The effect of westerlies on East African rainfall and the associated role of tropical cyclones and the Madden-Julian Oscillation
The effect of westerlies on East African rainfall and the associated role of tropical cyclones and the Madden-Julian Oscillation
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DOI：
10.1002/qj.3698
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发表时间：
2019-12-15
影响因子：
8.9
通讯作者：
Hardy, Sam
中科院分区：
文献类型：
--
作者：
Finney, Declan L.;Marsham, John H.;Hardy, Sam
东非降雨量的多变性对生活和生计有重大影响。从洪水到干旱，从短的每日时间尺度到较长的十年时间尺度，这种变化都很重要，这从近几十年来东非干旱的破坏性影响中可见一斑。过去的研究强调了刚果气团在增强东非降雨量方面的作用。我们对这一特征的详细分析表明，有西风湿气气流的日子会带来刚果气团，根据一年中的不同时间，降雨量比日平均高出100%。相反，在有强东风气流的日子里，降雨会受到抑制。有西风水汽输送的天数在所有季节都是少数，但我们发现，长时间的降雨和更多的西风日数更潮湿，并且在最近10年发生了更频繁的干旱(与“东非气候悖论”有关)，很少有这样的西风天气。我们还研究了马登-朱利安振荡(MJO)和热带气旋的影响及其与西风流的相互作用。我们发现，在MJO的第3和第4阶段，以及当有一个或多个热带气旋存在时，更有可能出现西风水汽通量。此外，热带气旋更有可能在MJO的这些阶段形成，并且更有可能在马达加斯加以东形成时与西风带重合。总体而言，我们的分析汇集了许多不同的过程，这些过程在文献中已经讨论过，但尚未完全结合起来考虑。结果表明刚果气团在每日气候时间尺度上的重要性，并由此为今后东非降雨预报研究提供了有用的调查角度。
Variability of rainfall in East Africa has major impacts on lives and livelihoods. From floods to droughts, this variability is important on short daily time-scales to longer decadal time-scales, as is apparent from the devastating effects of droughts in East Africa over recent decades. Past studies have highlighted the Congo airmass in enhancing East African rainfall. Our detailed analysis of the feature shows that days with a westerly moisture flow, bringing the Congo airmass, enhance rainfall by up to 100% above the daily mean, depending on the time of year. Conversely, there is a suppression of rainfall on days with a strong easterly flow. Days with a westerly moisture flux are in a minority in all seasons but we show that long rains with more westerly days are wetter, and that during the most-recent decade which has had more frequent droughts (associated with the "Eastern African climate paradox"), there has been few days with such westerlies. We also investigate the influence of the Madden-Julian Oscillation (MJO) and tropical cyclones, and their interaction with the westerly flow. We show that days of westerly moisture flux are more likely during phases 3 and 4 of the MJO and when there are one or more tropical cyclones present. In addition, tropical cyclones are more likely to form during these phases of the MJO, and more likely to be coincident with westerlies when forming to the east of Madagascar. Overall, our analysis brings together many different processes that have been discussed in the literature but not yet considered in complete combination. The results demonstrate the importance of the Congo airmass on daily to climate time-scales, and in doing so offers useful angles of investigation for future studies into prediction of East African rainfall.