Theoretical validation of ground-based microwave ozone observations

Abstract : Ground-based microwave measurements of the diurnal and seasonal variations of ozone at 42+/-4.5 and 55+/-8 km are validated by comparing with results from a zero-dimensional photochemical model and a two-dimensional (2D) chemical/radiative/dynamical model, respectively. O-3 diurnal amplitudes measured in Bordeaux are shown to be in agreement with theory to within 5%. For the seasonal analysis of O-3 variation, at 42+/-4.5 km, the 2D model underestimates the yearly averaged ozone concentration compared with the measurements. A double maximum oscillation (similar to 3.5%) is measured in Bordeaux with an extended maximum in September and a maximum in February, whilst the 2D model predicts only a single large maximum (17%) in August and a pronounced minimum in January. Evidence suggests that dynamical transport causes the winter O-3 maximum by propagation of planetary waves, phenomena which are not explicitly reproduced by the 2D model. At 55+/-8 km, the modeled yearly averaged O-3 concentration is in very good agreement with the measured yearly average. A strong annual oscillation is both measured and modeled with differences in the amplitude shown to be exclusively linked to temperature fields.