The Hurricane’s Inner Core Region. I. Symmetric and Asymmetric Structure

Abstract

Observational information from 533 radial flight legs executed by the National Hurricane Research Laboratory over a 13-year period (1957–69) is used to present the structural characteristics and the variability of the hurricane’s inner core region. Tangential and radial winds, D-values, and adjusted temperatures are composited with respect to the Radius of Maximum Wind (RMW) in order to construct a five-level mean symmetric storm and a five-level mean asymmetric storm. The slope of the RMW with height and the position of the RMW relative to the inner cloud wall are presented. Utilizing these results, an idealized, steady-state schematic model of the flow conditions in the inner hurricane core is presented. Storms are stratified by deepening and filling tendency, intensity and storm speed. Finally, the variations of the RMW with latitude, maximum wind, inner radar radius, central pressure, and other features are discussed. Many significant features are noted: 1) storm inflow is confined almost exclusively to the lowest layer and occurs at radii larger than the RMW; 2) inside the RMW (i.e., in the eye) outflow is present; 3) the warmest cyclone temperatures result from subsidence and occur just inside the eye-wall cloud edge where the sinking is strongest; 4) the largest D-value and adjusted temperature gradients occur at and just outside the RMW; 5) the largest convergence occurs in the lowest layer at the RMW; 6) the slope of the RMW with height is small and appears to be a function of intensity; 7) the maximum winds occur within the eye wall cloud area; 8) inner core winds are shown to have a natural asymmetry beyond that induced by storm motion; 9) vertical wind shears in deepening storms are much smaller than in filling storms; 10) in intense storms the maximum winds occur closer to the center than in weaker storms; 11) faster moving storms were more intense than slower moving storms; and 12) at high latitudes the maximum winds occur further away from the storm center than at low latitudes. Other features are shown and discussed.