The influence of southeastern African river valley jets on regional rainfall
The influence of southeastern African river valley jets on regional rainfall
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DOI：
10.1007/s00382-021-05846-1
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发表时间：
2021-06
期刊：
影响因子：
4.6
通讯作者：
R. Barimalala;R. Blamey;Fabien Desbiolles;C. Reason
中科院分区：
文献类型：
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作者：
R. Barimalala;R. Blamey;Fabien Desbiolles;C. Reason
通过在林波波河和赞比西河流域（LRV和ZRV）的地形间隙形成的低空急流对南部非洲气候的影响进行了研究。ERA-5再分析数据和使用区域气候模式的数值试验表明，这两个山谷作为西南印度洋来源的水分流入南部非洲的主要门户。LRV急流的影响是静止的，主要局限于林波波以南。通过阻塞LRV，次大陆内部的水汽辐合减弱，导致安哥拉低压和非洲东南部脊状高压减弱。这些都是不利于水汽向南输送的条件，导致亚热带南部非洲夏季总降雨量减少了50%。相比之下，赞比西河急流的影响随季节而变化。在南半球初夏，一个阻塞的ZRV导致在次大陆的降雨量的整体赤字。然后，它导致莫桑比克海峡槽减弱，安哥拉低压增强，因此1月和2月的降雨量增加。在夏季结束时，赞比西河急流的消失使更多的来自热带大西洋的湿气渗透到大陆，然后与来自印度洋的湿气汇合，引发热带地区的过量降雨。这些结果有重要的影响，了解在夏季半年的次大陆的季节内和年际降水变化。
The impacts of the low level jets that form through the gaps in the topography in the Limpopo and Zambezi River Valleys (LRV and ZRV) on southern African climate are investigated. ERA-5 reanalysis data and numerical experiments using regional climate models reveal that the two valleys act as main gateways for southwest Indian Ocean-sourced moisture inflows into southern Africa. The effects of the LRV jet are stationary and mostly confined to south of Limpopo. By blocking the LRV, the moisture convergence in the interior of the subcontinent reduces and leads to a weakening in both the Angola Low and the ridging high over southeastern Africa. These are unfavorable conditions for the southward transport of moisture, causing a decrease of up to 50% of the subtropical southern African total summer rainfall. In contrast, the influence of the Zambezi jet varies with the season. During early austral summer, a blocked ZRV results in an overall deficit in rainfall in the subcontinent. It then leads to a weaker Mozambique Channel Trough, intensified Angola Low, hence increase in rainfall during January and February. Toward the end of the austral summer season, the absence of the Zambezi jet allows more moisture from the tropical Atlantic to penetrate into the mainland which then converges with moisture transported from the Indian Ocean and triggers excess rainfall over the tropical areas. These results have important implications for understanding the intraseasonal and interannual rainfall variability over the subcontinent during the summer half of the year.