Analysis on characteristics and causation of a meso βscale paroxysmal rainstorm on Loess Plateau

In order to improve the forecasting and early warning capabilities of meso β scale paroxysmal rainstorm on Loess Plateau, NCEP data, MICAPS data, Doppler radar data, etc. were used to analysis the large-scale field and physical environment of a meso β scale paroxysmal rainstorm on Loess Plateau on August 14, 2011. The results showed that the meso β scale rainstorm was mainly caused by activity of a meso β scale convective cell. A tongue of low meso-scale energy ratio that was accompanied by a weak cold air activity invaded south along the Yellow River, which is one of the trigger mechanisms of the rainstorm. The formation of meso β scale cyclonic convergence in the lower troposphere, accompanied by meso β scale strong divergence in the radial scale in the upper troposphere constituted the basic characteristics of vertical circulation during the strongest storm rainfall periods. The analysis of vorticity budget showed that when convective clouds were developed in the rainstorm area, the dominant factors are horizontal advection and horizontal divergence term in the formation of strong positive vorticity below 600 hPa. The dominant factor is horizontal advection term in the formation of negative vorticity from 550 to 250 hPa. The horizontal divergence term plays a main role when the strong convective clouds in rainstorm area dissipate.