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1.
Atmospheric Circulation Characteristics Associated with the Onset of Asian Summer Monsoon 总被引：1，自引：0，他引：1
The onset of the Asian summer monsoon has been a focus in the monsoon study for many years. In this paper, we study the variability and predictability of the Asian summer monsoon onset and demonstrate that this onset is associated with specific atmospheric circulation characteristics. The outbreak of the Asian summer monsoon is found to occur first over the southwestern part of the South China Sea (SCS) and the Malay Peninsula region, and the monsoon onset is closely related to intra-seasonal oscillations in the lower atmosphere. These intra-seasonal oscillations consist of two low-frequency vortex pairs, one located to the east of the Philippines and the other over the tropical eastern Indian Ocean. Prior to the Asian summer monsoon onset, a strong low-frequency westerly emerges over the equatorial Indian Ocean and the low-frequency vortex pair develops symmetrically along the equator. The formation and evolution of these low-frequency vortices are important and serve as a good indicator for the Asian summer monsoon onset. The relationship between the northward jumps of the westerly jet over East Asia and the Asian summer monsoon onset over SCS is investigated. It is shown that the northward jump of the westerly jet occurs twice during the transition from winter to summer and these jumps are closely related to the summer monsoon development. The first northward jump (from 25–28N to around 30N) occurs on 8 May on average, about 7 days ahead of the summer monsoon onset over the SCS. It is found that the reverse of meridional temperature gradient in the upper-middle troposphere (500–200 hPa) and the enhancement and northward movement of the subtropical jet in the Southern Hemispheric subtropics are responsible for the first northward jump of the westerly jet. 相似文献
2.
赤道涡旋与南海夏季风爆发 总被引：10，自引：0，他引：10
文中应用１９７９－１９９５年共１７ａ的８５０ｈＰａ风场资料和ＮＯＡＡ卫星的ＯＬＲ资料，分析了南海夏季风爆发的特征。证实南海夏季风爆发，落后于同纬度的中南半岛和菲律宾岛屿地区。但在南海的东部和西部，季风爆发几乎是同时的，具有某种驻波的特征。文中还证实，大多数年份的４，５月间在１０５°Ｅ附近有赤道涡旋形成，这个涡旋引导它上游的赤道西风或南半球西风进入南海南部，为南海的季风爆发创造有利条件。这种涡旋不活跃的年份，季风爆发往往偏晚。它们之间可能存在某种联系。４月中旬，这个涡旋的形成和１０５°Ｅ越赤道气流的初步建立是同时的。进入５月份，这支越赤道气流逐渐加强。南海夏季风的活动与这支气流可能关系密切。如果称位于１０５°Ｅ附近的赤道涡旋为东亚的爆发涡旋，它显然与南亚季风的情况有较大差别。南亚的爆发涡旋与季风爆发的关系是直接的，而在东亚，则是间接的，这也说明了东亚季风比南亚季风更具有复杂性。 相似文献
3.
使用1998年南海季风试验期问高质量资料和NCEP／NCAR40年再分析资料分析了南海季风建立前后的大尺度环流特征和要素的突变及爆发过程。发现南亚高压迅速从菲律宾以东移到中南半岛北部，孟加拉湾槽加深加强，赤道印度洋西风加强并向东向北迅速扩展和传播，以及伴随的中低纬相互作用和西太平洋副高连续东撤是南海夏季风建立的大尺度特征。与此同时，亚洲低纬地区的南北温差和纬向风切变也发生相应的突变。数值试验结果表明，印度半岛地形的陆面加热作用在其东侧激发的气旋性环流对于孟加拉湾槽的加强有重要作用，并进而有利于南海夏季风先于印度夏季风爆发。 相似文献
4.
