1306号热带气旋“温比亚”非对称降水的环境场特征

利用常规气象观测资料、NCEP1°×1°逐6h全球格点资料以及区域自动站降水资料、FY-2E卫星云图与多普勒天气雷达拼图资料,分析2013年第6号热带气旋(TC)"温比亚"在广西造成的非对称降水的环境场特征。结果表明,受副热带高压西南侧稳定而深厚的东南气流引导,"温比亚"西北行深入到广西中部,有利于广西出现较大范围暴雨。200hPa上TC流出气流的中心偏于其中心的南侧,为降水不对称分布提供了动力背景;TC风场分布明显不对称,导致涡度、散度动力场结构呈不对称分布;低层辐合区主要分布在TC中心南侧,整层水汽通量辐合中心位于TC中心南侧,从而使暴雨集中在TC中心南侧。环境风垂直切变矢量指向TC移动路径的左侧,有利于TC移动路径左侧出现强的对流及降水,结合水汽辐合条件,可将其作为TC暴雨落区预报的一个判据。相对湿度(RH)呈均匀分布,假相当位温(θse)呈准对称分布,表明TC降水的非对称分布主要由动力因子而非热力因子引起。

Characteristics of environment fields of asymmetrical precipitation induced by tropical cyclone Rumbia （1306）

Using data from conventional meteorological observations, NCEP 6-hourly global reanalysis with resolution 1 °×1 °, rainfall ob-servations from automatic weather stations, FY-2E satellite cloud images and regional mosaics of Doppler weather radars, we analyzed char-acteristics of environment fields of asymmetrical precipitation in Guangxi induced by tropical cyclone （TC） Rumbia （1306）. It is concluded that Rumbia moved northwestward and reached in central Guangxi under steering of stable and deep southeasterly airflow in the southwest side of subtropical high over the west Pacific, which is favorable to the occurrence of large-scale heavy rain in Guangxi. The center of outward airflow at 200 hPa tilting to the south side of TC provides dynamical condition for the asymmetrical precipitation of Rumbia. The clear asym-metrical wind field of TC causes asymmetrical vorticity and divergence fields. The distribution of heavy rain locating in the south side of TC is corresponding with the convergence zone in the low-level and the convergence center of water vapor flux in the whole layer in the same loca-tion. Wind vertical shear pointing to the left of the moving path of TC is advantageous to the strong convection and rain occurring in the same side, which is regarded as one of the criteria predicting rainfall distribution associated with tropical cyclones, along with water vapor conver-gence. The facts that the relative humidity is fairly well-distributed and the pseudo-equivalent potential temperature field is quasi-symmetry indicate that the asymmetrical precipitation of Rumbia is not mainly attributed to thermodynamic but dynamical factors.