Motivated in part by satellite and radar observations of non-axisymmetric convective bursts near incipient tropical vortices and full-fledged hurricanes, we study the the vortex adjustment problem defined by adding small but finite amplitude disturbances to an initially circular basic state vortex in gradient wind balance. For simplicity, a barotropic f-plane shallow water model is used to illustrate the basic physics and a range of vortex intensities is considered.
Non-axisymmetric convective bursts are parameterized as localized disturbances in the wind and/or height field. The adjustment process is observed to consist of an approximate superposition of gravity-inertia waves which propagate to infinity and vortex Rossby waves which are bound to the near-core region of the vortex. Linear and nonlinear contributions to changes in the mean vortex are examined by comparing the nonlinear calculations with corresponding linear calculations using the initially circular vortex as the basic state.
The spin up of the vortex is found to be most significant when the vortex is subject to disurbances in the vorticity field. The spinup mechanism occurs essentially via the vortex Rossby wave component of the response. Once excited, the vortex Rossby waves transport a portion of the like-sign vorticity anomalies into the parent vortex and eject the remaining like- and unlike-sign vorticity anomalies to the periphery.
Application of these findings to the problems of hurricane formation, hurricane intensification, and shallow water turbulence will be discussed.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics