Development of a Misaligned Tropical Cyclone
Development of a Misaligned Tropical Cyclone
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DOI：
10.1175/jas-d-19-0074.1
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发表时间：
2019-12
影响因子：
3.1
通讯作者：
D. Schecter;K. Menelaou
中科院分区：
文献类型：
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作者：
D. Schecter;K. Menelaou
采用云分辨模式研究了在对流层中下层旋转中心之间存在不同程度不对准的初始化热带气旋的几乎无剪切的演化过程。将旋转中心的初始位移（倾斜）从一个可以忽略不计的值增加到几百公里，将飓风形成的时间尺度从1天延长到10天。在强摄动系统的表面上，最大切向速度的阻碍放大与不完全的早期衰减和随后的倾斜幅度的瞬态增长所导致的失调持续时间的延长有关。长时间的不对中与长时间的非对称对流相吻合，非对称对流在远离涡旋表面中心的地方达到峰值。采用Sawyer-Eliassen模式分析了热带风暴前高、低对中度涡旋的方位速度趋势差异。虽然没有单一因素能完全解释增强率的差异，但更大的失调与微物理云过程加热引起的平均二次环流分量较弱的正方位角速度强迫有关。值得注意的是，在动力学方面，增强的倾斜对表面涡旋核心外动能的增长速度影响不大，而在核心内严重阻碍了湍流的增强，至少持续数天。控制与低效率开发相关的不对准演变的过程被详细地检查了一个选定的模拟。研究发现，绝热机制能够驱动倾斜的瞬态放大，而绝热过程对热带气旋的最终走向至关重要。
A cloud-resolving model is used to examine the virtually shear-free evolution of incipient tropical cyclones initialized with different degrees of misalignment between the lower- and middle-tropospheric centers of rotation. Increasing the initial displacement of rotational centers (the tilt) from a negligible value to several hundred kilometers extends the time scale of hurricane formation from 1 to 10 days. Hindered amplification of the maximum tangential velocity υm at the surface of a strongly perturbed system is related to an extended duration of misalignment resulting from incomplete early decay and subsequent transient growth of the tilt magnitude. The prolonged misalignment coincides with a prolonged period of asymmetric convection peaked far from the surface center of the vortex. A Sawyer–Eliassen model is used to analyze the disparity between azimuthal velocity tendencies of selected pre–tropical storm vortices with low and high degrees of misalignment. Although no single factor completely explains the difference of intensification rates, greater misalignment is linked to weaker positive azimuthal velocity forcing near υm by the component of the mean secondary circulation attributed to heating by microphysical cloud processes. Of note regarding the dynamics, enhanced tilt only modestly affects the growth rate of kinetic energy outside the core of the surface vortex while severely hindering intensification of υm within the core for at least several days. The processes controlling the evolution of the misalignment associated with inefficient development are examined in detail for a selected simulation. It is found that adiabatic mechanisms are capable of driving the transient amplification of tilt, whereas diabatic processes are essential to ultimate alignment of the tropical cyclone.