Some Aspects of Midlevel Vortex Interaction in Tropical Cyclogenesis

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  • 1 Department of Meteorology, Naval Postgraduate School, Monterey, California
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Abstract

The mechanisms by which mesoscale midlevel vortices that form in the stratiform anvil regions of mesoscale convective systems develop downward in the atmosphere are explored in the context of tropical cyclone genesis. Using simple two- and three-dimensional models, a theory for the processes by which midlevel vortices may interact both with each other, and with their large-scale environment in order to develop a storm-scale vortex, is developed. It is found that absorption of the circulation of one vortex by another results in a vortex of greater horizontal and vertical extent. Embedding the vortices in an enhanced vorticity environment such as might be found in the monsoon trough results in more efficient merger and greater downward development of the circulation associated with the merged vortex.

This theory is used to interpret a real case of the development of Tropical Cyclone (TC) Oliver in the Australian region during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) experiment in 1993. High-resolution flight-level and dropwindsonde data were collected during the interaction and merger phase of two large mesoscale convective systems that were embedded in the monsoon trough. Multiple mesoscale vortices were observed to interact and merge during the development phase of TC Oliver with consequences for the downward development of the vortex, and subsequent eye development.

Abstract

The mechanisms by which mesoscale midlevel vortices that form in the stratiform anvil regions of mesoscale convective systems develop downward in the atmosphere are explored in the context of tropical cyclone genesis. Using simple two- and three-dimensional models, a theory for the processes by which midlevel vortices may interact both with each other, and with their large-scale environment in order to develop a storm-scale vortex, is developed. It is found that absorption of the circulation of one vortex by another results in a vortex of greater horizontal and vertical extent. Embedding the vortices in an enhanced vorticity environment such as might be found in the monsoon trough results in more efficient merger and greater downward development of the circulation associated with the merged vortex.

This theory is used to interpret a real case of the development of Tropical Cyclone (TC) Oliver in the Australian region during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) experiment in 1993. High-resolution flight-level and dropwindsonde data were collected during the interaction and merger phase of two large mesoscale convective systems that were embedded in the monsoon trough. Multiple mesoscale vortices were observed to interact and merge during the development phase of TC Oliver with consequences for the downward development of the vortex, and subsequent eye development.

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