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江南雨季地理区域及起止时间的客观确定

     

摘要

Using the 1 675 gauge data from National Meteorological Information Center and the NCEP/NCAR rean-alysis data,the pentad mean averaged precipitation index which can eliminate the regional differences between gau-ges is defined.The rotated empirical orthogonal function decomposition (REOF)is applied to investigate the sea-sonal march of the pentad mean precipitation over the entire China.We obtain two leading modes (e.g.the South and North mode)and their time coefficients.The second mode of REOF presents well the Jiangnan Rainy Season (JRS).Given the consistence of three independent criterion,e.g.,the seasonal process of pentad mean precipitati-on,the interannual variability of precipitation index seasonal variation (April -June mean minus June-August mean)and the interannual variability of mean state of rainy season (April-June)in south of China (south of 31° Nand east of 110°E),the overlap region of these three is objective defined as the geographic region of JRS.Using three variables in the defined geographic region of JRS,e.g.,the rainfall index,regional 925 hPa meridional wind and the western North Pacific subtropical high ridge line position at 500 hPa,the onset and retreat dates of JRS from 1961 to 2012 are determined objectively.The purposes of this paper are to provide reference for monitoring JRS and scientific basis for its prediction.%本文基于国家气象信息中心整编的全国1675个台站观测资料以及 NCEP/NCAR 的再分析资料,定义了候降水指数,利用旋转正交经验函数分解(REOF)法对全国候降水的季节进程进行了诊断分析,得到了表征气候态降水逐候进程的南、北方模态及各自的时间系数,发现 REOF 第二模态对应降水季节进程中的江南雨季。综合考虑我国南方(31°N 以南、110°E 以东区域)气候态降水的候进程、降水季节进程(4-6月降水指数减去6-8月降水指数)年际变率以及雨季(4-6月降水指数)降水年际变率的一致性,客观定义了江南雨季的地理范围。利用客观划定区域内的降水指数、925 hPa 经向风以及西北太平洋副热带高压500 hPa 脊线位置3个指标,制定了判定江南雨季起止时间的方法,进而对1961-2012年江南雨季起止时间进行了客观确定,给出了江南雨季起止时间序列。本文旨在为规范江南雨季的监测提供参考和借鉴,并为其预测提供科学基础。

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