STATISTICAL TEMPERATURE PROFILE RETRIEVALS IN CLEAR-AIR USING PASSIVE118-GHZ O-2 OBSERVATIONS

Linear statistical temperature profile retrievals from nadiral passive 118-GHZ O2 spectra are demonstrated using time- and space-coincident microwave observations and radiosonde profiles. The nadiral aircraft-b ased brightness observations were made using the Millimeter-wave Tempe rature Sounder (MTS) instrument aboard the NASA ER-2 high-altitude pla tform during the Genesis of Atlantic Lows Experiment (GALE) and the Co operative Huntsville Meteorological Experiment (COHMEX). Separate retr ievals are demonstrated for winter and summer midlatitude conditions i n clear-air over land; observations during both day and night are incl uded. The retrieval operator is a linear-statistical minimum mean-squa red-error estimator. A purely statistical retrieval operator circumven ts the effects of radiative transfer model uncertainties and biases in either the radiosonde or MTS data. The retrieved profile root-mean-sq uare errors are approximately 0.7 - 1.2 K for either the winter or sum mer tropospheres. These are substantially smaller than the a priori te mperature profile variations, demonstrating that 118-GHz aircraft or s atellite observations can provide useful information on atmospheric ve rtical thermal structure. However, classification of retrieval operato rs by prevailing meteorological conditions appears to be important for operational purposes. Correlations between MTS antenna temperatures a nd radiosonde kinetic temperatures are nearly consistent with calculat ions based on a radiative transfer model, indicating both the validity of the model and the sensitivity of the MTS channels to atmospheric t emperature. The predicted and observed correlations exhibit the same g eneral trends, although the predicted values are usually slightly grea ter.