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1.
1990s年代际转型前后南海季风系统的气候季节内振荡(CISO)特征 总被引：1，自引：0，他引：1
利用多变量经验正交分解(MV-EOF)等方法,研究了在季节内振荡尺度上南海季风系统的时空分布特征。结果表明:南海夏季风的爆发时间在1993/1994年前后存在显著的年代际转型,由爆发偏晚转变成爆发偏早。第一模态反映了南海夏季风爆发时季风系统的时空特征,转型前后特征类似,降水场自赤道向北依次呈现干-湿-干交替分布的特征,南海中心为异常气旋。相应的大范围环流场主要反映了转型前的偏晚年,南海夏季风槽位置偏南,转型后的偏早年,南海夏季风槽位置偏北。第二模态体现了南海季风系统夏季的时空特征,转型前后共同特征表现为南海地区夏季北湿南干的南北偶极子降水分布及南海中心区的异常西风。相应的大范围环流场主要反映了南海季风活动与东亚季风呈现反位相的特点,且对流信号向北传播。转型前的偏晚年,季风活动受准双周振荡控制,对流信号由西北方向传入南海;转型后的偏早年,季风活动以30～60天振荡为主,对流信号由东南方向传播至南海。 相似文献
2.
3.
应用GMS TBB资料对2001年亚洲夏季风活动作了诊断分析，得到中南半岛和我国南海共经历了3次季风爆发过程，且强度都强于历史同期水平；揭示了印度—孟加拉湾、中南半岛以及我国南海3个季风区季风爆发与间歇的特征。分析了季风对华南及长江中下游地区三次（6月上旬至中旬初、6月下旬至7月上旬、8月末）暴雨过程的影响，指出季风爆发及其与北方南下冷空气的结合，是造成东南部地区出现大范围长时间强降水的必要条件，从而为该地区强降水过程预报提供某些重要线索。 相似文献
4.
利用南海季风试验分析场和NCAR向外长波辐射通量(OLR)资料研究了1998年孟加拉湾季风和南海季风爆发期间副热带环流的大尺度和天气尺度特征,探讨了孟加拉湾季风爆发与南海季风爆发之间的物理联系及孟加拉湾季风气旋的对流凝结潜热释放对副热带高压“撤出”南海的影响。结果表明,1998年5月爆发的东亚季风展现出典型的从孟加拉湾地区东传发展到南海地区的过程。随着孟加拉湾季风爆发和对流活动增强、北移,南海北部出现了低层西风和对流活动,领先于副热带高压在南海地区减弱和撤退。结果还显示南海北部地区的对流凝结加热有助于该地区经向温度梯度的反转,在热成风关系的制约下南海上空副热带高压脊面的垂直倾斜由冬季型转向夏季型,季风爆发。 相似文献
5.
伴随南海夏季风爆发的大尺度大气环流演变 总被引：39，自引：11，他引：39
主要基于美国NCEP和NCAR的再分析资料（1980～1996年），针对南海夏季风爆发日期进行合成分析，研究了伴随南海夏季风爆发的大尺度大气环流演变。其结果清楚地表明伴随南海夏季风爆发，南亚和东南亚地区的对流层低层风场、对流层高层位势高度场以及大气湿度场和垂直运动场都有极显著的变化。南亚和东南亚850 hPa上涡旋对的发展和活动以及500 hPa副高从南海地区的东撤对南海季风爆发起着重要作用。伴随南海夏季风的爆发，在孟加拉湾到南中国海一带整层湿度和500 hPa垂直上升运动都出现了极明显的增加。对流层高层和对流层低层环流演变的特征也清楚表明，南海夏季风爆发既是全球环流冬夏演变的一个部分，又有显著的区域性特征。本文还指出南海夏季风在北部比中部和南部早建立的结论依据不足，进而补充给出了亚洲季风爆发日期示意图。 相似文献
6.
