Impacts of Spatially Varying Eddy Diffusion in the Lower Thermosphere on the Ionosphere and Thermosphere using GITM - Sensitivity Study
Journal Article
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.
