晚春初夏西太平洋副热带高压南撤过程的气候学特征

利用1979—2006年多年平均逐日NCEP/NCAR再分析资料、NOAA的OLR和逐候CAMP降水资料，从气候学角度探讨了晚春初夏季节转换时期，西太平洋副热带高压（副高）脊线位置变化及其与亚洲夏季风爆发的关系。发现晚春初夏时期西太平洋副高在向北移动过程中存在一次显著的南撤过程，之后西太平洋副高发生第一次北跳，南撤主要发生在对流层高层和低层，南撤生命期可达2周，且高层的南撤过程结束时间比低层的南撤过程开始时间早约1旬，这为预测低层副高南撤及其第一次北跳提供了有意义的前期信号。低层西太平洋副高南撤的同时伴随着一次显著东退过程。在低层副高南撤结束后（约5月底），由于气温经向梯度的变化使副高脊轴倾斜发生反转。n晚春初夏的西太平洋副高南撤过程与亚州夏季风爆发、强对流活动和降雨带的移动变化关系密切。在对流层高层西太平洋副高南撤过程的中后期（约4月底），夏季风在安达曼海和临近孟加拉湾爆发。在对流层低层西太平洋副高南撤过程开始后，南海夏季风开始爆发（5月14—15日）；南撤过程结束后（6月初），印度夏季风爆发；在副高脊线返回日后（6月中），东亚夏季风爆发。西太平洋副高南撤过程不同阶段的建立时间为预知亚洲不同地区夏季风的爆发时间提供了非常有用的信息。n此外，在西太平洋副高主体南北两侧存在两支强的雨带，与副高主体控制的少雨带构成一个典型的“湿干湿”三明治雨型，这个雨型的变化与西太平洋副高脊线移动有关。

Climatological features of the Western Pacific subtropical high southward retreat process in late-spring and early-summer

Based on the climatological daily mean NCEP/NCAR reanalysis data,NOAA outgoing longwave radiation(OLR)data,and weekly NOAA CAMP precipitation from 1979 to 2006,the variation of the Western Pacific subtropical high(WPSH)ridge during late-spring and early-summer and its relationship with the onset of the Asian summer monsoon is discussed from an climatological view.It is found that there is a remarkable southward retreat process(SRP)of the WPSH during late-spring and early-summer,mainly at both low and high levels of the troposphere,with an approximate two week lifespan.Afterwards,the first northward jump of the WPSH occurs.The end date of the WPSH SRP in the upper troposphere is about 10 days earlier than the beginning of the WPSH SRP in the lower troposphere,showing a meaningful leading signal for predicting the WPSH SRP in the lower troposphere and the subsequent northward jump of the WPSH.The WPSH SRP at tropospheric low levels happens simultaneously with a notable eastward shift of the WPSH.After the WPSH SRP at tropospheric low levels concludes around the end of May,the incline of the WPSH ridge axis turns over due to the change of the meridional gradient of air temperature.The Asian summer monsoon onset and associated variations of strong convection and rainfall in Asia are closely related to the WPSH SRP during late-spring and early-summer.In the mid and late period of the WPSH SRP at tropospheric high levels around the end of April,the summer monsoon onset takes place in the Andaman Sea and the Bay of Bengal(BOB).,Following the start of the WPSH SRP at tropospheric low levels,the South China Sea summer monsoon breaks out(May 14-15).By the end of the WPSH SRP,in the beginning of June,the Indian summer monsoon kicks off.Upon the end of the WPSH return stage,the East Asian summer monsoon begins.The commencement of each component system of the summer monsoon corresponds nicely to a particular stage of the WPSH SRP.This offers valuable information for monsoon onset prediction in different sectors of Asia.In addition,it is found that there is a typical wet-dry-wet sandwich precipitation pattern,with two rainfall belts in the regions south and north to the WPSH main body,and a dry belt under it.The variation of this rainfall pattern is related to the shift of WPSH ridge.