Understanding the Effects of Lower Boundary on the Ionosphere-Thermosphere System using GITM and WACCM-X

Abstract:

The exchange of energy between lower atmosphere with the ionosphere thermosphere (IT) system is not well understood. A number of studies have observed day-to-day and seasonal variabilities in the difference between data and model output of various IT parameters. It is widely speculated that the forcing from the lower atmosphere, variability in weather systems and gravity waves that propagate upward from troposphere into the upper mesosphere and lower thermosphere (MLT) may be responsible for these spatial and temporal variations in the IT region, but their exact nature is unknown. In this study, we investigate the sensitivity of the thermospheric and ionospheric properties, O/N2, total electron content (TEC), Equatorial Ionization Anomaly (EIA) to two different lower boundary conditions in the GITM. We use WACCM-X to drive the lower atmospheric boundary in GITM at ~97 km, and compare the results with the current MSIS-driven version of GITM and the original WACCM-X. The tidal structures are dissipated in WACCM-X at the lower boundary resulting in spatial and temporal structures in the O/N2 and TEC of the WACCM-X driven GITM with smaller tidal amplitude. We also find that because of larger meridional temperature gradients, WACCM-X driven GITM has larger upwelling of atomic oxygen and lower O/N2 in the summer hemisphere. In the ionosphere, during equinox conditions, the WACCM-X driven GITM has weaker EIA crests, whereas during solstice, it has stronger EIA crests. This can be linked to the difference in the E-region winds and ion diffusion along magnetic field field lines between the two simulations. On comparing the TEC with GPS observations, we find that MSIS driven GITM is closer to the observations during equinox while WACCM-X driven run is better during solstice. These simulations highlight the importance of lower thermosphere boundary on the upper thermosphere and ionosphere numerical models.