2007年南海夏季风爆发前后大气环流的非典型性突变特征

Untypical Abrupt Change Features of the General Circulation during Onset Period of South China Sea Summer Monsoon in 2007

南海夏季风爆发的一般特征是南亚高压移至中南半岛北部;西太平洋副热带高压连续向东撤出南海地区,移到120°E以东的热带洋面上;高(低)空东北(西南)气流占据南海大部分地区,相应的105°E附近的越赤道气流建立,南海季风槽形成并同时伴有对流降水的发展和温、湿等要素的突变。国家气候中心的监测表明,2007年南海夏季风于5月第5候爆发。该年季风爆发后,虽然源自热带地区的低空西南气流迅速占据南海上空,高空盛行东北气流,且南亚高压西移至中南半岛上空,但对流、高度场以及降水场的突变特征均很不明显,表现为季风爆发后南海上空的对流依然偏弱,副高没有马上撤离南海,同时华南地区的降水量也没有迅速增强。因此,2007年南海夏季风爆发前后大气环流的变化特征具有非典型性。

The South China Sea （SCS） summer monsoon （SCSSM） has great influences on the monsoon rainfall belt, both on the position and intensity. The results of the SCSSM experiments since 1998 show that the basic features of the general circulations after the monsoon onset include ： 1 ） the South Asia high moves to the north part of the Indo-China peninsula;2） the western Pacific subtropical high moves to the tropical ocean east of 120°E from the SCS region;3 ） the southwest （northeast） monsoon flow prevails at lower （higher） troposphere over most of the SCS ;4） the cross-equatorial flow along 105°E and the SCSSM trough establish ;5 ） both the convective rainfall over South China and the circulations over the SCS abruptly change. According to the monitoring results of National Climate Center, the SCSSM in 2007 onsets in the 5th pentad of May ;but during its onset period,the abrupt changes of the general circulations are not significant. To better understand and monitor the SCSSM, it is necessary to study the untypical abrupt change features.