气候平均场中的西太平洋副热带高压双脊线特征及其与季风槽准10天振荡的关系

Climatological View on Double Ridges Process of the Western Pacific Subtropical High and Its Relation to Quasi-10-day Oscillation of Monsoon Trough

副热带高压双脊线过程几乎历年均存在,其"季节锁相"与地域性使得在气候平均场上西太平洋副热带地区也存在明显的双脊线过程。作者利用43年NCEP/NCAR再分析资料对5~10月气候平均场中的西太平洋副热带高压双脊线过程进行了分析。气候平均场上5~10月西太平洋副热带高压共出现6次双脊线过程,集中发生在7月下旬至9月下旬,表明每年这个时段最易发生双脊线事件。每次双脊线过程均表现为副高南侧新生一脊线,发展几天后就减弱消失,北侧脊线(原脊线)继续维持。初步的诊断分析表明,6次双脊线过程中南侧脊线的生成与季风槽8~10天周期的"间歇性增强东伸"密切相关,这一准10天振荡在7月下旬至9月下旬的突然增强造就了双脊线的"季节锁相"。进一步分析发现,季风槽8~10天的"间歇性增强东伸"与两支分别来自西太平洋的西传准10天振荡和来自赤道的北传准10天振荡有关,这两支振荡同位相,其有利于位相同时传入南海季风区(10°N^15°N,110°E^120°E),共同作用,引起季风槽的"间歇性增强东伸"。

The subtropical high experiences double ridges process （DRP） nearly every year, of which the phase-locking and geographical preference result in the similar behavior in the western Pacific Subtropical High （WPSH） on a climatological basis. In this study, the 43-year NCEP/NCAR reanalysis datasets are employed to examine the characteristics of WPSH DRP during the period of May to October. Six cases are found to occur during the period of late July to late September, indicating the preference time of the occurrences of WPSH DRP. Unexceptionally, each of them is characterized by a new-born ridge in the south of WPSH which persists for several days before its vanishment and by the maintenance of the original one in the northern portion of WPSH. The onset of new-born ridge for each case is closely associated with the anomalous activities of monsoon trough, e. g. , intermittent enhancement and eastward extension with a timescale of 8 - 10 days. The sudden development of monsoon trough during late July to late September usually leads to the phase-locking of WPSH DRP. Further studies show that the 8 - 10-day oscillation of monsoon trough is due to a westward-propagating quasi-10-day oscillation from the western Pacific and a northward-propagating quasi-10-day oscillation from the equatorial region. The monsoon trough tends to reinforce and extend eastward when those two oscillation disturbances overlap each other in a preferable phase （e. g. , westerly phase） over the South China Sea region （10°N. 15°N, 110°E- 120°E）.