Role of ocean mesoscale structures in shaping the Angola-Low pressure system and the southern Africa rainfall
Role of ocean mesoscale structures in shaping the Angola-Low pressure system and the southern Africa rainfall
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DOI：
10.1007/s00382-020-05199-1
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发表时间：
2020-03
期刊：
影响因子：
4.6
通讯作者：
Fabien Desbiolles;Emma Howard;R. Blamey;R. Barimalala;N. Hart;C. Reason
中科院分区：
文献类型：
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作者：
Fabien Desbiolles;Emma Howard;R. Blamey;R. Barimalala;N. Hart;C. Reason
南部非洲的气候同时受到热带和亚热带系统的影响，这导致了一个复杂的区域，在那里重要的相互作用在大范围的时空尺度上共存。位于热带和亚热带南部非洲交界处的安哥拉低压(AL)被诊断为该地区从日到季时间尺度上水分分布的关键驱动因素。已经证明，高度气压系统对邻近海洋的动态很敏感，但迄今为止还没有研究考虑模拟这种敏感性所需的海-气相互作用的模式分辨率。利用一个区域大气模式的敏感性试验，该模式仅在中尺度海表面温度(SST)强迫特征(包括SST变率的全谱或仅包括其大尺度分量)方面有所不同，我们首先量化了SST梯度对AL强度和变率的重要性。结果表明，安哥拉-本格拉锋区(ABFZ)的中尺度SST变率对ALA活动起着关键作用，尤其是在夏末。形成AL的天气尺度热带低压被自动检测到，结果表明，当模式受到中尺度SSTs的强迫时，会发生更极端的事件(无论在哪里，只在ABFZ地区)。这些事件导致的降雨量表明，热带低气压事件与安哥拉和纳米比亚近15%的总降雨量有关。文中还讨论了大气动力学和湿周期之间的联系，当海洋完全分解时，前者表现出不同的空间模式和频率。
Southern African climate is under the influence of both tropical and subtropical systems which result in a complex region where important interactions co-exist over a large spectrum of spatiotemporal scales. The Angola Low (AL), situated on boundary between tropical and subtropical southern Africa, has been diagnosed as a key driver of moisture distribution in the region on daily to seasonal time scales. It has been demonstrated that theALpressure system is sensitive to the dynamics of the neighbouring oceans, but to date no study has considered the model resolution of air–sea interactions required to simulate this sensitivity. Using sensitivity experiments with a regional atmospheric model, which differ only in the mesoscale sea surface temperature (SST) forcing characteristics (either the full spectrum ofSSTvariability or only its large-scale components are included), we first quantify the importance of SST gradients on the AL strength and variability. The results suggest that the mesoscale SST variability of the Angola–Benguela Frontal Zone (ABFZ) plays a key role inALactivity, particularly during the late summer. Synoptic-scale tropical lows, which form the AL, are automatically detected, and the results suggest more extreme events occur when the model is forced by mesoscaleSSTs (everywhere and in theABFZarea only). The rainfall resulting from those events suggests that tropical-low episodes are associated with nearly 15% of the total rain in Angola and Namibia. The link betweenALdynamics and wet spells is also discussed, with the former showing a different spatial pattern as well as frequency when the ocean is fully resolved.