南印度洋海温偶极子型振荡及其气候影响

印度洋海表温度（Sea Surface Temperature,简称SST）的方差分析和相关分析表明南印度洋也存在一个海温偶极子型振荡,并定义了一个南印度洋海表温度异常偶极子指数.夏、秋季（南半球冬、春）的南印度洋偶极子指数与后期热带500hPa和100hPa高度场异常有显著而持续的相关,在冬、春达到最大,并可以持续到次年夏、秋.前期夏、秋季节的南印度洋偶极模对次年我国大陆东部夏季降水异常有显著的影响,对应偶极子正位相,次年夏季印度洋、南海（东亚）夏季风偏弱;副高加强且南撤、西伸,南亚高压偏强且位置偏东,易形成我国长江流域降水偏多,华南降水偏少;负位相年反之.后期冬季西太平洋暖池是联系南印度洋偶极子与次年我国夏季降水异常关系的一条重要途径.南印度洋偶极子表现出了明显的独立于ENSO（El Nio-Southern Oscillation,简称ENSO）的特征.     

夏季西北太平洋大气环流异常及其与热带印度洋—太平洋海温变化的关系

本文分析了夏季西北太平洋大气环流异常特征及其与海温变化的关系,发现夏季西北太平洋异常反气旋/气旋(WNPAC/WNPC)是西北太平洋地区对流层中低层存在的重要大气环流异常现象,与东亚—西北太平洋低纬度至高纬度的经向PJ波列及欧亚中高纬度东西纬向波列的变化有关,通过与中高纬度环流变化的联系,对东亚及欧亚中高纬度气候有重要影响.夏季WNPAC/WNPC与热带海温变化的关系存在明显的不对称性,显著的WNPAC一般出现在El Niño衰减年夏季,与前期El Niño成熟年冬季的赤道东太平洋暖海温异常和El Niño衰减年春夏季印度洋海盆尺度的暖海温异常有明显的正相关关系,进一步表明了WNPAC在El Niño事件影响夏季气候中的重要桥梁作用;而夏季显著的WNPC与前期和同期热带海温变化的关系存在明显的不确定性,主要与夏季热带印度洋和赤道中东太平洋之间东暖西冷的热力差异异常引起的孟加拉湾—赤道西太平洋西风异常有关.进一步分析WNPAC/WNPC与海温变化关系不对称的可能原因,发现El Niño和La Niña衰减年夏季热带印度洋和太平洋海温变化所引起的印—太之间海温(热力)差异的一致性特征可能是导致WNPAC/WNPC与海温变化关系不对称的主要原因.     

Teleconnection between the Indian summer monsoon onset and the Meiyu over the Yangtze River Valley

Based on the Indian and Chinese precipitation data and the NCEP-NCAR reanalysis circulation data, the relationship between the Indian summer monsoon (ISM) onset and the Meiyu over the Yangtze River Valley has been discussed by the methods of correlation analysis and composite analysis. The results show that the date of ISM onset over Kerala in the southwestern coast of the Indian Peninsula is about two weeks earlier than the beginning of the Meiyu over the Yangtze River Valley. After the outbreak of ISM, the teleconnection mode sets up from the western coast of India via the Bay of Bengal (BOB) to the Yangtze River Valley and southern Japan. It is different both in time and space from the telecon- nection mode which is from the northwest of India via the Tibetan Plateau to northern China. The for- mer mode is defined as the "south" teleconnection of the Asian summer monsoon, forming in the pe- riod of ISM onset; while the latter mode is called the "north" teleconnection, mainly occurring in the Asian monsoon culminant period. During the process of the "south" teleconnection’s formation, the Asian monsoon circulation has experienced a series of important changes: ISM onset, the northward movement of the south Asia high (SAH), the onset vortex occurrence, the eastward extension of the stronger tropical westerly belt, and the northeastward jump of the western Pacific subtropical high (WPSH), etc. Consequently, since ISM sets up over Kerala, the whole Asian continent is covered by the upper SAH after about two weeks, while in the mid- and lower troposphere, a strong wind belt forms from the Arabian Sea via the southern India, BOB and the South China Sea (SCS), then along the western flank of WPSH, to the Yangtze River Valley and southern Japan. With the northward moving of the subtropical jet streams, the upper westerly jet stream and the low level jet have been coupled ver- tically over east Asia, while the Yangtze River Valley happens to locate in the ascending motion area between the upper jet stream and the low level jet, i.e. right of the entrance of the upper jet stream and left of the low level jet. Such a structure of the vertical circulation can trigger the Meiyu onset over the Yangtze River Valley.     

