Springtime transition in lower thermospheric atomic oxygen

International audienceObservations from three optical ground stations and the wind imaging interferometer on the upper atmosphere research satellite have been combined to describe a “springtime transition” in atomic oxygen. At each station the transition is characterized by a rapid 2-day rise in the night-time oxygen airglow emission rate by a factor of between 2 and 3, with a subsequent decrease by a factor of about 10 in the same period of time. This latter state of extremely weak oxygen airglow indicates a depletion of atomic oxygen that persists for many days. The characteristic signature is similar at both mid-latitude and high-latitude stations and is also observed in the hydroxyl airglow, except that immediately following the enhancement, the hydroxyl emission rate does not fall below the value it had before the event. Airglow rotational temperatures behave coherently with the emission rate. WINDII data show that the airglow emission rate perturbation is a planetary scale feature associated with strong vertical motions and that the event may be associated with the winter-to-summer zonal wind reversal. Data from the northern springtimes of 1992 and 1993 are reported upon in detail, with additional data from 1995 to confirm the persistence of the phenomenon