Evaluating the variability of the thermospheric-exospheric coupling of Hydrogen using Balmer alpha intensities

Understanding the dynamics of the exosphere is crucial for atmospheric chemistry and energetics, magnetospheric energy dissipation, and ion-neutral coupling. Several ground-based and spaceborne studies have used solar Lyman alpha series airglow emissions as a proxy to estimate the state of the atomic Hydrogen in the exosphere, the dominant constituent in this region. Night-time ground-based studies have used Balmer alpha fluorescence airglow obtained at Pine Bluff Observatory (PBO), WI, with a high spectral resolution Fabry-Perot spectrometer, and found a dusk-to-dawn asymmetry in the airglow intensity that was highest (smallest) for the winter (summer) months. These results were compared with modeled outputs from the so called lyao_rt model of Bishop (1999) for a series of PBO datasets during the 2000-2001 period. The lyao_rt model extends the NRLMSISE-00 thermosphere model using the Bishop analytic exosphere evaporative model to obtain temperature, hydrogen density and column density for calculations of radiative transport of atmospheric hydrogen emissions in the thermosphere and geocorona that can be compared with observations. Even though these early comparisons showed an overall agreement, they also showed discrepancies during the winter season that were generally attributed to poor knowledge of the exobase parameters used by lyao_rt. In this study, we have extended the TIMEGCM outputs up to exosphere altitudes using MONACO, which is a multiphase, multi-species Monte Carlo approach. We will present comparisons of the TIMEGCM-MONACO outputs with a carefully revised version of the PBO dataset to evaluate the seasonal dusk-to-dawn assymetries shown by the geocorona hydrogen airglow.