南海夏季风撤退期的气候特征I——40年平均

CLIMATIC CHARACTERISTICS OF THE RETREAT OF SOUTH CHINA SEA SUMMER MONSOON I——40-year Means

关键词:  南海夏季风  撤退期  40年平均  气候特征

Key words:  South China Sea summer monsoon  retreat period  40-year means  climatic characteristics

摘要:

用NCAR/NCEP1958～1997年共40年资料对南海夏季风撤退的气候特征进行了分析。8月上旬西伯利亚冷空气开始南进,由于青藏高原的阻挡作用,在我国东部大陆推进得很快,到达南海后继续向南推进,最后导致9月中旬左右南海夏季风从南海撤退。就个别年份而言,最早的撤退时间是8月中,最晚的是10月中,可以差两个月。南海夏季风撤退与建立过程是很不相同的,南海夏季风和夏季风雨带的建立都是爆发性的,在全区域几乎是同时建立,但撤退是由北向南缓慢撤退的,历时一个月左右。在撤退期间,南海降水形势变化不大,但在撤退之后,南海夏季风雨季转变为ITCZ雨季,其相应和雨区随着太阳南移向南推进。南海夏季风撤退后,南海降水30～60天振荡明显减弱,而准两周振荡仍比较活跃。

Abstract:

Analyses are made on climatic characteristics of the retreat of South China Sea(SCS) summer monsoon using the 40-year NCAR/NCEP data between 1958 and 1997.We believe that the Siberian cold air starts to pledge southwards in the first 10 days of August and,with the blocking effect of the Tibetan Plateau,the cold air progresses quickly in eastern China and continues to move to the south,resulting in the retreat of SCS summer monsoon.Among individual years,the earliest retreat happens in mid-August while the latest in mid-October,with a difference of two months.The retreat process and the onset process of SCS summer monsoon are quite different;both the South China Sea Summer Monsoon and the rain establish abruptly and cover almost the whole region,while the retreat process happens slowly from north to south in about one month.During the retreat,the rainfall pattern has little change;but after the retreat,the ITCZ rain replaces SCS summer monsoon rain,with the respective rain region following the south-moving Sun.The 30 to 60-day oscillations of SCS rainfall weaken obviously while the quasi-two-week oscillations are still active.