The latitudinal and temporal variation of atomic oxygen (O) is opposite between the empirical model, MSIS and the whole atmosphere model, WACCM-X at 97-100 km. The [O] from WACCM-X has maxima at solstices and summer mid-high latitudes, similar to [O] from SABER. We use the densities and dynamics from WACCM-X to drive the Global Ionosphere Thermosphere Model (GITM) at its lower boundary, and compare it with the MSIS driven GITM. We focus on the differences in the modeling of the thermospheric and ionospheric semiannual oscillation (T-I SAO). Our results reveal that driving GITM with WACCM-X shifts the phase of T-I SAO to maximize around solstices. Nudging the dynamics in GITM towards WACCM-X, reduces the amplitude of the oppositely-phased SAO but does not completely correct its phase. We find that during solstices, WACCM-X driven GITM has a smaller temperature gradient between the hemispheres and weaker meridional and vertical winds in the summer hemisphere. This leads to accumulation of [O] at lower latitudes due to weaker meridional transport, resulting in solstitial maxima in global means. WACCM-X itself has the right phase of SAO in the upper thermosphere but wrong at lower altitudes. The exact mechanisms that can correct the phase of SAO in IT models while using SABER-like [O] in the MLT are currently unknown and warrant further investigation. We suggest mechanisms that can reduce the solstitial maxima in the lower thermosphere, for example, stronger interhemispheric meridional winds, stronger residual circulation, seasonal variation in eddy diffusion, and momentum from breaking gravity waves.

The eddy diffusion coefficient (Kzz) parameterizes the effects of gravity wave (GW) turbulence in the mesosphere and lower thermosphere (MLT) on the ionosphere and thermosphere (IT), and its spatial variation remains unclear. We use the Global Ionosphere Thermosphere Model (GITM) to understand the impacts of spatially varying MLT Kzz on the IT system. Using the observations from the SABER instrument, studies have observed that GW activity in the MLT exhibits latitudinal variability with seasons. We introduce similar latitudinal bands of increased Kzz at low latitudes during equinoxes and at high latitudes during solstices. The primary effect of non-uniform Kzz is in introducing spatially variability in the IT, and the net change in globally averaged thermospheric quantities is small (∼2-4%). The net effect of Kzz depends on the total area of the turbulent patch and spreads globally when low-latitude Kzz is increased. If however the turbulent conduction is turned off, changes in the IT state are more localized. When low-latitude Kzz is raised during equinoxes, a decrease in global [O], temperature, O/N2, TEC and an increase in [N2] are observed at a constant pressure level, inducing changes in meridional winds across the globe. During solstices, when high-latitude Kzz is raised, the IT state of the winter hemisphere exhibits larger decrease in O/N2, due to more effective composition change of O through vertical advection. If a larger Kzz is introduced in the summer hemisphere, an increase in O/N2 is observed because of the influence of lower background O/N2.