Analysis on cause of a mesoscale rainstorm event induced by the residual spiral cloud band fromthe tropical depression Hagibis (1407)

Using conventional observation data, NCEP reanalysis data with 1°×1° resolution, Doppler weather radar products and intensive observations from automatic weather stations, we study the cause of a mesoscale rainstorm event induced by the residual cloud band from tropical depression (TD) after the tropical cyclone (TC) Hagibis (1407) weakened. The results show that the severe precipitation generated by residual circulation of TD is characterized by mesoscale. It belongs to the typical mesoscale rain cluster induced by the outer spiral cloud band of Hagibis. It is found that some key factors have lead to the development of the mesoscale structure of spiral cloud band, including the warm shear between southwesterly jet and southeasterly jet, the coupling of convergence in the low-level and divergence in the upper level and the development of secondary circulation. In addition, an extended VAP (EVAP) method is used to retrieve wind fields in the center of Hagibis to further verify the existence of a significant mesoscale spiral structure around the tropical depression (TD). Consequently, severe precipitation is primarily induced by the mesoscale rain clusters under TD with spiral cloud band.