云南大理边界层风垂直变化观测研究

Study on the Vertical Change of Wind in Boundary Layer in Dali of Yunnan Province

利用2008年3月云南大理风廓线雷达观测资料,分析其上空局地环流特征。通过对云南大理上空三维风场的分析发现当地受地形影响明显,600 m以下午后至夜晚以西南风为主,出现下沉气流,风速较大,凌晨至中午以东南风为主,风速较小;600 m以上主要是西南和西北风,风速较大。这说明影响该地区的环流高度为600 m,表明该地区低层以山谷风、湖陆风及峡谷的风叠加为主导的环流特征是该地区的局地环流日变化基本特征。云南大理上空气流的逐日变化在600 m以下主要以东南风为主,高空是西北风、西南风交替出现,并且垂直运动以上升气流为主,偏西气流的加强导致垂直运动加强,南风、北风变化与垂直气流关系不是很明显,西风气流的变化对云南大理的垂直运动有重要的影响;云南大理上空在600 m以下风速变化不大,600 m以上风速随高度线性增大,点苍山高度(2 000 m)以下夜间风速大于白天风速,2 000 m以上白天风速大于夜间风速。无论是白天还是夜间100 m和1 000 m高度主导风向都相反,500 m高度能看出白天的东南风转换为夜间西南风。

The local circulation characteristics over Dali of Yunnan Province was analyzed based on wind profile radar observations in March of 2008.The study on the three-dimension wind field of Dali showed the obvious influence of the local terrain.The prevailing wind direction below 600 m was southwest from afternoon to night,with large wind speed and downdraft,while eastsouth wind from dawn to morning with small wind speed.The prevailing wind direction over 600 m was southwest and northwest with large wind speed,which indicated that the 600 m height circulation played a role over this area.The characteristics of the daily variation of local circulation in this area was the combination of mountain-valley breeze,lake-land breeze and ravine wind.The daily variation of air at lower layer of Dali was southeast wind below 600 m,the northwest wind and southwest wind appeared alternatively in the upper air,and the main vertical motion was the updraft,the westerly airstream increased the vertical motion,there was no obvious relationship between the change from south wind to north wind and vertical airflow.The variation of westerly airstream had an important effect on the vertical motion.The wind speed below 600 m changed little but over 600 m it increased linearly with height,the wind speed at night was larger than that during day below the height of Diancang mountain,and vice versa.The prevailing wind was opposite at the height of 100 m and 1 000 m during both day and night,it can be showed that the wind changed from southeast during day to southwest at night at 500 m height.