西北太平洋热带气旋快速加强过程中的水汽特征分析

利用NCEP的1°(纬度)×1°(经度)全球最终分析资料和JTWC(Joint Typhoon Warning Center)最佳路径资料,对2002~2011年西北太平洋热带气旋(TC)非减弱阶段快速加强(Rapid Intensification,RI)和缓慢加强及强度稳定(Non-RI)过程中,TC环境场及其内部各区域水汽分布和输送特征进行统计分析,揭示水汽因子对TC随后24 h强度变化的影响,为TC强度突变的趋势预报提供依据。结果表明:对流层低层900 h Pa层半径3~10纬距区域平均相对湿度(RH_3-10)能明显区分RI与Non-RI过程,说明西北太平洋TC强度变化对水汽的敏感高度较大西洋更接近洋面;RI初始时刻的RH_3-10显著大于Non-RI,而水平水汽通量(F_all)则弱于Non-RI,说明RI开始时刻TC环境表现为高水汽含量和较小的水汽输送,而随着RI过程TC内强对流发展对水汽的消耗,水汽含量明显减小故水汽通量则出现增强;RI和Non-RI过程水汽因子的分布和输送在TC内核区和外雨带差异明显,初始时刻RI过程净水汽获得区域大于Non-RI。相关性分析同样表明,适宜的相对湿度和水汽通量是非减弱阶段RI的有效潜势预报因子。

A Statistical Analysis of Moisture Characteristics during the Rapid Intensification of Tropical Cyclones over the Northwestern Pacific

The tropical cyclones (TCs) that occurred during 2002-2011 in the northwestern Pacific Ocean and the connection between the moisture and their ability to subsequently undergo rapid intensification (RI) are investigated with the NCEP FNL (Final Analysis) data and the best-track datasets of the JTWC (Joint Typhoon Warning Center), which is organized into 24-h intervals of either RI and slow intensification/constant intensity (non-RI) periods. The environmental and internal distributions of moisture and its transport at each interval are statistically analyzed to reveal their significant influence on the intensity change in the subsequent 24 hours. The results show that relative humidity area-averaged from the radius of 3° to 10° latitude at 900 hPa (RH_3-10) can clearly distinguish RI from non-RI, which means the sensitive vertical level of moisture in the northwestern Pacific Ocean is lower than that in the Atlantic Ocean. In addition, larger RH_3-10 values and smaller horizontal moisture flux (F_all) mark the beginning of RI. With the consumption of the convection development in RI, the environmental humidity decreases and the moisture flux is enhanced. The obvious differences of the moisture distribution and transfer between the TC inner-core and outer-rainband region are also studied, showing that the net convergence region of moisture flux in RI is larger than that in non-RI. The correlative analysis also indicates that intensity forecasts and RI predictions in particular may be aided by the use of the moisture and its flux, both in the environmental and internal region.