DEPLETION OF OXYGEN IN AURORA - EVIDENCE FOR A LOCAL MECHANISM

A ground-based and rocket investigation of the response of the neutral atmosphere to E region auroral heating has been carried out at Poker Flat, Alaska. The temporal evolution of the atomic oxygen to molecular nitrogen ratio (O/N-2) in the lower thermosphere has been monitored u sing the optical emissions from the aurora as a diagnostic. Comparison s between the changes in the O/N-2 ratio and the auroral Joule and par ticle heating have shown several examples of close similarity between the durations of the heating events and the depletions. Using the ther mospheric winds measured during the rocket flights and the temporal st ructure of the depletions, the upper limit on the horizontal scale siz e of the depletions has been estimated at 200-400 km. Moreover, in sit u rocket measurements of atomic oxygen showed significant differences at points separated horizontally by approximately 220 km. It is also c oncluded from the near coincidence between the depletion events and th e Joule heating events that the dynamical mechanism(s) that drive the depletions were not far distant from the observing site, that is, loca l processes are sometimes dominant during periods of moderate auroral activity. We suggest that the observation of a strong wind shear in th e 100- to 120-km altitude region [Larsen et al., 1997] could be respon sible for turbulence that contributes to the changes in minor constitu ent composition.