Sensitivity of Tropical Cyclones to Surface Exchange Coefficients and a Revised Steady-State Model incorporating Eye Dynamics

Abstract

Numerical and theoretical models of tropical cyclones indicate that the maximum wind speed in mature storms is sensitive to the ratio of the enthalpy and momentum surface exchange coefficients and that the spinup time of tropical cyclones varies inversely with the magnitude of these coefficients. At the same time, the Carnot cycle model developed by the author predicts that the central pressure of mature cyclones is independent of the magnitude of the exchange coefficients. The author presents numerical simulations that prove this last prediction false and suggest that the reason for this failure is the neglect of eye dynamics in the steady-state theory. On this basis, the existing theory is modified to account for eye dynamics, and the predictions of the revised theory are compared to the results of numerical simulations. Both the revised theory and the numerical modeling results, when compared to observations, suggest that the ratio of enthalpy to momentum exchange coefficients in real hurricanes lies in the range 0.75–1.5, contradicting published speculations about the behavior of this ratio at high surface wind speed.