关键词: 暴雨, 地形, 地表感热, 地表潜热

Abstract:

An extremely severe weather process happened in the southern Shaanxi province during 8-9 June 2002 which is rare in history causing flashflood, landslide and a death of more than 450 people.The MM 5 model, successfully simulated the weather systems and related mesoscale convec tive complex, that caused the severe heavy rain in the southern Shaanxi province during 8-9 June 2002.The simulated precipitation is quite similar to the obse rvations at three extremely heavy centers at Ningqiang, Foping and Ningshan of southern Shaanxi. On the basis of successful control simulations(CTRL), two sens itivity experiments about surface sensible and latent flux are done. By analyzing the results of the sensitivity experiments about surface sensible and latent flux which is important for extremely heavy rainfall in the southern Shaanxi proince during 8-9 June 2002, it is found that the distributions of surface tempe rature, surface sensible and latent flux are highly correlated with special topo graphy of eastern Tibetan Plateau, with isolines of surface temperature and heat flux parallel to the isohypse of terrain, with obvious features between plains and mountains which indicate that orographic thermal forcing plays a key role in heavy rainfall; and that simulations with no surface latent flux are much less than observations especially in Foping and Ningshan counties on the southeastern slope of Qinling mountains where precipitation decreased by over 100 mm, and su rface latent flux is more important than surface sensible flux which makes preci pitation reduction in the mountainous areas and increment in plains and valleys because of mountain-valley wind circulation. The effect of surface flux on rai nfall is realized by increasing surface convergence and vorticity over the south eastern slope of Qinling mountains, forming lee vortex, furthermore causing seco ndary vertical circulation by topographic mechanical and thermal forcing.

Key words: torrential rain, topography, surface sensible flux, surface latent flux