南海—西北太平洋季风槽中热带气旋异常活动特征

Characteristics of TC Abnormal Activities in SCS-WNP Monsoon Trough

应用1979—2005年的台风资料和NCEP/DOE AMIP-Ⅱ再分析资料,分析了生成于南海—西北太平洋季风槽中的热带气旋(MTTC)活动特征及季风槽强弱对MTTC异常的影响。结果表明:①1979—2005年5—10月南海和西北太平洋生成的热带气旋(TC)共有672个,年平均24.9个,其中MTTC为491个,占73.1%,占登陆中国TC频数的79.2%。②27年间MTTC年频数经历了正常期(1979—1987年)—多台期(1988—1994年)—少台期(1995—2005年)3个阶段;具有准4年和准2年的变化周期,1994年为MTTC频数由多台向少台转换的转折点。③MTTC频数异常年份,MTTC生成起止日期和生成位置有明显差异:MTTC异常偏少(多)年,MTTC活动起始日期较晚(早),且5—10月皆不活跃(活跃),MTTC生成海区范围较小(大)。④南海—西北太平洋季风槽强度和位置异常与MTTC活动异常密切相关。

Based on the typhoon data and NCEP/DOE AMIP-II reanalysis data from 1979 to 2005,a study is performed of the behaviors of tropical cyclones generated in the monsoon trough（MTTC） in the South China Sea（SCS） and western North Pacific（WNP） as well as the effects of the monsoon trough intensity on MTTC.Analysis suggests：（1） The total number of tropical cyclones（TCs） is 672 over the South-China Sea and the western North Pacific during May to October from 1979 to 2005,of which MTTC is 491,making up 73.1% of the total and 79.2% of the onland typhoons.The grasp of the regularity of MTTCs activities means the grasp of the principal regularity of the western North Pacific TCs,which are TCs mainly affecting China.（2） During this period,the annual occurrence frequency variation of MTTCs experienced three stages： normal（1979 to 1987）,more MTTCs（1988 to 1994）,and fewer MTTCs（1995 to 2005）;there was periodic variation in MTTC with quasi-four-year and quasi-two-year periods,with 1994 being the turning point.（3） In the years of anomalous MTTCs,there was great difference in onset/ending dates and generation positions.In the years of fewer/more MTTCs,in comparison with the mean condition,MTCCs started later（earlier） and continued to be in inactive（active） phase from May to October with a smaller（larger） generation area.（4） The monsoon trough intensity and position affect greatly the generation position and annual number of MTTCs.