期刊名称：Tellus A: Dynamic Meteorology and Oceanography
电子版ISSN：1600-0870
出版年度：2018
卷号：70
期号：1
页码：1-31
DOI：10.1080/16000870.2018.1525245
摘要：An approximate method is developed for finding and analysing the main instability modes of a tropical
cyclone whose basic state is obtained from a cloud resolving numerical simulation. The method is based on a
linearised model of the perturbation dynamics that distinctly incorporates the overturning secondary
circulation of the vortex, spatially inhomogeneous eddy diffusivities, and diabatic forcing associated with
disturbances of moist convection. Although a general formula is provided for the latter, only
parameterisations of diabatic forcing proportional to the local vertical velocity perturbation and modulated
by local cloudiness of the basic state are implemented herein. The instability analysis is primarily illustrated
for a mature tropical cyclone representative of a category 4 hurricane. For eddy diffusivities consistent with
the fairly conventional configuration of the simulation that generates the basic state, perturbation growth is
dominated by a low azimuthal wavenumber instability having greatest asymmetric kinetic energy density in
the lower tropospheric region of the inner core of the vortex. The characteristics of the instability mode are
inadequately explained by nondivergent 2D dynamics. Moreover, the growth rate and modal structure are
sensitive to reasonable variations of the diabatic forcing. A second instability analysis is conducted for a
mature tropical cyclone generated under conditions of much weaker horizontal diffusion. In this case, the
linear model predicts a relatively fast high-wavenumber instability that is insensitive to the parameterisation
of diabatic forcing. The prediction is in very good quantitative agreement with a previously published
analysis of how the instability develops in a cloud resolving model on the way to creating mesovortices
slightly inward of the central part of the eyewall.
