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，东非降雨的季节性很复杂，包括双峰和单峰雨季。 在肯尼亚、索马里南部、埃塞俄比亚南部和坦桑尼亚北方，通常在赤道7度范围内出现双峰雨季，降水量最大，农业生长季节在春季和秋季。这种降雨分布传统上被解释为与每年有两次太阳从头顶经过有关。 然而，这个解释是不完整的，因为从赤道10度或15度的地区每年有一个雨季，尽管太阳在这些纬度上有两次从头顶经过。此外，赤道中部和西部非洲气候潮湿，全年降雨。 这表明，一个更完整的了解东非降雨的季节性应考虑这些因素的作用，印度洋，地形，近赤道大气动力学（与一个小的或没有科里奥利力），除了太阳强迫。该研究项目旨在促进我们对东非降雨季节性是如何确定的理解，并将这种更好的理解应用于气候变异和变化问题，包括影响。 对观测结果的分析、对这一数据贫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用于调查这些物理过程，以更全面地了解降雨的季节性如何在东非分布。了解降雨的季节性对提高我们预测变化和变异的能力至关重要，特别是在人口高度脆弱的东非等地区。 降雨量的变化，包括其季节性，强烈影响该地区的农业，经济和水资源，这反过来又影响生计和政治稳定。 这些问题将在本项目内直接处理，办法是将观测和模拟的气候变量变化和趋势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计算自然植被的变化，使用的模型将植被类型与气候条件联系起来。 还将评估生长季节天数和地表水可用性的变化和趋势。 这些表述将为影响分析提供直接投入。 该研究项目有利于气候建模领域更普遍地促进区域尺度气候模拟的发展，包括可以显式解决控制方程内对流的高分辨率模型。 这一点很重要，因为在分辨率较低的模式（如全球气候模式）中，对流的参数化会降低模拟的质量。 研究计划的更广泛影响还包括STEM领域研究生的教育。

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.