P2C2: Extratropical Mechanisms, Land-Surface Properties, and Seasonal Precipitation Processes on Saharan Rainfall and Simulation of the African Humid Period

这个项目的总体目标是发展对季节性非季风过程的理解，以便量化它们对北非气候变化的贡献。具体来说，该研究旨在深入了解西非季风（WAM）、温带气旋、地中海冷空气涌动和热带羽流对非洲湿润期（AHP）降雨的相对贡献（距今约14800 - 5000年）。在千年的时间尺度上，北非经历了剧烈的气候和环境变化。在全新世早期到中期，当今世界上最大的热沙漠——撒哈拉沙漠，获得了充足的降雨，并支持了广泛的湖泊、湿地和植被。考虑到当今撒哈拉在地球辐射收支中的关键作用及其对萨赫勒降雨、全球矿物粉尘浓度、生物地球化学循环和热带气旋形成的影响，撒哈拉的气候变率，例如在全新世期间观测到的气候变率，对全球气候系统产生了深远的影响。通过评估这些过程对AHP降雨的贡献，这项研究将有助于解释在撒哈拉-阿拉伯沙漠带的代用记录中记录的水分来源，这些记录目前尚不明确，因为它们位于热带季风和中纬度降雨制度的边界附近。对社区地球系统模式（CESM）内新的动态土壤反照率方案的影响进行评估，将为气候模式的开发和AHP的改进模拟提供切实的见解。在一般环流模式中检测热带羽流的客观算法的开发将公开提供，并可用于研究过去、现在和未来气候中影响全球热带羽流事件的过程。更广泛的影响包括通过我们参与密歇根大学（U-M）地球营，增加未被充分代表的少数民族（URM）学生进入地球科学领域的潜力。地球营是一个面向底特律地区初入职场的高中生的住宿营地，向他们提供有关地球科学和地球科学职业的教育。密歇根大学地球夏令营原本只有一个暑假，但为了增加学生们在大学里学习地球科学的几率，它正在扩大到多个夏令营。作为我们参与地球营的一部分，该项目的参与者将在密歇根州安娜堡的第一个夏季体验中开发和指导为期一天的大气科学和气候组件，并为在怀俄明州的密歇根大学野外站的第二个夏季体验创建为期四天的组件。除了扩大URM在地球科学领域的参与外，该项目还将支持一名年轻科学家和至少一名本科生的培训和职业发展。

This project generally aims to develop an understanding of seasonal non-monsoon processes in order to quantify their contribution to climate change in northern Africa. Specifically, the research aims to provide insights into the relative contributions of the West African Monsoon (WAM), extratropical cyclones, Mediterranean cold air surges, and tropical plumes to African Humid Period (AHP) rainfall (~14,800 - 5,000 years Before Present. At millennial timescales, northern Africa experienced dramatic climate and environmental change. During the early to mid-Holocene AHP, the world's largest present-day hot desert, the Sahara, received abundant rainfall and supported widespread lakes, wetlands, and vegetation. Given the critical role of the present-day Sahara in Earth's radiation budget and its influence on Sahel rainfall, global mineral dust concentrations, biogeochemical cycles, and tropical cyclogenesis, climate variability in the Sahara, such as that observed during the Holocene, has profound impacts on the global climate system. By evaluating the contribution of these processes to AHP rainfall, the research will assist in interpreting the sources of moisture recorded in proxy records from the Sahara-Arabian desert belt which are currently ambiguous because they lie near the border of the tropical monsoon and mid-latitude rainfall regimes. An assessment of the impact of the new dynamic soil albedo scheme within the Community Earth System Model (CESM) will offer tangible insights for climate model development and improved simulation of the AHP. The development of an objective algorithm for the detection of tropical plumes within general circulation models will be made publicly available and could be used to study the processes that influence tropical plume events across the globe in past, present, and future climates.The Broader Impacts involve the potential for increasing the pipeline of underrepresented minority (URM) students into the earth sciences through our participation in the University of Michigan (U-M) Earth Camp. Earth Camp is a residential camp for early-career, high-school students from the Detroit-area that educates them about the earth sciences and careers in the earth sciences. The U-M Earth Camp has consisted of a single summer experience, but is expanding to a multi-summer camp in order to increase the odds that students will study earth sciences in college. As part of our participation in Earth Camp, the participants in this project will develop and instruct a one-day atmospheric science and climate component to the first summer experience in Ann Arbor, MI and create a four-day component for the second summer experience at the U-M field station in Wyoming. In addition to broadening URM participation in the earth sciences, this project will also support the training and career-development of a young scientist and at least one undergraduate student.