Tracing Future Spring and Summer Drying in Southern Africa to Tropical Lows and the Congo Air Boundary
Tracing Future Spring and Summer Drying in Southern Africa to Tropical Lows and the Congo Air Boundary
复制标题
追踪南部非洲未来春季和夏季干燥至热带低气压和刚果空气边界的情况
DOI：
10.1175/jcli-d-19-0755.1
复制
发表时间：
2020
影响因子：
4.9
通讯作者：
Howard E
中科院分区：
文献类型：
--
作者：
Howard E
在南部非洲，耦合模式相互比较项目第5阶段的模式预测，未来将出现强有力的干旱，这与南部春季雨季推迟开始以及南部夏季出现一系列湿润和干燥模式有关。本文将这些降雨量的变化与两类天气系统的动态变化联系起来：刚果空气边界（CAB）和热带低压。客观算法用于跟踪CMIP 5模型输出中的这些特征。然后，建立这些系统的气候位置和频率是合理的，以及CMIP5模式。RCP8.5对21世纪末世纪的预测与历史上对20世纪末世纪的模拟进行了比较。未来的预测在热带低的位置和频率分歧，但表明整体平均下降15%，在某些情况下，北移。热带低频分布的空间变化与南方夏季降水分布的空间变化呈弱正相关。同时，未来的预测表明，从10月到12月，CAB频率将增加13%。这与世纪末RCP 8.5预测中平均半个月后发生的气候CAB逐渐崩溃有关。CAB的季节性逐渐下降的延迟阻止了CAB平均位置以南的降雨，其中大部分降雨发生在CAB崩溃的日子里，因此产生了南方春季干燥的信号和延迟的雨季开始。CAB频率增加幅度的模型间变异能够解释预测干燥的模型间变异。
In southern Africa, models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) predict robust future drying associated with a delayed rainy-season onset in the austral spring and a range of wetting and drying patterns in the austral summer. This paper relates these rainfall changes to dynamical shifts in two classes of weather systems: the Congo Air Boundary (CAB) and tropical lows. Objective algorithms are used to track these features in CMIP5 model output. It is then established that the climatological locations and frequencies of these systems are reasonably well represented in the CMIP5 models. RCP8.5 end-of-twenty-first-century projections are compared with historical end-of-twentieth-century simulations. Future projections in tropical-low locations and frequencies diverge, but indicate an overall average decrease of 15% and in some cases a northward shift. The projected spatial change in the tropical-low frequency distribution is weakly positively correlated to the projected spatial change in the austral summer rainfall distribution. Meanwhile, future projections indicate a 13% increase in CAB frequency from October to December. This is associated with the gradual climatological CAB breakdown occurring half a month later on average in end-of-twenty-first-century RCP8.5 projections. A delay in the gradual seasonal decline of the CAB prevents rainfall to the south of the CAB’s mean position, most of which is shown to occur on CAB breakdown days, hence creating the austral spring drying signal and delayed wet-season onset. Intermodel variability in the magnitude of CAB frequency increase is able to explain intermodel variability in the projected drying.