The impact of air-sea coupling and ocean biases on the seasonal cycle of southern West African precipitation
The impact of air-sea coupling and ocean biases on the seasonal cycle of southern West African precipitation
复制标题
海气耦合和海洋偏差对西非南部降水季节周期的影响
DOI：
10.1007/s00382-019-04973-0
复制
发表时间：
2019
期刊：
影响因子：
4.6
通讯作者：
Wainwright C
中科院分区：
文献类型：
--
作者：
Wainwright C
在西非南部地区，一年两次的季节性降雨的特点是有两个雨季，中间被7月至8月的“小旱季”隔开。在这个干旱季节期间，降雨量减少可能对依赖农业产出的人口密集地区的作物产量不利。耦合模型相互比较项目第5阶段（CMIP 5）模型没有正确地捕捉到这种季节性制度，而是产生一个单一的雨季，在观察到的时间小旱季达到峰值。因此，对该地区未来气候预测的现实性值得怀疑。在这里，代表性的小旱季耦合模式模拟的影响，阐明导致这种误解的因素。英国气象局统一模式的全球海洋混合层配置对于探索这种错误表述特别有用，因为它可以在保持海气耦合的同时分离不同海洋盆地中耦合模式海洋偏差的影响。大西洋SST偏差导致西非南部的季节性制度不正确。8月的高层下降减少了沿着海岸线的上升，这与观测到的小旱季降雨量减少有关。当耦合模式大西洋偏差引入，上升的海岸线更深，降雨总量更高，在7月至8月。因此，这项研究表明了大西洋偏见带来的不利影响，并强调了西非地区生产有意义的气候变化预测所需的模型开发领域。
The biannual seasonal rainfall regime over the southern part of West Africa is characterised by two wet seasons, separated by the ‘Little Dry Season’ in July–August. Lower rainfall totals during this intervening dry season may be detrimental for crop yields over a region with a dense population that depends on agricultural output. Coupled Model Intercomparison Project Phase 5 (CMIP5) models do not correctly capture this seasonal regime, and instead generate a single wet season, peaking at the observed timing of the Little Dry Season. Hence, the realism of future climate projections over this region is questionable. Here, the representation of the Little Dry Season in coupled model simulations is investigated, to elucidate factors leading to this misrepresentation. The Global Ocean Mixed Layer configuration of the Met Office Unified Model is particularly useful for exploring this misrepresentation, as it enables separating the effects of coupled model ocean biases in different ocean basins while maintaining air–sea coupling. Atlantic Ocean SST biases cause the incorrect seasonal regime over southern West Africa. Upper level descent in August reduces ascent along the coastline, which is associated with the observed reduction in rainfall during the Little Dry Season. When coupled model Atlantic Ocean biases are introduced, ascent over the coastline is deeper and rainfall totals are higher during July–August. Hence, this study indicates detrimental impacts introduced by Atlantic Ocean biases, and highlights an area of model development required for production of meaningful climate change projections over the West Africa region.