关于南海夏季风建立的大尺度特征及其机制的讨论 总被引：28，自引：3，他引：25
使用1998年南海季风试验期间高质量资料和NCEP/NCAR40年再分析资料分析了南海季风建立前后的大尺度环流特征和要素的突变及爆发过程。发现南亚高压迅速地从菲律宾以东移到中南半岛北部,印缅槽加强,赤道印度洋西风加强并向东向北迅速扩展和传播,以及相伴随的中低纬相互作用和西太平洋副高连续东撤是南海夏季风建立的大尺度特征,与此同时,亚洲低纬地区的南北温差和纬向风切变也发生相应的突变。数值实验结果指出,印度半岛地形的陆面加热作用在其东侧激发的气旋性环流对于印缅槽的加强有重要作用,并进而有利于南海夏季风先于印度夏季风爆发。 相似文献
5.
6.
利用17年（1979～1995）的NMC全球格点分析资料及从NOAA极轨卫星观测的地球向外长波辐射（OLR）资料,研究了南海夏季风暴发的年际变化特征。用本文的定义标准,南海季风从1979年到1995年间暴发的平均日期是5月第4候。南海夏季风暴发前后,南海周围地区对夏季风暴发的直接影响来自南海上游70°～90°E的赤道西风的加强和北抬东伸,同时索马里越赤道气流的加强和阿拉伯海高压在海上消失通过影响赤道西风也间接影响到南海。其中阿拉伯海反气旋的消失可能是南海夏季风暴发的一个重要信号。南海夏季风暴发的年际变化较 相似文献
7.
Low-Frequency Vortex Pair over the Tropical Eastern Indian Ocean and the South China Sea Summer Monsoon Onset 
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下载免费PDF全文 In this paper,the relationship between a pair of low-frequency vortexes over the equatorial Indian Ocean and the South China Sea(SCS) summer monsoon onset is studied based on a multi-year(1980-2003) analysis.A pair of vortexes symmetric about the equator is an important feature prior to the SCS summer monsoon onset.A composite analysis shows that the life cycle of the pair of vortexes is closely associated with the SCS summer monsoon onset.The westerly between the twin cyclones is an important factor to the SCS summer monsoon onset process. 相似文献
8.
南海-西太平洋春季对流10~30天振荡强度对南海夏季风爆发早晚的影响 总被引：1，自引：3，他引：1
采用NCEP再分析资料,揭示了南海-西太平洋春季对流存在显著的10~30天振荡周期。在年际尺度上,南海-西太平洋春季对流10~30天振荡强度（简称SCSWP_SISO）与南海夏季风爆发日期存在显著的负相关关系。当春季菲律宾和西太平洋海温偏高、赤道太平洋中部及以东地区海温偏低时,索马里、110 °E越赤道气流会加强,南海-西太平洋偏西风加强,产生异常气旋性环流,垂直上升运动增强,水汽异常偏多,东西风切变增强,有利于SCSWP_SISO增强。而SCSWP_SISO增强时,有由南往北、自西向东的异常气旋传播,从而减弱低层副热带高压使之较早撤出南海,南海夏季风得以较早爆发。反之亦然。在不同的年代际背景下,SCSWP_SISO经历了偏弱、较弱和偏强的变化,但影响其变化的因子并不完全一致。在第一阶段（1958—1976年）,主导因子是南海-西太平洋冷的海温与异常下沉运动、异常减弱的水汽-对流条件。在第二阶段（1977—1993年）,主导因子为中东太平洋异常偏冷的海温以及局地异常减弱的风场垂直切变。在第三阶段（1994—2011年）,主导因子为热带海温的整体偏暖、风场垂直切变的增强以及水汽-对流的加强。但随着SCSWP_SISO的年代际增强,其与南海夏季风爆发日期的相关关系却呈现下降趋势。 相似文献
9.
Summary Interannual variations of the summer monsoon onset over the South China Sea (SCS) have been studied using data from over
seventeen years (1979–1995) of NMC global analysis and of Outgoing Longwave Radiation (OLR) observed with NOAA polar-orbitting
satellites. It was found that the summer monsoon onset in the SCS occurs abruptly with a sudden change of zonal wind direction
from easterly to westerly and an exploding development of deep convection in the whole SCS region in the middle of May.