利用2004年和1998年强弱南海夏季风年的逐日位势高度场资料,从能量传播的角度诊断分析了南海夏季风爆发期间的波包传播特征及其与季风爆发的联系.结果表明(1)孟加拉湾是南海季风爆发的关键区域.(2)南海季风爆发前,南海地区的波包值有明显的突变,可能体现了季风爆发的爆发性特征.(3)1998弱夏季风年波包值相对较小,传播较慢;2004强夏季风年波包值相对较大,传播迅速.(4)南海夏季风爆发前,对流层整层的波包值都随时间增加,爆发前一天低层和高层的波包值有相同的变化,夏季风爆发之后,低层波包值与高层的波包值有反相的变化. 相似文献
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南海地区降水的时空特征 总被引：33，自引：3，他引：30
文中利用美国 NCEP重分析资料中的 1 979～ 1 995年 1 7a逐旬的全球降水资料 ,采用小波分析方法分析了南海地区降水的多时间层次和多空间层次结构 ,研究了南海季风的爆发及时间演变 ,探讨了南海季风爆发的机制。结果表明 :( 1 )南海季风爆发于 5月中旬 ,季风爆发过程实际上是小范围 ( 32个经度 )降水向大范围 ( 64个经度 )降水调整的过程 ,一旦出现较强的大范围降水 ,并到达南海地区 ,就爆发了南海季风 ,调整完毕则是印度季风和东亚季风的相继爆发。( 2 )在 1 0°N以北的地区 ,季风最早发生在南海 ,然后逐渐西移到印度 ,达到印度季风最盛期后 ,迅速东撤。( 3)南海地区可分为 3个区域 :北部 ( 2 0～ 2 2°N)、中部 ( 1 0～ 2 0°N)和南部 ( 1 0°N以南 )。南海雨季主要发生在 1 0°N以北的北部和中部 ,北部雨季是平稳增强的单峰型 ,而中部雨季是突发性的 ,雨季内降水起伏较大。( 4 )南海季风区有很强的年变化 ,30～ 60 d和 2 0～30 d的变化也比较显著 ,还有 3个月左右的周期变化。除年振荡以外 ,各种周期振荡随时间变化较大 ,在雨季表现得最强烈。( 5)南海季风的爆发与 2 0～ 30 d和 30～ 60 d两种低频振荡有关。 相似文献
8.
南海季风试验与东亚夏季风 总被引：66，自引：14，他引：66
南海季风试验是一次国际性大气与海洋的联合试验 ,旨在更好地了解南海季风的爆发、维持与变化 ,以改进东亚和东南亚地区的季风预报。 1998年 5～ 8月进行的外场试验取得了圆满成功 ,获得了大量气象与海洋资料。不少国家对这些资料进行四维资料同化 ,并改进数值模拟和预报 ;同时也为东亚与南海地区季风的研究提供了必要的资料集。文中总结了中国科学家在这方面的主要研究成果 ,共包括 6个方面 :(1)南海夏季风的爆发过程与机理 ;(2 )南海季风爆发过程中对流与中尺度系统的发展及其与大尺度环流的相互作用 ;(3)低频振荡与遥相关作用 ;(4 )南海海 气通量的测量及其与季风活动的关系 ;(5 )夏季风时期南海海洋的热力结构、环流和中尺度涡旋及其与ENSO事件的关系 ;(6 )南海与东亚季风的数值模拟。 相似文献
9.
简要归纳了不同时期随着观测资料的更新对亚洲季风季节进程的若干认识。南海季风试验前,研究认识了东亚季风系统与南亚季风系统的区别。南海季风试验后,对季风进程有了更多的认识,江南副热带雨季开始于4月初,中印半岛热带雨季开始于4月底,南海热带雨季突然建立于5月中旬,都具有半年际的干湿转换。南海中部季风爆发后,亚洲季风在南亚、青藏高原东侧和东亚-太平洋地区全面爆发并由南向北推进。利用近年来高分辨率资料并考虑热带地区半岛陆海地形与热力的影响,认识到亚洲存在5个夏季季风槽与降水相联系的系统,它们分别是西南亚(阿拉伯海)夏季热带季风、南亚(孟加拉湾)夏季热带季风、东南亚(南海)夏季热带季风、西北太平洋夏季热带季风和东亚夏季副热带季风。 相似文献
10.
中南半岛与南海热力差异对南海季风爆发的影响 总被引：5，自引：1，他引：4
利用1958-1998年NCEP/NCAR再分析资料和1975-1998年OLR资料,分析了中南半岛与南海热力差异的季节和年际变化特征,以及这种热力差异对南海季风爆发的影响.结果表明,中南半岛与南海热力差异存在明显的季节变化,从第3候歼始,感热加热的作用使中南半岛地表温度高于南海并一直持续到第25候,之后,中南半岛与南海热力差异发生逆转,这种逆转是由于第22-23候出现在中南半岛的对流及降水造成中南半岛地表温度降低所致.进一步研究指出,中南半岛与南海热力差异的上述季节变化特征还表现出最著的年际差异,这种年际差异对南海季风的爆发有着重要影响.首先,上述热力差异的逆转是南海季风爆发的一个必要条件:1958-1998年,逆转时间均早于(或等于)南海季风爆发时间;其次,中南半岛地表温度高于南海的持续时间与南海季风爆发日期之间呈显著正相关,即中南半岛地表温度高于南海的时间越早、转为低于南海的时间越迟,则南海季风爆发越迟. 相似文献
11.
Cloud structure and evolution of Mesoscale Convective Systems(MCSs) retrieved from the Tropical Rainfall Measuring Mission Microwave Imager(TRMM TMI) and Precipitation Radar(PR) were investigated and compared with some pioneer studies based on soundings and models over the northern South China Sea(SCS).The impacts of Convective Available Potential Energy(CAPE) and environmental vertical wind shear on MCSs were also explored.The main features of MCSs over the SCS were captured well by both TRMM PR and TMI.However,the PR-retrieved surface rainfall in May was less than that in June,and the reverse for TMI.TRMM-retrieved rainfall amounts were generally consistent with those estimated from sounding and models.However,rainfall amounts from sounding-based and PR-based estimates were relatively higher than those retrieved from TRMM-TMI data.The Weather Research and Forecasting(WRF) modeling simulation underestimated the maximum rain rate by 22% compared to that derived from TRMM-PR,and underestimated mean rainfall by 10.4% compared to the TRMM-TMI estimate,and by 12.5% compared to the sounding-based estimate.The warm microphysical processes modeled from both the WRF and the Goddard Cumulus Ensemble(GCE) models were quite close to those based on TMI,but the ice water contents in the models were relatively less compared to that derived from TMI.The CAPE and wind shear induced by the monsoon circulation were found to play critical roles in maintaining and developing the intense convective clouds over SCS.The latent heating rate increased more than twofold during the monsoon period and provided favorable conditions for the upward transportation of energy from the ocean,giving rise to the possibility of inducing large-scale interactions. 相似文献
12.
1. Introduction China is located in the East Asian monsoon re- gion. Every year's weather and climate in this region is deeply affected by the monsoon activities. Es- pecially, during flooding season (May to September), the summer monsoon controls large-scale precipitation patterns, the movement of seasonal rain belt and oc- currence of drought/flood disasters. The Asian mon- soon can be divided into two systems (Tao and Chen, 1987). As a major component and its unique location, the South … 相似文献
13.
1. Introduction The strong convective weather is developed under the favorable large-scale circulations, which demon- strated the large-scale weather system's controlling ef- fect on strong convections. Once the convection is formed, it will produce the feedback effect on the large-scale environmental conditions by transporting momentum, heat and moisture upward, and influence or change the environmental wind, humidity, tem- perature, atmospheric stratification fields and so on, thus forming t… 相似文献
14.
A Study on the Mesoscale Convective Systems during the Summer Monsoon Onset over the South China Sea in 1998 Part Ⅱ: Effect of Mesoscale Convective Systems on Large-Scale Fields 
下载免费PDF全文
下载免费PDF全文 LIU Yanju DING Yihui 《Acta Meteorologica Sinica》2005,19(3):289-301
The apparent heat sources and apparent moisture sinks, and large-scale wind, temperature as well as the surface pressure fields during the summer monsoon onset over the northern South China Sea (SCS) in 1998 were diagnosed. The results suggested that there was a kind of positive feedback mechanism between large-scale circulations and mesoscale convective systems (MCSs). Before the monsoon onset, the largescale background provided favorable synoptic and dynamic conditions for the summer monsoon onset and the formation of mesoscale convective activities, whereas after the summer monsoon onset, occurrence of the persistent and extensive mesoscale convective activities produced obvious feedback effect on large-scale circulations. Because of the release of latent heating produced by enhanced convective activities, the intense atmospheric heating appeared over the northern SCS, which resulted in: (1) the meridional temperature gradient over the SCS reversed from upper-level to low-level and then the large-scale circulations were changed seasonally;(2) correspondingly, the surface pressure over the northern SCS deepened continually and formed a broad monsoon trough and the obvious pressure-fall areas, thus making the subtropical high move out of the SCS eventually;(3) with the development of the low pressure circulations in the middle and low troposphere, the MCSs further enhanced and extended southward, which was conducive to the SCS monsoon onset and maintenance over the middle and southern SCS;and (4) the deepening of monsoon trough facilitated the monsoon flow and moisture transport on its southern side, thus the monsoon onset reaching peak period. 相似文献
15.
通过对1998年南海季风爆发过程中大尺度风场、温度场、厚度场、地面气压场以及视热源与视水汽汇的演变分析研究了对流活动对大尺度场的作用,结果表明:大尺度环流与中尺度对流活动之间可能存在着一种正反馈机制。在季风爆发早期,大尺度背景与中尺度对流活动的关系主要表现为前者为季风爆发以及中尺度对流活动的发生提供有利的天气和动力条件;季风爆发后期持续的大范围中尺度对流活动反过来会对大尺度环流存在明显的反馈作用。由对流活动强烈发展产生的凝结潜热释放在南海北部造成了显著的大气加热,使对流层中上层出现一明显的加热中心,这导致:(1)南海上空经向温度梯度由高层向低层发生反向,形成北高南低的温度梯度,从而使大尺度环流发生季节性改变;(2)相应南海北部地面气压不断加深,形成宽广的季风槽和明显的减压区,促使副热带高压从南海地区最后撤离;(3)随着中低层低压环流的不断发展,对流系统和降水区进一步加强并向南扩展,有利于南海季风在南海中、南部地区爆发和维持;(4)季风槽的加深使其南侧的季风气流与水汽输送进一步加强,促使季风爆发过程达到盛期。 相似文献
16.
Yan Junyue 《大气科学进展》1997,14(2):277-287
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17.
This paper presents a study on the temporal and spatial variations of the precipitation over the area of the South China Sea (SCS) during the monsoon onset period. The data used are from the Tropical Rainfall Measuring Mission (TRMM) observations between April and June over the nine years from 1998 to 2006. This study focuses on the central and northern part of South China Sea (110-120°E, 10-20°N). Based on the observations, the 27th pentad is selected as the occurrence time of the SCS monsoon onset. The conclusions are as follows. (1) After the monsoon onset, the specific area, defined as the ratio of the number of pixels with certain type of precipitation to the number of total pixels, extends significantly for both convective and stratiform rain, with the latter having a larger magnitude. The specific rainfall, defined as the ratio of the amount of certain type of precipitation to the total amount of precipitation, decreases for convective rain and increases for stratiform rain. (2) Results also show significant increase in heavy rain and decrease in light rain after the monsoon onset. (3) Changes are also observed in the rainfall horizontal distributions over the SCS before and after the monsoon onset, manifested by the relocation of precipitation minima for both convective and stratiform rain. (4) After the monsoon onset, the variability in characteristics of precipitation vertical structure increases significantly, leading to more latent heat release and consequently deeper convection. Meanwhile, the bright-band altitude of stratiform precipitation is also elevated. 相似文献
18.
