西北太平洋夏季风的气候学研究

THE CLIMATE RESEARCH OF SUMMER MONSOON OVER THE WESTERN NORTH PACIFIC

西北太平洋季风区(5°～25°N,120°～160°E)是亚洲-太平洋季风区与亚洲-澳大利亚季风区的一个重要部分,也是一个独立的季风区.文中对西北太平洋夏季风进行了气候学研究,发现西北太平洋夏季风的爆发发生在31候(6月上旬)前后.爆发后,夏季风经历了3次活跃-中断循环,每个循环都相应于独立的干期和湿期.第1个循环是从6月初到7月中旬,降水与低层西风的中心主要位于5°～10°N.第2个循环是7-下旬至9-下旬,降水与低层西风明显向东北方向移动,位于10°～20°N.这个循环是西北太平洋夏季风最强盛的时期.第3个循环是从9月末到10月末,降水与低层西风又向南退回到5°～10°N,达到了西北太平洋夏季风最弱的阶段.这个循环的结束也就预示着西北太平洋夏季风的结束.西北太平洋季风区有明显的季节内振荡(ISO),这种气候的季节内振荡(CISO)主要由30～60 d与10～20 d两种周期组成,但是主要以30～60 d的低频振荡为主.根据西北太平洋的对流和低层西风在不同位相分布的分析,可以看出西北太平洋的低频对流和西风是向西向北传播的.西北太平洋的季风降水、对流与西风的活跃-中断循环在很大程度上受30～60和10～20 d低频振荡的调制.

The monsoon region of western North Pacific（WNP） （5° - 25°N, 120° - 160°E） is an important part of Asian-Pacific and Asian-Australian monsoon region, and is a distinct monsoon region. The climate features of WNP summer monsoon have been studied. The results show that WNP summer monsoon onsets in pentad 31 （early June） or so. After onset, summer monsoon experiences three active-break cycles. Every cycle has a dry and wet period. The first cycle is from early June to mid-July and the center of precipitation and lower-level west wind is mainly located between 5° - 10°N. The second cycle is from late July to late September, precipitation and lower-level west wind move to northeast obviously and are located between 10° -20°N. In this cycle, WNP summer monsoon is the most prosperous. The third one is from late September to early October and is the weakest period, in which the precipitation and lower-level west wind retreat south again and lie between 5° - 10°N. The end of the third cycle indicates the end of WNP summer monsoon. There are obviously intraseasonal oscillation （ISO） in WNP monsoon region, this climatological ISO is mainly composed of 30 - 60 and 10 - 20 day oscillation. But low-frequency oscillation of 30 - 60 days is significant. Base on the analysis of convection and lower-level west wind distributing in different phases over WNP, low-frequency convection and west wind propagate to northwest. To a large extent, the active-break cycle of monsoon rain, convection and lower-level west wind over WNP are all modulated by 30 - 60 and 10 - 20 day low-frequency oscillation.