飑线结构和强度对低层湿度和环境垂直风切变的敏感性研究

The sensitivity of the structure and strength of squall line to low-level humidity and environmental vertical wind shear

利用数值模式WRF进行二维飑线理想数值试验。通过改变初始场低层湿度和低层环境垂直风切变探讨了初始环境场对飑线在触发阶段与发展初期结构和强度的影响。低层湿度试验表明,增加低层湿度有利于初始启动阶段对流的发生从而使对流系统强度更强;飑线强度增加,对流上升运动增强,更有利于冷池前沿激发出新生对流单体,系统发展更快;同时激发更多降水,冷池强度增强。低层环境垂直风切变试验表明,在飑线触发阶段,更强的环境垂直风切变使对流主体前倾趋势更大,对对流的触发有阻碍作用;冷池和环境垂直风切变的相互作用被认为是飑线发展的重要机制,基于RKW理论,在飑线发展初期,近地面冷池相对较弱,在更弱的环境垂直风切变作用下更容易使对流结构呈直立状态从而产生更强和更深的上升运动,飑线强度增强。

The sensitivity of the structure and strength of a squall line in the initial and early development stages to initial low-level humidity and environmental vertical wind shear is investigated in a two-dimensional idealized squall line simulation using the WRF model.The results of the sensitivity test of low-level humidity indicate that increasing low-level humidity is favorable for convective triggering and stronger convective systems.The increased squall line intensity and upward movement make it easier for new convective cells to form at the leading edge of the cold pool.The increased low-level humidity also leads to more precipitation,which raises the intensity of the cold pool.In addition,the results of the sensitivity test of low-level environmental vertical wind shear show that the convection is easier to become downshear tilted in the initial stage with stronger low-level environmental vertical wind shear,which is unfavorable for convective triggering.According to RKW theory,the interaction between cold pool and low-level environmental vertical wind shear is considered as an important mechanism for the development of squall lines.The cold pool is relatively weak during the early stages of squall line development,and with weaker low-level environmental vertical wind shear,it is easier for the convection to become upright,resulting in a stronger and deeper upward movement that is favorable to the strength of the squall line.