A climatology of the diurnal variations in stratospheric and mesospheric ozone over Bern, Switzerland

The ground-based radiometer GROMOS, stationed in Bern (47.95 N, 7.44 E), Switzerland, has a unique data set: it obtains ozone profiles from November 1994 to present with a time resolution of 30 min and equivalent quality during nightand daytime. Here, we derive a monthly climatology of the daily ozone cycle from 17 years of GROMOS observation. We present the diurnal ozone variation of the stratosphere and mesosphere. Characterizing the diurnal cycle of stratospheric ozone is important for correct trend estimates of the ozone layer derived from satellite observations. The diurnal ozone cycle from GROMOS is compared to two models: the Whole Atmosphere Community Climate Model (WACCM) and the Hamburg Model of Neutral and Ionized Atmosphere (HAMMONIA). Generally, observation and models show a good agreement: in the lower mesosphere, daytime ozone is for both GROMOS and models around 25 % less than midnight ozone. In the stratosphere, ozone reaches its maximum in the afternoon showing values several percent larger than the midnight value. Further, GROMOS and models indicate a seasonal behaviour of the diurnal ozone variations in the stratosphere with a larger afternoon maximum during daytime in summer than in winter. Using the 17 years of ozone profiles from GROMOS, we find strong interannual variations in the diurnal ozone cycle for both the stratosphere and the mesosphere. Interannual variability in temperature, atmospheric circulation and composition may explain the observed interannual variability of the diurnal ozone cycle above Bern.