北京降水特征与西太副高关系的若干统计

Beijing Region Precipitation Feature and Some Statistics of Relationship between It and SHWP

利用北京地区20个测站1975-2004年降水资料，以及国家气候中心定义的西太平洋副热带高压（下称西太副高）各指数资料，对北京地区降水的时空分布特征以及与西太副高的统计特征等进行了分析，结果表明：（1）北京地区降水分布不均匀，降水量大值区主要位于怀柔、平谷等中部山区，呈现东部和南部降水多，西部和北部降水少的分布形势。其夏季降水占年降水量的72．5％，其中，北京东部和南部的降水季节性特征比西部和北部更显著。（2）北京地区各站每年平均大雨以上的降水日数在3～8天之内；北京区域平均年降水量与中雨以上的各量级降水日数都为显著正相关关系，尤其是大雨日数降水的贡献，其次是暴雨日数。（3）北京地区年降水有连枯、连丰、枯丰交替的年际变化特征；其夏季降水有弱的准2年的周期振荡。（4）近30年来，随着年代演变，西太副高对北京地区夏季降水的作用有增强趋势。（5）北京区域性强降水日主要出现在7、8月份，约占总区域强降水日数的72％。其中有45．5％的区域强降水日与西太副高影响有关，特别是西太副高与西风槽共同作用的形势约占94．8％。（6）当西太副高平均脊线位于31．6°N，120°E处，西伸脊点位于110．6°E处，副高5880gpm等高线北界位于37．1°N，120°E处，以及西风槽中点位于108．8°E，40°N，槽线北端位于46．6°N，槽底位于34．8°N时，最有利于北京出现区域强降水。

Using the data of precipitation of 20 observation stations from 1975 to 2004 in Beijing and the indices of Subtropical High over West Pocific（SHWP） defined by the Climate Center, Chinese Administration of Meteorology, the temporal and spatial characteristics of precipitation and the statistic relationship between it and the SHWP is analyzed. The results are as follows. （1）The precipitation in Beijing show obvious local characteristics. The higher values of precipitation is mostly ,local at the middle mountainous areas such as Huairou and Pinggu et al. and precipitation of east- and south parts tend to more than of west- and north-ones. Summer average precipitation is 72.7% of annual average rainfall. The seasonal differences are obvious between the precipitation of northwest and southeast areas. （2）The day numbers with severe rain in which precipitation is larger than 25 mm/d rainfall is three to eight days. There is an distinct positive correlation between regional and annual average precipitation and day numbers with severe rain day, the severe rain days have the main contribution to the Beijing＇s rainfall. （3）Beijing year-to-year rainfall have change trends of continuous-abundance and -lack, as well as alternately abun- dance or deficiency with years. The summer precipitation has the weak quasi-two year periodicity. （4）The impact of the SHWP on Beijing rainfall has a severe interdecadal trend in the past 30 years. （5）About 72 percent of rainstorms occur in July and August in Beijing, of which the rainstorms are directly affected by the SHWP are 45.5 percent, especially the combination of the SHWP and westerly trough（about 95%）. （6） The following 500 hPa potential height field situation is specially favoured for the severe precipitation in Beijing region summer, ie, the ridge line of the SHWP is located at 31.6°N° the west ridge point of 120° E, 110.6°E; the north boundary of 588 gpdm line of 120°E, 37°N° of 584 gpdm, 39. 1°N° mid-point of westerly trough, 108.8°E, 40°N; the south end of westerly trough, 34.8°N.