Oxygen aurora during the recovery phase of a major geomagnetic storm

A. W. Stephan, K. F. Dymond, S. A. Budzien, S. E. Thonnard, R. P. McCoy


We have analyzed ultraviolet spectra measured in the postsunset auroral zone on
16 July 2000, during the recovery phase of the major geomagnetic storm of 14Ð16
July 2000. We find enhanced oxygen ion and neutral line emissions above 300 km
in the postsunset sector of the auroral oval during the initial fast recovery
phase of the storm, also called the Bastille Day storm. No comparable emissions
are seen in simultaneous measurements of nitrogen and hydrogen emission
features, indicating that these features are not related to electron or proton
aurora. The enhancements are seen slightly equatorward of all other nitrogen
line and band emissions that are presumed to comprise the nominal diffuse
electron auroral oval. On the basis of the altitude profile, location, and
timing of the enhancements, we interpret these oxygen emissions as a product of
precipitating ring current oxygen ions in the auroral atmosphere, possibly after
pitch-angle scattering by electromagnetic ion cyclotron waves. These emissions
may provide an important measure of the contribution of collisions and charge
exchange interactions to the loss of oxygen ions and the recovery of geomagnetic
storms and substorms.

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Journal of Geophysical Research, 109, A09208, doi:10.1029/2004JA010557, 2004