Observations of an extended mesospheric tertiary ozone peak

The OSIRIS instrument onboard the Odin spacecraft has recently made observations of the Oxygen InfraRed Atmospheric band and OH Meinel band volume emission rate profiles in the mesosphere. Features similar to the tertiary ozone peak reported earlier by other investigators are clearly present in the observed emission profiles. This peak, caused by a photochemical imbalance between the destruction of odd-oxygen by odd-hydrogen and the production of odd-oxygen, was previously believed to be confined to the winter hemisphere just equatorward of the polar terminator. However, northern hemisphere measurements made by OSIRIS in the spring of 2002 indicate that the tertiary peak is also present in the afternoon and early evening throughout the springtime, with the altitude of the peak rising steadily from around 70 km in the polar regions near local noon to about 80 km near the equator at sunset. These new observations of the extended tertiary peak are presented and it is shown that they are directly related to the previously observed tertiary ozone peak and are consistent with a simple one-dimensional time-dependent photochemical model.