Study On The Mechanism Of Double Vortex Rainstorm Of Huang Huai

By use of the NCEP1°*1°reanalysis data every6hours, the conventional ground upper-air observation data and the results from numerical simulation system, that is WRF model, the preliminary analysis and diagnosis of the storm that occurred in Huang Huai area Henan Province on2012July4-5caused by a double Vortex. The results show that, the subtropical high is stable, and the generation of the low level shear line and southwest jet provides dynamic conditions and abundant moisture supply for the rainstorm; the upper trough carrying cold air moves toward south and invades the rear of the double vortex, making the Yellow River vortex (northwest vortex) moves to the southeast and the Southwest China vortex moves to northeast along the shear line, the storm occurred under the influence of this double vortex; this paper analyses the evolution characteristics of the double vortex by use of the satellite images and points out that the connection of the positive vorticity cloud system of Yellow River vortex and the low cloud system from Southwest China vortex is the major cause of the storm.The NCEP data are used to diagnose the heavy rainfall caused by this double vortex, the specific humidity field provides the ample water vapor condition for the strong precipitation in the whole stage; the moisture flux divergence center between1000hPa and900hPa reaches to more than-12×10-7g·cm-2·hPa-1·s-1during the combination period of low vortex cloud system. This indicates that during the strong precipitation, abundant water vapor gathers in the storm area; the conditions that the convergence on low levels, divergence on upper-level, which is also called the aspiration mechanism, the strong vertical ascending motion and the positive vorticity on low levels, negative vorticity vorticity on high levels, which cross Henan Province from west to east, provide a favorable dynamic environment for the development of the heavy rain; the evolution characteristics of the vertical helicity on700hPa is corresponding to the vortex center on850hPa, the heavy rainfall center is located in the large value areas of vertical helicity, the vertical helicity maximum occurs ahead of the precipitation for about3-6h, Therefore, the vertical helicity has certain forecast significance to the future heavy rainfall area. It is worth to mention that, the negative center of moist potential vorticity develops from the Yellow River vortex to the south, the symmetric instability region expands toward south and is superposition with the negative area in southwest vortex, which control the heavy rainfall area, lead to the strengthening of the ascending motion and the vertical transport of the water vapor, is conducive to precipitation increasing.Analysis shows that:the strength and location of the rain band are consistent with the position of the double vortex and the surface convergence line, the ground rainbelt moves with the surface convergence line, the strength of the precipitation center increases with the strengthening of the surface convergence line, which indicate that the development of the surface mesoscale systems provides powerful lifting mechanism for the strong precipitation; the rainstorm clouds lies in the overlapping area of the right side of the entrance of the upper level jet and the left side of the exit of the low-level jet on the satellite image; the strong echo clusters or bands on radar echo image is closely related with the occurrence of the β-scale disturbance, which is the main mesoscale systems that cause the rainstorm.The results of numerical simulation shows that, the fine grid model simulates the rainbelt located in Henan province Huang Huai area, the two precipitation locations and the intensity of the precipitation more better. Based on the successful simulation and by use of the high temporal and spatial resolution model output data, the analysis of the evolution characteristics of the double vortex are conducted:the analysis of the hourly wind field data on500hPa,700hPa and850hPa confirmed the whole process of the genesis, development, movement and merging of the double vortex. In the double vortex process, the cooperation of the high and low level vortex increases the baroclinicity, strengthens the convergence of the shear line which is southwest-northeast towards, and evokes the strong ascending motion, which leads to the generation of the heavy rainfall. This case provides a good sample for the interaction of two vortex.Based on the analysis of the heavy rainstorm process, the evolution features of the mesoscale system structure and development in the process of the double vortex rainstorm are initially revealed, providing the reference for the rainstorm weather forecast.