2009年秋季冀中南暴雪过程的地形作用分析

2009年11月10-11日,河北中南部地区出现了回流暴雪天气,强降雪中心位于太行山喇叭口地形南侧迎风坡处。本文使用MM5数值试验结果分析中小尺度地形对于降雪的影响。结果表明：在喇叭口地形作用下北侧为下坡风,南侧为迎风坡,出现上升运动;由于向东开口的喇叭口地形对于气流有汇聚作用,整个喇叭口地形上空到800 hPa为地形辐合产生的上升运动。垂直剖面显示低层地形产生的上升运动冲破逆温层（或与逆温层内波动的上升支叠加）,与700 hPa以上的西风带低槽系统引起的上升支叠加,加强了垂直上升运动,且东北风遇山后呈现出两支气流,一支在山前堆积下沉,一支在山前冷空气堆前上升,且山前冷空气下沉支逐步形成环流圈,说明冷空气在山前堆积,气流在冷空气堆以东上升。这可能是降雪中心在平原而不在山坡的主要原因。

Terrain Effect on Heavy Snowstorm in Hebei Province

Based on the observed data and output data from MM5, the terrain effect on the blizzard process in central and south of Hebei Province from November 10 to 11 in 2009 is analyzed. The results show that there is a downward motion on the north side of the trumpet shaped terrain, and an upward motion on the south side; the eastward flow has been brought together due to the role of the trumpet shaped terrain, the terrain effect exists under the 800 hPa and an upward motion is generated. Vertical profiles show that the low level upward motion generated by terrain penetrates through the inversion layer, and merged with upward streams caused by westerly trough, thus strengthening the vertical upward movement. The northeast flow encountered Taihang Mountains is divided into two flows, a flow sinking in the piedmont, and the other flow ascending before the cold air heap and gradually forms a piedmont circulation of cold air sinking branch, indicating accumulation of cold air in the piedmont. This may be the main reason for snowfall center occurring generally in the plains and not in the hill.