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，NSF资助了一大批科学家收集这些夜间雷暴的数据。 该奖项将通过进行非常小规模的数值模拟研究来利用这些数据，以确定最初引发雷暴的原因，这一过程被称为对流启动。 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何时何地可能发生的信息。 该奖项还将通过资助早期职业研究人员，为本科生提供参与研究项目的机会，并允许研究人员开发基于现场活动的研讨会课程，为人力资源开发做出贡献。平原夜间高架对流（俗称PECAN）现场活动于2015年6月和7月在大平原地区进行。 这一行动包括许多观测平台，如移动的雷达、飞机、垂直剖面仪和水面仪器。 在这个项目中，研究人员打算同化活动的数据到一个集合嵌套的中尺度和对流解决网格。 研究的主要重点是准确地再现夜间中尺度环境的演变，其中对流开始发生，并确定哪些特定的小尺度和大尺度过程导致包裹解除到自由对流的水平。 集合数据同化试验将使用WRF-ARW和数据同化研究试验台（DART）集合分析软件，配置为一个包围调整卡尔曼滤波器。 将使用50个集合成员，研究人员计划采用三重嵌套模式网格策略，最小网格间距为0.4至0.6公里。 除了识别触发夜间对流的过程外，研究人员还将进行预报敏感性实验。

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.