The Role of the Precipitation Mass Sink in Tropical Cyclone Dynamics

在强降水期间，大量的水蒸气从大气中被移到地面，由于上覆柱的质量减少，导致静水压力降低。这种降水质量汇的表示在目前的大气模式中要么不存在，要么不完整，因为水蒸气质量连续性没有明确地与总质量连续性或压力趋势方程耦合。对于降水速率可能超过200毫米/天的热带气旋，压力当量的质量去除是不可忽略的，约为20 hPa。由于降水造成的气压下降将部分被水平质量辐合所补偿。然而，这种辐合入流可能对水汽输送和涡度产生至关重要，特别是在强旋转存在的情况下。要验证的初步假设是，由于降水去除大气质量而导致的气压降低是热带气旋的一级动力过程。第二个相关的假设是，在数值天气预报模式中明确地包括质量汇效应将提高其准确预测热带气旋形成、强度和路径的能力。研究的重点是了解降水质量汇的物理机制，因为它与热带气旋动力学有关。首席研究员将通过进行一系列的数值模型实验来分离重要的机制，这些实验有选择地包括和排除控制方程中的质量汇项。该项目的具体目标是：1。开发和测试一个数值模型，该模型包括模型连续性、压力趋势和动量方程中的水负荷和降水质量汇效应。2. 对飓风莉莉（和/或其他情况）进行全面的观测数据分析，包括现场飞机数据、遥感数据（雷达和卫星）和下投探空仪。观测分析将允许对数值模式模拟进行详细评估。3. 对丽丽飓风或其他情况进行一系列敏感性实验。分析将包括质量、湿度和动量预算。随着风暴移动的圆柱形体的风暴相对预算将分离出水负荷和降水质量汇对热带气旋动力学的相对重要性。分析的核心将是潜在涡度（PV）诊断，包括预算计算和分段反演。制定一个考虑质量汇机制作用的热带气旋形成和增强的概念模式。这项研究的影响包括i)可能改善热带气旋形成、增强和路径的数值预报。ii)提高了对降水在热带气旋动力学中所起作用的认识。

During heavy precipitation, significant quantities of water vapor are removed from the atmosphere to the surface, resulting in a hydrostatic pressure reduction due to the decrease of mass in the overlying column. The representation of this precipitation mass sink is either non-existent or incomplete in current atmospheric models because water vapor mass continuity is not explicitly coupled to the total mass continuity or pressure tendency equations. For tropical cyclones in which precipitation rates may exceed 200 mm per day, the pressure-equivalent mass removal is not negligible, on the order of 20 hPa. The pressure decrease due to precipitation would be partially compensated by horizontal mass convergence. However, this convergent inflow may be critical to moisture transport and vorticity generation, especially in the presence of strong rotation. The initial hypothesis to be tested is that the pressure reduction due to the removal of atmospheric mass by precipitation is a first-order dynamical process in tropical cyclones. A second, related hypothesis is that including the mass sink effect explicitly in numerical weather prediction models will improve their ability to accurately predict tropical cyclone genesis, intensity, and track.The focus of the research will be on understanding the physical mechanism of the precipitation mass sink as it relates to tropical cyclone dynamics. The Principal Investigator will isolate the important mechanisms by undertaking a series of numerical model experiments that selectively include and exclude the mass sink terms in the governing equations. The specific objectives of this project are to:1. Develop and test a numerical model that includes both water loading and precipitation mass sink effects in the model continuity, pressure-tendency, and momentum equations. 2. Conduct a thorough observational data analysis for Hurricane Lili (and/or other cases) including in-situ aircraft data, remotely sensed data (radar and satellite) and dropsondes. The observational analysis will allow detailed evaluation of numerical model simulations. 3. Conduct a series of sensitivity experiments on Hurricane Lili or other cases. The analysis will include mass, moisture, and momentum budgets. Storm-relative budgets for a cylindrical volume moving with the storm will isolate the relative importance of water loading and the precipitation mass sink to tropical cyclone dynamics. A centerpiece of the analysis will be a potential vorticity (PV) diagnosis, including budget computations and piecewise inversions.4. Formulate a conceptual model for tropical cyclogenesis and intensification that accounts for the role of the mass sink mechanism.The impacts of the research include i) potentially improved numerical forecasts of tropical cyclone formation, intensification, and track. ii) Improved understanding of the role that precipitation plays in the dynamics of tropical cyclones.