WINDII observations of the 558 nm emission in the lower thermosphere: the influence of dynamics on composition

Abstract

Abstract The understanding of airglow variability is a long-standing problem, having been first identified by Lord Rayleigh, more than sixty years ago. Despite extensive observations over several decades, it is only recently that a coherent picture has begun to emerge. Combined wind and volume emission rate data acquired by WINDII, the WIND Imaging Interferometer on the Upper Atmosphere Research Satellite have contributed to this understanding by clearly showing that most of what has been called variability results from dynamical influences on airglow emission rate. The objective of this article is to describe ways in which these dynamical influences on airglow can be identified, using WINDII data as an example. The large volume of WINDII O( 1 S) daytime data allows both the dayglow and nightglow to be included in the discussion. The largest dynamical feature of the upper atmosphere is the tide, which has a particularly dominant effect on emission rates at the equator, though the effects are also strong at mid-latitude. Planetary waves are the next most dominant influence. The influence of both of these sources on the night-time emission rate are readily identified. For the daytime emission, data are presented which are consistent with such influences, but more independent information is required for complete confirmation.