Structure of the Indian Ocean Meridional Overturning Circulation and its relationship with the zonal wind stress

We studied the structure of the Indian Ocean(IO)Meridional Overturning Circulation(MOC)by applying a nonlinear inertia theory and analyzed the coupled relationship between zonal wind stress and MOC anomalies.Our results show that the inertia theory can represent the main characteristics of the IO MOC:the subtropical cell(STC)and cross-equator cell(CEC).The stream function in equatorial and northern IO changes a sign from winter to summer.The anomalies of the zonal wind stress and stream function can be decomposed into summer monsoon mode,winter monsoon mode,and abnormal mode by using the singular vector decomposition(SVD)analysis.The first two modes correlate with the transport through 20°S and equator simultaneously whereas the relationship obscures between the third mode and transports across 20°S and equator,showing the complex air-sea interaction process.The transport experiences multi-time scale variability according to the continuous power spectrum analysis,with major periods in inter-annual and decadal scale.     

Intraseasonal Variability of the Summer Monsoon over the North Indian Ocean as Revealed by the BOBMEX and ARMEX Field Programs

During the summer monsoon season over India a range of intraseasonal modulations of the monsoon rains occur due to genesis of weather disturbances over the Bay of Bengal (BOB) and the east Arabian Sea. The amplitudes of the fluctuations in the surface state of the ocean (sea-surface temperature and salinity) and atmosphere are quite large due to these monsoonal modulations on the intraseasonal scale as shown by the data collected during the field programs under Bay of Bengal Monsoon Experiment (BOBMEX) and Arabian Sea Monsoon Experiments (ARMEX). The focus of BOBMEX was to understand the role of ocean-atmospheric processes in organizing convection over the BOB on intra-seasonal scale. ARMEX-I was aimed at understanding the coupled processes in the development of deep convection off the West Coast of India. ARMEX-II was focused on the formation of the mini-warm pool across the southeast Arabian Sea in April-May and its role in the abrupt onset of the monsoon along the Southwest Coast of India and its further progress along the West Coast of India. The paper attempts to integrate the results of the observational studies and brings out an important finding that atmospheric instability is prominently responsible for convective organization whereas the upper ocean parameters regulate the episodes of the intraseasonal oscillations.     

南太平洋和北太平洋年代际振荡与华北盛夏降水的关系及可能物理机制

利用降水、大气环流和海表温度等多种再分析资料和偏相关方法,研究了1951—2007年南太平洋年代际振荡（SPDO）和北太平洋年代际振荡（即PDO,本文称为NPDO）分别与华北盛夏（7—8月）降水在年代际时间尺度上的关系及其可能物理机制.结果表明：在去除SPDO和NPDO的相关性之前,它们与华北盛夏降水的关系均偏弱;但在去除两者相关性之后,SPDO（NPDO）与华北盛夏降水存在显著正（负）相关关系.去除两者相关性之后,当SPDO处于正位相时,热带西北太平洋海温异常显著偏暖,这将在对流层中下层从热带西太平洋—东亚沿岸激发出"气旋-反气旋-气旋"的负位相东亚—太平洋型遥相关（EAP）波列,该波列导致东亚夏季风异常增强,有利于低纬地区水汽输送至华北地区,从而使得华北盛夏降水异常偏多,反之,当SPDO处于负位相时,华北盛夏降水异常将偏少;对NPDO来说,当其处于正位相时,不仅热带西北太平洋异常显著偏冷,而且印度洋大部分海温异常显著偏暖,在两者共同作用下,对流层中下层从热带西太平洋—东亚沿岸出现"反气旋-气旋-反气旋"的正位相EAP波列,这将引起东亚夏季风异常减弱,不利于低纬地区水汽输送至华北地区,华北盛夏降水异常因此减少,反之,当NPDO处于负位相时,华北盛夏降水异常将偏多.