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 observations from automatic weather stations, FY-2E satellite cloud images and regional mosaics of Doppler weather radars, we analyzed characteristics 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 asymmetrical 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 location. 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 convergence. 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.