Global simulations and observations of O(1S), O2(1Σ) and OH mesospheric nightglow emissions

Abstract

Despite a large number of observations of mesospheric nightglow emissions in the past, the quantitative comparison between theoretical and experimental brightnesses is rather poor, owing primarily to the short duration of the observations, the strong variability of the tides, and the influence of short‐timescale gravity waves. The high‐resolution Doppler imager (HRDI) instrument onboard the upper atmosphere research satellite (UARS) provides nearly simultaneous, near‐global observations of O(1S) green line, O2(0–1) atmospheric band, and OH Meinel band nightglow emissions. Three days of these observations near the September equinox of 1993 are presented to show the general characteristics of the three emissions, including the emission brightness, peak emission altitude, and their temporal and spatial variabilities. The global distribution of these emissions is simulated on the basis of atmospheric parameters from the recently developed National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM). The most striking features revealed by the global simulation are the structuring of the mesospheric nightglow by the diurnal tides and enhancements of the airglow at high latitudes. The model reproduces the inverse relationship observed by HRDI between the nightglow brightness and peak emission altitude. Analysis of our model results shows that the large‐scale latitudinal/tidal nightglow brightness variations are a direct result of a complex interplay between mesospheric and lower thermospheric diffusive and advective processes, acting mainly on the atomic oxygen concentrations. The inclination of the UARS spacecraft precluded observations of high latitude nightglow emissions by HRDI. However, our predicted high‐latitude brightness enhancements confirm previous limited groundbased observations in the polar region. This work provides an initial validation of the NCAR‐TIMEGCM using airglow data.