2004年南海夏季风的爆发及中南半岛陆面过程的可能影响Ⅱ:数值试验

THE FEATURES OF SOUTH CHINA SEA SUMMER MONSOON ONSET OF 2004 AND THE POSSIBLE EFFECTS OF LAND-SURFACE PROCESS IN INDO-CHINA PENINSULA II: NUMERICAL SIMULATION

在对南海夏季风的爆发及中南半岛陆面过程的可能影响进行了诊断分析的基础上,应用MM5/NOAHLSM模式,研究了中南半岛陆气相互作用对2004年南海夏季风爆发过程的可能影响。结果发现:在南海夏季风爆发前,中南半岛南海地区低层气温差确实出现低值,甚至负值;尽管短期内中南半岛土壤湿度和降水的变化没有引起季风爆发日期的改变,但对季风爆发的强度有影响。土壤湿度和降水变化引起的干异常可导致地表感热通量的增大和地表温度的升高,致使中南半岛与南海之间低层的温差异常(负温差)减小,季风爆发强度减弱;不同的是,湿异常可引起季风爆发强度增强。这一结果说明,在南海夏季风爆发前期,中南半岛上空对流活动和降水异常及其引起的土壤湿度的异常变化在一定程度上会影响到季风爆发的过程。文章还比较了不同温湿地表条件下低层大气状态的差异和地表能量、水分平衡过程的不同,分析了陆气相互作用对季风活动产生影响的物理机制。

Based on the diagnostic studies in part Ⅰ, this second companion paper addresses the issue of possible effects of land-surface process over Indo-China Peninsula on the establishment of 2004 South China Sea （SCS） summer monsoon by using the MM5/NOAH LSM modeling systems. A series of numerical simulations were performed in order to investigate the sensitivity of SCS summer monsoon onset to regional soil moisture and precipitation anomalies. It is found that though the SCS summer monsoon onset date is essentially unaltered, soil moisture and precipitation anomalies over Indochina peninsula can make contributions to the intensity variations of SCS summer monsoon. Dry anomalies induced by the decrease of initial soil moisture and precipitation are associated with sensible heat flux increase and positive surface air temperature anomalies, which may led to the decrease of low-level air temperature difference （negative difference） between Indo-China Peninsula and SCS, and then weaken the SCS summer monsoon. In contrast, wet anomalies may intensify the SCS summer monsoon. These results revel that prior to the SCS summer monsoon onset, convection, and precipitation variations over the In-do-China Peninsula and the associated soil moisture anomalies to some extent affect the SCS summer monsoon establishment process. The article also discuss the associated low-level atmospheric condition and land surface energy and hydrology budgets over different land surface properties, analyze the corresponding physical mechanisms of how land surface process affect the SCS summer monsoon.