GLOBAL SIMULATIONS AND OBSERVATIONS OF O(S-1), O-2((1)SIGMA) AND OH MESOSPHERIC NIGHTGLOW EMISSIONS

Despite a large number of observations of mesospheric nightglow emissi ons in the past, the quantitative comparison between theoretical and e xperimental 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 D oppler imager (HRDI) instrument onboard the upper atmosphere research satellite (UARS) provides nearly simultaneous, near-global observation s of O(S-1) green line, O-2(0-1) atmospheric band, and OH Meinel band nightglow emissions. Three days of these observations near the Septemb er equinox of 1993 are presented to show the general characteristics b f the three emissions, including the emission brightness, peak emissio n altitude, and their temporal and spatial variabilities. The global d istribution of these emissions is simulated on the basis of atmospheri c parameters from the recently developed National Center for Atmospher ic Research (NCAR) thermosphere-ionosphere-mesospher-electrodynamics g eneral circulation model (TIME-GCM). The most striking features reveal ed by the global simulation are the structuring of the mesospheric nig htglow by the diurnal tides and enhancements of the airglow at high la titudes. The model reproduces the inverse relationship observed by HRD I between the nightglow brightness and peak emission altitude. Analysi s of our model results shows that the large-scale latitudinal/tidal ni ghtglow brightness variations are a direct result df a complex interpl ay between mesospheric and lower thermospheric diffusive and advective processes, acting mainly on the atomic oxygen concentrations. The inc lination of the UARS spacecraft precluded observations of high latitud e nightglow emissions by HRDI. However,our predicted high-latitude bri ghtness enhancements confirm previous limited groundbased observations in the polar region. This work provides an initial validation of the NCAR-TIMEGCM using airglow data.