Extended Abstract (16K)17A.1
Vertical Profiles of Thermodynamic Variables in Hurricanes Bonnie (1998) and Mitch (1998): Implications for Energy Transport in the Inflow Layer
Gary Barnes, University of Hawaii, Honolulu, HI; and R. Schneider and S. Houston
On 26 August 1998 the two NOAA WP-3ds deployed 85 GPS dropwindsondes in Hurricane Bonnie just prior to landfall near Wilmington, North Carolina. NOAA and the Air Force deployed another 30 sondes in Hurricane Mitch near the Honduran coast on 29 October 1998. The sondes are evenly distributed within 250 km of the circulation center for Bonnie while they are concentrated in and near the robust eyewall of Category 5 Mitch.
The thermodynamic profiles in the lowest 2 km reveal several conditions that depart from the typical tropical boundary layer. These unusual structures impact the energy content of the inflow layer, and ultimately, hurricane intensity.
In Bonnie the profiles of equivalent potential temperature (Өe) often have increasing values with height, but well below the level where this is commonly observed in the tropics (650 hPa). These layers of high Өe appear to be correlated with radial outflow and inhibit the loss of energy from the adjacent inflow layer below.
The second feature of interest is the appearance of moist absolutely unstable layers (MAULs). These saturated layers have a steeper lapse rate than moist adiabatic and form when the rate of mesoscale lifting exceeds the convective-scale updrafts that would eliminate the instability. MAULS appear in the hub cloud, and radial outward of strong rainbands and the eyewall. They are indicative of the reduced convective available potential energy as one approaches the radius of maximum winds.
Most intriguing are the vertical profiles of moisture and temperature in the 100 m layer adjacent to the sea surface. Humidity profiles can be classified into two types, one of which is spurious due to wetting of the hygristor. The other type appears to be real, and a result of the large fluxes at the air-sea interface. Temperature profiles contain adiabatic and super adiabatic lapse rates; such conditions support the argument that spray is not undergoing large evaporation rates, but that the spray droplets are rapidly surrendering their sensible heat. The super adiabatic layer deepens and strengthens with increasing wind speed.
We will discuss some common problems with the sensors and link the structures determined to be real to the recent findings concerning drag coefficient behavior in hurricane conditions.
Session 17A, Tropical cyclone air-sea interaction
Friday, 7 May 2004, 10:15 AM-11:45 AM, Le Jardin Room
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