前约20 d(约1/2个周期),其对于孟加拉湾西南季风季节内振荡的影响可持续整个季风期,使西南季风的季节内振荡不仅酝酿期和活跃期提前发生,季风期有所延长,季节内振荡也更强。西南季风季节内振荡具有明显的北传和东传特征,北传沿孟加拉湾通道从赤道向副热带推进,而东传则沿10°—20°N从孟加拉湾向东传至南海地区。春末夏初时热带东印度洋MJO的异常状况,正是通过对西南季风季节内振荡东传和北传的影响,进而对孟加拉湾西南季风季节内振荡在季风期的酝酿、维持和活跃产生作用,这种作用同时体现在强度和时间上。孟加拉湾西南夏季风季节内振荡强度与热带东印度洋MJO在4月21日—5月5日的活动呈现显著负相关,当热带东印度洋MJO在春末夏初较活跃时,孟加拉湾西南夏季风季节内振荡的强度较大,在5—8月经历3次季节内振荡波动,低频对流场和环流场在1—3位相(孟加拉湾西南夏季风季节内振荡为正位相)和4—6位相(负位相)时呈反位相特征,这是由MJO低频对流的东传及在孟加拉湾和南海这两个通道上的北传引起的。从印度半岛到菲律宾群岛的降水在1—3位相和4—6位相上分别为正异常和负异常,其中,在第2位相(孟加拉湾西南季风季节内振荡波峰)和第5位相(孟加拉湾西南季风季节内振荡波谷)时分别为降水最大正异常和最大负异常。反之,在热带印度洋MJO在春末夏初不活跃年时,孟加拉湾西南夏季风季节内振荡活动较弱,强度偏弱且振荡也不规律。 相似文献