Abstract: Wind-field diagnostic analysis and historical observation data are used to reveal general flow patterns of lower atmosphere over Beijing area. The preliminary results show that air flows in this area could be classified into autumn-winter pattern and spring-summer pattern. The former is under effect of more strong synoptic systems, while the latter shows more characteristics of mesoscale thermal circulation induced by topography. The mesoscale circulation determines basic air flow patterns in this area, which is typical in spring-summer season and in calm weather of autumn-winter season. Air flow under strong wind condition in autumn-winter season is seriously perturbed by topography. The perturbation displays as a horizontal vortex covering whole city of Beijing and part of mountain area in northwest.

Key words: flow patterns, lower atmosphere, Beijing area

摘要： 用风场诊断方法和实际观测资料对北京地区低层大气的背景流动情况进行分析，获取当地流动时空演变的总体型式或模态。所获初步结果表明，该地区大气流动总体分为秋冬型和春夏型。秋冬型更多受强天气系统的影响，春夏型则更多表现出局地中尺度热力环流特征。中尺度环流是该地区低层大气流动的基本模态，春夏季和秋冬季弱系统条件下的区域流动大体按这种模态演变。秋冬季大风天气的流动受地形的动力扰动作用明显，扰动表现为水平涡旋形态，其影响范围包括北京城区及西北部山地。

关键词: 流动模态, 低层大气, 北京地区