Springtime transition in lower thermospheric atomic oxygen

Observations from three optical ground stations and the wind imaging interf erometer on the upper atmosphere research satellite have been combined to d escribe a "springtime transition" in atomic oxygen. At each station the tra nsition is characterized by a rapid 2-day rise in the night-time oxygen air glow emission rate by a factor of between 2 and 3, with a subsequent decrea se 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 a i;glow, except that immediately following the enhancement, the hydroxyl emi ssion rate does not fall below the value it had before the event. Airglow r otational temperatures behave coherently with the emission rate. WINDII dat a show that the airglow emission rate perturbation is a planetary scale fea ture associated with strong vertical motions and that the event may be asso ciated with the winter-to-summer zonal wind reversal. Data from the norther n springtimes of 1992 and 1993 are reported upon in detail, with additional data from 1995 to confirm the persistence: of the phenomenon.