MMM
SEMINAR NCAR
Binary Vortex Interaction and the Formation of
Concentric Eyewalls in Typhoons
Hung-Chi Kuo
Department of Atmospheric Sciences
Dritschel and Waugh in 1992 described the general interaction of two barotropic vortices with equal vorticity but different sizes. The resulting structures can be classified into elastic interaction, merger, and straining-out regimes. The complete straining out regime of the binary vortex interaction shows a small, weaker vortex being sheared out into thin filaments of vorticity surrounding the large, stronger vortex with no incorporation into the large vortex. The regime resembles the concentric vorticity structure except the filaments are too thin to be called a concentric eyewall. Typhoon Lekima observations indicate that it is a huge area of convection with weak cyclonic vorticity outside the core vortex that wraps around the inner eyewall on a time scale of 12 hours. The interaction of a small and strong vortex with a large and weak vortex was not studied by Dritschel and Waugh as their vortices are of the same strength and their larger vortex was always the ``victor" and the smaller vortex was the one often being partially or totally destroyed. With the introduction of a parameter of vorticity strength ratio into the binary vortex interaction problem, we have added a new dimension to the Dritschel-Waugh vortex interaction scheme that provides a proper concentric vorticity structure as well as the tripole vortex structure. We have showed that one way to produce a concentric vorticity structure is through a binary vortex 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). The results highlight the pivotal role of the vorticity strength of the inner core vortex in maintaining itself, and in stretching, organizing and stabilizing the outer vorticity field. The negative vorticity anomaly in the moat serves as a ``shield" or a barrier to the further inward mixing the outer vorticity field. The binary vortex interactions with Rankine vortices, Rankine vortices with different extended vorticity gradient, and baroclinic vortices will be presented. Typhoon observations which support the notion of binary vortex interaction will be discussed.
Thursday, 11 August 2005,
3:30 PM
Refreshments
NCAR-Foothills Laboratory
Bldg 2 Auditorium (Rm1022)