南海夏季风爆发前后海-气界面热交换特征

AIR-SEA HEAT FLUX EXCHANGE FEATURE OVER THE SOUTH CHINA SEA BEFORE AND AFTER THE SCS SUMMER MONSOON ONSET

文中利用 2 0 0 0与 2 0 0 2年二次南海海 气通量观测资料和同期西沙站资料 ,研究了南海夏季风爆发前后海洋表面热收支变化特征。研究表明 :南海夏季风爆发前后 ,影响海面热收支变化的主要分量是净短波辐射通量和潜热通量 ,在季风爆发前后不同阶段 ,二个分量的变化有不同表现形式 ,但不论二者如何变化 ,季风爆发与活跃期 ,海面热收入减小或为净支出 ;季风爆发前及中断期间 ,海面热收入逐渐增加 ;由于大的热惯性 ,海温变化落后于海面热收支的变化 ,海温的这种滞后效应通过影响潜热通量调节海面热收支的变化 ,又反过来影响自身的变化 ,形成短期振荡过程 ,这种振荡过程与季风的活跃、中断过程相对应。

This paper is devoted to the features of sea-surface heat exchange in the different phases before and after the summer monsoon onset in the South-China Sea (SCS) by analysis of the observed air-sea heat fluxes of year 2000 and 2002 and data from Xisha Island Weather Station in the same period. Results suggest that the primary factors affecting sea-surface thermal budget are the latent heat flux and the net shortwave radiation because the sensible heat fluxs and net longwave radiation have low magnitude or a smaller change range, but the net solar shortwave radiation and the latent heat flux have high value and bigger change range which the daily mean value could differ almost fivefold. The comparison analysis finds that there is better relation between the low cloud amount and the net shortwave radiation. The sharp reduction of the net shortwave radiation is usually in association with precipitation. Among the different phases before and after the summer monsoon onset in the South-China Sea (SCS), the variations of the net solar shortwave radiation and the latent heat flux have different ways. In the phase before the summer monsoon onset or break phase, the variation range of the latent heat flux is smaller but the net shortwave radiation maintains high value. In the onset or active phase, there is complex change among them. In year 2000, during the first emergence of southwest monsoon, the net loss happened due to the dramatic diminution of the net shortwave radiation resulting from increased cloud system and intense precipitation, which was a situation of local convection that the ocean release energy to atmosphere in the form of precipitation; In the second span of the gales, there was little change in the net solar shortwave radiation because of less precipitation cloud system, but the dramatic growth of latent heat flux resulting from intense evaporation could be responsible for vapor transport far away from the source by means of large-scale strong SW winds. Regardless of their changing ways, the thermal gain was reduced or became net loss at the active stage or the onset stage and the thermal gain gradually increased before the onset stage or in the lull periods; That means the monsoon burst or active process is the process that ocean release the energy and the monsoon break process or the period before the onset is the process that ocean gain the energy. It is also found that the variation of SST is not synchronous with that of sea-surface thermal budget. Owing to great thermal inertia of water, SST change lags behind that of heat budget over the sea surface, and the lagging is responsible for regulating the budget by affecting latent heat fluxes, which, in turn, effected upon the change of the SST, thereby forming short-term oscillations that are in association with the active/break phases of the monsoons. Part of the conclusions have been borne out by the observational study based on 1998.