Atmospheric tropical modes are important drivers of Sahelian springtime heatwaves
Atmospheric tropical modes are important drivers of Sahelian springtime heatwaves
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DOI：
10.1007/s00382-020-05569-9
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发表时间：
2020-12
期刊：
影响因子：
4.6
通讯作者：
Kiswendsida H. Guigma;F. Guichard;M. Todd;P. Peyrillé;Yi Wang
中科院分区：
文献类型：
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作者：
Kiswendsida H. Guigma;F. Guichard;M. Todd;P. Peyrillé;Yi Wang
热浪对全世界的人类健康构成严重威胁，但在非洲的记录仍然很少。本研究主要使用ERA 5数据集来研究北方春季萨赫勒地区的大尺度驱动因素，重点是热带变率模式的作用，包括Madden-Julian振荡（MJO）和赤道Rossby波和Kelvin波。热浪的定义从每日最低和最高温度使用的方法，只保留大的空间范围内的季节尺度事件。结果表明，热带模态对萨赫勒地区热浪的发生有很大的影响，在较小的程度上，对它们的强度。根据它们的对流阶段，它们可以增加或抑制热浪的发生，其中MJO是最重要的研究驱动程序。观察到对地理位置和昼夜周期的一定敏感性，夜间热浪更多地受到萨赫勒东部模式的影响，而白天热浪更多地受到萨赫勒西部模式的影响。物理机制的分析表明，这种调制是通过区域环流的扰动实现的。因此，热带模态控制着水汽和随后的长波辐射，以及热空气的平流。对2003年4月发生的一次重大事件进行的详细个案研究进一步证实了这些结论。鉴于热带模态在季节内尺度上提供的潜在可预测性，这项研究对萨赫勒地区的热浪风险管理具有重要意义。
Heatwaves pose a serious threat to human health worldwide but remain poorly documented over Africa. This study uses mainly the ERA5 dataset to investigate their large-scale drivers over the Sahel region during boreal spring, with a focus on the role of tropical modes of variability including the Madden–Julian Oscillation (MJO) and the equatorial Rossby and Kelvin waves. Heatwaves were defined from daily minimum and maximum temperatures using a methodology that retains only intraseasonal scale events of large spatial extent. The results show that tropical modes have a large influence on the occurrence of Sahelian heatwaves, and, to a lesser extent, on their intensity. Depending on their convective phase, they can either increase or inhibit heatwave occurrence, with the MJO being the most important of the investigated drivers. A certain sensitivity to the geographic location and the diurnal cycle is observed, with nighttime heatwaves more impacted by the modes over the eastern Sahel and daytime heatwaves more affected over the western Sahel. The examination of the physical mechanisms shows that the modulation is made possible through the perturbation of regional circulation. Tropical modes thus exert a control on moisture and the subsequent longwave radiation, as well as on the advection of hot air. A detailed case study of a major event, which took place in April 2003, further supports these findings. Given the potential predictability offered by tropical modes at the intraseasonal scale, this study has key implications for heatwave risk management in the Sahel.