Impacts of SABER CO <sub>2</sub> -based eddy diffusion coefficients in the lower thermosphere on the ionosphere/thermosphere

<p>This work estimates global-mean <em>K</em><sub>zz</sub> using Sounding of the Atmosphere using Broadband Emission Radiometry/Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics monthly global-mean CO<sub>2</sub> profiles and a one-dimensional transport model. It is then specified as a lower boundary into the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). Results first show that global-mean CO<sub>2</sub> in the mesosphere and lower thermosphere region has annual and semiannual oscillations (AO and SAO) with maxima during solstice seasons along with a primary maximum in boreal summer. Our calculated AO and SAO in global-mean CO<sub>2</sub> are then modeled by AO and SAO in global-mean <em>K</em><sub>zz</sub>. It is then shown that our estimated global-mean <em>K</em><sub>zz</sub> is lower in magnitude than the suggested global-mean <em>K</em><sub>zz</sub> from Qian et al. (2009) that can model the observed AO and SAO in the ionosphere/thermosphere (IT) region. However, our estimated global-mean <em>K</em><sub>zz</sub> is similar in magnitude with recent suggestions of global-mean <em>K</em><sub>zz</sub> in models with explicit gravity wave parameterization. Our work therefore concludes that global-mean <em>K</em><sub>zz</sub> from global-mean CO<sub>2</sub> profiles cannot model the observed AO and SAO in the IT region because our estimated global-mean <em>K</em><sub>zz</sub> may only be representing eddy diffusion due to gravity wave breaking. The difference between our estimated global-mean <em>K</em><sub>zz</sub> and the global-mean <em>K</em><sub>zz</sub> from Qian et al. (2009) thus represents diffusion and mixing from other nongravity wave sources not directly accounted for in the TIE-GCM lower boundary conditions. These other sources may well be the more dominant lower atmospheric forcing behind the AO and SAO in the IT region.</p>
Year of Publication
Journal of Geophysical Research: Space Physics
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Date Published