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转移到地表，由于上覆柱的质量减少而导致静水压力降低。 在当前的大气模型中，这种降水质量汇的表示要么不存在，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。 对于降水量可能超过每天 200 毫米的热带气旋，压力当量质量去除不可忽略，约为 20 hPa。 由于降水造成的压力下降将通过水平质量会聚部分补偿。 然而，这种汇聚的流入可能对水分输送和涡度产生至关重要，特别是在存在强烈旋转的情况下。 要测试的初始假设是，由于降水去除大气质量而导致的压力降低是热带气旋的一级动力学过程。 第二个相关假设是，在数值天气预报模型中明确包含质量汇效应将提高其准确预测热带气旋发生、强度和路径的能力。研究的重点将是了解与热带气旋动力学相关的降水质量汇的物理机制。 首席研究员将通过进行一系列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． 开发并测试一个数值模型，其中包括模型连续性、压力趋势和动量方程中的水荷载和降水质量汇效应。 2. 对飓风莉莉（和/或其他案例）进行彻底的观测数据分析，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型模拟进行详细评估。 3. 对飓风莉莉或其他案例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积的风暴相关预算将隔离水负荷和降水质量沉降对热带气旋动力学的相对重要性。 分析的核心是位涡 (PV) 诊断，包括预算计算和分段反演。4． 制定热带气旋形成和强化的概念模型，以解释质量汇机制的作用。该研究的影响包括 i) 可能改进热带气旋形成、强化和路径的数值预报。 ii) 更好地了解降水在热带气旋动态中所起的作用。

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.