夏季巴拉望岛西北部海域净热通量的时空变化特征和形成机理初析

摘要

Using climatical monthly mean OAFLUX heat flux and IMI cloudy, rain, SST and QuikScat wind data, this paper studied the spatial and temporal characteristics of the net heat flux in the South China Sea(SCS) , especially in the northwest waters off the Palawan Island. The results showed that there was a net heat flux minimal value area in the northwest waters of the Palawan Island in summertime, with a significant heat loss up to 20W/m2 in July. According to our analysis, the local heat flux anomaly may be associated with the onset and development of SCS warm water, that was to say the onset of the southwest monsoon, strengthened convection above there. On the one hand, strengthened evaporation led to the increase of the latent heat and cloud, which resulted in the reduction of the incoming shortwave radiation; on the other hand, the precipitation increase led to the occurrence of the barrier layer there, and the air-sea positive feedback caused by the barrier layer strengthened the local convection, which caused the intensified heat loss process, hence the local heat flux anomaly in the northwest waters off the Palawan Island. Further empirical orthogonal function (EOF) showed that the first EOF mode (89. 1% ) for the seasonal variability of the net heat flux in the SCS varied on the same phase, which indicated that the winter and summer monsoon alternately controlled the SCS; the fact that the amplitude was the largest in northern SCS (the belt zone between Hainan Island and southern Taiwan Island ) was associated with the existence of the maximum average wind speed there. The second EOF mode ( 10. 0% ) showed contrary phase variability on the north and the south side of Luzon Island to Leizhou Peninsula and had significant local characteristics, which showed not only the seasonal variability of the Kuroshio current and the circulation in SCS, but also a minimum area northwest Palawan Island corresponding to the net heat flux anomaly area in summer.%利用OAFLUX气候态月平均热通量资料及TMI云量、降雨、SST和QuikScat风场资料,对南海、特别是巴拉望岛西北海域净热通量的时空特征进行了深入分析.研究发现,夏季在巴拉望岛西北海域存在一局域净热通量极小值区,在7月份该海域海洋甚至呈现失热达20 W/m2情况.分析认为该局地净热通量异常可能与南海暖水的发生、发展有关,即由于西南季风爆发,巴拉望岛西北海域对流加强,一方面,蒸发增大使得潜热增大、云量增多,导致入射太阳短波辐射的减少；另一方面,降水的增大使得该海域出现障碍层现象,障碍层导致的局地海温正反馈进一步增强了局地对流,从而加剧海洋失热过程,促成了巴拉望岛西北海域净热通量局地异常的出现.进一步的经验正交模态(EOF)分析表明,在季节变化尺度上,南海净热通量的第一模态(89.1％)呈同位相变化,反映了南海受冬、夏季风的交替驱动特征；其中南海北部(海南岛至台湾海峡南段的带状海域)为振幅最大区,这与该海域存在年平均最大风速有关；第二模态(10.0％)以吕宋岛至雷州半岛一线为界,南北两侧反相,并具有显著的局域特征；不仅反映了黑潮入侵与南海环流的季节变化,而且还发现巴拉望岛西北海域存在一局地极值域,对应夏季净热通量异常区.