Analyzing intensifying thunderstorms over the Congo Basin using the Gálvez-Davison index from 1983–2018
Analyzing intensifying thunderstorms over the Congo Basin using the Gálvez-Davison index from 1983–2018
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DOI：
10.1007/s00382-020-05513-x
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发表时间：
2020-11
期刊：
影响因子：
4.6
通讯作者：
K. Alber;A. Raghavendra;Liming Zhou;Yan Jiang;Heather S. Sussman;Stephen L. Solimine
中科院分区：
文献类型：
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作者：
K. Alber;A. Raghavendra;Liming Zhou;Yan Jiang;Heather S. Sussman;Stephen L. Solimine
位于赤道非洲的刚果盆地是地球仪上第二大雨林的所在地，在地球气候系统中发挥着重要作用。例如，刚果是世界上对流最多的地区之一，并增强了热带大尺度环流。虽然热带对流对降雨和维持雨林至关重要，但最强烈的雷暴不一定会在赤道非洲产生最大的降雨量。为了更好地了解刚果降雨量减少的趋势，本文使用Gálvez-Davison指数（GDI）分析了1983年至2018年雷暴强度的趋势，即，用来测量雷暴可能性的热力学指数。与以前的研究一致，刚果的雷暴活动在所有季节都有所增加。GDI表明，雷暴活动的增加趋势可归因于流体静力不稳定性的增加。更具体地说，GDI表明，（1）500 hPa冷槽的增加，（2）700和950 hPa之间温度梯度的增加，以及（3）等效位温梯度随高度的减小共同作用于促进更高，更强的雷暴。本研究最后提出反馈机制解释雷暴的加剧。这些机制突出了对流层中层的冷却和增湿，地面和对流层低层的干燥和变暖，以及垂直稳定度和对流抑制的减少。这些因素可能会加强干旱的趋势，在过去的40年里，这种趋势一直在给刚果的热带雨林造成压力。
The Congo Basin situated in equatorial Africa is home to the second largest rainforest on the globe and plays an important role in the Earth’s climate system. For instance, the Congo is one of the most convective regions in the world and enhances the tropical large-scale circulation. Although tropical convection is crucial for rainfall and the sustenance of the rainforest, the most intense thunderstorms do not necessarily produce the largest amounts of rainfall over equatorial Africa. Aiming to better understand the decreasing rainfall trend over the Congo, trends in thunderstorm intensity from 1983 to 2018 are analyzed in this paper using the Gálvez-Davison index (GDI), i.e., a thermodynamic index used to measure thunderstorm potential. Consistent with previous studies, thunderstorm activity increased during all seasons over the Congo. The GDI suggests that the increasing trends in thunderstorm activity are attributable to an increase in hydrostatic instability. More specifically, the GDI shows that (1) an increase of cold troughs at 500 hPa, (2) an increase in the temperature gradient between 700 and 950 hPa, and (3) a decrease of the equivalent potential temperature () gradient with height collectively act to promote taller, more intense thunderstorms. This study concludes by proposing feedback mechanisms explaining the intensification of thunderstorms. The mechanisms highlight the cooling and moistening of the mid-troposphere, drying and warming at the surface and lower troposphere, and a decrease in vertical stability and convective inhibition. These factors may act to re-enforce the drying trend which has stressed the Congo rainforest over the past 40-years.