SGER: Sensitivity of the West African Monsoon to Gulf of Guinea Sea Surface Temperatures (SSTs)

将对最先进的大气/海洋耦合全球模式的输出进行检查，以评估这些模式捕捉西非地区降雨变化的独特模式的能力。例如，当大西洋东部(几内亚湾)温暖时，观察到非洲南部(几内亚)海岸的夏季风降水特别强烈。同时，北部萨赫勒地区的降雨量往往远低于正常水平，导致作物歉收，给人口带来严重困难。过去在模型和观测中对这种变异性模式的研究已经确定了导致这种偶极降水响应的物理过程。沿海降水增加的原因是温暖的几内亚湾向南蒸发增加，因为赤道(东/西)Walker环流的存在及其在海湾的下沉分支防止了与较暖的海面相关的局部对流增强。萨赫勒地区降水减少是700百帕附近从撒哈拉高压向赤道方向流动的暖干空气加强下沉的结果，以及对这种气流的位涡守恒的要求。将检查模式输出，以了解模式模拟降水偶极子的能力与其分辨率和物理处理之间的关系。大气水汽收支、涡度和湿静态能量收支分析将被用来评估模拟变率的机制。未来随着海洋温度的上升，偶极子模式将更频繁地出现或永久确立的可能性将被调查。这项研究将有助于我们从根本上了解萨赫勒干旱是如何发生的，并有助于提高在所有时间尺度上预测非洲干旱的能力。它还将就世界这一地区气候预测的质量向环境管理人员和政策制定者提供指导。

Output from state-of-the art coupled atmosphere/ocean global models will be examined to evaluate the models' ability to capture a distinct mode of rainfall variability over WestAfrica. When the eastern Atlantic (Gulf of Guinea) is warm, for example, summer monsoon precipitation is observed to be especially strong along the southern (Guinean) coast of Africa. At the same time, rainfall in the Sahel region to the north tends to be much lower than normal, bringing crop failure and severe hardship for the population.Past studies of this mode of variability in models and observations have identified the physical processes that lead to this dipole precipitation response. Enhanced precipitation along the coast is due to increased evaporation to the south over the warm Gulf of Guinea, since the presence of an equatorial (east/west) Walker circulation with its sinking branch over the Gulf prevents locally-enhanced convection in association with the warmer sea surface. Reduced precipitation over the Sahel is a consequence of the enhanced sinking of warm, dry air flowing equatorward out of the Saharan high near 700 hPa, and the requirements of potential vorticity conservation for this flow.Model output will be examined to understand the relationship between a model's ability to simulate the precipitation dipole and its resolution and physical treatments. Atmospheric moisture budget, vorticity, and moist static energy budget analyses will be used to evaluate the mechanisms of the simulated variability. The possibility that the dipole pattern will occur more frequently, or become permanently established, in the future as ocean temperatures rise will be investigated. This study will contribute to our fundamental understanding of how drought occurs in the Sahel and lead to an improved ability to predict African drought on all time scales. It will also provide guidance to environmental managers and policy makers regarding the quality of climate projections for this part of the world.