Dynamics of Heavy Precipitation over Mesoscale Mountains

这项研究的目的是促进对地形降雨的科学认识。本文将解决三个主要问题：(1)除了湿润弗劳德数外，还有哪些主要的非量纲参数控制地形诱导的中尺度对流系统在山区的传播？(2)地形中尺度对流系统中对流单体的形成和传播机制是什么？(3)高空急流是如何与低空气流耦合形成有利于强地形降水的环境的？为了解决第一个问题，首席研究员将扩展先前的研究，以研究有条件不稳定地形流的其他主要控制参数。利用中尺度数值模式进行一系列理想化数值实验，研究基本流速、不稳定性、含水率、山宽高比、科里奥利力和垂直风切变对湿流状态的影响。为了解决第二个问题，首席研究员假设平流是对流细胞产生的主要机制。该平流机制将通过一系列数值实验进行验证。关于第三个问题，假设在边界层流动和高空急流条纹之间存在一个垂直耦合过程，创造了一个非常有利于强地形降水的环境。为了回答这个问题，我们将采用一个中尺度数值模式来进行实际的数值实验。这种方法的智力价值主要来自于将理想数值模拟、实际数据数值模拟和观测数据分析独特地多方面综合起来，应用于为什么强地形降雨发生在中尺度山区的问题。更广泛的影响将通过利用研究成果来发展改进的极端地形降雨预测技术来实现。预计这将挽救生命和减少财产损失。

The objective of this research is to advance scientific understanding of orographic rainfall. Three major questions will be addressed:(1) In addition to the moist Froude number, what are other major non dimensional parameters that control the propagation of orographically induced mesoscale convective systems over mountains?(2) What are the formation and propagation mechanisms of convective cells embedded in an orographic mesoscale convective system?(3) How does an upper-level jet streak couple with the low-level flow to create an environment that is highly favorable for heavy orographic precipitation?In order to address the first question, the Principal Investigator will extend previous studies to investigate other major control parameters for a conditionally unstable orographic flow. A series of idealized numerical experiments will be performed using a mesoscale numerical model to study the effects of basic flow speed, instability, moisture content, aspect ratio of the mountain, Coriolis force and vertical wind shear on moist flow regimes. In order to address the second question, the Principal Investigator hypothesizes that advection is the major mechanism for the generation of convective cells. This advection mechanism will be tested by performing a series of numerical experiments. Regarding the third question, it is hypothesized that there is a vertical coupling process between the boundary layer flow and upper-level jet streak that creates an environment that is highly favorable for heavy orographic precipitation. A mesoscale numerical model will be adopted to perform real-case numerical experiments to help answer this question. The intellectual merit of this approach is largely derived from the unique multi-faceted synthesis of idealized numerical modeling, real data numerical modeling and observational data analyses as applied to the problem of why heavy orographic rainfall occurs over mesoscale mountains.The broader impacts will be achieved by utilizing the research findings for the development of improved forecast techniques of extreme orographic rainfall predictions. It is anticipated that this will result in the saving of lives and the reduction of property losses.