用过程透雨量确定的东亚夏季风北边缘特征

利用1951—2006年全国715个站逐日降水资料及NCEP/NCAR逐日和月平均再分析资料, 以农作物生长角度为出发点, 采用过程透雨量 (20 mm) 标准确定4—10月出现6次及6次以上过程透雨量作为东亚夏季风区, 以北边缘历年波动范围确定夏季风边缘带, 根据连续透雨过程达到无旱标准来判断东亚夏季风的开始时间。主要分析了夏季风北边缘的年际、年代际变化特征和夏季风边缘带的变化范围以及夏季风边缘的推进过程和北边缘变化机制及其对我国降水的影响。结果表明:透雨标准较好地确定了边缘带位置, 夏季风北边缘呈现向南偏移的趋势, 边缘带范围有所扩大; 北边缘变化与偏南风强弱和水汽输送联系紧密, 并且对我国雨带的分布以及北方降水有一定影响, 北边缘偏北, 雨带偏北, 则华北降水偏多。

Determination on the North Boundary of Summer Monsoon in East Asian with Soaking Rainfall

The summer monsoon brings plentiful water vapor, which is important for vegetation's growth and people's subsistence. The relation between monsoon's northward advance and north boundary's location is consanguineous. There are many monsoon indexes, and northward advancing of summer monsoon has also been investigated a lot. The research method considering vegetation growth angles proves to be accordant with the monsoon's influences on China. Station data and grid data including the daily rainfall data of 715 stations of China from 1951 to 2006 are used to depict the summer monsoon's advancing process. Moisture transport is also investigated using NCEP/NCAR monthly mean and daily reanalysis data. First, the soaking rainfall index is defined to determine the East Asian summer monsoon area. It takes appearing six times and more soaking rainfall (20 mm) processes during April to October as the standard, then the boundary belt positions for summer monsoon are defined according to the range of six times soaking rainfall lines waving variance annually, and wind vector changes in the boundary belt. Analyzing the continual soaking rainfall processes, the time when periods of drought ends is defined as the start time for summer monsoon in East Asian. This start time can represent the summer monsoon's northward advance. Besides, the characteristics of annual and decade variance of East Asian summer monsoon's north boundary and the variance of boundary belt's scopes are analyzed. Furthermore, the advanced process of East Asian summer monsoon's north boundary and its influence to the rainfall in China are investigated. To seek the cause a-bout north boundary for summer monsoon waving unconventionally, it is important to analyze moisture transport which maybe one important gene. The results show that; the soaking rainfall standard ascertains boundary belt location for East Asian summer monsoon preferably, and it appears a tendency of southward moving and the scopes of boundary belt are enlarged. In brief, the location variance of East Asian summer monsoon's north boundary have a close correlation with south wind strength and moisture transport. It also has a certain influence to the rain band distribution of China as well as the precipitation in north of China, north boundary inclined north, also does the rain band, and the rainfall is relatively more in the north of China.