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气象:2013,39(3):291-301
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华北秋季强弱线型对流发展时天气尺度环境条件探讨
A Discussion on the Synoptic Condition for the Autumn Linear Convection Developing in Huabei Area
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投稿时间:2012-05-02    修订日期:2012-07-26
中文摘要: 华北地区进入秋季以后,弱对流过程增加。为了提高秋季对流天气强度的诊断识别能力,选择了9月份发生在相似背景下,强弱不同的两个线型对流个例作了对比分析。结果表明,强对流发生在深厚的天气尺度上升区中(上升运动伸展到200 hPa附近),而且对流层低层环境大气的绝对湿度较大;而弱对流发展时,上升运动仅存在于500 hPa以下,边界层内的比湿只有5~7 g·kg-1,较强对流个例低2~5 g·kg-1。它们是导致对流强弱不同的主要原因。强对流个例深厚的上升运动源于低层辐合切变线、露点锋和高空槽的强迫,此外对流层上部的强辐散叠置在低层辐合区上空,有利于上升运动加强并向高层发展。弱对流产生时,冷空气侵入到对流层中层以下,造成下沉区的下边界较低,不能产生深厚的上升运动。这是强弱个例垂直运动伸展高度不同的动力因素。热力学条件差异主要在对流层中下层。强对流产生时,对流区内有能量聚积,CAPE达到1087 J·kg-1,而且暖湿层和对流性不稳定层伸展到600~700 hPa。弱对流个例,仅边界层相对暖湿,CAPE只有68 J·kg-1。上述关于力和热动力条件差异研究结果表明,天气尺度上升运动伸展的高度、对流层下层空气的绝对湿度、暖湿层和不稳定层的厚度等可能是影响华北秋季对流强弱的重要环境因素。
Abstract:In autumn, the weak convection case covers more percentage in Huabei (North China). In order to improve the ability to diagnose the convection intensity, two linear cases are analyzed which develop in the similar synoptic background but in different strength. The result indicates that strong convection develops in the deep upward current (to 200 hPa). And the absolute humidity in the lower troposphere is higher. However, in the weak one, the ascending current exists below 500 hPa only. At the same time, the specific humidity in the BL (boundary layer) is just (5-7) g·kg-1 which is (2-5) g·kg-1 lower than that of the strong case. These lead to the convection in different strength mainly. The deep anaflow in the strong case is caused by convergence line, dewpoint front and upper level trough. Furthermore, a strong divergence appearing in the upper troposphere overlaps the convergence layer. As the result, upward current enhances and goes up further. But for weak case, the cold air invades to the mid troposphere and makes the ascending current which could reach to the upper levels. The thermodynamic background difference appears in the lower troposphere. When strong convection develops, the instable energy accumulates in the convective area and CAPE reaches 1087 J·kg-1. Besides, from the surface to 600 or 700 hPa, it is warm and moist and being instable also. In the weak case, CAPE is 68 J·kg-1. Above the BL, it is cold and dry comparatively. Therefore, the following items could be helpful in the diagnosis of the convection strength in autumn: the depth of the upward current, the absolute humidity in the lower troposphere, the thickness of a layer which is not only unstable but also warm and wet.
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基金项目:公益性行业(气象)科研专项(GYHY200906003)和北京市气象局创新团队(CX2011003)共同资助
引用文本:
廖晓农,2013.华北秋季强弱线型对流发展时天气尺度环境条件探讨[J].气象,39(3):291-301.
LIAO Xiaonong,2013.A Discussion on the Synoptic Condition for the Autumn Linear Convection Developing in Huabei Area[J].Meteor Mon,39(3):291-301.