Diurnal and seasonal variations of stratomesospheric ozone: Analysis of ground‐based microwave measurements in Bordeaux, France

Abstract

Atmospheric ozone spectra recorded since September 1985 with a millimeter‐wavelength radiotelescope located at Bordeaux Observatory are used to determine ozone profiles. These concentrations are retrieved using the Backus‐Gilbert inversion method. The experimental difficulties due to the so‐called baseline effect, calibration errors, and fluctuations in the temperature profile are discussed and their influence on the ozone density evaluated. Three heights are optimally selected at 33, 42, and 55 km. The main source of measurement error is the baseline effect. As this affects strongly the ozone density retrieved at 33 km, results are given only for two layers: 42±4.5 km and 55±8 km. Diurnal variations can be estimated in the 42±4.5 km layer during three periods, September 1985, September 1989, and October 1989 with the daytime decrease about 5%–10%. In the 55±8 km layer the variations for these three periods can reach 30%. For both layers the measured variation is greater than that predicted by models because the resolving power of the measurement spreads over higher layers where the variation is actually larger. At 42±4.5 km, seasonal variations in ozone concentration exhibit a semiannual oscillation with summer maxima and pronounced winter peaks. At 55±8 km the daytime and nighttime seasonal variations in ozone concentration exhibit a semiannual oscillation with large summer maxima and small winter peaks.