STRUCTURE AND EVOLUTION OF HURRICANE CLAUDETTE ON 7 SEPTEMBER 1991 FROM AIRBORNE DOPPLER RADAR OBSERVATIONS - PART-II - THERMODYNAMICS

In Part I, the kinematic and precipitating fields of Hurricane Claudet te have been analyzed, using airborne Doppler radar data collected on 7 September 1991 by the two National Oceanic and Atmospheric Administr ation (NOAA) WP-3D research aircraft. Evidence of an incipient ''eyewa ll replacement cycle'' and its influence on Hurricane Claudette circul ation have been revealed through the EVTD (extended velocity track dis play) method. This study has been conducted for six successive analyse s in a domain of 200 km x 200 km x 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 p reviously EVTD-derived wind fields. The relation between the evolution of the circulation and the thermodynamic structure of Hurricane Claud ette can now be studied. The main feature deduced from this method is a positive temperature perturbation about 8-9 K warmer than the enviro nment at the center of the storm circulation, associated with a pressu re deficit of about 25 hPa at the sea level. During the considered per iod, the temperature perturbation maximum changed according to the evo lution of the inner eyewall, while warming in the middle part was rela ted to intensifying external outward motions and cooling in the outer part, due to stronger inflow. Meanwhile, there is no distinct evolutio n of the pressure perturbation field. Comparisons between the retrieve d thermodynamic fields and in situ data collected by both aircraft alo ng their flight track show qualitatively good agreement, although the EVTD-retrieved values have substantially lower amplitudes, probably du e to the strong spatial and temporal filtering. Analyses of fields wit h different time filtering confirms that inertia-gravity waves that ma y propagate outward from the system do not seem to affect the retrieve d kinematic and thermodynamic fields. Considering only the symmetric p art (wavenumber 0) of this EVTD kinematic and thermodynamic descriptio n of Hurricane Claudette, the authors have verified that throughout mo st of the considered domain of the study, gradient wind balance, hydro static equilibrium, and thermal wind relation are nearly verified. Nev ertheless, there are some indications that supergradient winds may be found locally in the lower inner part of the eyewall.