MMM SEMINAR NCAR
THE FORMATION OF CONCENTRIC VORTICITY STRUCTURES IN
TROPICAL CYCLONES
Hung-Chi Kuo
Department of Atmospheric Sciences
National Taiwan
University, Taipei, Taiwan
An important issue in the
formation of concentric eyewalls in a tropical cyclone is the development of a
symmetric structure from asymmetric convection. We propose, with the aid of a
nondivergent barotropic model, that concentric vorticity structures result from
the interaction between a small and strong inner vortex (the tropical cyclone
core) and neighboring weak vortices (the vorticity induced by the moist
convection outside the central vortex of a tropical cyclone). The results
highlight the pivotal role of the strength of the inner core vortex in
maintaining itself, in stretching, organizing and stabilizing the outer
vorticity field, and the shielding effect of the moat to prevent further merger
and enstrophy cascade processes in concentric eyewall dynamics. The straining out of a large, weak vortex into a
concentric vorticity band can also result in the contraction of the outer
tangential wind maximum. Our binary vortex experiments suggest that the
formation of a concentric vorticity structure requires: 1) a very strong core
vortex with a vorticity at least six times stronger than the neighboring
vortices, 2) a large neighboring vorticity area that is larger than the core
vortex, and 3) a separation distance between the neighboring vorticity field
and the core vortex that is within three to four times the core vortex radius.
Thursday, August 5, 2004,
3:30 PM
NCAR-Foothills
Laboratory
3450 Mitchell Lane
Bldg 3, Rm 2072