天山天池一次强降水过程中的地形效应

2010年6月22日至23日,新疆天山天池发生了一次特大暴雨过程,6 h累积降水量高达124 mm。利用WRF中尺度数值模式对本次强降水过程进行数值模拟,探讨了天山地形在本次强对流过程的作用。结果表明,控制北疆地区的西北气流遇博格达山脉阻挡,除了一部分西北气流以12 m·s-1的速度沿迎风坡爬升之外,另一部分偏西绕流因为狭管效应以18~24m·s-1速度沿山体西侧绕流爬升,两支气流在山顶汇合造成的对流增强为本次大暴雨过程的发生提供了动力条件。由于地形阻挡和狭谷效应,博格达山西坡上低层偏西气流的垂直分布随高度递减,造成山坡上水平辐合增强,对应的气旋式涡度进一步加强,最大值达136×10-5s-1,有利于降水量增加。高低层风场配置相反,垂直风切变加强,有利于强对流的发生。东北偏东方向移动的多单体系统受博格达山西坡地形阻挡抬升与局地生成的对流单体合并,是本次天池发生大暴雨过程的主要原因。

The orographic influence on intense precipitation at Tianchi

A strong heavy rainfall occurred in Xinjiang Tainchi during 22~23 June 2010,accumulated precipitation of 6 hours was up to 124 mm. The above-mentioned case has been analyzed using WRF model. The impacts of Tianshan Mountains on the severe convection are discussed. The results show that the low-level northwest airflows of northern Xinjiang were blocked by the topography of the Bogda, and a portion of the winds at a speed of 12 m.s?1 climbed along the windward slope, another part of the air flow around the west side along the mountain climb, and because of the funneling, west air velocity was up to 18~24 m.s?1. The two flows provided dynamic conditions. Because of the terrain blocks and the narrow tube effect, low-levels horizontal airflow velocity decreased with height on the Bogda Mountains of the western slope, causing the hillside to further enhance the level of convergence, relative positive vorticity reached as high as 136×10?5 s?1 which was in favour of precipitation. High and low wind field configuration contrary and vertical wind shear strengthened was conducive to strong convection occurs. Multi-cell merge with local convective cells is the main reason of the occurrence of rainstorm.