秦岭邻近地区旬降水气候学及其大气环流特征

Climatology of dekadly precipitation around the Qinling mountains and characteristics of its atmospheric circulation

利用秦岭及其邻近地区76个气象台1961～2000年的旬降水量和NCEP/NCAR850hPa格点风场资料,分析了该地区的降水气候时空特征及其与大气环流变化的联系。结果表明,秦岭地区多年平均汛期出现在6月下旬至10月上旬,其间7月上旬和9月上旬先后出现两次降水峰值。该地区平均汛期降水量为403mm,占年总降水量的60%。秦岭南侧气候平均汛期降水量明显高于秦岭北侧,但秦岭南、北汛期降水年际变化基本一致。从流场分析看,秦岭及其邻近地区的汛期降水既受西南季风,又受到东南季风系统的影响。合成分析表明,汛期降水量偏多(少)的年份通常对应于同期对流层低层研究区南侧偏南气流的增强(减弱)。回归分析发现,汛期中旬雨量增加与超前2旬索马里急流和热带印度洋西南气流增强,以及超前1旬及同期台湾附近距平反气旋的发展密切相关。

Using 1961～2000 dekadly precipitation from 76 weather stations in the Qinling mountains and the surroundings and large-scale grid winds at 850 hPa from NCAR/NCEP,the climatology spatial-temporal characteristics of the precipitation and their associations with the atmospheric circulation have been analyzed in this paper.The results show that the flood season for the 40-year average occurs in the period from the third dekad of June to the first dekad of October,during which there are two peaks of precipitation:the first dekad of July and the first dekad of September.The rainfall in the south side of the Qinling mountains is obviously higher than that in the north side,although the interannual variations of both are basically consistent.The Qinling mountains and the surroundings are mainly controlled by the southwesterly monsson in the flood season,especially in the midsummer,but are mainly impacted by the southeasterly monsoon in the early autumn.The composite analyses show that when the precipitation is more(less)than normal,the southerly wind at the south boundary of the study area is often stronger(weaker)than normal in the flood season.By the regression analyses,it is found that the increased rainfall in a dekad in the flood season generally corresponds to the strengthened Somali Jet and southwesterly monsoon in the dekad with a two-dekad lead,and an anomaly anticyclone near Taiwan in the one-dekad lead dekad and the same dekad.