Coupled Climate Model Simulation of Tropical-Extratropical Cloud Bands over Southern Africa
Coupled Climate Model Simulation of Tropical-Extratropical Cloud Bands over Southern Africa
复制标题
南部非洲热带-温带云带的耦合气候模型模拟
DOI：
10.1175/jcli-d-19-0731.1
复制
发表时间：
2020
影响因子：
4.9
通讯作者：
James R
中科院分区：
文献类型：
--
作者：
James R
利用气候模式输出进行适应规划的努力越来越多，但与此同时，人们对模式如何代表区域气候的理解往往有限。本文分析了在全球耦合气候模式中对南部非洲主要降雨产生机制：热带温带槽（TTTs）的模拟。将一种图像处理算法应用于卫星和模型的外发长波辐射数据，以创建TTT事件集。所研究的所有模式产生的ttt具有与观测到的相似的循环特征。然而，不同的模式在事件的数量、强度和首选经度方面存在很大差异。确定了五组模型。第一种模式产生的ttt太少，而且与其他模式相比，非洲南部相对干燥。第二组产生更多的ttt和湿偏差。这两组之间的对比表明ttt的数量可以解释气候降雨的模式间变化。然而，还有第三组模式，它们模拟的TTT比观测到的多92%，但没有大的降雨偏差，因为每次TTT事件相对较弱。最后，还有两组分别将ttt集中在次大陆或海洋上。这些模式之间的差异与刚果盆地的对流活动量、进入南部非洲的水汽通量的大小以及高层西风流的纬向不对称程度有关。模式发展的重点是热带对流和地形表征，这对于改进ttt的模拟是必要的，因此也需要改进南部非洲降雨的模拟。
There are increasing efforts to use climate model output for adaptation planning, but meanwhile there is often limited understanding of how models represent regional climate. Here we analyze the simulation in global coupled climate models of a key rainfall-generating mechanism over southern Africa: tropical temperate troughs (TTTs). An image-processing algorithm is applied to outgoing longwave radiation data from satellites and models to create TTT event sets. All models investigated produce TTTs with similar circulation features to observed. However, there are large differences among models in the number, intensity, and preferred longitude of events. Five groups of models are identified. The first group generates too few TTTs, and relatively dry conditions over southern Africa compared to other models. A second group generates more TTTs and wet biases. The contrast between these two groups suggests that the number of TTTs could explain intermodel variations in climatological rainfall. However, there is a third group of models that simulate up to 92% more TTTs than observed, but do not have large rainfall biases, as each TTT event is relatively weak. Finally, there are a further two groups that concentrate TTTs over the subcontinent or the ocean, respectively. These distinctions between models are associated with the amount of convective activity in the Congo Basin, the magnitude of moisture fluxes into southern Africa, and the degree of zonal asymmetry in upper-level westerly flow. Model development focused on tropical convection and the representation of orography is needed for improved simulation of TTTs, and therefore southern African rainfall.