Forced, Balanced, Axisymmetric Shallow Water Model for Understanding Short-Term Tropical Cyclone Intensity and Wind Structure Changes
Forced, Balanced, Axisymmetric Shallow Water Model for Understanding Short-Term Tropical Cyclone Intensity and Wind Structure Changes
复制标题
用于了解短期热带气旋强度和风结构变化的强迫、平衡、轴对称浅水模型
作者：
E. Hendricks;J. Vigh;C. Rozoff
介绍了一种用于理解热带气旋强度和风结构变化的最小模拟系统：浅水轴对称强度模型（SWAMI）。强迫的、平衡的、轴对称的浅水方程被简化为典型的位涡（PV）产生和反演问题，其中PV通过质量汇（与绝热加热有关）产生，并通过PV/绝对角动量可逆性原理进行反转。由于可逆性原理是非线性的，采用牛顿-克雷洛夫方法迭代求解离散问题的数值解。描述了模型的两个版本：忽略径向PV平流的物理半径版本（SWAMI-r）和自然包含准拉格朗日坐标平流的势半径版本（SWAMI-r）。在理想化的数值模拟中，SWAMI-R比SWAMI-R产生更薄、更强的PV环，证明了轴对称径向PV平流在眼壁演化中的作用。由于光伏足迹效应的减少主导了峰值幅度增加效应，因此SWAMI-R的强化率始终低于SWAMI-R。接下来，利用新增加的FLIGHT+ Dataset方面角手段对三个例子进行初始化和强迫，证明了SWAMI-r是一个潜在有用的短期风结构预测工具：缓慢增强事件、快速增强事件和二次最大风形成事件。然后利用63个强化病例对SWAMI-r进行评估。尽管该模型是最小的，但它在短期强度预测方面具有一定的技巧，突出了涡旋惯性稳定性的径向结构与绝热加热速率之间关系的已知关键作用。由于模型的简单性，SWAMI仿真可以在几秒钟内完成。因此，它们可能对飓风临近预报和短期（小于24 h）强度和结构预报有一定的用处。由于SWAMI对热带气旋增强的有利假设，它的一个潜在用途是在风暴增强时合理的短期上限强度预测。
A minimal modeling system for understanding tropical cyclone intensity and wind structure changes is introduced: Shallow Water Axisymmetric Model for Intensity (SWAMI). The forced, balanced, axisymmetric shallow water equations are reduced to a canonical potential vorticity (PV) production and inversion problem, whereby PV is produced through a mass sink (related to the diabatic heating) and inverted through a PV/absolute–angular–momentum invertibility principle. Because the invertibility principle is nonlinear, a Newton–Krylov method is used to iteratively obtain a numerical solution to the discrete problem. Two versions of the model are described: a physical radius version which neglects radial PV advection (SWAMI-r) and a potential radius version that naturally includes the advection in the quasi-Lagrangian coordinate (SWAMI-R). In idealized numerical simulations, SWAMI-R produces a thinner and more intense PV ring than SWAMI-r, demonstrating the role of axisymmetric radial PV advection in eyewall evolution. SWAMI-R always has lower intensification rates than SWAMI-r because the reduction in PV footprint effect dominates the peak magnitude increase effect. SWAMI-r is next demonstrated as a potentially useful short-term wind structure forecasting tool using the newly added FLIGHT+ Dataset azimuthal means for initialization and forcing on three example cases: a slowly intensifying event, a rapid intensification event, and a secondary wind maximum formation event. Then, SWAMI-r is evaluated using 63 intensifying cases. Even though the model is minimal, it is shown to have some skill in short-term intensity prediction, highlighting the known critical roles of the relationship between the radial structures of the vortex inertial stability and diabatic heating rate. Because of the simplicity of the models, SWAMI simulations are completed in seconds. Therefore, they may be of some use for hurricane nowcasting to short-term (less than 24 h) intensity and structure forecasting. Due to its favorable assumptions for tropical cyclone intensification, a potential use of SWAMI is a reasonable short-term upper-bound intensity forecast if the storm intensifies.