夏季北太平洋副热带高压系统的活动

AN OBSERVATIONAL STUDY ON THE BEHAVIOR OF THE SUBTROPICAL HIGH OVER THE WEST PACIFICIN SUMMER

中文关键词:  西太平洋  副热带高压  年际变化  短期变化

英文关键词:Subtropical high,West Pacific,Inter-annual variations,Short period(5-10 days)variations

中文摘要:

      文中根据NCEP/NCAR再分析资料,分析了北太平洋副热带高压系统的变化。5～9月由于亚洲夏季风的建立及活动,北半球副热带高压系统在60～120°E出现断裂,夏季西太平洋副热带高压脊点平均伸展到120°E,其年际变化反映了亚洲夏季风的强弱。强夏季风年500hPa西太平洋副热带高压脊线位于30°N以北,并分裂成两个中心,印度低压强;弱夏季风年西太平洋副热带高压脊线位于30°N以南,表现为北太平洋高压中心向西伸展的高压脊,印度低压弱。夏季西太平洋副热带高压的季内活动有两种模态:第1种表现为副热带高压系统以20～30d的周期从北太平洋中部的副热带高压中心一次次地向西扩张到120°E以西,这类过程大多出现在亚洲夏季风强度偏弱年;第2种模态表现为副热带高压系统以20～30d的周期一次次地由东向西扩充时,在125～155°E停滞,这类过程大多出现在亚洲夏季风强度偏强年。江淮流域梅雨的中断和结束与北太平洋副热带高压系统20～30d季内振荡有关。西太平洋副热带高压5～10d的短期活动受35～45°N西风带活动的影响,当西风槽在中国沿海和西太平洋地区向南伸展到30°N以南后,西太平洋副热带高压有一次加强活动。

英文摘要:

      The behavior of the subtropical high(SH) over the West Pacific in summer manifests marked inter-annual,seasonal,intra-seasonal and short period(5-10 days) variations.In strong summer monsoon years the ridge of SH extends fur ther northward than in weak monsoon years,and there are two separ ate anticy clone centers,one is over the West Pacific and the other over the Middle Pacific.In the weak monsoon years the behavior of SH mainly manifests a ridge extending west ward from the Middle Pacific.For seasonal variations the ridge of SH is situated to the south of 20°N before June,extends to 25°N when the Meiyu seaso n in the Yangt ze River Valley begins,and extends further northward to the north of 30°N in mid July,when the Meiyu season ceases in Septem ber ther idge of SH retreats rapidly southward.For intra-seasonal variations there are two modes,The firstmode is the extension of the ridge of SH west ward from the Middle Pacific with a period of 20-30 days.The second mode is that the ridge of SH extends west ward from the Middle Pacific,intensifies to form a separate high pressure center,and stag nates in the West Pacific.The extension or retreat of the ridge of SH has a close relation to the break or cease of the Meiyu in China.For short period (5-10 days)variations,when a trough in the westerly in the middle latitudes moves east ward,intensifies rapidly to the east o f Japan Islands,and extends southw ard into the subtropical,the ridge of SH to the west of the digging trough intensifies and extends into the China mainl and.