中国东部西太平洋副热带季风和降水的气候特征及成因

中国东部—西太平洋副热带季风和降水的气候特征及成因分析

1,2113

赵 平 周秀骥 陈隆勋 何金海

1. 中国气象科学研究院，北京，100081 2. 灾害天气国家重点实验室，北京，100081 3. 南京信息工程大学，南京，210044

摘 要

利用1981—2000年候平均NCEP/NCAR再分析资料和CMAP全球降水资料，分析了从中国东部大陆到西太平洋副热带地区季风和降水季节变化的特征及其与热带季风降水的关系，探讨了季风建立和加强的原因。夏季东亚—西太平洋盛行的西南风开始于江南和西太平洋副热带的春初，并向北扩展到中纬度，热带西南风范围向北扩展的迹象不明显。从冬到夏，中国西部和西太平洋副热带的表面加热季节变化可以使副热带对流层向西的温度梯度反转比热带早，使西南季风在副热带最早开始；从大气环流看，青藏高原东侧低压槽的加强和向东延伸，以及西太平洋副热带高压的加强和向西移动，都影响着副热带西南季风的开始和发展；初夏江南的南风向北扩展与副热带高压向北移动有关，随着高原东侧低压槽向南延伸，槽前的偏南风范围向南扩展。随着副热带季风建立和向北扩展，其最大风速中心前方的低层空气质量辐合和水汽辐合以及上升运动也加强和向北移动，导致降水加强和雨带向北移动。热带季风雨季开始晚，主要维持在热带而没有明显进入副热带，江淮梅雨不是由热带季风雨带直接向北移动而致，而是由春季江南雨带北移而致。在热带季风爆发前，副热带季风区水汽输送主要来自中南半岛北部和中国华南沿海，而在热带季风爆发后，水汽输送来自孟加拉湾和热带西太平洋。

关键词：中国东部，西太平洋，西南季风，降水，水汽

资助课题：财政部/科技部公益类行业专项(GYHY200706005)。

作者简介：赵平，研究方向：季风和气候。E-mail:zhaoping@cams.cma.gov.cn 2007-09-26收稿,2007-11-21改回. 中图法分类号 P462.2

Characteristics of subtropical monsoon and rainfall over eastern China and western

North Pacific and associated reasons.

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ZHAO Ping ZHOU Xiuji CHEN Longxun HE Jinhai

1. Chinese Academy of Meteorological Sciences, Beijing 100081, China 2. State Key Laboratory of Severe Weather, Beijing 100081, China

3. Nanjing University of Information Science and Technology, Nanjing 210044, China

Abstract

Using the NCAR/NCEP reanalysis data and the NOAA's Climate Prediction Center's merged analysis of precipitation (CMAP) during 1981-2000, we investigated the seasonal evolution of the southwesterly wind and associated precipitation over the eastern Chinathe subtropical western North Pacific area and its relationship with the tropical monsoon and rainfall, and analyzed reasons responsible for the onset and development of the wind. It was found that the persistent southwesterly wind appears over southern China and the subtropical western Pacific earliest in the early spring, and then expands southwards to the tropics and advances northwards to the midlatitudes. From winter to summer, the seasonal variation of surface heating over western China and the subtropical western Pacific may result in an earlier reversal of the westward tropospheric temperature gradient over the subtropics relative to

the tropics, which may contribute to the earliest beginning of the subtropical southwesterly wind. Additionally, the strengthening and eastward expanding of the trough near the eastern Tibetan Plateau as well as the strengthening and westward moving of the western Pacific subtropical high also exerts positive influence on the beginning and developing of the subtropical southwesterly wind. In the early summer, the northward expansion of the southwesterly wind over southern China is associated with a northward shift of the subtropical high, and the southward stretch of the southwesterly wind is associated with a southward stretch of the trough in the east side of the plateau. With the begining and northward expansion of the subtropical southwesterly wind (namely-southwest-monsoon), convergences of the low-level air and water vapor and associated upward motion in front of the strongest southwesterly wind core also strengthens and moves northwards, leading to an increase of rainfall intensity and a northward shift of the rain belt. Accordingly, the subtropical rainy season occurs earliest over southern China in spring, moves northward to the ChangjiangHuaihe River valley in early summer, and arrives at North China in mid summer. Compared to the subtropical rainy season, the tropical rainy season begins later and stays mainly over the tropics, not pronouncedly moving into the subtropics. Clearly, the meiyu rainfall over the ChangjiangHuaihe valley in early summer results from a northward shift of the spring rainy belt over southern China, instead of a northward shift of the tropical monsoon rainfall belt. Before the onset of the tropical monsoon, water vapor over the subtropical monsoon region comes mainly from the coasts of the northern Indochina Peninsula and southern China. After the onset, one branch of water vapor flow comes from the Bay of Bengal, entering into eastern China and the subtropical western Pacific via southwestern China and the South China Sea, and another branch comes from the tropical western North Pacific, moving northwestwards along the west edge of the western Pacific subtropical high and entering into the subtropics. Key words ：Eastern China， Western Pacific, Southwest monsoon, Precipitation, Water vapor

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