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，主要问题不是是否会沿着给定的边界发展深对流，而是沿该边界的何时何地会有风暴。研究人员进行的初步和相关的模拟研究以及最近的观察表明，沿外流和其他汇聚边界的异常/不稳定性与对流启动之间存在联系。将使用三维对流云模式来更好地理解在沿流出和其他汇聚边界的特定位置引发深层对流的过程。作为这项研究的一部分，将在有利于沿流出前沿的特定不稳定的环境中研究流出边界的详细三维结构和相关的湿对流强迫。在可能的情况下，将使用观测值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。该项目的具体主要目标包括：1.研究沿具有明显水平切变的流出边界(即垂直涡旋层)的米斯气旋环流在湿对流启动中的作用；2.研究湿对流强迫以及沿流出边界的叶和裂隙不稳定的基本结构和形态。第二个目标将包括全面研究在没有明显前沿水平切变的环境中流出边界的精细三维结构(与项目1相反)。这些目标涉及关键要素，以加深我们对沿流出边界的对流起始的理解。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，该计划涉及通过改善对边界层过程的了解来改进降水预报。

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.