Solar Tides in the Upper Equatorial Thermosphere: A Comparison between AE-E (Atmosphere Explorer-E Satellite) Data and the NCAR Thermospheric General Circulation Model.

Abstract : Numerical calculations of the equatorial thermospheric tidal temperatures and densities are compared with mass spectrometer data from the Atmosphere Explorer-E SATELLITE (AE-E) for solar minimum solstice conditions. The model calculations were made using the National Center for Atmospheric Research thermospheric general circulation model (TGCM), which includes the effects of viscosity, conductivity, diffusion, ion drag, winds, and temperature gradients. The thermospheric diurnal and semidiurnal tides are excited in situ by solar heating and by ion-neutral momentum coupling. The semidiurnal tidal calculations also include the effects of upward propagating waves generated by heating in the lower atmosphere. The semidiurnal propagating component is modeled by use of the classical tidal perturbations as lower boundary conditions. The model has been tuned by adjusting the propagating tidal forcing term until calculated semidiurnal winds and temperature fields best approximate incoherent scatter observations. The TGCM reproduces the gross tidal features, including the nighttime maxima. The largest discrepancy is the relative weakness of the model's diurnal amplitudes. This may be due to uncertainties in the EUV heating rates and thermospheric cooling rates. On the other hand, the model semidiurnal density amplitudes are considerably larger than those of the data. The terdiurnal amplitudes match fairly well, but the data exhibit a great asymmetry about the geographic equator.