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移到地面，由于上覆柱的质量减少，导致静水压力降低。 在目前的大气模式中，这种降水质量汇的表示要么不存在，要么不完整，因为水汽质量连续性没有明确耦合到总质量连续性或压力趋势方程。 对于降水率可能超过每天200毫米的热带气旋，压力当量质量的去除是不可忽略的，约为20百帕。 降水引起的气压下降将被水平质量辐合部分补偿。 然而，这种收敛流入可能是至关重要的水分输送和涡度的产生，特别是在存在强旋转。 初步的假设是要测试的是，由于大气质量的降水是一个一阶动力过程中的热带气旋的压力降低。 第二个相关假设是，在数值天气预报模式中明确包含质量汇效应将提高它们准确预报热带气旋生成、强度和路径的能力。研究的重点将是理解降水质量汇与热带气旋动力学相关的物理机制。 主要研究者将通过进行一系列数值模型实验来分离重要的机制，这些实验选择性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式，该模式在模式连续性、压力趋势和动量方程中包括水负荷和降水质量汇效应。2. 对“丽丽”飓风（和/或其他情况）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）和投下式探空仪。 观测分析将允许对数值模型模拟进行详细评价。3. 对“丽丽”飓风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。 随风暴移动的圆柱体的风暴相对收支将隔离水负荷和降水量汇对热带气旋动力学的相对重要性。 分析的核心将是位涡诊断，包括预算计算和分段反演。 建立一个热带气旋生成和加强的概念模型，该模型考虑了质量汇机制的作用。研究的影响包括i）可能改进热带气旋形成、加强和路径的数值预报。 ㈡增进对降水在热带气旋动态中所起作用的了解。

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.