Some dynamical aspects of tropical cyclone concentric eyewalls

Abstract

AbstractThe intensification of tropical cyclones is often interrupted by an eyewall replacement cycle, a process in which an outer eyewall forms, contracts, and replaces an inner eyewall. The radial distributions of inertial stability and diabatic heating change during such events, impacting the transverse circulation. To examine the effects of such changes, an analytical solution of the transverse circulation equation associated with a balanced vortex model is derived using a parameterization that distinguishes five radial regions subdividing the domain by each region's values of inertial stability and diabatic heating. These regions define the eye, inner eyewall, moat, outer eyewall, and far‐field. In mature concentric eyewall situations, the solutions do not support the hypothesis that the inner eyewall collapses as a direct result of subsidence from the outer eyewall. However, the results suggest subsidence and warming temperatures in the moat are governed by enhanced inertial stability associated with a strengthening outer eyewall. The model solutions also illustrate how the diabatic heating in the inner eyewall, imbedded in a region of high inertial stability, induces larger temperature tendencies than the diabatic heating in the outer eyewall, which borders the far‐field region of low inertial stability. Thus, as the inner eyewall dies, the storm temporarily loses its ability to produce an intense, localized warm region. This ability is restored during the contraction and intensification of the outer eyewall. These results provide a partial dynamical explanation of how an eyewall replacement cycle can act as a temporary brake on tropical cyclone intensification. Copyright © 2008 Royal Meteorological Society