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气象:2013,39(7):911-922
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影响北京的一例沙尘天气过程的起沙沉降及输送路径分析
(国家气象中心,北京 100081)
Analysis on Sand Entrainment and Deposition and Transportation Pathways of One Sand Dust Process in Beijing
(National Meteorological Centre, Beijing 100081)
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投稿时间:2013-01-24    修订日期:2013-05-26
中文摘要: 本文选取2012年4月27—28日影响北京的一次沙尘天气过程进行分析,发现在本次过程中,沙源地区的沙尘暴主要发生在地面冷锋和500 hPa槽后,在近地层强烈的感热加热与中低层冷平流的共同作用下,形成了不稳定层结及深厚的混合层,最高可达600 hPa,是沙尘天气能够影响下游地区的重要条件。本文还通过分析等熵混合层厚度变化及其平流过程来追踪沙尘天气的输送路径和定位沉降地,发现本次过程有两种传输路径,一种是沿辽宁北部向东而后转向东北方向,主要沿等熵混合层平流向下游移动,之后随着等熵混合层的接地沉降到近地层,该路径影响高度较高;另一种是沿辽宁南部向东南方向移动,混合层平流较清楚,但沉降时与东北路径明显不同,在辽东半岛东部地面辐散气流及下沉运动的作用下发生沉降,并随冷锋后冷高压南侧的东风回流向西输送影响北京地区。另外,由于混合层之上的稳定层明显下压,使沙尘输送高度偏低。运用HYSPLIT模式模拟的前、后向轨迹证实了上述两种输送路径,表明北京的扬沙天气是由东风回流造成的。
Abstract:The sand and dust weather that affected Beijing on 27-28 April 2012 is studied. The finding suggests that the sandstorm in sand source area happens mainly behind the cold front and the 500-hPa trough, where, because of the strong surface sensible heating and the cold advection in middle and lower troposphere, the deep mixed layer or even the unstable stratification forms and can reach up to 600 hPa, and such instability of stratification is an important condition for the sandstorm to affect the downstream area. Moreover, based on the analysis of the variation of the mixed layer thickness and its advective process we also study the transportation pathways and locate the deposition area of the sandstorm. It is found that there are two transportation pathways. One extends eastwards along the northern part of Liaoning Province and then turns to northeast with a higher height. Dust particles move downstream with the advection of the mixed layer. Afterwards, with the decreasing height of the mixed layer, the deposition occurs and sand particles reach the surface. The other extends southeastwards along the south of Liaoning Province. At the stage of transportation, the advection of the mixed layer is clear, but the mechanism of the deposition is different from the former one. The deposition occurs due to the descent in lower troposphereand the surface divergence. Afterwards, along the easterlies on the south side of the cold anticyclone behind the cold front, the sand particles are transported westwards to Beijing. In addition, the latter path is lower than the former because the stable layer which lies above the mixed layer descends obviously. Based on HYSPLIT model the backward and forward trajectories are computed. It proves the above two transportation pathways, showing that it is the easterly return flow that results in the sand dust event in Beijing.
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基金项目:国家自然科学基金青年基金项目(41205031)资助
引用文本:
张亚妮,张碧辉,宗志平,吴英,2013.影响北京的一例沙尘天气过程的起沙沉降及输送路径分析[J].气象,39(7):911-922.
ZHANG Yani,ZHANG Bihui,ZONG Zhiping,WU Ying,2013.Analysis on Sand Entrainment and Deposition and Transportation Pathways of One Sand Dust Process in Beijing[J].Meteor Mon,39(7):911-922.