Impact Of Vertical Wind Shear And Moisture On The Organizational Of Squall Lines

The redistributions of physical factors and its impacts on the intensity of squall lines under the influence of the low-level vertical wind shear (VWS) and moisture content are examined through two-dimensional idealized simulations with the ARPS model. It shows that the redistribution of momentum, heat and moisture during the evolution of squall lines lead to the change of inner vertical circulation and the configuration of perturbation temperature and humidity, which affects the organization of deep convection and the intensity of the system. The results of sensitive tests of low-level VWS and moisture content show that the increasing (decreasing) of the low-level VWS decelerates (accelerates) the propagation of squall line, and make the connection (separation) between the middle-level upward current and the new forced updrafts at the front edge of the cold pool, which corresponds to the intensification (weakness) of the squall line. On the other hand, the increasing (decreasing) of the low-level moisture content results in the raising (reducing) of the moisture delivery from low level to middle level, which enhances (weakens) the middle-level latent heating and the upward movement. The energy analysis indicates that the low-level moisture change influences the releasing of convective available potential energy (CAPE), and the intensity of the new convection. The combination effects of latent heating and CAPE releasing from low-level moisture change also affect the squall line intensity through exerting the influence on the organization of the upper-level upward currents and the new forced updrafts at the front edge of cold pool. Analysis of the squall line occurred in Jiangsu, Anhui Province on 14Jun,2009 show that the conditions of moisture, instability and lift are conducive to produce this process. The simulation results show that the squall line has the typical structure of the mesocale surface features. The weaking of squall line intensity associated with the decreasing of low-level VWS and moisture content in the process of development and that can be explained by the finding of the ideal test.