Circulation controls on southern African precipitation in coupled models: The role of the Angola Low
Circulation controls on southern African precipitation in coupled models: The role of the Angola Low
复制标题
耦合模型中环流对南部非洲降水的控制：安哥拉低压的作用
DOI：
10.1002/2016jd025736
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
R. Washington
中科院分区：
文献类型：
--
作者：
C. Munday;R. Washington
在南部非洲，来自最新的耦合模式相互比较项目的模式产生了各种各样的降雨气候。在雨季（12月至2月; DJF），模型之间的降雨量差异达到70%，中位数模型在整个年周期中高估了15%至40%的降雨量。本文研究了未充分研究的区域环流特征（安哥拉低压）在区分降水模型估计值方面的作用。在南部春季，安哥拉低压是一个热低压，由强烈的地面加热驱动，而在DJF，它更类似于热带低压，并与潮湿的不稳定。在南方的夏天，我们发现，安哥拉低的模拟强度与模型平均降雨量在整个次大陆的模型间的变异性的40%和60%之间。这种关系沿着从安哥拉到莫桑比克海峡的西北、东南轴线特别牢固。沿着这条轴，具有较强安哥拉低压的模式模拟了增强的东北和西北水汽输送，增强幅度高达50 g kg−1 ms−1。增强的向南水汽通量的模式与相对较深的安哥拉低增加了次大陆中部地区的水汽辐合率，并减少了莫桑比克海岸的水汽发散。结果强调，需要更好地了解安哥拉低和南部非洲降雨之间的联系，并建议，改善安哥拉低的模拟可以帮助约束模型估计南部非洲降雨。
In southern Africa, models from the latest Coupled Model Intercomparison Project produce a wide variety of rainfall climatologies. Differences between models in rainfall amount reach 70% in the rainy season (December–February; DJF), and the median model overestimates rainfall by between 15 and 40% throughout the annual cycle. This paper investigates the role of an understudied regional circulation feature, the Angola Low, in differentiating between model estimates of precipitation. In austral spring, the Angola Low is a heat low, driven by strong surface heating whereas in DJF it is more similar to a tropical low and is associated with moist instability. In the austral summer, we find that the simulated strength of the Angola Low is associated with between 40 and 60% of the intermodel variability in model mean rainfall across the subcontinent. The relationship is particularly strong along a northwest, southeast axis aligned from Angola down to the Mozambican Channel. Along this axis, models with stronger Angola Lows simulate enhanced, by up to 50 g kg−1 ms−1, northeasterly and northwesterly moisture transport. The enhanced southward moisture flux in models with relatively deep Angola Lows increases the rate of moisture convergence in central areas of the subcontinent and reduces moisture divergence across the Mozambican coast. The results highlight the need to better understand the links between the Angola Low and southern African rainfall and suggest that improving the simulation of the Angola Low can help to constrain model estimates of southern African rainfall.