东亚夏季风的变化特征及其对甘肃夏季暴雨日数的影响

采用NCEP/NCAR再分析资料，计算了1974—2013年乔云亭等定义的东亚季风指数，研究了东亚夏季风的变化特征，利用甘肃省80个站逐日降水资料，分析了东亚夏季风对夏季甘肃暴雨日数的影响。结果表明：（1）夏季，西南季风、东南季风和偏北季风存在明显的年际变化且有所差异。（2）夏季，西南季风、东南季风对甘肃省暴雨日数的影响存在很大差异：当西南季风盛行时，西太平洋副热带高压位置偏西，东亚大槽位于贝加尔湖至中国西北部，冷空气与西太平洋副热带高压输送的暖湿气流在陇东南一带交汇，贝加尔湖至张掖为西南暖湿和西北干冷气流，孟加拉湾水汽输送在陇东南地区辐合，造成河东陇南南部、天水东部、平凉、庆阳西部一带和河西张掖地区暴雨日数偏多；当东南季风盛行时，西太平洋副热带高压西伸北抬，冷暖空气主要交汇于甘肃中西部，孟加拉湾西南水汽输送在河东西南部辐合，造成甘南高原、甘肃中部、河西武威一带和酒泉地区暴雨日数偏多。

Variation of East Asian Summer Monsoon and Its Influences on Summer Rainstorm Days in Gansu,China

By using the NCEP/NCAR reanalysis datasets during 1974-2013, East Asian Monsoon indexes defined by Qiao Yunting are calculated and changes of the indexes are studied. The effect of East Asian Summer Monsoon on summer rainstorm days in Gansu is analyzed by using daily precipitation data at 80 stations in Gansu Province. The results show that the southwest monsoon, the southeast monsoon and the north monsoon are obviously inter-annual varied and different in summer. The southwest monsoon, the southeast monsoon has different effect on summer rainstorm in Gansu. When the prevalence of southwest monsoon, East Asian Trough is located from the Lake Baikal to the northwest China, and cold air and warm wet air from the Western Pacific subtropical high joins together at the southeast of Gansu. The region from the Lake Baikal to the Zhangye is occupied by southwest warm-wet air and northwest cold dry air, the water vapor from the Bengal Gulf meets in the southeast of Gansu, which causes rainstorm in the southeast of Gansu, the eastern Tianshui, the Pingliang, the western Qingyang and the Zhangye. When the prevalence of southeast monsoon, the western Pacific subtropical high extends westwards and northwards, cold air and warm air joins together at the mid-west of Gansu, the southwest water vapor from the Bengal Gulf meets in the southwest of Hedong, which causes the rainstorm in the Gannan Plateau, the middle of Guansu, Wuwei and Jiuquan.