南海西沙地区季风季节变化的气候特征

Seasonal Evolution of Climatic Characteristics of Summer Monsoon over Xisha Area

利用位于南海中北部的西沙观测站１９５９～１９８８年３０年常规地面观测资料和１９８０～１９８８年９年探空资料，分析了西沙地区季风季节变化气候特征。３０年的地面观测资料平均结果表明，西沙地区５月中旬西南（或南）风建立，对流突然加强，云量陡增，６月上旬降水量剧增。利用本文定义的季风指数，可以将西沙夏季风季节变化过程分为３个阶段：东南夏季风阶段（４月初至５月初）、西南夏季风阶段（５月中至９月初）和夏季风结束阶段（９月中至１０月初）。这种阶段的划分不但与广东省汛期降水有较好的对应关系，而且与南海大气环流的季节演变也有很好的联系。

In this study, the 30-year (1959～1988) conventional surface observations and the 9-year (1980～1988) radiosonde data at Xisha station located in the mid-northern part of the South China Sea were used to analyze the annual evolution of summer monsoon at Xisha. The analyzed results show that the southwest wind (or south wind) at Xisha prevails in middle of May, the convection and cloud amount increase suddenly at the same moment and rainfall increases greatly in early June. Using the monsoon indices 1 and 2 proposed by us, the annual evolution of summer monsoon can be divided into three phases, the southeast monsoon phase (from early April to early May), the southwest monsoon prevailing phase (from mid-May to early September) and the ending phase (from mid-September to early October). These phases are associated with both the seasonal precipitation variation in Guangdong and the annual evolution of atmospheric circulation over the South China Sea.