西北太平洋热带气旋快速增强与环境垂直风切变统计分析

利用1990-2009年美国联合台风警报中心整编的热带气旋（TC）最佳路径资料和NCEP/NCAR再分析等压面流场资料，在分析西北太平洋TC每24 h强度变化统计特征的基础上，确定了西北太平洋TC快速增强的阈值，对比不同阈值条件下，TC快速增强初始时刻的强度，TC快速增强发生的季节变化和空间分布特征，进一步研究环境垂直风切变与TC快速增强的关系。结果表明：在西北太平洋海区，当TC强度24 h变化达到样本累积百分率的88%、90%、93%和96%的概率时，对应的强度变化值分别为25 KT、30 KT、35 KT和40 KT，定义它们为TC快速增强的阈值。该阈值越大，快速增强初始时刻的强度也越强。60%左右的TC快速增强发生在8-10月，TC快速增强的空间分布集中于125°-150°E、10°-25°N的矩形区域内。对流层不同层次的垂直风切变与TC快速增强的关系有差异，TC快速增强阈值为40 KT时对应的对流层中上层（200~500 hPa）、对流层中下层（500~850 hPa）和对流层（200~850 hPa）的垂直风切变值的概率分布显示：当垂直风切变≥12 m/s时，分别只有9.7%、1.5%、11.1%的TC可以快速增强；且其与TC快速增强时强度变化的相关系数分别为-0.15、0、-0.04，以200~500 hPa的最为显著，表明对流层中上层垂直风切变对TC强度增强的抑制作用最明显。在TC快速增强阈值为40 KT的初始时刻，将200~850 hPa垂直风切变划分为东风切变和西风切变的统计表明，57%的TC在东风切变的环境下可以快速增强。

Rapid Intensification of Tropical Cyclones and Vertical Wind Shear over the Northwest-Pacific

In this paper the statistical characteristics of per 24h intensity change for tropical cyclone (TC) are analyzed, the thresholds of tropical cyclone rapid intensification (RI) are defined by using the tropical cyclone best track data of Joint Typhoon Warning Center (JTWC) and the NCEP/ NCAR reanalysis data from 1990 to 2009, and with comprehensive comparison and analysis of initial intensity, the seasonal variation and spatial distribution characteristics of TC rapid intensification are given in different thresholds of tropical cyclone rapid intensification. According to the calculation, the paper defines the thresholds of tropical cyclone rapid intensification as 25KT, 30KT, 35KT, 40KT, which respectively represent the 88th, 90th, 93th, 96th percentiles of 24-h overwater intensity changes of tropical cyclones in the Northwest-Pacific area. The initial intensity of tropical cyclone rapid intensification will increase when the threshold increases. About 60% of tropical cyclones undergo RI during the period from August to October. And, most of the tropical cyclones undergo RI in the region of 125°E-150°E,10°N-25°N. It is found that the relationship between the vertical wind shear at different levels in troposphere and tropical cyclone rapid intensification is different. When the threshold of tropical cyclone rapid intensification is 40KT in 200-500hPa, 500-850hPa and 200-850hPa, only 9%, 5%, 7% of tropical cyclones can undergo RI. The correlation coefficient between tropical cyclone rapid intensification and the vertical wind shear at different levels are -0.15, 0, -0.04 respectively. So, it is obvious that the vertical wind shear in 200-500hPa is less favorable for TC to undergo RI. The vertical wind shear can be divided into east vertical shear and west vertical shear. When the threshold is 40KT in 200-850hPa, about 57% of the TC can undergo RI under the circumstance of east vertical shear.