2D.2
Nonlinear motion of a two-layer baroclinic hurricane in shear
Robert W. Jones, NOAA/AOML/HRD, Miami, FL; and H. E. Willoughby
The nonlinear semispectral vortex tracking model of Willoughby has been generalized to a two-layer model topped by an inert layer similar to the linear spectral tracking model of Jones and Willoughby. The cylindrical coordinate translates with the low-level vortex. Gradient balance is imposed upon the symmetric vortex. Wave number three truncation is currently used on a 4000 km domain with a 4 km radial mesh. The coupling between the layers is by the pressure force that depends upon the density and the depth of the lower layers. Horizontal mixing is needed to control vortex scale instabilities. The instabilities limit the parameter ranges for stable integration compared with the linear model where the intabilities were controlled by the initial, invariant vortex. Results are given for westerly shear ranging from 1 to 10 m/s. For appropriate parameters, stable cyclonic looping of the vortices about their common centroid is observed and by 10 days the upper vortex moves slowly relative to the lower vortex with separations ranging from a few hundred meters to a few kilometers. Looping may change from stable to unstable as vortex winds diminish. Increasing the strength of the shear increases the strength of the lower vortex slightly, while the upper vortex strength decreases. For 10 m/s shear, the upper vortex may diminish to zero by 10 days, although part of this decrease is the result of increased horizontal mixing for larger shear. Environmental shear destroys a vortex from the top down. In these cases, the looping becomes eratic and the vortices may separate by hundreds of kilometers, although they seem to remain coupled.
Session 2D, Tropical Cyclone Motion (Parallel with Sessions 2A, 2B, & 2C)
Monday, 29 April 2002, 2:00 PM-3:15 PM
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