Distribution of extreme rainfall events and their environmental controls in the West African Sahel and Soudan
Distribution of extreme rainfall events and their environmental controls in the West African Sahel and Soudan
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DOI：
10.1007/s00382-022-06171-x
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发表时间：
2021-10
期刊：
影响因子：
4.6
通讯作者：
E. Vizy;K. Cook
中科院分区：
文献类型：
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作者：
E. Vizy;K. Cook
当强中尺度对流系统（MCS）在短时间内产生大量降雨时，西非萨赫勒和苏丹的极端降雨事件是有影响的。NASA IMERG降雨量估计和ERA 5再分析的检查，以了解前100个最高的12 Z-12 Z 24小时降雨总量和MCS风暴的成因发生，并评估其生成环境条件的相对重要性，包括大气湿度和垂直风切变的影响。前100个事件中的大多数位于苏丹14° N以南。事件集中在三个地区，即马里、布基纳法索和北方尼日利亚。相关的MCS通常不是本地生成的，而是在上游大于100公里的距离处形成的。合成显示，大气中的水分含量显着增加之前发生的发展，但没有证据表明，在600-925 hPa的垂直风切变的显着变化。这表明垂直风切变的变化对极端风暴发展的影响小于大气湿度预处理。对前10名事件进行了进一步评估。这些风暴的方向和速度在最大降雨量位置附近的变化是常见的，这表明MCS正在峰值降雨强度时间附近重组。三种大气条件与这些事件有关。它们是：（1）大气的水分预处理，（2）风暴在反气旋流区尾流中的相互作用，（3）风暴在反气旋流区尾流和萨赫勒/热带干线边界中的相互作用。
West African Sahel and Soudan extreme rainfall events are impactful when strong mesoscale convective systems (MCSs) produce large amounts of rainfall in short periods. NASA IMERG rainfall estimates and the ERA5 reanalysis are examined to understand where the top 100 highest 12Z–12Z 24-h rainfall totals and MCS storm genesis occur, and to assess the relative importance of environmental conditions in their generation including the influence of atmospheric moisture and vertical wind shear. Most of the top 100 events are located south of 14° N over the Soudan. Events cluster over three regions, namely, Mali, Burkina Faso, and northern Nigeria. The associated MCSs are typically not locally generated, forming instead at distances greater than 100 km upstream. Composites reveal that a significant increase in atmospheric moisture content occurs prior to development, but there is no evidence of significant changes in the 600–925 hPa vertical wind shear. This indicates that changes in vertical wind shear are less influential in extreme storm development than atmospheric moisture preconditioning. The top 10 events are further evaluated. A change in these storms’ direction and speed near the maximum rainfall location is common, suggesting the MCSs are reorganizing around peak rainfall intensity time. Three atmospheric conditions are associated with these events. They are (1) moisture preconditioning of the atmosphere, (2) interaction of the storm in the wake of a region of anticyclonic flow, and (3) interaction of the storm in the wake of a region of anticyclonic flow and the Sahel/tropical dryline boundary.