Based on the criteria defined in this paper for the SCS summer monsoon onset, the average onset date over the SCS from 1979
to 1995 is around the fourth pentad of May. The airflow and general circulation over the SCS changes dramatically after the
onset. The ridge of the subtropical high in the western Pacific in the lower troposphere weakens and retreats eastward from
the SCS region with an establishment of westerly winds over the whole region. During the SCS monsoon onset, the most direct
impact in the vicinity of the SCS are the equatorial westerlies in the Bay of Bengal through their eastward extension and
northward movement. An indirect influence on the SCS onset is also caused by the enhancement of the Somali cross-equatorial
flow and the vanishing Arabian High over the sea; the latter may be a signal for the SCS onset.
There are quite significant interannual variations in the SCS onset. In the years of a delayed onset, the most profound feature
is that the easterly winds stay longer in the SCS than on average. Deep convection activities are suppressed. The direct cause
is the abnormal existence of the western Pacific subtropical high over the SCS region. Moreover, compared to the average,
the equatorial westerlies in the Bay of Bengal are also weaker in the years of a delayed onset. No significant changes for
the cross-equatorial flow at 105 °E are observed for these years. It has also been found that the interannual variations of
the SCS onset are closely related with the ENSO events. In the years of a delay, the Walker circulation is weaker, and the
sea surface temperature (SST) anomalies in the western Pacific are negative.
Received April 14, 1997 Revised July 11, 1997 相似文献
10.
索马里跨赤道气流对南海夏季风爆发的重要作用 总被引：33，自引：8，他引：25
通过分析NCEP/NCAR多年再分析资料,清楚地揭露了南海夏季风爆发与索马里跨赤道南风气流建立之间的重要关系.对应南海夏季风爆发,总是已先期在赤道印度洋地区有西风加强和索马里跨赤道南风气流的建立;而且,若南海夏季风爆发偏早(晚),赤道印度洋地区西风的加强和索马里跨赤道南风气流的建立也偏早(晚).可以认为,索马里跨赤道南风气流的稳定建立是南海夏季风爆发的重要物理机制之一,它的建立导致赤道印度洋地区西风的持续加强和向东扩展,并最终在南海地区形成西南气流. 相似文献
11.
南海夏季风活动的年际和年代际特征 总被引：40，自引：1，他引：40
利用NCEP风场资料和候平均向外长波辐射（OLR）资料分析了南海区域低层风场与对流活动的关系,在此基础上,采用南海中南部的纬向风平均值来定义南海夏季风的爆发,确定了长序列（1949～1998）的南海夏季风爆发日期和强度指数,并研究南海夏季风活动的年际和年代际变化特征。结果表明：南海夏季风爆发日期和强度指数呈显著的反相关;50年来的气候趋势是,爆发日期逐渐偏晚,强度指数逐渐减弱。二者都存在着明显的年际和年代际变化,它们在不同阶段上的波动是各种时间尺度振荡叠加的结果,而年代际尺度具有非常重要的作用。东印度洋海温异常在南海夏季风爆发前后,均与南海夏季风强度指数呈显著的反相关。东太平洋海温异常在南海夏季风爆发之前,与强度指数反相关,而爆发之后,与强度指数正相关。这体现了南海夏季风活动与ENSO事件的密切关系。 相似文献
12.
南海西南季风爆发日期及其影响因子 总被引：40，自引：6，他引：34
利用1950～1999年NCEP全球格点日平均资料,在总结南海西南季风爆发前后850 hPa大气环流特征的基础上,提出了一个较为客观的确定南海西南季风爆发日期的大气环流方法.在与1980～1991年其他多种指标确定的爆发日期比较后,作者认为该大气环流方法所确定的爆发日期基本合理,并给出了1950～1999年各年南海西南季风爆发的日期.通过合成对比分析和相关分析发现,前期热带太平洋地区海温异常分布是影响南海西南季风爆发早晚的重要因素.菲律宾以东洋面海温偏高,赤道太平洋中部偏东地区海温偏低,可以使低层西太平洋副高减弱、高层中东太平洋洋中槽加深,印度洋热带地区偏西风偏强,印度洋-太平洋热带地区Walker环流偏强,为热带对流在孟加拉湾-南海地区发展提供了有利的环境.在孟加拉湾南部偏西气流的作用下,南海地区对流活动较为容易发展起来,低层较弱的西太平洋副热带高压也容易较早地撤出南海上空,使得南海西南季风较早爆发.反之亦然. 相似文献
13.
