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Impacts of Spatially Varying Eddy Diffusion in the Lower Thermosphere on the Ionosphere and Thermosphere using GITM - Sensitivity Study
  • Garima Malhotra,
  • Aaron J. Ridley
Garima Malhotra
University of Colorado Boulder

Corresponding Author:[email protected]

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Aaron J. Ridley
University of Michigan-Ann Arbor
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Abstract

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.