A Study on the Mesoscale Convective Systems during the Summer Monsoon Onset over the South China Sea in 1998 Part Ⅰ: Analysis of Large-Scale Fields for Occurrence and Development of the Mesoscale Convective Systems 下载免费PDF全文
下载免费PDF全文 LIU Yanju DING Yihui ZHAO Nan 《Acta Meteorologica Sinica》2005,19(3):275-288
The summer monsoon onset over the northern South China Sea (SCS) in May 16-20, 1998 was characterized by the abrupt onset of mesoscale convective activities and rapid increase of precipitation. The possible mechanism for formation of the mesoscale convective systems (MCSs) and related rain belts were revealed through discussing their forming physical conditions under the large-scale background: (1) The high pseudo-equivalent potential temperature and the convective instability in the lower troposphere, the low-level southwesterly confluence and the high-level divergence over South China and the northern SCS provided the favorable large-scale thermodynamic and dynamic conditions for development of MCSs. The southwesterly flow from the Bay of Bengal (BOB) interacted with that to the western flank of the subtropical high, which constituted the major moisture channels, thus bringing about deep wet layers and strong moisture convergence;(2) triggered by several cold troughs from high and mid latitudes, the convectively unstable energy was released and the convective activities over the northern SCS broke out abruptly;(3)analysis of retrieved precipitation based on the dual-Doppler radar during South China Sea Monsoon Experiment (SCSMEX) indicated that active convection influenced by the monsoon trough and corresponding wind shear line organized and formed continually some mesoscale convective rainbelts. During May 15-19,about 12 precipitation processes with 6-12-hour life span or more were observed;and (4) under the favorable synoptic conditions, establishment of the monsoon trough and shear line in the low levels, as well as production and development of mesoscale low vortex were all necessary conditions for the formation and maintenance of MCSs. 相似文献
19.
以2004年5月初及5月中旬我国华南等地两次较大暴雨过程为例, 分析了西南季风潮与我国前汛期降水的关系。初步结论指出:西南季风潮的爆发与我国华南降水, 特别是大暴雨的形成关系极为密切, 而这次西南季风潮的爆发又与来自南半球的越赤道气流直接有关。同时指出, 这次西南季风潮的爆发主要与来自85°~95°E孟加拉湾地区所在经度的越赤道气流有关, 它们是印度洋“半球间宏观系统”的一个部分。而南海季风潮仅仅是西南季风潮的一种特例, 在这两次重大降水过程中没有南海季风潮的爆发和影响。 相似文献
20.
南海西南季风爆发的气候特征 总被引：56，自引：9，他引：56
利用多年的海洋船舶、岛屿站和沿岸站观测记录及卫星观测的高反射云（ＨＲＣ）资料，揭示南海西南季风爆发和建立时期的环流特征及要素变化。在南海，西南季风爆发的平均时间为５月中旬，北部略早（５月１２日），南部略迟（５月２０日），但年际差别可达一个月左右。伴随着西南季风的爆发，南海云量和降水量增多，对流加强，但海区之间具有很大的不均匀性。西南季风建立以后，强对流区稳定于南海中部，季风雨带没有明显的跳跃现象。西南季风爆发之前，南海表层温度迅速升高，其开始时间较季风爆发约提前一个月，海面水温的升高为季风爆发提供了热量和水汽条件。４—５月，南海海面热交换分量（海面吸收的太阳辐射、潜热输送等）发生明显的改变，特别是潜热交换和蒸发量明显增大，它可能是西南季风首先在南海爆发的原因之一。 相似文献