The Summer Monsoon Onset over the Tropical Eastern Indian Ocean： The Earliest Onset Process of the Asian Summer Monsoon 总被引：9，自引：2，他引：9
The onset process of the tropical eastern Indian Ocean (TEIO) summer monsoon (TEIOSM) and its relationship with the cross-equatorial flows are investigated via climatological analysis. Climatologically, results indicate that the earliest onset process of the Asian summer monsoon occurs over the TEIO at pentad 22 (April 15–20). Unlike the abrupt onset of the South China Sea (SCS) summer monsoon, the TEIOSM onset process displays a stepwise advance. Moreover, a close relationship between the TEIOSM development and the northward push of the cross-equatorial flows over 80–90E is revealed. A difference vorticity center, together with the counterpart over the southern Indian Ocean, constitutes a pair of difference cyclonic vortices, which strengthens the southwesterly wind over the TEIO and the northerly wind to the west of the Indian Peninsula from the end of March to late May. Therefore, the occurrence of the southwesterly wind over the TEIO is earlier than its counterpart over the tropical western Indian Ocean, and the cross-equatorial flows emerge firstly over the TEIO rather than over the Somali area. The former increases in intensity during its northward propagation, which provides a precondition for the TEIOSM onset and its northward advance. 相似文献
14.
孟加拉湾风暴(简称孟湾风暴)和孟加拉湾夏季风(简称孟湾夏季风)是初夏活动于孟加拉湾(简称孟湾)地区的两个重要环流系统, 对中国西南地区的天气气候和亚洲夏季风的季节进程有十分重要的影响。为了进一步认识两个环流系统活动异常的特征及其影响因子, 从气候角度出发初步分析了两者活动的相互联系及其影响的前兆信号因子和环流变化特征。结果表明两者有一定的联系, 孟湾夏季风爆发偏早时孟湾风暴活动时间偏早且活动频数偏多, 反之, 风暴活动时间偏晚且活动频数偏少。初夏两个系统的异常活动与前期环流变化密切联系, 由于孟湾夏季风爆发早晚与大尺度环流的季节转换有关, 爆发早晚其前期的环流变化有十分显著的差异, 对流层低层赤道印度洋异常西风(东风)和孟湾异常气旋(反气旋)活动, 以及对流层高层东亚持续稳定的异常反气旋(气旋)是孟湾夏季风爆发偏早(偏晚)的重要前兆信号特征, 而这些异常环流变化为孟湾风暴的生成发展提供了极为有利(不利)的环流背景条件。进一步分析发现, 前期冬季1月赤道太平洋地区西暖东冷的海温异常分布对后期2-4月孟湾区域异常气旋环流的生成发展有十分重要的影响, 其中赤道西北太平洋异常暖海温的变化有利于在其西北侧南海南部激发异常气旋环流, 而赤道太平洋西暖东冷的海温差异对赤道印度洋异常西风的加强及其南北两侧气旋对的发展西移有重要作用, 是影响孟湾区域气旋性环流发生发展的重要外强迫因子。 相似文献
15.
ABRUPT CHANGE IN ELEMENTS AROUND 1998 SCS SUMMER MONSOON ESTABLISHMENT WITH ANALYSIS OF ITS CHARACTERISTIC PROCESS 总被引：1，自引：0，他引：1 下载免费PDF全文
下载免费PDF全文 The latest dataset from the SCS(South China Sea)Monsoon Experiment is used to investigatethe features of abrupt change in some meteorological elements before,during and after the summermonsoon's establishment in 1998 and explore its onset characteristic process.We have arrived at apreliminary conclusion that the 1998 Asian summer monsoon is established first in the SCS as earlyas May 23,which is representative of the earliest indicator of the conversion from a winter into asummer monsoon situation in Asia;the continued retreat eastward of the western Pacificsubtropical high from the SCS region has direct effect on the SCS summer monsoon establishmentbecause the withdrawal favors the release of unstable energy,responsible for the sudden onset ofthe monsoon.Our tentative investigation indicates that the eastward extension of the westerly andrainfall band from the equatorial Indian Ocean into the Indo-China Peninsula and the southwardspreading of an active South-China stationary front,acting as the interaction between mid and lowlatitude systems,are likely to be the characteristic events contributing to the subtropical high'seastward retreating and the summer monsoon's onset over the SCS. 相似文献
16.
