孟加拉湾季风活动与云南5月降雨量

Activities of Bay of Bengal Monsoon and Beginning Date of Rain Season in Yunnan

利用1958—1997年NCEP再分析高低层经纬向风分量、比湿场资料以及云南32个测站降水资料,通过相关分析等方法,从风场演变和水汽输送等方面分析了孟加拉湾季风活动及其与云南初夏降水变化的关系。结果表明:与阿拉伯海和南海相比,孟加拉湾低层纬向西风出现时间最早,盛夏期间的峰型结构与南海西风的峰型结构极为相似,出现双峰型。孟加拉湾季风爆发平均日期在5月3候,是亚洲季风区爆发最早的季风之一,比南海季风爆发的平均日期(5月4候)早1候。孟加拉湾季风活动与云南初夏降水有一定关系,季风爆发偏晚,云南5月降雨量偏少;而当季风爆发偏早或正常,云南5月降雨量的多少主要与中低纬度地区冷空气的活动有关。

Based on pentad and monthly mean wind and specific humidity data of NCEP from 1958 to 1997 and precipitation data of 32 stations in Yunnan, the activities of the Bay of Bengal(BB) monsoon and the correlation relation between BB monsoon and precipitation in early summer of Yunnan have been studied, and we got some interesting evidences. First, on 850 hPa, comparing with SCS and Arab zonal wind, the appearing of BB zonal wind is the earliest and the its variation is similar to that of SCS zonal wind during summer monsoon. Second, the onset date of southern BB summer monsoon is 6 pentads in April and that of northern BB summer monsoon is 3 pentads in May, and it is the earliest in the onset of Asian summer monsoon. The onset of southern BB summer monsoon is earlier than onset of northern BB summer monsoon. Last, May precipitation in Yunnan increases while the onset of BB summer monsoon islaterabout 2～3 pentads, whereas more and less May precipitation in Yunnan is closely relative to the activities of cold air at midlatitude, it may increases or decreases while the onset of BB summer monsoon is early or later about 1 pentad.