Radiometric Observations during the Canadian Atlantic Storms Program

Abstract

Radiometrically determined temperature profiles were compared with radiosonde observations during the Canadian Atlantic Storms Program (CASP). A total of 108 profiles were available for the comparison, taken during diverse weather conditions. The root-mean-square difference between the temperature determined by radiometer and by radiosonde generally increased with height, from approximately 1°K near the ground to about 3.5°K at the 400 mb level. The accuracy of the radiometer estimates rapidly deteriorated at altitudes above this level. These results are consistent with the accuracy expected from the retrieval method used and with the results reported by others. The total sample was stratified to examine possible effects of precipitation type, fog, and temperature inversions on the accuracy of the retrieved temperature profiles. It was found that fog and rain cause a bias in the measurements, with the retrieved temperatures too warm by an average amount of up to 2°K, depending on altitude. Snow, however, was found to cause no degradation in the accuracy of radiometric temperature estimates. Temperature inversions near the ground were fairly accurately identified by the radiometer, although inversions aloft were imprecisely measured. Thicknesses of standard layers from radiometer observations agreed closely with those determined by radiosonde. The root-mean-square percentage differences were less than 2%. Radiometric estimates of total water vapor were also accurate, agreeing within 13% of the radiosonde data and having a correlation coefficient of 0.97. These estimates were less accurate when rain or fog was present.