祁连地形云与垂直风的关系

摘要

Using UVW anemometer and surface observation data on July to August in 2007, analyzed the relation between formation of orographic cloud and vertical wind in south of Qilian Mountain region. According to the reason of formation of orographic cloud, we classified the weather background to be five types. The result showed: there are a nearly relation among the precipitation and low clouds amount and air current lifting ( W: vertical component of UVW anemometer). While the W is positive value (air current ascending) , the dominating wind is southwest wind and low clouds amount is increased. Whereas the W is negative (air current descending) , the dominating wind is northeast wind and low clouds amount is decreasing. A great number of precipitation occurred in period of time that dominating wind is southwest wind and W is positive value. In most cases, there are 1 to 2 hours between rainfall time and the original ascending time of W. In addition, there are an obvious relation between the variation of turbulence intensity and precipitation. Usually there are more low clouds amount and precipitation while the W was larger. Contrary, there are less low clouds amount and precipitation while the W was smaller. The time that was rainfall or later 1 to 2 hours rainfall, the W was larger U and V. The reason of this precipitation maybe happened low clouds or high clouds which formed by orographic cloud.%利用2007-07-12至2007-08-19的地面观测资料和三轴风速仪资料,对祁连地形云的形成与垂直风速之间的关系进行了分析.按照地形云形成的天气背景,将其分为5类过程进行了分析,结果表明:降水量和低云量以及气层的抬升(三轴风垂直分量W)有着密切的关系.当该地区主导风向为西南风时,W为正值(气层抬升),低云量增加,此时有降水或降水强度较大；该地区主导风向为东北风时,W为负值(气层下降),低云量减少,此时无降水或降水强度较小；多数情况下,降水发生在主导风向为西南风时,降水时间与W开始抬升时刻相差1～2 h.另外,湍流强度的垂直分量变化也与降水有很明显的关系.一般情况下,湍流强度的垂直分量比较大时,伴随着有较大低云量和降水强度；湍流强度的垂直分量比较小时,伴随着有较小的低云量和降水强度.当湍流强度的垂直分量大于水平分量时,也正是降水发生的时间或与降水时间相差1～2h.这种情况可以说明降水的产生与地形抬升后的大气形成的低云降水或者中高云降水有关系.