R. H. Kripalani J.-H. Oh J.-H. Kang S. S. Sabade A. Kulkarni 《Theoretical and Applied Climatology》2005,82(1-2):81-94
Summary The influence of the Indian Ocean Zonal Mode on the extreme summer monsoon rainfall over East Asia (China, Korea, Japan) has been investigated applying simple statistical techniques of correlation and composite analysis. While the observed rainfall data are used as a measure of rainfall activity, the NCEP-NCAR Reanalysis data are used to examine the circulation features associated with the extreme monsoon phases and the dynamics of the zonal mode – monsoon variability connections. The data used covers the period 1960 to 2000.The equatorial Indian Ocean is dominated by westerly winds blowing towards Indonesia. However, during the positive phase of the zonal mode, an anomalous, intensified easterly flow prevails, consistent with the positive (negative) sea surface temperature anomalies over the western (southeastern) equatorial Indian Ocean. This positive phase of the zonal mode enhances summer monsoon activity over China, but suppresses the monsoon activity over the Korea-Japan sector, 3 to 4 seasons later. The relationship is more consistent and stronger over the Korea-Japan region than over China.The Indian Ocean influences the monsoon variability over East Asia via the northern hemisphere mid-latitudes or via the eastern Indian Ocean/west Pacific route. The monsoon-desert mechanism induces strong subsidence northwest of India due to the anomalous convection over the Indian Ocean region associated with the positive phase of the zonal mode. This induces a zonal wave pattern over the mid-latitudes of Asia propagating eastwards and displacing the north Pacific subtropical high over East Asia. The warming over the eastern Indian Ocean/west Pacific inhibits the westward extension of the north Pacific sub-tropical high. The location and shape of this high plays a dominant role in the monsoon variability over East Asia. The memory for delayed impact, three to four seasons later, could be carried by the surface boundary conditions of Eurasian snow cover via the northern channel or the equatorial SSTs near the Indonesian Through Flow via the southern channel. 相似文献
17.
东亚副热带西风急流位置变化与亚洲夏季风爆发的关系 总被引：1，自引：0，他引：1
利用1961～2000年的NCEP/NCAR候平均再分析资料,初步探讨了季节转换期间东亚副热带西风急流南北和东西向位置变化与亚洲季风爆发之间的联系。结果表明,亚洲夏季风爆发伴随着东亚副热带西风急流轴线的北跳和急流中心西移,急流轴北跳至35°N以北的青藏高原上空,南支西风急流消失,亚洲季风环流形势建立。南海季风爆发早年,低纬的东风向北推进的时间早,到达的纬度偏北,中纬的西风急流强度偏弱,季风爆发晚年则相反。同时,南海夏季风爆发早年,青藏高原上空急流核出现较早,西太平洋上空急流核减弱较快,急流中心“西移”较早。而在南海夏季风爆发晚年,西太平洋上空的急流核减弱较迟,青藏高原上空急流核形成偏晚,急流中心“西移”较迟。此外,急流中心东西向位置和强度变化与江淮流域梅雨的开始和结束也有密切关系。 相似文献
18.
