Improving Understanding of Convection Initiation in Nocturnal Environments During PECAN (Plains Elevated Convection at Night) Using High-Resolution Ensemble Data Assimilation

美国中部的夜间雷暴为农业生产地区提供降雨，但也可能通过洪水和强风对生命和财产造成危害。2015年，美国国家科学基金会资助了一大批科学家来收集这些夜间雷暴的数据。该项目将利用这些数据进行小规模的数值模拟研究，以确定雷暴的初始触发因素，这一过程被称为对流起始。这项研究有可能提高对这些事件的理解和建模，为预报员提供更多关于雷暴发生的时间和地点的信息。该奖项还将资助一名早期职业研究人员，为本科生提供参加研究项目的机会，并允许研究人员根据实地活动制定研讨会课程，从而促进人力资源的发展。2015年6月和7月在大平原地区进行了平原夜间高架对流（俗称PECAN）野外试验。该活动包括许多观测平台，如移动雷达、飞机、垂直剖面仪和地面仪器。在这个项目中，研究人员打算将来自战役的数据吸收到一个具有嵌套中尺度和对流解析网格的集成中。研究的主要重点是准确地再现夜间中尺度环境的演变，在这种环境中对流开始发生，并确定哪些特定的小尺度和大尺度过程导致包裹上升到自由对流的水平。集成数据同化实验将采用WRF-ARW和数据同化研究试验台（DART）集成分析软件配置为集成调整卡尔曼滤波器。将使用50个集成成员，研究人员计划采用三重嵌套模型网格策略，网格间距最小为0.4至0.6公里。除了识别夜间对流触发过程的工作外，研究人员还将进行预测灵敏度实验。

Nocturnal thunderstorms in the central United States provide rainfall for productive agricultural regions but also can pose hazards to lives and property through flooding and severe winds. In 2015, NSF funded a large group of scientists to collect data on these nighttime thunderstorms. This award will make use of that data by conducting very small scale numerical modeling studies to determine what initially triggers the thunderstorms, a process known as convective initiation. The research has the potential to improve understanding and modeling of these events, giving forecasters more information about when and where thunderstorms may happen. The award would also contribute to human resource development by funding an early-career researcher, providing an opportunity for an undergraduate student to participate in a research project, and allowing the researcher to develop a seminar course based on the field campaign.The Plains Elevated Convection at Night (known colloquially as PECAN) field campaign was conducted in the Great Plains region in June and July of 2015. The campaign included numerous observational platforms, such as mobile radars, aircraft, vertical profilers and surface instrumentation. In this project the researcher intends to assimilate data from the campaign into an ensemble with nested mesoscale and convection-resolving grids. The primary focus of the research is to accurately reproduce the evolution of the nocturnal mesoscale environment in which convective initiation occurs and to determine which specific small- and large-scale processes result in parcels lifted to their level of free convection. The ensemble data assimilation experiments will employ the WRF-ARW and the Data Assimilation Research Testbed (DART) ensemble analysis software configured as an Ensemble Adjustment Kalman Filter. Fifty ensemble members will be used and the researcher plans to employ a triple nested model grid strategy with the finest grid spacing of 0.4 to 0.6km. In addition to the work on identifying processes triggering nocturnal convection, the researcher will also conduct forecast sensitivity experiments.