How do coupled models represent the African Easterly Jets and their associated dynamics over Central Africa during the September–November rainy season?
How do coupled models represent the African Easterly Jets and their associated dynamics over Central Africa during the September–November rainy season?
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耦合模型如何代表 9 月至 11 月雨季期间非洲东风急流及其在中部非洲的相关动态？
DOI：
10.1007/s00382-022-06467-y
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发表时间：
2022
期刊：
影响因子：
4.6
通讯作者：
R. Washington
中科院分区：
文献类型：
--
作者：
Giresse Kuete;Wilfried Pokam Mba;R. James;E. Dyer;T. Annor;R. Washington
气候模型对于评估中部非洲地区气候变化的影响至关重要。建立模型如何重现关键流程对于我们对这些工具的信心非常重要。本研究以 16 个常用评估的 CMIP5 和 CMIP6 模型为样本，并进行了两次重新分析（ERA5 和 MERRA2），研究了非洲东风急流 (AEJ) 北部和南部 9 月至 11 月特征的模型表示，例如位置和强度。分析不断发展，从能量相互作用、中层高压和热低压的特征以及表面热加热的性质来评估AEJ的关键驱动因素。在西非，一些模型错过了 AEJ-N 核心的东南-西北方向，导致喷气机的位置存在约 6^0 的差距，而大多数 CMIP5 模型也无法在中非南部找到 AEJ-S。一般来说，与 CMIP6 等效模型相比，CMIP5 样本在重新分析周围模拟 AEJ 位置的分布更大，表明在这 16 个模型子集中从 CMIP5 到 CMIP6 的改进。然而，某些 CMIP6 模型（例如 GISS-E2-1-G 和 MIROC6）中的这种改进与最大表面经向温度梯度无关。大多数 CMIP5 和 CMIP6 模型低估了 AEJ-N 区域的表面温度梯度。作为喷气机加速度的一阶诊断，大多数耦合模型更好地模拟了 AEJ-N 区域的大气能量相互作用，这导致与 AEJ-S 相比，它对 AEJ-N 的维护有很大的贡献。这项研究通过检测耦合模型中维持 AEJ 的机制中的差距，加强了我们对中部非洲中层环流的理解，并强调了未来整体中应改进的过程。
Climate models are vital to the assessment of the impacts of climate change in the Central African regions. Establishing how well models reproduce key processes is important to the confidence we attach to these tools. This study examines model representation of the September to November characteristics, such as location and intensity, of the African Easterly Jet (AEJ) north and south in a sample of 16 commonly evaluated CMIP5 and CMIP6 models and in two reanalyses (ERA5 and MERRA2). The analysis evolves to assess key drivers of the AEJ from energetic interactions, the characteristics of mid-level highs and thermal lows and the nature of surface thermal heating. Over West Africa, several models miss the southeast-northwest orientation of the AEJ-N core, leading to a gap of around 6^0 in the location of the jet while most CMIP5 models also fail to locate AEJ-S over southern Central Africa. In general, the spread of simulated AEJ locations around reanalyses is larger for the CMIP5 sample compared to CMIP6 equivalent models, indicating improvement from CMIP5 to CMIP6 in this 16 model subset. However, this improvement in some CMIP6 models (e.g. GISS-E2-1-G and MIROC6) is not related to a maximum surface meridional gradient in temperature. Most CMIP5 and CMIP6 models underestimate the surface temperature gradient over AEJ-N region. As a first order diagnostic of the jet's acceleration, most coupled models better simulate the atmospheric energetic interactions over AEJ-N region that leads to its strong contribution to AEJ-N maintenance compared to AEJ-S. This study strengthens our understanding of the mid-level circulation over Central Africa by detecting gaps in the mechanisms maintaining the AEJ in coupled models and highlights processes that should be improved in future ensembles.
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