华北汛期的起讫及其气候学分析

基于对汛期的理解和认识, 利用Samel等人设计的半客观统计分析方法、Mann-Kendall突变分析、滑动t检验等方法, 通过分析和研究1957—2006年华北台站的日降水资料, 确定了华北汛期起讫的日期。结果表明:华北汛期始于6月30日, 止于8月18日, 持续期为50d。华北汛期的起讫日期、持续天数以及空汛发生的频次, 具有鲜明的地域特征:冀北山地汛期开始最早, 结束较迟, 持续天数较长, 空汛发生频次最少; 黄土高原汛期开始较迟, 其北部汛期结束最迟, 持续期也最长, 发生空汛的频次也比较多; 黄河下游地区汛期开始比较早, 结束最早, 汛期最短, 发生无大汛的频次较大; 河北平原地区, 汛期开始最迟, 结束较迟, 汛期较长, 发生无大汛的频次最多。与华北汛期开始和结束日相对应的东亚大气环流特征是:当西太平洋西部上空500hPa存在正的位势高度距平, 华北上空存在负的位势高度距平, 同时地面为“东高西低”的异常海平面气压场配置时, 异常偏南风到达30°N, 华北汛期开始; 当华北上空500hPa为较小的位势高度正距平, 日本海为位势高度正距平, 而地面上, 我国大陆和西太平洋之间为“西高东低”的异常海平面气压场配置时, 异常偏北风控制我国东部地区, 华北汛期结束。

Identification on the Beginning Date and End Date of Rainy Season over North China and Their Climatology

Semi-objective analysis method designed by Samel et al, Mann-Kendall test method and moving t-test technique are used based on the understanding of rainy season in order to investigate the beginning and end dates of rainy season over North China.The yearly initial date and final date of rainy season over North China are set up, and their climatological dates are further identified. The results show that rainy season in North China has an average duration of 50 days, starting on Jun 30 and ending on Aug 18 from climatology aspect. The period of heavy rainfall for the rainy season in North China is from Jul 19 to Aug 14, which is also the mature period of summer monsoon.The initial date, end date and the duration of rainy season and the frequency of no rainy season have regional features over North China. Rainy season has the earliest staring dates, late ending dates, longer duration days and the lowest frequency of no rainy season in the mountainous areas on the north of Hebei Province. Late starting dates and higher frequency of none rainy season are in the Loess Plateau while the latest ending dates and the longest duration days are on the north of the Loess Plateau. The earlier starting date, the earliest ending date, the shortest duration days and higher frequency no rainy season are in the mid-lower Basins of Yellow River, and the latest starting date, late ending date, longer duration days and highest frequency of none rainy season are in the west of Hebei plain. There are different trends for the initial dates, end dates, duration days of rainy season and frequency of none rainy season over North China. Duration days of rainy season have the most significant decreasing trend and the end dates also have obvious decreasing trend, while the total stations have significant increasing trend and the initial dates also have a slight increasing trend. All of these trends are of benefit to the decrease of summer rainfall over North China. There are close relationships between the rainfall of rainy season over North China and the initial dates, duration days of rainy season, the total stations of none rainy season. When rainy season begins earlier(later), duration days of rainy season last longer(shorter), the total stations are more(less), rainfalls of rainy season over North China are more(less).When positive anomalies of geo-potential height over the west Pacific exit, meanwhile negative anomalies of geo-potential height in the 500 hPa filed exit over North China, and the pattern is an anomalies of "east high and west low" between the Chinese mainland and west Pacific in the surface, the results are that the anomalies of south wind reach 30°N, the rainy season begins over North China. However, when smaller positive anomalies of geo-potential height in the 500 hPa field exit over North China, positive anomalies of geo-potential height in the 500 hPa field exit over Japanese sea, and the pattern is anomalies of "west high and east low" between the Chinese mainland and west Pacific, the results are that the anomalies of north wind influence Eastern China, the rainy season ends in North China.