Warm-Ring Structures in Intense Hurricanes

Abstract:

Typical hurricanes have a warm-core structure such that the warmest temperatures occur in the center of the hurricane. However, weather reconnaissance aircraft data has observed warm-rings in intense hurricanes. A warm-ring structure results when the warmest temperature anomalies occur on the outer edge of the eye. Schubert et al. (2007) suggests the Eliassen transverse circulation equation can model intense hurricanes with a warm-core structure in the upper troposphere and also a warm-ring structure in the lower. Although the thermal wind equation was used in the derivation of the transverse circulation equation, the thermal wind equation has not been used explicitly in an attempt to create such a temperature field. This study derives the thermal wind equation from the hydrostatic and the gradient wind equations to analyze the temperature, tangential velocity, and the absolute vorticity fields. Using observed hurricanes, a warm-ring structure is simulated with the thermal wind equation as the basis. With a prescribed temperature profile, the calculated tangential velocity and absolute vorticity fields resemble those of a realistic hurricane. Thus, the thermal wind equation can be used to create a realistic, intense hurricane with a warm ring structure. Schubert et al. (2007) discusses subsidence as a mechanism that leads to the warm-ring but the tangential velocity and absolute vorticity fields suggest some influence of boundary layer processes that should be explored in future research for a further understanding of warm-rings.