A Numerical Investigation of Convection Initiation by Instabilities along Outflow Boundaries

风暴外流的三维特征在对流风暴的形成中起着重要的作用。在许多预报情景中，主要问题不是深对流是否会沿着沿着给定边界发展，而是风暴在沿着该边界的何处和何时将受到青睐。研究人员的初步和相关的模拟研究以及最近的观测结果表明，沿沿着和其他辐合边界的异常/不稳定性与对流启动之间存在联系。一个三维对流云模式将被用来提高对在沿着流出边界和其他辐合边界的特定位置处促使深对流开始的过程的理解。作为这项研究的一部分，详细的三维结构的流出边界和相关的湿对流强迫将在有利于特定的不稳定性沿着流出前缘的环境进行调查。在可能的情况下，将使用观测结果来验证数值模拟的结果。该项目的基本目标是通过应用从这项研究中获得的知识来改进对风暴初始位置的预测。该项目的主要目标包括：1。调查沿着流出边界的具有明显水平切变的微气旋环流的作用（即，垂直涡面）在湿对流启动中的作用;2.检查湿对流强迫和基本结构以及沿着流出边界的瓣和裂不稳定的形态。这第二个目标将包括在没有明显前缘水平切变（与第1项相反）的环境中流出边界的精细尺度三维结构的综合研究。这些目标涉及到进一步理解沿着流出边界的对流起始的关键要素。此外，这些目标与美国天气研究计划的一个关键目标是一致的，该计划涉及通过改进边界层过程的知识来改进降水预报。

Three-dimensional aspects of storm outflow play an important role in the initiation of convective storms. In many forecast scenarios, the primary question is not whether deep convection will develop along a given boundary but where and when along this boundary will storms be favored. Preliminary and related modeling studies by the investigators as well as recent observations suggest a link between anomalies/instabilities along outflows and other convergence boundaries and convection initiation. A three-dimensional convective cloud model will be employed to improve understanding of the processes that prompt deep convection initiation at specific locations along outflow and other convergence boundaries. As part of this study, the detailed three-dimensional structure of outflow boundaries and related moist convective forcing will be investigated in environments favoring specific instabilities along the outflow leading edge. Observations will be used where possible to validate the results from the numerical simulations. The underlying objective of the project is to improve the prediction of initial storm location by applying the knowledge obtained from this research. Specific primary objectives of the project include:1. Investigating the role misocyclone circulations along outflow boundaries with marked horizontal shear (i.e., a vertical vortex sheet) play in moist convection initiation;2. Examining the moist convective forcing and basic structure and morphology of lobe and cleft instability along outflow boundaries. This second objective will include a comprehensive examination of the fine-scale three-dimensional structure of outflow boundaries in environments without marked leading edge horizontal shear (in contrast to item 1).These objectives involve critical elements for furthering our understanding of convection initiation along outflow boundaries. Further, these objectives are consistent with a key goal of the U.S. Weather Research Program involving the refinement of precipitation forecasts with improved knowledge of boundary layer processes.