Tidal influence on the oxygen and hydroxyl nightglows: Wind Imaging Interferometer observations and thermosphere/ionosphere/mesosphere electrodynamics general circulation model

Abstract

Longitudinal zonally averaged Wind Imaging Interferometer (WINDII) (on UARS) nighttime oxygen (O(1S)) and hydroxyl (P(3) line in the OH(8,3) Meinel band) volume emission rates exhibit dramatic spatial and temporal variations. The recently improved thermosphere/ionosphere/mesosphere electrodynamics general circulation model (TIME-GCM) produces simulations for the two airglows through the input of (1,1) upward propagating diurnal tides. The model simulations show excellent agreement with WINDII observations in both the local time domain and the latitudinal domain between 40° S and 40° N. The influence of diurnal tides on the two airglows in strongest in the tropical region. In the local solar time domain the emission rate and peak altitude at the equator show large tidal perturbations, but they are fairly stable at midlatitude. In the latitudinal domain there is an equatorial trough in the oxygen emission rate which exists regardless of local time and season. The hydroxyl emission rate is more dependent on local time and season. At equinox it has a prominent equatorial maximum which disappears at dawn, whereas at solstice it has a very weak equatorial maximum at dusk, changing soon after midnight to an equatorial minimum. These features of emission rates are also compared to TIME-GCM simulations for meridional wind, temperature, and atomic oxygen density, [O], with and without upward propagating diurnal tides. The results are as follows: (1) The large oscillations of the two nightglows as well the atomic oxygen density in the tropical region are driven by the diurnal propagating tides. In altitude the mesosphere and lower thermosphere is divided into two type of cells, one with meridional winds converging at the equator, higher temperature, and enhanced [O] and airglow emission rates, and the other with meridional winds diverging from the equator, lower temperature, and depleted [O] and airglow emission rates; all these are essentially related to the wavelength and phase of the diurnal tides. (2) The relatively stable airglow emission rates at around 20° are related to the minimum fluctuation of temperature and stable meridional wind directions in spite of the maximized wind speed in this region. (3) The year-around equatorial depletion in the oxygen airglow and the double-peaked profile in the hydroxyl airglow are most likely produced by the diurnal tides. Further investigation is needed particularly for the absolute value of the oxygen emission rate, the interhemispheric comparison of the oxygen emission rate, why WINDII observes maximum summer emissions whereas the TIME-GCM gives maximum winter emission, and the effects of waves in addition to the diurnal tides. Copyright 2001 by the American Geophysical Union.