Friday, 2 May 2008: 8:00 AM
Palms H (Wyndham Orlando Resort)
This study examines the role of the frictional boundary layer in initiating the formation of the hurricane eye. If the frictional surface stress is proportional to the square of the geostrophic wind, Eliassen's 1959 treatment on frontogenesis shows that the upward forcing at the top of the boundary layer must maximize at some radius away from the center, rather than at the center. From Eliassen's balanced vortex model (1952), the condensational heating triggered by such a ring of ascent drives a transverse circulation, with a branch of ascending motion through the heating ring, and two branches of descending motion radially inward and outward of the heating ring. The descending branch within the vortex center opposes the weak ascent of air forced upward out of the top of the frictional boundary layer, so eye formation may occur when the downdrafts of the heating-induced transverse circulation overwhelm the weak upward forcing throughout the vortex center. The transverse circulation also emplaces strong low-level radial convergence at the original location of upward frictional forcing, so the formation of the eye/eyewall structure may be thought of as an example of circular frontogenesis in which both friction and latent heating play critical and intertwined roles. This study will elaborate on these historical ideas and connect them with the development of the core of high inertial stability which plays a role in setting the intensity threshold at which eye formation occurs.
Supplementary URL: http://euler.atmos.colostate.edu/~vigh/tendency/
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