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Hurricane Structure and Evolution as Simulated by an Axisymmetric, Nonhydrostatic Numerical Model

Huge E. WilloughbyHurricane Research Division, AOML/NOAA, Miami, FL 33149

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Han-Liang JinHurricane Research Division, AOML/NOAA, Miami, FL 33149

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Stephen J. LordHurricane Research Division, AOML/NOAA, Miami, FL 33149

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Jacqueline M. PiotrowiczHurricane Research Division, AOML/NOAA, Miami, FL 33149

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Abstract

This paper reports numerical simulations of the hurricane vortex by an axisymmetric, nonhydrostatic numerical model with 2 km maximum horizontal resolution. Moist convection is modeled explicitly using two different microphysical parameterizations. The first simulates liquid water processes only, whereas the second includes ice processes as well.

Although concentric rings of convection associated with local maxima of the tangential wind form in both versions of the model, they are much more common when ice processes are included. As they contract about the vortex center, the outer ones supplant the inner. Their contraction follows the mechanism suggested by balanced-vortex models. Some of the rings appear to form through symmetric instability of the vortex, and others—particularly when ice processes are included—through interactions between precipitation-induced downdrafts and the boundary layer. Both the rings’ evolution and the detailed structure of the vortex core are similar to recent aircraft and radar observations. Among the realistic features are: outward slope of the eyewall updraft and tangential wind maximum; relative location of the updraft, wind maximum, and precipitation maximum; stratiform precipitation and mesoscale downdrafts outside the eye; and midlevel radial inflow.

Abstract

This paper reports numerical simulations of the hurricane vortex by an axisymmetric, nonhydrostatic numerical model with 2 km maximum horizontal resolution. Moist convection is modeled explicitly using two different microphysical parameterizations. The first simulates liquid water processes only, whereas the second includes ice processes as well.

Although concentric rings of convection associated with local maxima of the tangential wind form in both versions of the model, they are much more common when ice processes are included. As they contract about the vortex center, the outer ones supplant the inner. Their contraction follows the mechanism suggested by balanced-vortex models. Some of the rings appear to form through symmetric instability of the vortex, and others—particularly when ice processes are included—through interactions between precipitation-induced downdrafts and the boundary layer. Both the rings’ evolution and the detailed structure of the vortex core are similar to recent aircraft and radar observations. Among the realistic features are: outward slope of the eyewall updraft and tangential wind maximum; relative location of the updraft, wind maximum, and precipitation maximum; stratiform precipitation and mesoscale downdrafts outside the eye; and midlevel radial inflow.

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