Some aspects of hurricane inner-core dynamics and energetics

Abstract

The energy cycle of the mature hurricane resides in the secondary circulation that passes through the storm's eyewall. By equating the generation of energy in this cycle to boundary layer dissipation, an upper bound on wind speed is derived. This bound depends on the degree of thermodynamic disequilibrium between the tropical ocean and atmosphere, on the difference between sea surface and outflow absolute temperatures, and also on the ratio between the enthalpy exchange and surface drag coefficients. Such a bound proves to be an excellent predictor of maximum wind speeds in two different axisymmetric numerical models and does not appear to depend on the existence of the hurricane eye. But further consideration of the detailed dynamics of the eye and eyewall show that the intensification of hurricanes is accelerated by feedbacks associated with a component of eye subsidence forced by radial turbulent diffusion of momentum. This radial momentum diffusion is an inevitable by-product of the strong frontogenesis that the author here shows to be a fundamental characteristic of flow in the eyewall. Thus, while the upper bound on hurricane wind speed is independent of the eye dynamics, the intensification of hurricanes is indirectly accelerated by turbulent stresses that occur in the eye and eyewall.