Seasonality of East African Rainfall

从北部的埃塞俄比亚到南部的马拉维和莫桑比克，东非降雨量的季节性是复杂的，包括双峰型和单峰型雨季。在肯尼亚、索马里南部、埃塞俄比亚南部和坦桑尼亚北部，雨季双峰式的地区，降水量最大，农业生长季节在春季和秋季，通常发生在赤道约7度的范围内。这种降雨量的分布传统上被解释为与每年有两次太阳通过有关。然而，这一解释并不完整，因为赤道10度或15度的地区每年都有一个雨季，尽管在这些纬度有两次太阳从头顶经过。此外，赤道中西部非洲气候潮湿，常年降雨。这表明，要更全面地了解东非降水的季节性，除太阳强迫外，还应考虑印度洋、地形和近赤道大气动力学(有小的或没有科里奥利力)等因素。这一研究项目的目的是促进我们对东非降雨季节性如何确定的理解，并将这种理解应用于气候多变性和变化问题，包括影响问题。对观测数据的分析、对这一数据匮乏地区的多个数据集的比较以及高分辨率模式模拟的输出将被用来调查这些物理过程，以更全面地了解降雨的季节性如何在整个东非分布。了解降雨的季节性对于提高我们预测变化和变异性的能力至关重要，特别是在人口高度脆弱的东非等地区。降雨的变化，包括其季节性，严重影响该地区的农业、经济和水资源，进而影响生计和政治稳定。这些问题将在该项目内直接解决，方法是将观测和模拟的气候变量变化和趋势与与影响更直接相关的变量联系起来。气候变量的变化将被用来通过将植被类型与气候条件相关联的模型来计算自然植被的变化。还将评估生长季日数和地表水可获得性的变化和趋势。这些表述将为影响分析提供直接输入。该研究项目总体上有利于气候模拟领域的发展，促进了区域尺度气候模拟的发展，包括能够显式求解控制方程内对流的高分辨率模型。这一点很重要，因为众所周知，在具有较粗分辨率的模式(如全球气候模式)中对流的参数化会降低模拟的质量。该研究计划的更广泛影响还包括STEM领域的研究生教育。

The seasonality of rainfall in East Africa from Ethiopia in the north to Malawi and Mozambique in the south is complex, including bimodal and unimodal rainy seasons. Regions with bimodal rainy seasons, with precipitation maxima and agricultural growing seasons in the spring and fall, occur generally within about 7 degrees of the equator in Kenya, southern Somalia, southern Ethiopia, and northern Tanzania. This rainfall distribution is traditionally explained as being related to having two overhead passes of the sun each year. However, this explanation is not complete since regions 10 or 15 degrees from the equator have one rainy season each year despite two overhead passes of the sun at these latitudes. In addition, equatorial central and western Africa experience humid climate with rainfall throughout the year. This suggests that a more complete understanding of the seasonality of East African rainfall should consider such factors as the roles of the Indian Ocean, topography, and near-equator atmospheric dynamics (with a small or absent Coriolis force) in addition to the solar forcing. This research project is aimed at advancing our understanding of how the seasonality of rainfall in East Africa is determined, and to apply that improved understanding to issues of climate variability and change, including impacts. Analysis of observations, comparing multiple datasets in this data-poor region, and output from high-resolution model simulations will be used to investigate these physical processes to produce a more comprehensive understanding of how the seasonality of rainfall is distributed across East Africa.It is crucial to understand the seasonality of rainfall to improve our ability to predict change and variability, especially in regions such as East Africa where the population is highly vulnerable. Variations in rainfall, including its seasonality, strongly impact the region's agriculture, economy, and water resources which, in turn, affect livelihoods and political stability. These issues will be directly addressed within the project by relating observed and simulated variations and trends in climate variables to variables more directly related to impacts. Changes in climate variables will be used to calculate changes in natural vegetation using a model that relates vegetation type to climate conditions. Changes and trends in growing season days and surface water availability will also be evaluated. These representations will provide direct input for impacts analysis. The research project benefits the climate modeling field more generally in contributing to the development of regional-scale climate simulation, including high-resolution models that can explicitly resolve convection within the governing equations. This is important since the parameterization of convection in models with coarser resolution, such as global climate models, is known to degrade simulations. Broader impacts of the research program also include the education of graduate students in STEM fields.