冷暖空气入侵对西南低涡发生发展影响研究

Study about the Effect of Cold/warm Air Intrusion on the Development of the Southwest Low Vortex

本文采用WRF模式模拟了2008年7月20～22日四川省一次由西南涡活动引发的大暴雨过程,并分析了对流层中层至中低层冷/暖空气入侵在西南涡发生发展过程中的作用,研究结果表明:冷/暖空气从北部入侵会改变对流层中、低层流场,当降低模式北边界温度,增强西北气流南下,致使四川省上空没有形成西南涡,取而代之为一深槽,同时雨区内上升运动减弱、低层辐合减弱,对流层中层温度增加、比湿略减小,雨区集中在深槽附近,雨区范围和强度都显著减弱且小于控制试验。增加模式北部温度引起北部东北气流向南输送,低值系统南移,增温促进了周围空气向降水中心辐合,增强了中低层大气的辐合上升运动,对流层中、中高层增温,雨带南压,雨区强度显著增强且大于控制试验。降低或增加模式西边界温度对流场、低涡强度和位置影响相对较小,降温使得低涡位置偏北、对流层风速增强与减弱区交替分布;增温使得低涡偏东、对流层中层至中低层风速减弱高层风速增强,二者对降水落区影响亦较小,对大暴雨中心强度有不同程度影响。

Using the WRF model to simulating a rainstorm process occurred in Sichuan reduced by the southwest vortex ac- tivity from 20 to 22, July, 2008, the article analyzes the effect of cold/warm air intrusion on the development of the southwest vortex, numerical results show that： the cold/warm air intrusion from north boundary can change streamline field in the middle and low troposphere. While reduceing temperature at north boundary, strengthening the northwest air current to going south, there is no southwest vortex in Sichuan, replaces it with a trough, simultaneously in the rain area the ascend movement weak- ens, the low level convergence to be weaken, the temperature in middle troposphere increases, specific humidity reduces, the rainfall area concentrates nearby the trough, the rainfall area and the intensity weaken obviously and they are smaller than the control test. Increasing temperature at the north boundary to cause northeast air transport to the south, the low value system moves southward, warming promoted the surrounding air convergence to the precipitation center, strengthened the middle and lower atmosphere convergence ascend movement, the temperature in middle troposphere and has been increased, rain belt move southward, the rainfall intensity strengthen obviously and they were great than the control test. Reduce or increase the tempera- ture of the western boundary has relatively small effect on the flow field pattern, intensity and location of the vortex, cool makes the vortex northward, wind speed of troposphere increased and weakened area alternates distribution ; warming makes the vortex eastward, the lower middle troposphere reduced but high - level wind speed increased, the two effects on the precipitation area is also small, has different effects on the intensity of heavy rain center.