Extratropical Dry-Air Intrusions into the West African Monsoon Midtroposphere: An Important Factor for the Convective Activity over the Sahel
Extratropical Dry-Air Intrusions into the West African Monsoon Midtroposphere: An Important Factor for the Convective Activity over the Sahel
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温带干燥空气侵入西非季风对流层中层：萨赫勒地区对流活动的重要因素
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
J. Redelsperger
中科院分区：
文献类型：
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作者：
R. Roca;J. Lafore;C. Piriou;J. Redelsperger
摘要 本文研究了西非大尺度动力学、水汽和有组织对流之间的关系。利用简化的凝结假设，由 NCEP 分析的风提供的后向轨迹模型被用来重建 1992 年 7 月至 8 月期间非洲上空的对流层中层湿度场。该方法记录了水分含量和气团的起源。气象卫星红外图像用于表征对流系统。案例研究分析表明，非常干燥的空气斑块（相对湿度 < 5%）位于典型飑线的紧邻对流层中层环境中。研究表明，这种干燥空气结构起源于 50°N 极地急流反气旋侧的高层（200-250 hPa）。以萨赫勒地区为重点，利用季风期间500 hPa相对湿度分布的时间序列来隔离干旱事件。这些干燥事件被证明是由温带空气组成。综合分析...
Abstract This paper investigates the relationship between large-scale dynamics, water vapor, and organized convection over West Africa. Making use of a simplified condensation hypothesis, a back-trajectory model fed by NCEP-analyzed winds is used to reconstruct the midtropospheric humidity field over Africa during July to August 1992. The approach documents both the moisture content and the origin of the air masses. Meteosat satellite infrared imagery is used to characterize the convective systems. A case study analysis reveals that very dry air patches (RH < 5%) are located in the immediate midtropospheric environment of a typical squall line. Such dry-air structures are shown to originate in the upper levels (200–250 hPa) on the anticyclonic side of the polar jet stream at 50°N. Focusing on the Sahel region, dry events are isolated using the time series of the 500-hPa relative humidity distribution during the monsoon period. These dry events are shown to be composed of extratropical air. Composite analy...