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

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. These variabilities can be interpreted in two ways: variations in state (density, temperature, wind) of the upper mesosphere or spatial and temporal changes in the small-scale mixing (Eddy diffusion that is parameterized within the model). In a previous study, while analyzing the sensitivity of the thermospheric densities, O/N2, TEC to the turbulence from the lower atmosphere we estimated a seasonal and latitudinal variation in the eddy diffusion coefficient (Kzz) that would be required to match the measurements with the Global Ionosphere Thermosphere Model (GITM) results and found that often the Kzz shoots over the preferred range indicating that there are other processes contributing to these thermospheric properties as well. In this new study, we now investigate the sensitivity of the thermospheric parameters O/N2, total electron content (TEC) - to various 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. The tidal structures seem dissipated in WACCM-X resulting in different spatial and temporal structures in the O/N2 and TEC of the WACCM-X driven GITM. Also, because of larger difference between MSIS and WACCM-X O densities at 100 km during solstices, larger differences are seen in the ionospheric TEC during solstices as compared to equinoxes. We also perform a GITM simulation with MSIS lower boundary and introduce a latitudinal variation in Kzz to understand its effects in the thermosphere. We find that the variation of zonal mean densities, temperature and vertical velocity are in accordance to the governing equations of continuity and energy.