西北太平洋热带气旋强度与环境气流切变关系的气候分析

采用NCEP/NCAR再分析资料和JTwC(美国关岛联合台风警报中心)资料,对1974～2004年5～10月西北太平洋热带气旋(TC)强度和环境风垂直切变进行了趋势特征、振荡周期和空间结构分析.结果表明:西北太平洋热带风暴强度以上TC的最大风速和环境风垂直切变在时间上有相反的变化趋势,弱的环境风垂直切变有利于TC强度的增大;前12 h的环境风垂直切变对TC强度的发展影响最大.环境风垂直切变在两北太平洋TC最强的年份表现为环境风切变值小,TC发生密集;最弱的年份表现为环境风切变值大,TC发生稀疏.

Influence of Environmental-Wind Vertical Shear on Intensity Variation of Tropical Cyclones over Northwestern Pacific

The NCEP/NCAR and JTWC (Joint Typhoon Warning Center) reanalysis data are used to investigate the trends of the frequency, distribution and oscillation periods of maximum wind speed and environmental wind vertical shear of tropical cyclones over the Northwestern Pacific from May to October, 1974 to 2004. Results show that there are contrary variation trends between maximum wind speed and environmental wind vertical shear. The weak vertical shear is propitious to the development of tropical cyclones. The impact of the vertical shear on intensity variation of tropical cyclones at 12 hours before is the greatest. In strong TC years, the environmental wind vertical shear is relatively small, and there are more tropical cyclones; while in weak TC years, the environmental wind vertical shear is large, and there are less tropical cyclones.