边界层对青藏高原东北边坡地区一次冰雹天气影响的数值诊断分析

Diagnostic Analysis of the Effect of Planet Boundary Layer on a Hail Event in the Northeastern Edge of Qinghai-Tibetan Plateau

通过使用WRF V3.4模式,对发生在青藏高原东北边缘地区的一次区域性严重冰雹灾害事件从边界层进行了分析,研究发现这次灾害是由于前期能量积蓄和地形等原因导致分配不均匀,进而引发次级环流,配合天气尺度环流系统,造成了这一历时短、强度强、突发性强、局地性强和多灾种并发的特大灾害性天气事件;强天气过程发生时的对流边界层高度远小于平均状况,但是前期的最大对流边界层高度呈逐步增厚的特征,说明在进行能量积蓄,且边界层对强天气过程有显著影响;潜热和感热通量在发生前远超过平均状况,而其中又以感热通量差异最大,说明热力作用对对流天气过程占有主导地位;在近地面的条件不稳定层结之上存在一个绝对稳定层结,它的厚度逐渐减小,绝对稳定层结之上的条件不稳定层结的假相当位温减温率在13:00峰值达到0.88 K·(100m)-1,而水平位温梯度也基本在这时达到最大;边界层的摩擦速度在天气过程发生前后均呈现出了显著增大,这可能是由于湍流动量和中尺度动量输送异常造成的。

The paper studied a heavy hail disaster occurring on the northeastern edge of Qinghai-Tibetan Plateau on 10 th May 2012 based on an analysis to planet boundary layer and land surface process by using WRF V3. 4 model. The results indicated that the hail disaster was caused by a secondary circulation because of the prior energy accumulating. The hail disaster was a extraordinarily serious calamitic event with the characteristics of a short-duration,high intensity,breaking out suddenly and multi-disasters accompanied with the synoptic-scale systems. At the time,the maximum height of convective boundary layer（ CBL） in the early stage became thicker as a result of the energy accumulating,although the height was greatly lower than the average one. All of this demonstrated that the thermal convection environment of boundary layer maybe was the important energy source for the convection of weather development. Judging from the distribution of convective available potential energy（ CAPE）,the energy gradient was pretty and the thermodynamic system was extremely in homogenous. The latent heat flux and sensible heat flux value exceeded the average before the disaster. The height of absolute stable stratification,above the conditional unstable stratification in the near surface,was decreased gradually. The lapse rate of potential pseudo-equivalent temperature in conditional unstable layer had the tendency of increasing first and then decreasing,and its peak was 0. 88 K·（ 100m）- 1at 13： 00. In the meanwhile,the horizontal gradient of potential temperature was maximum. The friction velocity exhibited a significant increase before and after this process probably because of the abnormal transfer of turbulent momentum and meso-scale momentum flux.