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

热带气旋(TC)路径和强度的预报仍然是业务上的重大挑战。路径预报在过去50年中逐渐得到改善，这主要是对控制TC运动的环境转向流的改进观测和建模的反应。相比之下，强度方面的进展缓慢，统计技术仍然提供最好的预测指导。热带气旋增强的基本过程是将从海洋中提取的潜热转化为可用势能和风动能。本奖项将开展的研究包括两个方面：1)TC涡旋对外加热源的响应分析；2)双层斜压类TC涡旋的线性和非线性运动的理论研究。这些研究中使用的解析轴对称斜压平均涡旋结构将是来自大量现场观测的实际热带气旋的真实表示。主要研究人员将通过研究对外加热源的响应来探索热带气旋增强过程，这些热源在时间和方位上都表示为截断的傅立叶级数。只有热源的轴对称、时间恒定的部分才提供净热量。它的影响很容易从经典的Sawyer-Eliassen方程中计算出来。下一级的复杂性使用了轴对称的热源，该热源在时间上呈正弦变化。在静力平衡和梯度平衡条件下，由平均涡线性化的N-S方程导出了一个单一的控制方程。扰动流可以是非静力的，也可以是亚梯度或超梯度的。如果热源变化的频率足够低，该模型计算应该与稳定强迫的结果相似。在更高的频率下，诸如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影响可能成为因素。下一层次的复杂性考虑了具有给定方位波数和频率的非对称加热的类似推导方程。要研究的现象包括：涡旋响应随强迫频率的变化，浮力和动力压力的作用，非绝热诱导的超梯度和次梯度风，由于扰动而产生的热通量或动量涡流导致的平均涡旋的演变，以及为模拟真实飓风而构建的平均流涡的水动力稳定性。涡旋运动研究将使用两层半光谱涡旋跟踪模式来研究回弹和重排。需要解决的问题包括：共振-阻尼理论的重新审视，非线性和对称涡旋演化的作用的评估，环境位涡和行星涡度梯度的研究，以及现实的初始平均涡旋结构的影响。这项研究的更广泛的影响包括：对准确跟踪至关重要的基本的新的物理理解，特别是强度预测和对佛罗里达国际大学(FIU)新生的气象学计划的支持。

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.