Two Distinct Regimes in the Kinematic and Thermodynamic Structure of the Hurricane Eye and Eyewall

Using aircraft flight-level data, the present work demonstrates that the kinematic and thermodynamic distributions within the eye and eyewall of strong hurricanes are observed to evolve between two distinct regimes. In the first regime, angular velocity is greatest within the eyewall and relatively depressed within the eye. In the second regime, radial profiles of angular velocity are nearly monotonic, with maxima found at the eye center. Considering sequential profiles within individual hurricanes, the authors find that the evolution of the kinematic distribution is often marked by a transition from the first regime to the second. The transition can occur in less than 1 h. Also noted during the transition are dramatic changes in the thermodynamic structure of the hurricane. Prior to the transition (regime 1), the eye is typically very warm and dry, and the equivalent potential temperature is often elevated within the eyewall and relatively depressed within the eye. After the transition (regime 2), eye temperatures may be lower, higher, or unchanged; dewpoints are higher; and equivalent potential temperature profiles are often nearly monotonic with maxima at the hurricane center. A mechanism is suggested, based on horizontal vorticity mixing, whereby the observed transitions within the hurricane eye and eyewall might be well explained within an idealized 2D barotropic framework.