华西秋雨起止与秋冬季节大气环流转换  

Onset-withdrawal dates of autumn persistent rains over western China and the associated autumn to winter evolution of the atmospheric circulation

作　　者：袁旭[1] 刘宣飞[1] 

机构地区：[1]南京信息工程大学气象灾害省部共建教育部重点实验室,南京210044

出　　处：《气象学报》2013年第5期913-924,共12页Acta Meteorologica Sinica

基　　金：江苏高校优势学科建设工程项目(PAPD)

摘　　要：根据1961—2010年平均的逐候NCEP/NCAR再分析资料、1979—2008年平均的逐候CMAP降水资料以及1961—2010年逐候平均的中国553个台站降水资料,讨论了华西秋雨起止日期与秋冬季大气环流转换特征的关系。结果表明,华西地区降水年变化表现为明显的夏、秋双峰特征,8月4—8日(第44候)为双峰间的低谷,10月8—12日(第57候)以后降水降至年平均以下。由此,将华西秋雨建立和结束日期分别确定为8月9—13日(第45候)和10月8—12日(第57候)。华西秋雨的建立对应于东亚夏季风开始向冬季风转变,其标志性环流调整特征是江南地区的西南风转为东南风。东亚经向海平面气压梯度在8月9—13日(第45候)由南高北低转为南低北高,造成850 hPa江南地区的西南风转为东南风,该东南风与来自孟加拉湾的热带西南季风交汇于华西地区,形成风向和水汽的辐合,使得华西地区的降水在夏峰之后再次增强,华西秋雨由此建立。华西秋雨的结束则对应于孟加拉湾热带西南季风结束和东亚冬季风完全建立,其标志性环流调整特征是孟加拉湾地区的西南风转为东北风。随着东亚纬向海平面气压梯度由北向南依次发生东高西低向东低西高的转变,东亚冬季风也逐步向南推进,9月8—12日(第51候)东北冬季风到达江南地区,10月8—12日(第57候)进一步推进到南海地区,此时来自孟加拉湾的热带西南季风消失,造成华西地区完全受大陆冷高压控制,东亚季风经圈环流也转为冬季型哈得来环流,东亚冬季风完全建立,华西秋雨也随之结束。因此,华西秋雨起止可能与东亚夏季风、南亚夏季风向冬季风的转变时间不同步有关,东亚季风与南亚季风的共同作用使得华西秋雨成为亚洲夏季风在中国大陆上的最后一个雨季。Based on the NCEP/NCAR reanalysis pentad dataset （1961-2010）, the CMAP pentad rainfall dataset （1979-2008）, and the conventional pentad rainfall records （1961-2010） over the 553 stations in China, the relationship between the autumn to winter evolution of the atmospheric circulation and onset-withdrawal dates of the autumn persistent rains （APR） over western China （WC） is investigated. The results show that the seasonal variation of rainfall over the WC is characterized by double peaks, one in summer and the other in autumn. The trough between the peaks happens in early August （pentad 44）, while the rainfall decreases to below its annual mean in mid-October （pentad 57）. Therefore, the onset and withdrawal dates of APR are defined in mid-August （pentad 45） and mid-October （pentad 57）, respectively.The onset of APR corresponds with the starting of the transition from the east Asian summer monsoon （EASM） to winter monsoon （EAWM）, with the landmark circulation change being SW to SE wind shift at 850 hPa over south of the middle and lower reaches of the Yangtze River （SMLRYR）. The positive to negative reversal of the meridional SLP gradient （SLP in the sea minus SLP over the land） in East Asia happens in mid-August （pentad 45）, causing the 850 hPa SW wind over the SMLRYR replaced by the SE wind. Such a SE wind will meet over the WC with the SW wind from the Bay of Bengal （BOB）, thus forming convergence there both in the wind direction and water vapor. As a result, the rainfall over WC will strengthen again after its summer peak and the APR is thereby established.The ending of APR is associated with the retreat of the tropical SW monsoon from the BOB and the complete establishment of EAWM, with the landmark circulation change being SW to NE wind shift at 850 hPa over the BOB. As the negative to positive reversal of the zonal SLP gradient （SLP over land minus SLP in the sea） in East Asia occurs progressively from the north to the south, the EAWM will advanc

关 键 词：华西秋雨 气压梯度反转 东亚夏季风 东亚冬季风 

分 类 号：P461[天文地球—大气科学及气象学]