飑线组织化过程对环境垂直风切变和水汽的响应

Impact of Vertical Wind Shear and Moisture on the Organization of Squall Lines

利用ARPS模式对飑线发生发展过程进行二维理想数值试验,讨论了低层环境垂直风切变和水汽条件变化时,飑线内部物理因子配置变化及其与系统强度演变的联系。研究表明,飑线发展过程中出现的动量、热量和水汽的再分配过程,造成系统内垂直环流结构和扰动温湿场分布发生变化,从而影响系统内部深对流的组织化过程和飑线强度的发展。基于低层环境垂直风切变和水汽两个要素的敏感性试验研究表明,低层环境垂直风切变增大(减小)时,飑线移速减慢(加快),冷池前沿激发的新对流与中高层的垂直运动相互贯通(分离),飑线系统强度随之增强(减弱)。此外,当低层水汽增加(减少)时,会导致输送到中层的水汽增加(减少),中层凝结潜热释放增多(减少),该层垂直运动增强(减弱);同时,飑线系统区域环境释放的对流有效位能(CAPE)增大(减小),新生对流的强度增强(减弱)。低层水汽条件通过水汽输送和能量释放,改变冷池前沿新对流与中高层垂直环流的组织化结构,从而影响飑线强度。

The redistribution of physical factors and its impacts on the intensity of squall lines under the influence of low-level Vertical Wind Shear （VWS） and moisture content are examined through two-dimensional idealized simulations with the ARPS model （the University of Oklahoma＇s Advanced Research Prediction System）. It shows that the redistribution of momentum, heat and moisture during the evolution of squall lines leads 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 sensitivity tests of low-level VWS and moisture content show that increasing （decreasing） the low-level VWS decelerates （accelerates） the propagation of the squall line, and makes the connection （separation） between the mid-level upward current and the new forced updrafts at the front edge of the cold pool, which corresponds to the intensification （weakening） of the squall line. On the other hand, increasing （decreasing） the low-level moisture content results in an increase （decrease） of moisture delivery from the low to middle level, which enhances （weakens） the mid-level latent heating and upward movement. Energy analysis indicates that the low-level moisture change influences the release of Convective Available Potential Energy （CAPE）, and the intensity of the new convection. The combined effects of latent heating and CAPE released from low-level moisture change also affect the squall line intensity through exerting an influence on the organization of the upper-level upward currents and the new forced updrafts at the front edge of the cold pool.