Application of Vertical Component of Convective Vorticity Vector to the Diagnosis of a Rainstorm Brought by Southwest Vortex

Convective vorticity vector (CVV) is employed to analyze the rainstorm caused by the shallow system of southwest vortex during 16—18 July 2010, using convective vorticity vector vertical component (C_z). The relationship between every component of the CVV and the 6-hour accumulated precipitation is investigated, particularly the meaning of vertical component in rainstorms caused by southwest vortex. It shows that the vertical component of CVV is a good indicator of the rainstorm caused by southwest vortex. The occurring time of strong precipitation and the peak value of vertical component of CVV are consistent. If C_z reaches an extreme value, the precipitation will change significantly, probably leading to heavy rain phenomenon.Thus the peak time of C_z can be an indicator of the heavy rain forecast. When the rainstorm begins, the precipitation region shows consistently positive values of C_z, with the heavy rain to strengthen. When the positive values of C_z expand larger, the contours become intensive, and the gradient increases. The scope of positive values of C_z and the rain belt are largely the same. In the distribution of lower troposphere 850 hPa level, the rainstorm area locates near the center of the positive values of C_z and tend to the larger gradient of C_z. The main cause is the positive vorticity advection in front of the westerly trough, so that the vorticity in southern Sichuan and eastern Sichuan enhance, and the wet isentropic surface becomes steeply. The rising movement and the water vapor deliver strengthens, which is beneficial to the formation of heavy rain. Along the vertical distribution of C_z in the storm center, the storm intensity increases significantly when vertical components from lower to higher troposphere show consistent positive values. This rainstorm case confirms that the convective vorticity vector can be used for analyzing the shallow meso-scale system like southwest vortex. However, there are very limited cases, so further validation and improvements are needed.