南海夏季风维持期的气候特征Ⅰ——40年平均  

THE CLIMATIC CHARACTERISTICS OF MAINTAINING PERIOD OF SOUTH CHINA SEA SUMMER MONSOON Ⅰ——40 Yearly Average

作　　者：林建恒[1] 王安宇[2] 冯瑞权[2] 唐天毅[1] 吴池胜[2] 李国丽[2] 李江南[2] 吴尚森[3] 

机构地区：[1]澳门地球物理暨气象局 [2]中山大学大气科学系/季风与环境研究中心,广东广州510275 [3]中国气象局广州热带海洋气象研究所,广东广州510080

出　　处：《热带气象学报》2005年第2期113-122,共10页Journal of Tropical Meteorology

基　　金：中国科学院知识创新工程项目(ZKCX-2-SW-210)资助

摘　　要：使用NCEP的1958～1997年逐日格点气象资料,对我国南海地区(105～120°E,5～20°N)夏季风维持期40年平均的气候特征进行了分析,分析时间尺度是候.南海夏季风维持期由活跃期和非活跃期组成.我们将南海上空850hPa连续有40%以上面积盛行暖湿的西南风的候定义为南海夏季风的活跃期,不足40%则定义为非活跃期.这里所指的暖湿西南风是θse必须大于335K,西南风的风速必须大于2m/s.就40年平均而言,南海夏季风维持时间大约为23候约4个月,每年南海夏季风活跃期约出现4.3次,每次的平均维持时间约为3.9候,非活跃期约出现3.3次,每次的平均维持时间约为2.4候,活跃期每年的总长度约为17候,非活跃期约为8候.无论是南海夏季风活跃期还是非活跃期,南海上空850hPa都为一个低槽辐合区,200hPa为高压辐散区,也就是说与活跃期相比非活跃期主要气候特征表现为季风的减弱,在环流的偏差场上(活跃期减非活跃期)在南海上空850hPa上为西风,200hPa上为东风.活跃期无论在850hPa或在200hPa上都比非活跃期要暖一些,与此相应,非活跃期的季风降水要比活跃期的小得多,对流活动也大大减弱.南海夏季风和夏季风降水都有明显的30～60天的低频振荡,在多数情况下夏季风和夏季风降水的低频振荡的位相比较一致.By using 40-yearly NCEP reanalysis daily grid data (1958～1997), we have analyzed the 40-yearly mean climatic characteristics of maintaining period of the South China Sea(SCS)(105～120oE, 5～20oN) summer monsoon pentad by pentad. The maintaining period of SCS summer monsoon consists of the active periods and inactive periods. We define the active periods of South China Sea summer monsoon as the time when the pentad in which the area of warm and wet southwesterlies over the SCS in 850hPa are over 40% continuously; if the area is less than 40%, it is defined as inactive periods. The warm and wet southwesterlies should meet the two conditions: (1) At 850hPa, θse should be greater than 335K. (2) At 850hPa, the southwesterlies should be greater than 2m/s. According to the 40-yearly mean, the mean maintaining time of the SCS summer monsoon was about 25 penteds, which was four months approximately, the active period of SCS summer monsoon appear 4.3 times every year, each time the mean maintaining time was about 3.9 pentad, the inactive periods appear 3.3 times a year, each time the mean maintaining time was about 2.4 pentad. The active period was about 17 pentads totally and the inactive was about 8 pentads every year. Whether it was the active periods or the inactive periods in SCS, it is the low trough area with convergence in SCS at 850hPa and high pressure area with divergence at 200hPa. In other words, comparing the active period with the inactive period, the main climatic characteristics is that the monsoon weakens and displays as westerlies at 850hPa and easterlies at 200hPa in the circulation deviation field over the South China Sea(active time reduces inactive time). Regardless of 850hPa or 200hPa, it was warmer inactive periods than in inactive periods, obviously rainfall was less and the convection activity was weakened greatly in the inactive periods. Both the SCS summer monsoon and the summer monsoon precipitation has 30～60 day-long low frequency vibrations obviously. In most situations, the low frequ

关 键 词：南海夏季风 活跃期和非活跃期 40年平均 气候特征 

分 类 号：P425.42[天文地球—大气科学及气象学]