The Role of the Precipitation Mass Sink in Tropical Cyclone Dynamics

在强降水期间，大量的水汽被从大气中移到地面，由于上覆柱中质量的减少，导致静水压力降低。由于水汽质量连续没有显式地耦合到总质量连续方程或气压趋势方程，在现有大气模式中，这种降水质量汇的表示要么是不存在的，要么是不完整的。对于日降水量可能超过200毫米的热带气旋，相当于气压的质量移动量是不可忽略的，约为20百帕。水平质量辐合可以部分补偿降水引起的气压下降。然而，这种汇聚流入对水汽输送和涡度产生可能是关键的，特别是在存在强烈旋转的情况下。需要检验的初始假设是，在热带气旋中，由于降水去除大气质量而导致的气压下降是一个一级动力学过程。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，将提高它们对热带气旋发生、强度和路径的准确预测能力。研究的重点将放在了解降水质量汇与热带气旋动力学有关的物理机制上。首席调查员将通过进行一系列数值模型实验来分离重要的机制，这些实验选择性地在控制方程中包括和排除质量下沉项。本项目的具体目标是：1.在模型连续性、压力趋势和动量方程中发展和检验一个同时考虑水负荷和降水质量汇效应的数值模式。2.对飓风莉莉(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)和落差探测仪。观测分析将允许对数值模式模拟进行详细评估。3.对飓风丽丽或其他案例进行一系列敏感性实验。分析将包括质量、水分和动量预算。随着风暴移动的圆柱体积的风暴相对预算将隔离水负荷和降水质量下沉对热带气旋动力学的相对重要性。分析的中心部分将是位涡(PV)诊断，包括预算计算和分段反转。建立一个热带气旋发生和加强的概念性模式，解释质量下沉机制的作用。研究的影响包括：i)热带气旋形成、加强和路径的潜在改进的数值预报。2)更好地了解降水在热带气旋动力学中的作用。

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.