Tropical Cyclone Response to Time-Dependent Heating and Theory of Tropical Cyclone Motion

热带气旋对随时间变化的加热的响应和热带气旋运动理论

• 批准号: 0454501
• 负责人: Hugh Willoughby
• 金额: --
• 依托单位: Florida International University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-04-01 至 2011-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0454501&HistoricalAwards=false
• 关键词: Tropical; Cyclone; Response; Time; Dependent

Forecasts of tropical cyclone (TC) track and intensity remain significant operational challenges. Track forecasts have improved gradually over the last five decades, largely in response to improved observation and modeling of the environmental steering currents that control TC motion. By contrast, progress on intensity has been slow and statistical techniques still provide the best forecast guidance. The fundamental process in TC intensification is conversion of latent heat extracted from the sea into available potential energy and kinetic energy of the wind. The research to be undertaken under this award has two aspects 1) analysis of the TC vortex response to imposed heat sources and 2) theoretical studies of linear and nonlinear motion of a two-layer baroclinic TC-like vortex. The analytical axially symmetric, baroclinic mean-vortex structures used in these studies will be realistic representations of actual TCs derived from a large sample of in situ observations.The Principal Investigator will explore TC intensification processes by studying the responses to imposed heat sources with these sources being represented as truncated Fourier series in both time and azimuth. Only the axially symmetric, temporally constant component of the heat source supplies net heating. Its effect is readily computed from the classical Sawyer-Eliassen equation. The next level of complexity uses an axially symmetric heat source that varies sinusoidally in time. A single governing equation is derived from the Navier-Stokes equations linearized on a mean vortex in hydrostatic and gradient balance. The perturbation flow may be nonhydrostatic and sub- or super-gradient. If the frequency with which the heat source changes is low enough, this model calculation should resemble the results from steady forcing. At higher frequencies, effects such as changes in the effective local deformation radius due to time variation or projection onto gravity-wave modes can become factors. The next level of complexity considers a similarly derived equation for asymmetric heating with a given azimuthal wavenumber and frequency. Phenomena to be studied include changes in vortex response as a function of forcing frequency, the roles buoyancy and dynamic pressure, diabatically induced super- and sub-gradient winds, evolution of the mean vortex as a result of eddy fluxes of heat or momentum due to the perturbations, and hydrodynamic stability of mean-flow vortices constructed to model real hurricanes. The vortex-motion studies will use a two-layer semi spectral, vortex-tracking model to study the resiliency and realignment. Questions to be addressed include re-examination of resonant-damping theory, assessment of the roles of nonlinearity and evolution of the symmetric vortex, study of environmental potential vorticity and planetary vorticity gradients, and the effects of realistic initial mean-vortex structures. Broader impacts of this study include: fundamental new physical understanding essential to accurate track and especially intensity forecasts and support of Florida International University's (FIU) nascent meteorology program.

热带气旋 (TC) 路径和强度的预测仍然是重大的业务挑战。 在过去的五年中，轨道预报逐渐得到改善，这主要是由于对控制热带气旋运动的环境转向电流的观测和建模的改进。 相比之下，强度方面的进展缓慢，统计技术仍然提供最佳的预测指导。 TC强化的基本过程是将海洋中提取的潜热转化为可用的风势能和风动能。 该奖项将进行的研究有两个方面：1）分析热带气旋涡对强加热源的响应；2）两层斜压类热带气旋涡的线性和非线性运动的理论研究。 这些研究中使用的分析轴对称斜压平均涡结构将是从大量现场观测样本中得出的实际 TC 的真实表示。首席研究员将通过研究对强加热源的响应来探索 TC 增强过程，这些热源在时间和方位角上均表示为截断傅里叶级数。 只有热源的轴对称、时间恒定的部分提供净热量。 其效果很容易从经典的 Sawyer-Eliassen 方程计算出来。 下一个复杂程度使用随时间呈正弦变化的轴对称热源。 单个控制方程是从在静水力和梯度平衡中的平均涡流上线性化的纳维-斯托克斯方程导出的。 扰动流可以是非静水力的、次梯度或超梯度的。 如果热源变化的频率足够低，则该模型计算应该类似于稳定强迫的结果。 在较高频率下，由于时间变化或投影到重力波模式而引起的有效局部变形半径的变化等效应可能成为因素。 下一级别的复杂性考虑了在给定方位角波数和频率下的不对称加热的类似导出方程。 要研究的现象包括涡旋响应随强迫频率的变化、浮力和动压的作用、非绝热引起的超梯度风和次梯度风、由于扰动引起的热或动量涡流通量导致的平均涡旋的演化，以及为模拟真实飓风而构建的平均流涡旋的水动力稳定性。涡旋运动研究将使用两层半光谱涡旋跟踪模型来研究弹性和重新排列。 要解决的问题包括重新审视共振阻尼理论、评估对称涡旋的非线性和演化的作用、研究环境位涡和行星涡度梯度以及现实初始平均涡旋结构的影响。这项研究的更广泛影响包括：对准确跟踪尤其是强度预测至关重要的基本新物理理解以及对佛罗里达国际大学 (FIU) 新生气象项目的支持。