Variability of African Easterly Waves and Their Interactions with Saharan Mineral Dust Aerosols

就像美国的每周天气报告关注暖锋和冷锋一样，西非的夏季天气报告可能会以非洲东风波（AEWs）为特色，这种天气模式的槽和脊相距约1500公里，向东移动，穿过萨赫勒地区和大西洋的大部分顺风区。报告可能还会提到一股巨大的撒哈拉沙尘，它们沿着与预警机类似的轨迹移动。撒哈拉沙尘流和预警系统的接近表明两者可能相互作用，因为与预警系统相关的风可能会搅动并运输沙尘，而沙尘吸收的太阳辐射可能会导致大气加热，从而影响预警系统的演变。但预警系统与尘羽的相互作用尚未得到广泛的研究，而预警系统扬起和输送的尘羽对预警系统的影响程度也尚不清楚。该奖项的主要研究者（pi）先前的工作表明，在理想的情况下，来自尘埃的辐射加热可以促进AEWs的发展（见奖项#1524767）。该奖项下的工作结合了观测分析和数值模型实验，以更好地了解预警和撒哈拉沙尘羽的相互作用。在观测方面，该项目利用了由NASA全球模拟和同化办公室制作的现代研究和应用回顾性分析第2版（MERRA-2）。MERRA-2是这项工作的宝贵资源，因为它基于卫星观测跟踪沙漠尘埃，并提供尘埃光学深度和辐射加热以及标准气象变量。建模组件在理想配置中使用天气研究和预报（WRF）模型来识别与预警相对应的不稳定模式。模拟在有尘埃辐射加热和没有尘埃辐射加热的情况下进行，以便评估其对AEW模式的波长、相速度和生长速率的影响。使用统一预报系统模型进行了额外的实验，同样有和没有粉尘辐射加热，以评估粉尘加热在更现实的环境中的影响。这项工作具有社会意义，因为它可能有助于改善天气和空气质量预报。更好的预警将使美国和西非国家受益，因为预警在飓风的形成中起着关键作用，包括那些在东海岸登陆的飓风。撒哈拉沙尘也是一个洲际问题，因为它影响着非洲、加勒比地区和美国的空气质量。pi与美国国家气象局气候预测中心非洲部合作，将研究成果纳入每周天气展望和短期沙尘预报。此外，该项目还为研究生提供支持和培训。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Just as weekly weather reports for the US focus on warm fronts and cold fronts, a summer weather report for West Africa might feature African Easterly Waves (AEWs), weather patterns with troughs and ridges separated by perhaps 1,500km that move eastward over the Sahel and across much of the downwind Atlantic. The report might also mention a vast plume of airborne Saharan dust moving along a similar trajectory to the AEWs. The proximity of Saharan dust plumes and AEWs suggests that the two might interact, since winds associated with an AEW could stir up dust and transport it, while solar radiation absorbed by the dust could cause atmospheric heating that would affect the evolution of the AEW. But the interaction of AEWs and dust plumes has not been extensively studied, and the extent to which dust lofted and transported by AEWs in turn affects the AEWs is not well understood. Previous work by the Principle Investigators (PIs) of this award shows, in an idealized context, that radiative heating from dust can contribute to the development of AEWs (see award #1524767).Work under this award uses a combination of observational analysis and numerical model experiments to better understand the interactions of AEWs and Saharan dust plumes. On the observational side the project takes advantage of the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) produced by the NASA Global Modeling and Assimilation Office). MERRA-2 is a valuable resource for the work because it tracks desert dust based on satellite observations and provides dust optical depth and radiative heating along with the standard meteorological variables. The modeling component uses the Weather Research and Forecast (WRF) model in an idealized configuration to identify unstable modes corresponding to AEWs. The simulations are performed with and without dust radiative heating so that its effects on the wavelength, phase speed, and growth rates of the AEW modes can be assessed. Additional experiments are performed using the Unified Forecast System model, again with and without dust radiative heating, to assess the influence of dust heating in a more realistic setting.The work has societal relevance due to its potential contribution to improving weather and air quality forecasts. Better forecasts of AEWs would benefit the US as well as the nations of West Africa since AEWs play a key role in generating hurricanes, including those that make landfall on the eastern seaboard. Saharan dust is also an intercontinental problem as it affects air quality in Africa, the Caribbean, and the US. The PIs work with the Africa Desk of the National Weather Service's Climate Prediction Center to incorporate research results into weekly weather outlooks and short-range dust forecasts. In addition, the project provides support and training to a graduate student.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.