首页|西太平洋副热带高压影响下北京区域性暴雨的个例分析

西太平洋副热带高压影响下北京区域性暴雨的个例分析

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  • 国家科技期刊平台
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北京地区大降水 (≥25 mm/d)天气有72%出现在7～8月份, 其中直接受西太平洋副热带高压 (副高)影响的大降水占46%, 它们主要产生在西风槽与副高相互作用的天气形势下.通过对该类暴雨的典型个例分析表明, 由于受副高的影响, 对流层低层副高南面的偏东气流将海上充沛的水汽输送到大陆, 并折向北与偏北气流相遇, 汇集在北京附近.同时, 副高西北边缘与西风槽之间形成较强的能量锋区, 该锋区南面的高温高湿气团蕴藏了较深厚的湿有效位能, 在湿位涡的斜压项作用下转化为动能, 倾斜垂直涡度发展激发了强烈的上升运动.在斜压扰动作用下, 对流层中层差动涡度平流和副高西侧的暖平流破坏了北京及邻近区域的准地转平衡, 动力强迫和热力强迫共同作用激发了次级环流, 该处的上升运动得到加强.暴雨就是产生在强的能量锋附近低层气旋性涡度发展、高层辐散显著的地方.此外, 副高西侧低层的暖湿气流北上, 较强的差动假相当位温平流促使大气层结向对流不稳定发展, 这对于暴雨局地的再增强是不可忽视的因素.由此, 形成对该类暴雨天气预报的着眼点.
A Case Study of the Influence of the Western Pacific Subtropical High on the Torrential Rainfall in Beijing Area
Summer is a pluvial season in Beijing area. There is high correlation between the total amount of precipitation and the number of days when there are heavy rain events during the rainy season. 72 percent of heavy rain events appear in July and August, and 46 percent among them are affected directly by the Western Pacific Subtropical High (WPSH) when it interacts with westerly trough. Furthermore, the precipitation in the Beijing area during summer is related to the strength, the area and the location of the ridge of the WPSH. In order to further reveal the impacts of the WPSH on the moisture transfer and the circulation situation under which heavy rain occurs, based on dynamic and thermodynamic diagnosis, a case study is performed by employing a 6-hourly and 1°×1° reanalysis data achieved at standard pressure levels for the period of 18 - 20 August 2001. Results show that during the heavy rain period in the lower troposphere, abundant water vapor over ocean is transferred towards continent by the easterlies along the south of the WPSH. The water vapor fluxes are then turned northward and converged with northerlies in the Beijing area. A strong energy front is formed between the westerly trough and the WPSH. The thick layer of moist available potential energy is found to the south of the front, which is then transformed to kinetic energy by the strong ascending motion associated with slantwise vorticity development. In the middle troposphere, the vertically differential vor-ticity advection and the warm advection to the west of the WPSH destroy the quasi-geostrophic balance in the Beijing area and its neighborhood, the secondary circulation is therefore forced both dynamically and thermodynamically in association with baroclinic perturbations, and in the area the vertical ascent is intensified. Torrential rain then occurs along such a strong energy front with strong low-level cyclonic vorticity development and high-level divergence. Furthermore, along the northward transfer of warm and moist current over the western flank of the WPSH, the stronger vertically differential advection of pseudo-equivalent potential temperature results in the development of convective instability, and is in favor of the intensification of rainfall. All these contribute to the occurrence of torrential rain in the Beijing area, and should be taken into consideration for predicting this kind of heavy rain events.

subtropical highBeijingtorrential rainenergy frontmoist available potential energyvertically differentialpseudo-equivalent potential temperatureadvection

刘还珠、王维国、邵明轩、王秀荣

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国家气象中心,北京,100081

副高 北京 暴雨 能量锋 湿有效位能 差动 假相当位温 平流

北京市自然科学基金国家自然科学基金

8042021040135020

2007

大气科学
中国科学院大气物理研究所

大气科学

CSTPCDCSCD北大核心
影响因子：2.11
ISSN：1006-9895
年,卷(期)：2007.31(4)
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