南海强夏季风(1994年)和弱夏季风(1998年)建立的机理分析

THE COMPARISON BETWEEN THE MECHANISM OF THE ONSET OF THE STRONG (1994) AND WEAK (1998) SOUTH CHINA SEA SUMMER MONSOON

关键词:  南海夏季风  机理分析  Hadley环流

Key words:  South China Sea summer monsoon  numerical simulation  Hadley circulation

摘要:

用NCEP/NCAR的再分析资料和局地纬向平均Hadley环流(反Hadley环流)诊断方程,探讨南海强夏季风年(1994年)建立初期(5月1~5日)和弱夏季风年(1998年)建立初期(5月21~25日)的物理机理。数值诊断结果表明:强南海夏季风(1994年)建立初期候平均气压梯度力(地转风)作用相对较小,而弱夏季风年(1998年)则相对较大。1994年5月第1候候平均非地转南风比1998年5月第5候候平均非地转南风强的主要原因是1994年南海地区稳定度较小。对1994年5月第1候南海地区近地面候平均最大非地转南风起正贡献的主要因子为:潜热加热,纬向温度平流,垂直温度对流,边界效应;对1998年5月第5候南海地区近地面候平均最大非地转起主要贡献因子为:潜热加热,边界效应,垂直温度对流。

Abstract:

According to previous studies,the South China Sea summer monsoon in 1994 started in the first pentad of May and was defined as a strong monsoon and that in 1998 started in the fifth pentad of May and was defined as a weak monsoon. To figure out the different mechanisms between the two eases, the meridional circulation over the South China Sea are successfully simulated by using the NCEP/NCAR reanalysis data and the linear diagnostic equation for the local zonal-averaged Hadley (anti-Hadley)circulation. The results show that pressure gradient force is stronger in the fifth pentad of May in 1998 than that in the first pentad of May in 1994. That ageosgtrophic wind is stronger in 1994 than that in 1995 is mainly resulted from the weaker stability in 1994. On the first pentad of May 1994, the main positive contributions to the simulated maximum southerly wind in the lower troposphere over the South China Sea are: latent heating processes, zonal temperature advection, vertical temperature convection and boundary effect. In the fifth pentad of May 1998, the main positive contributions mainly come from latent heating processes, boundary effect and vertical temperature convection.