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投稿时间：2010-11-23 修订日期：2011-05-13
投稿时间：2010-11-23 修订日期：2011-05-13
中文摘要: 北京地区的初雪平均在11月28日前后。 2009年10月31日夜间至11月1日白天北京出现雨转雨夹雪，再转大雪的天气过程。作为初雪，这是北京22年来罕见的。分析表明，这次过程降水前12和6 h华北中东部的黄河下游以北地区对流层中低层受一致的西北气流控制，前期水汽输送和积累不明显。北京地区在10月这样一个相对干燥的季节和前期水汽不充沛的环流形势下产生大雪局地暴雪，实不多见。文章利用中国气象局MICAPS常规气象资料和北京地区风廓线雷达、微波辐射仪、地面自动站等多种本地加密探测资料，对这次大雪过程进行了动力计算和成因分析。结果显示，由对流层上层贝加尔湖强冷空气向南爆发所引发的动力作用是北京这次初冬大雪形成的主要原因。大雪发生前500 hPa正涡度平流区、对流层中上层水平辐散中心、对流层中下层水平辐合中心呈垂直结构控制北京，为北京地区提供了有利的上升运动动力环境。山前和平原地区近地面东南风，边界层偏东风及边界层以上的对流层底层偏西风的风廓线分布在北京西部地形作用下产生动力抬升和局地对流，增强了北京西南部的降雪。这次北京大雪的水汽条件源于近地面偏南风和东南风的短时间局地增湿，以及这种增湿在高空强冷气团作用下产生的对流层中低层的局地水汽辐合。
中文关键词: 大雪成因， 风廓线， 微波辐射， 动力分析， 概念模型
Abstract:Usually, the time of the first snowfall in Beijing is about on November 28. During the period of the nighttime of October 31, 2009 to daytime of November 1, 2009, there was a weather process which never occurs over the past 22 years. In this process, the precipitation firstly acted as rain, then converted to sleet and finally in the form of snow. Analysis shows that, over the north region of the Yellow River in middle and east parts of North China, the lower troposphere was controlled by northwest flows for 6 hours even to 12 hours before this snowfall, thus the transport and accumulation of water vapor were not obvious. This snowfall process is infrequent for Beijing in such a dry condition in October. The dynamic calculation and analysis of this snowfall process were conducted with the MICAPS data of CMA, windprofiler, radiometric and surface automatic weather station observations in Beijing. The result shows that, the dynamic action of the southward outbreak of strong cold air from Baikal Lake in upper troposphere was the main reason for this snowfall process. A 500 hPa positive vorticity advection area, a middle and upper tropospheric divergence center and a middle and lower tropospheric convergence center were vertically distributed over Beijing, which support the favorable environment for vertical motion; the coactions of the warm and humid sourheast winds near the ground in piedmonts and plains, the cold and humid east winds in the boundary layer, the west winds in tropospheric bottom, which were seen in windprofiler, and the topographic effect in western Beijing will generate an uplift and local convection to enhance snowfall in southwest Beijing. This paper proposes a conceptual model about how the wind distribution in windprofiler in the piedmonts and plains of Beijing and the topographic effect will generate the uplift motion and local convection. The water vapor condition of this snowfall is from the short term growth of humidity by near surface southerly winds and southeast winds, and the local moisture convergence in the lower troposphere.
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基金项目:公益性行业（气象）科研专项（GYHY201006010）、 国家“十一五”科技支撑计划重点项目(2008BAC37B00和2008BAC37B05)及北京市气象局科研基金项目“偏东风对北京地区降雪影响的研究”共同资助
| 作者 | 单位 |
| 段 丽 | 中国气象局公共气象服务中心，北京 100081 |
| 张琳娜 | 北京市气象台，北京 100089 |
| 王国荣 | 北京市气象台，北京 100089 |
| 段 炼 | 内蒙古巴彦淖尔市气象处，巴彦淖尔 150000 |
引用文本：
段 丽,张琳娜,王国荣,段 炼,2011.2009年深秋北京大雪过程的成因分析[J].气象,37(11):1343-1351.
Duan Li,Zhang Linna,Wang Guorong,Duan Lian,2011.A Dynamic Diagnosis of the 091031 First Snowfall in Beijing with Some New Intensive Soundings[J].Meteor Mon,37(11):1343-1351.
段 丽,张琳娜,王国荣,段 炼,2011.2009年深秋北京大雪过程的成因分析[J].气象,37(11):1343-1351.
Duan Li,Zhang Linna,Wang Guorong,Duan Lian,2011.A Dynamic Diagnosis of the 091031 First Snowfall in Beijing with Some New Intensive Soundings[J].Meteor Mon,37(11):1343-1351.