Spatio-temporal observations of the tertiary ozone maximum

We present spatio-temporal distributions of the tertiary ozone maximum (TOM), based on GOMOS (Global Ozone Monitoring by Occultation of Stars) ozone measure- ments in 2002-2006. The tertiary ozone maximum is typi- cally observed in the high-latitude winter mesosphere at an altitude of 72 km. Although the explanation for this phe- nomenon has been found recently - low concentrations of odd-hydrogen cause the subsequent decrease in odd-oxygen losses - models have had significant deviations from existing observations until recently. Good coverage of polar night re- gions by GOMOS data has allowed for the first time to obtain spatial and temporal observational distributions of night-time ozone mixing ratio in the mesosphere. The distributions obtained from GOMOS data have spe- cific features, which are variable from year to year. In partic- ular, due to a long lifetime of ozone in polar night conditions, the downward transport of polar air by the meridional circu- lation is clearly observed in the tertiary ozone maximum time series. Although the maximum tertiary ozone mixing ratio is achieved close to the polar night terminator (as predicted by the theory), TOM can be observed also at very high latitudes, not only in the beginning and at the end, but also in the mid- dle of winter. We have compared the observational spatio- temporal distributions of the tertiary ozone maximum with that obtained using WACCM (Whole Atmosphere Commu- nity Climate Model) and found that the specific features are reproduced satisfactorily by the model. Since ozone in the mesosphere is very sensitive to HOx concentrations, energetic particle precipitation can signif- icantly modify the shape of the ozone profiles. In par- ticular, GOMOS observations have shown that the tertiary ozone maximum was temporarily destroyed during the Jan- uary 2005 and December 2006 solar proton events as a result of the HOx enhancement from the increased ionization.