Extended Abstract (172K)9C.4
The Vertical Alignment of an Incipient Tropical Cyclone
David A. Schecter, NCAR, Boulder, CO; and M. T. Montgomery and P. D. Reasor
During its early stages of development, an atmospheric vortex can be destroyed by vertical shear in the environmental wind. However, some vortices survive, because they have a dominant tendency to stand upright.
We will review a recent theory for the vertical alignment of a tilted quasi-geostrophic (QG) vortex (Schecter, Montgomery and Reasor, J. Atmos. Sci., in press). In this theory, vertical alignment occurs by the damping of a discrete vortex Rossby mode. The damping rate, g, is proportional to the vorticity gradient at a critical radius, where the rotation frequency of the vortex is resonant with the mode. Furthermore, g varies with the internal Rossby deformation radius, l: g can either increase or decrease with l, depending on the radial structure of the vortex.
We will also present a more general theory that covers the vertical alignment of non-QG vortices, such as incipient tropical cyclones. This new theory is based on the asymmetric balance equations of Shapiro and Montgomery (1993: J. Atmos Sci., 50, 3322-3335). As in QG theory, vertical alignment is viewed as the damping of a discrete vortex Rossby mode. Unlike QG theory, the damping rate, g, does not merely increase linearly with the mean rotation frequency, W, of a vortex with a given radial structure. Rather, there are cases in which g/W increases dramatically as the Rossby number of the vortex increases from zero to order unity.
Session 9C, Tropical Cyclogenesis II (Parallel with Sessions 9A, 9B, and 9D)
Wednesday, 1 May 2002, 11:00 AM-12:30 PM
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