Instrument Wetting Errors in Hurricanes: Magnitude, Frequency, and Effects upon Thermodynamic Structure

For decades the potential wetting of aircraft immersion thermometers by hydrometeors has prevented confident interpretations of air temperaturein clouds and precipitation. Sensor wettign results in erroneously cool temperatures. Radiometric thermometers provide an indirect measurement of air temperature with only minimal detrimental effects from hydrometeors, and show superior temeprature measurements in convective regions. A modified Barnes PRT-5 radiometer is used to reconstruct 579 radial thermodynamic profiles from 27 recent Atlantic and East Pacific hurricanes. The resulting radial profiles are shown to be accurate and free of instrument wetting errors.

Instrument wetting locations (IWL) are defined and analyzed within these hurricanes. IWL are identified in roughly 50 percent of the radial legs. The majority of IWL are located in cloudy updrafts associated with eyewall and rainband convection, and extend less than 15 km radially. Average IWL temperature errors range with height from 1.0 to 4.5 C and are statistically significant. Such temperature errors, combined with average specific humidity errors that range from 1.0 to 2.0 g/kg, result in virtual temperature errors ranging from 1.5 to 5.0 C and equivalent potential temperature errors ranging from 5 to 11 K. Average temperature and specific humidity errors in the eyewall range with height from 0.5 to 2.0 C and 0.5 to 1.0 g/kg, respectively.

Errors of such magnitudes can have a significant effect upon thermodynamic calculations in an near convection. Various aspects of hurricane thermodynamics are re-examined. Corrected temperature values show that instrument wetting errors significantly effect the composite radial structure and absolute thermodynamic values around the eyewall. Additionally, instrument wetting errors are shown to significantly effect calculations of thermal wind balance, buoyancy, and vertical heat fluxes in hurricanes.