Interpretation of satellite airglow observations during the March 22, 1979, magnetic storm, using the coupled ionosphere‐thermosphere model developed at University College London

Abstract

The University of California, Berkeley, extreme ultraviolet spectrometer aboard the U.S. Air Force STP 78‐1 satellite measured emission features in the Earth's dayglow due to neutral and ionized species in the atmosphere, in the 35‐140‐nm range. The spectrometer was operating between March 1979 and March 1980, including the period of the magnetic storm on March 22, 1979. Some of these measurements are interpreted using the predictions of the three‐dimensional time‐dependent coupled ionosphere‐thermosphere model developed at University College London. The observations show a reduction in the atomic oxygen 130.4‐nm airglow emission at high northern latitudes following the storm. Model simulations show that this reduction in 130.4‐nm emission is associated with an increase in the O2/O ratio. Analysis of model results using electron transport and radiative transport codes shows that the brightness of 130.4‐nm emission at high latitudes due to resonantly scattered sunlight is approximately twice that due to photoelectron impact excitation. However, the observed decrease in the brightness at high northern latitudes is mainly due to a change in the photoelectron impact source, which contributes approximately 75% of the total, as well as its multiple scattering component; for the photoelectron impact source at 70° latitude and 200 km altitude, the reduction in multiple scattering is 1.5 times greater than the reduction in the initial excitation. The reduction in the airglow emission is visible only in the northern hemisphere because the south pole was not sunlit over the storm period. The comparison of model results with observations suggests that 130.4‐nm emission may be a useful as a tracer for global changes in the concentration of atomic oxygen.