HIGH-LATITUDE NITRIC OXIDE IN THE LOWER THERMOSPHERE.

Abstract

High-latitude observations of fluorescent nitric oxide gamma bands were made before and during a strong magnetic storm with the Ogo 4 ultraviolet spectrometer. Brightness measurements of the (1-0) gamma band of nitric oxide indicate a slow buildup of NO during the disturbed period. The NO column density reaches a value as high as a factor of 8 greater than the mid-latitude value and shows no correlation with the brightness of the instantaneous aurora. A time-dependent model calculation indicates that the ionization and dissociation of N//2 by auroral electrons can increase the NO and N(**4S) densities. A steady state is not reached for NO until 10**5 s in an aurora characterized by an energy flux of 10 ergs/cm**2s. Dissociation by the solar ultraviolet radiation competes with horizontal and vertical transport as a loss process for the nitric oxide produced by the aurora. A high NO** plus /O//2** plus ratio is to be expected in the period following a strong auroral precipitation.