On the Marsupial Theory for Tropical Cyclogenesis Within Tropical Wave and Monsoon Trough Environments: A Multiscale Observational, Modeling and Theoretical Study

在大气动力学中，弱旋转对流区何时、何地以及如何发展成成熟的热带气旋仍然是一个基本上没有解决的问题，尽管这个问题对预测高影响天气有着不同寻常的重要意义。在这个项目中，Montomgery和他的团队将探索他的“有袋动物假说”，该假说将热带气旋的形成与热带波的关键层联系起来。“有袋假说”包括三个子假说：1)雷暴发展成热带气旋的弱旋转区域形成于热带行波的临界水平或转向水平。在这个水平波的速度等于背景风的速度，所以流体，包括弱旋转的“原涡旋”，随着波移动。2)对于较强的波浪，临界水平面演变为临界层，形成封闭流线的口袋。在这个口袋里，发展中的涡旋被部分隔离或保护（因此“有袋动物”理论），免受干燥空气的夹带和垂直切变的有害影响。(3)与这些原涡相关的潜热释放放大了热带波。这些假设将在观测分析和建模程序中进行检验。对大气数据的初步分析表明，如假设的那样，非洲东风波的关键层是热带气旋发展的首选区域，而波槽内的对流有助于维持这种波。这些分析将扩展到季风槽的情况，并且将与不发生气旋形成的零情况相平衡。热带地区再分析的问题——结果强烈受到积云参数化方案的影响——将通过分析其他来源的数据来规避，包括热带降雨测量任务（TRMM）卫星数据，以及2008年夏秋季T-PARC（观测系统研究和可预测性实验（THORPEX）太平洋亚洲区域运动）实地运动期间获得的现场数据。模式试验将使用天气研究与预报（WRF）模式进行。干式实验将检验产生原涡旋的热带波浪的涡旋脱落。对积云对流进行标准处理的潮湿实验将检验波的放大，云尺度模型将考虑原涡的增长。该项目的更广泛影响来自于对热带气旋形成的进一步了解所带来的社会效益，以及这种了解对预测的潜在影响。蒙哥马利的小组将与美国国家海洋和大气管理局飓风研究部门合作，开展年度实地研究项目。对军队毕业生进行培训。

When, where, and how weakly rotating convective regions develop into full-blown tropical cyclones remains an essentially unsolved problem in atmospheric dynamics, albeit a problem with unusually significant implications for forecasting high-impact weather. In this project Montomgery and his group will explore his "marsupial hypothesis," which relates tropical cyclogenesis to the critical layers of tropical waves. The "marsupial hypothesis" comprises three sub-hypotheses:1) The weakly rotating regions of thunderstorms that develop into tropical cyclones form at the critical level, or steering level, of tropical traveling waves. At this level the wave speed equals that of the background wind, so that fluid, including the the weakly rotating "proto-vortex," moves with the wave.2) For stronger waves, the critical level evolves into a critical layer, which forms a pocket of closed streamlines. In this pocket, the developing vortex is partially isolated or protected (thus "marsupial" theory) from the entrainment of dry air and the deleterious affects of vertical shear.3) Tropical waves are amplified by the latent heat release associated with these proto-vortices.These hypotheses will be tested in a program of observational analyses and modeling. Preliminary analyses of atmospheric data indicates that critical layers of African easterly waves are, as hypothesized, preferred regions for tropical cyclone development, and that convection within the wave trough helps to maintain the wave. These analyses will be extended to monsoon trough cases, and cyclogenesis cases will be balanced with null cases, in which cyclogenesis does not occur. Problems with reanalyses in the tropics - that the results are strongly conditioned by the cumulus parameterization scheme - will be circumvented by analyzing data from other sources, including the Tropical Rainfall Measurement Mission (TRMM) satellite data, and in-situ data obtained during the summer-fall 2008 T-PARC (THe Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign) field campaigns.Model experiments will be carried out using the Weather Research and Forecasting (WRF) model. Dry experiments will examine the vortex shedding from tropical waves that produces proto-vortices. Moist experiments with standard treatments of cumulus convection will examine wave-amplification, and cloud-scale modeling will consider the growth of proto-vortices.Broader impacts of this project derive from the societal benefits of improved understanding of tropical cyclogenesis and the potential impact of such understanding on prediction. Montgomery's group will collaborate with NOAA's Hurricane Research Division in their annual field program of research. Graduate students from the military services will be trained.