地表热通量对陕南强降水的影响

通过对2002年6月8～9日陕南大暴雨天气过程中地表感热和潜热通量的数值模拟表明:地表感热、潜热通量和温度的区域性分布与高原东部特殊的地形分布有关,地表热通量和温度的等值线与地形等高线大致平行,平原低洼地区和山脉所在地特征明显,从而可以说明地形热力状况在陕西强降水中发挥重要作用;地表潜热作用大于地表感热,去掉地表潜热的作用后,模式对降水的模拟结果与实况偏差较大;地表感热使山脊降水减少,使平原、山谷降水增加,这与夜间的山谷风环流密不可分。

The effect of surface thermal forcing on the extremely heavy rainfall in the southern Shaanxi provinceduring June 8 and 9, 2002

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.