青藏高原东北侧夏季异常高温的环流特征及诊断

利用青藏高原东北侧80个气象观测站(1960~2003年)逐日最高气温观测资料,NCEP/NCAR(1971~2000)再分析资料,探讨青藏高原东北侧(甘肃境内,下同)夏季高温天气的变化趋势;选取了异常高温天气的典型个例,进行了环流特征和动力诊断分析,以及同一次高温过程可能影响的最大范围分析。结果表明:西风指数由高指数调整为低指数,并且低指数维持时,高温天气出现并维持,由低指数调整为高指数时,高温天气结束;南亚高压与西太平洋副热带高压的上下叠加是引起高温天气最主要的环流特征;高空的正变温及上下一致的负涡度亦是高温维持的重要原因;兰州市的高温与其周边地区的高温具有较好的相关性,即当兰州出现高温时,青藏高原东北侧大部分地区也同时出现高温。

Analysis of Circulation Characteristic for Abnormal High Temperature over the Northeast Side of Tibetan Plateau

The summer high temperature trend over the northeast side of the Tibetan Plateau was investigated by using the daily high temperature data(1960-2003) of 80 stations there and 30 years'(1971-2000) NCEP/NCAR reanalysis data,and by selecting the typical case of abnormal high temperature,the circulation characteristic and the possible region influenced by the same weather process were analyzed.It was found that if the westerly index varied from high to low and maintained,the high temperature weather would occur and last,on the contrary,it would end.The main circulation characteristic of the high temperature weather was the addition of the South Asia high and the Northwest Pacific subtropical high.The positive temperature advection of the upper level and the negative vorticity throughout the whole level also induced the persistence of the high temperature weather.The temperature change over Lanzhou and its surrounding areas was consistent,when temperature high over Lanzhou,the northeast side of the Tibetan Plateau would reach the high temperature at the same time.