南海季风建立前后珠江三角洲的陆气热量交换与热力边界层结构特征

LAND-AIR HEAT EXCHANGE AND THERMAL BOUNDARY LAYER STRUCTURE BEFORE AND AFTER THE ESTABLISHMENT OF SOUTH CHINA SEA MONSOON OVER PEARL RIVER DELTA

根据动力与热力指标,2004和2005年南海季风建立前后可分成明显的4个阶段——季风建立前的雨期、非雨期;季风建立后的活跃期与非活跃期。对2004和2005年南海季风建立前后的广州番禺综合外场观测资料进行分析,得到了这4个阶段陆气热量交换与热力边界层的主要特征:净辐射与净短波辐射的变化趋势基本一致,净短波辐射与净长波辐射之比为3.49—4.81,净短波辐射是净辐射的主要贡献项,云量与降水是控制净短波辐射与净辐射的直接因素;季风活跃期间午间对流云系对太阳辐射衰减显著,造成了辐射各分量以及热通量的峰值区变窄,量值急剧变小;季风建立前后感热与潜热均是净辐射的主要消耗项,占净辐射的90%以上,潜热明显大于感热,2005年较2004年潜热的分配额有明显的增加,其原因可能与近地层的风速较大,总是维持向上的湿度梯度有关;季风建立前后除季风活跃期外边界层位温结构均具有明显的日变化特征,午间混合层可发展至1070m,而季风活跃期间午间混合层发展受到对流云释放潜热的抑制,导致季风活跃期混合层消失的现象,分析还发现季风建立前后各阶段夜间残余混合层均不明显。分析表明引起陆气能量过程及边界层热力结构差异的关键因素之一是云系与降水,加强边界层过程与降水宏微观过程相互作用的研究是深入认识陆气过程与边界层结构特征的关键。

Based on thermodynamic and dynamic indexes, the period around the establishment of South China Sea Monsoon （SCSM） in 2004 and 2005 can be divided into four different periods： rainy period, non-rainy period, monsoon active period, and monsoon non-active period. Analyses of field observations in the Fanyu area, Guangzhou from May to June in 2004 and 2005 have been made, and main characters of land-air processes and thermal boundary layer structures for four different periods before and after the establishment of SCSM obtained. The net radiation flux and net short-wave radiation flux displayed a similar trend, the ratio of net shortwave radiation flux to net long-wave one ranged from 3.49 to 4.81, and. the net short-wave radiation flux made major contribution to the net radiation flux. The cloud amount and rainfall were the factors directly controlling variations of net short-wave radiation flux and net radiation flux. In the monsoon active period, the afternoon convective cloud systems attenuated the solar radiation obviously, resulting in the narrow peak value areas of net radiation flux, net short-wave radiation flux, sensible heat flux, latent heat flux, and surface heat flux, and meantime, the quantities of the above variables dramatically diminished. Sensible and latent heat fluxes were the main consumers for the net radiation flux before and after the establishment of SCSM in 2004 and 2005, with the latter obviously larger than the former, and about more than 90% of the net radiation was used up by the both. The latent and sensible heat fluxes are close related to turbulence movement. The reason for obvious increase in the portion consumed by latent heat flux of the net radiation flux in 2005, in comparison with that in 2004, may be related to the larger wind speed and upward humidity gradient in the ground layer. In the four periods except the monsoon active period before and after the establishment of SCSM the vertical structures of boundary potential temperature showed the typical diurnal variation features, that means, the surface inversion layer developed at night, and the super-adiabatic layer and mixing layer in daytime, with a mixing layer up to about 1070 m in the afternoon. However in the period of monsoon active no mixing layer developed in the afternoon, the reason for this may be that the latent heat released from convective clouds suppressed the development of boundary mixing layer, and the analyses of observations also suggest that the remainder of mixing layer wasn＇ t obvious at night. The analyses show that one of key factors controlling the land-air energy processes and boundary layer thermal structure is cloud system and precipitation. It is crucial to enhance study on the interaction between boundary layer process and the macro- and micro-processes of precipitation for further understanding the land-air processes and boundary layer structure.