Structure and Evolution of Hurricane Claudette on 7 September 1991 from Airborne Doppler Radar Observations. Part II: Thermodynamics

Abstract

In Part I, the kinematic and precipitating fields of Hurricane Claudette have been analyzed, using airborne Doppler radar data collected on 7 September 1991 by the two National Oceanic and Atmospheric Administration (NOAA) WP-3D research aircraft. Evidence of an incipient ?eyewall replacement cycle? and its influence on Hurricane Claudette circulation have been revealed through the EVTD (extended velocity track display) method. This study has been conducted for six successive analyses in a domain of 200 km ? 200 km ? 12 km domain from 1700 to 2200 UTC. A thermodynamic retrieval method is adapted here to the EVTD geometry to deduce the temperature and pressure perturbation fields from the previously EVTD-derived wind fields. The relation between the evolution of the circulation and the thermodynamic structure of Hurricane Claudette can now be studied. The main feature deduced from this method is a positive temperature perturbation about 8?9 K warmer than the environment at the center of the storm circulation, associated with a pressure deficit of about 25 hPa at the sea level. During the considered period, the temperature perturbation maximum changed according to the evolution of the inner eyewall, while warming in the middle part was related to intensifying external outward motions and cooling in the outer part, due to stronger inflow. Meanwhile, there is no distinct evolution of the pressure perturbation field. Comparisons between the retrieved thermodynamic fields and in situ data collected by both aircraft along their flight track show qualitatively good agreement, although the EVTD-retrieved values have substantially lower amplitudes, probably due to the strong spatial and temporal filtering. Analyses of fields with different time filtering confirms that inertia?gravity waves that may propagate outward from the system do not seem to affect the retrieved kinematic and thermodynamic fields. Considering only the symmetric part (wavenumber 0) of this EVTD kinematic and thermodynamic description of Hurricane Claudette, the authors have verified that throughout most of the considered domain of the study, gradient wind balance, hydrostatic equilibrium, and thermal wind relation are nearly verified. Nevertheless, there are some indications that supergradient winds may be found locally in the lower inner part of the eyewall.