A GROUND-BASED MICROWAVE RADIOMETER DEDICATED TO STRATOSPHERIC OZONE MONITORING

A microwave radiometer has been developed for long-term measurements o f strato-mesospheric ozone profiles at midlatitudes. The instrument lo cated at the Bordeaux Observatory, France (45 degrees N) is operated i n the framework of the French atmospheric station, of the European Alp ine station belonging to the Network for the Detection of Stratospheri c Change. The instrument detects an ozone spectral line at 110.836 GHz , enabling the retrieval of ozone profiles from similar to 25 to simil ar to 75 km. The technical parameters are described as the observing t echnique, calibration procedures, and data acquisition. Two retrieval methods are used: the Backus-Gilbert method and the optimal estimation method. Strong emphasis is placed on the error analysis including a d etailed characterization of errors. To improve the retrieval, we discu ss which errors have to be taken into account in the retrieval process . Three cases have been selected for which retrieval errors due to tim e stochastic and time systematic errors are calculated. First, only th e thermal noise is introduced in the retrieval code; second, all error s are introduced; and finally, a selection among errors is searched in order to provide a good compromise between the retrieval error and th e vertical resolution. Diurnal variations of mesospheric O-3 are compa red with results from a photochemical model. The agreement is within 5 -10%. During the February-March 1996 period the temporal evolution of ozone at an altitude of 30 km is in good agreement with both satellite and three-dimensional model data. There is a good correlation with th e potential vorticity field calculated at the 850 ii isentropic temper ature. A crossing of the polar vortex over the site is associated with an O-3 decrease observed in the three data sets.