An Investigation of Spiral Gravity Waves Radiating from Tropical Cyclones Using a Linear, Nonhydrostatic Model
An Investigation of Spiral Gravity Waves Radiating from Tropical Cyclones Using a Linear, Nonhydrostatic Model
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DOI：
10.1175/jas-d-19-0259.1
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发表时间：
2020-05
影响因子：
3.1
通讯作者：
D. Nolan
中科院分区：
文献类型：
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作者：
D. Nolan
最近的一项研究显示，有观测和数值证据表明，热带气旋向外辐射的小规模重力波。这些波被切向风场的径向和垂直切变包裹成紧密的螺旋。重新审查以前研究的热带气旋模拟表明，这些波的主要来源是对流不对称旋转沿着眼壁，调制的强度由环境风切变矢量左侧的首选对流区。一个线性化的，非流体静力学模型的扰动平衡涡被用来研究波。用旋转和脉动的非对称热源强迫线性模型产生具有多个垂直和水平结构的辐射重力波。旋转热源的脉动产生两种类型的波：具有较大径向波长的快速深层波，以及具有较短径向和垂直波长的较慢二次波。较深的波产生表面压力振荡，其时间尺度与表面观测一致，而较短的波几乎没有表面指示，但产生垂直速度振荡，其较短的径向波长与飞机观测一致。没有脉动或没有旋转的对流强迫产生重力波，但它们与观测或模拟的波不相似。不同的气旋强度，强迫的不对称性，以及周围大气的静态稳定性的影响进行了探讨。
A recent study showed observational and numerical evidence for small-scale gravity waves that radiate outward from tropical cyclones. These waves are wrapped into tight spirals by the radial and vertical shears of the tangential wind field. Reexamination of the previously studied tropical cyclone simulations suggests that the dominant source for these waves are convective asymmetries rotating along the eyewall, modulated in intensity by the preferred convection region on the left side of the environmental wind shear vector. A linearized, nonhydrostatic model for perturbations to a balanced vortex is used to study the waves. Forcing the linear model with rotating and pulsing asymmetric heat sources generates radiating gravity waves with multiple vertical and horizontal structures. The pulsation of the rotating heat source generates two types of waves: fast, deep waves with larger radial wavelengths, and slower, secondary waves with shorter radial and vertical wavelengths. The deeper waves produce surface pressure oscillations that have time scales consistent with surface observations, whereas the shorter waves have little surface indication but produce oscillations in vertical velocity with shorter radial wavelengths that are consistent with aircraft observations. Convective forcing that is either not pulsing or not rotating produces gravity waves but they are not as similar to the observed or simulated waves. The effects of varying the intensity of the cyclone, the asymmetry of the forcing, and the static stability of the surrounding atmosphere are explored.