季风槽内热带气旋生成的基本特征分析

Characteristics of the tropical cyclogenesis in the summer monsoon trough

利用美国关岛联合台风警报中心(JTWC)所提供的热带气旋(TC)、热带扰动、TBB、QuikSCAT观测风场和NCEP再分析风场等资料,统计了生成于季风槽内的TC(MTC),归纳了与MTC生成有关的季风槽主要模态,并进一步分析了不同季风槽模态下MTC生成的基本规律及其生成过程中中尺度对流系统(MCS)活动的时空特征。结果表明:(1)MTC占总TC数量的71%,且MTC生成后易加强为热带风暴或台风;季风槽内热带扰动的发展概率远高于非季风槽内热带扰动。(2)与MTC生成有关的季风槽主要存在中国南海-西北太平洋型、西北太平洋型、反向型、夏末型和中国南海型5个主要模态;其中,影响中国的TC主要生成于中国南海-西北太平洋型、中国南海型和西北太平洋型模态。反向型模态中热带扰动发展为MTC的概率最大,而夏末型最小。(3)季风槽内TC群发是MTC生成的重要形式,其中,中国南海-西北太平洋型季风槽是MTC群发的主要模态,反向季风槽模态下最易出现高频次MTC群发。(4)MTC的生成常伴随2—4个MCS同时或相继出现。季风槽大尺度对流云团组织MCS频繁出现,MCS的活跃阶段正是季风槽内热带扰动向热带低压演变的阶段,特别当季风槽显著时,MCS异常活跃,易造成MTC的群发。

By using the tropical cyclone （TC） data from the Joint Typhoon Warning Center （JTWC）, the tropical disturbance （DB） alert messages from University of Illinois, the Geostationary Meteorological Satellite TBB data, the QuikSCAT oceanic wind data and the NCEP final reanalysis wind data, the statistics of TCs that form in the summer monsoon trough （MTC for short） is made, and the chief patterns of the monsoon trough associated with the tropical cyelogenesis are discussed. The paper further analyzes the characteristics of the tropical cyclogenesis within every pattern of the monsoon troughs and the features of the mesoscale convective systems （MCS） which occur 48 hours prior to the MTC formation. The main conclusions are as fol lows： （1） The percentage of the MTCs to all the TCs is about 71~/00 and the MTC can easily further develop into the tropical storm or typhoon. The probability of the DB in the monsoon trough that can develop into the tropical depression is much higher than that in the non-monsoon trough. （2） There are five chief monsoon trough patterns that are associated with the tropical cy clogenesis and they are the SCS-NWP pattern, NWP pattern, Reverse-Oriented fRO） pattern, Late-Season （LS） pattern and SCS pattern, respectively. The TCs that effect China come mainly from the SC^NWP pattern, NWP patterp and SCS pattern. The developmental probability of the DB in the RO pattern is the highest, but it is the lowest in the LS pattern. （3） The cluster of MTCs is the main way of the MTC formation. The SCS NWP pattern is the most important pattern for the cluster of MTCs, while the cluster of MTCs can very easily occur in the RO pattern. （4） During the process of MTC formation, there are usually more than two MCSs near the MTC formation position during 48 hours prior to the MTC formation. The large scale cloud clus ters of the monsoon trough can organize MCSs frequently; the period during which the MCSs are active is just the process that the DB transfers into the tropical depression. Especially when the monsoon trough is very strong, the MCSs are so active that the cluster of MTC can easily occur.