ABRUPT CHANGE IN ELEMENTS AROUND 1998 SCS SUMMER MONSOON ESTABLISHMENT WITH ANALYSIS OF ITS CHARACTERISTIC PROCESS* 下载免费PDF全文
下载免费PDF全文 The latest dataset from the SCS(South China Sea) Monsoon Experiment is used to investigate the features of abrupt change in some meteorological elements before,during and after the summer monsoon's establishment in 1998 and explore its onset characteristic process.We have arrived at a preliminary conclusion that the 1998 Asian summer monsoon is established first in the SCS as early as May 23,which is representative of the earliest indicator of the conversion from a winter into a summer monsoon situation in Asia;the continued retreat eastward of the western Pacific subtropical high from the SCS region has direct effect on the SCS summer monsoon establishment because the withdrawal favors the release of unstable energy,responsible for the sudden onset of the monsoon.Our tentative investigation indicates that the eastward extension of the westerly and rainfall band from the equatorial Indian Ocean into the Indo-China Peninsula and the southward spreading of an active South-China stationary front,acting as the interaction between mid and low latitude systems,are likely to be the characteristic events contributing to the subtropical high's eastward retreating and the summer monsoon's onset over the SCS. 相似文献
19.
Katherine H. Straub George N. Kiladis Paul E. Ciesielski 《Dynamics of Atmospheres and Oceans》2006,42(1-4):216
The observed sequence of events leading to the onset of the summer monsoon in the South China Sea (SCS) is described, with a particular focus on conditions during the South China Sea monsoon experiment (SCSMEX) in May–June 1998. During SCSMEX, SCS monsoon onset occurred within the context of a multitude of scale interactions within the ocean-atmosphere system on intraseasonal time scales. Results from the 1998 SCSMEX case study illustrate that SCS monsoon onset is preceded by the development of an eastward-propagating Madden-Julian Oscillation (MJO) in the Indian Ocean, as suggested by previous authors, and the subsequent emanation of a convectively coupled Kelvin wave into the Pacific. Remarkably similar results are obtained in an independent composite of 25 years of data. Since both the MJO and Kelvin waves generate westerly surface winds in their wake, it is suggested that these waves may accelerate or trigger the monsoon onset process in the southern SCS. A detailed analysis of the Kelvin wave that propagated through the SCS during SCSMEX shows that it was responsible for a large portion of the surface wind shift leading to monsoon onset in 1998. Finally, easterly wind anomalies in the eastern Pacific associated with the Indian Ocean MJO event during the SCSMEX period are shown to result in the sudden demise of the 1997–1998 El Niño event. 相似文献
20.
关于亚洲夏季风爆发及北半球季节突变的物理机理的诊断分析:Ⅰ季风爆发的阶段性特征 总被引：7，自引：1，他引：6
该工作将亚洲季风区作为一个复杂的海-陆-气耦合系统,来深入考察季风区海-气、陆-气相互作用的基本事实和物理过程,探讨它们在决定亚洲季风爆发及北半球行星尺度大气环流的季节突变的物理机理。本文是系列文章的第一篇,着重研究亚洲夏季风爆发的区域性和阶段性特征,以及过渡季节热带、副热带地区海-气、陆-气相互作用的基本事实,初步分析了它们之间的联系。研究表明,热带季风对流于4月底到5月初越过赤道进入北半球,首先出现在孟加拉湾东部-中南半岛西南部地区,然后于5月中旬和6月上旬末分别出现在南海和印度半岛地区,呈阶段性爆发的特征。季风对流在孟加拉湾东部-中南半岛西南部地区爆发阶段,在大气环流变化和对流活动中心位置出现区别于南海季风和印度季风爆发的特征。通过对地表感热通量和海表潜热通量的分析,表明热带海洋上海表感热通量甚小于海表潜热通量,南海季风爆发时期印度洋上海表潜热通量显著增大,印度季风爆发后海表潜热通量的高值中心在孟加拉湾和阿拉伯海上建立起来。印度洋上低层增强的过赤道气流引起的强烈的海-气相互作用导致海表水汽的大量蒸发,并通过其输送作用,为季风对流的爆发提供了充足的水汽来源。过渡季节在副热带地区(沿27.5～37.5°N纬带上), 青藏高原和西太平洋上地(海)表感热通量和潜热通量均有迅速的季节变化性, 但趋势相反。当青藏高原上地表感热通量和潜热通量呈阶段性的显著加大, 西太平洋上海表感热通量和潜热通量迅速减小。这种大陆和海洋对大气加热的显著的季节化的差异, 影响着大气环流的季节转变。 相似文献