Impacts of SABER CO2‐based eddy diffusion coefficients in the lower thermosphere on the ionosphere/thermosphere

This work estimates global‐mean Kzzusing Sounding of the Atmosphere using Broadband Emission Radiometry/Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics monthly global‐mean CO2profiles 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 CO2in 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 CO2are then modeled by AO and SAO in global‐mean Kzz. It is then shown that our estimated global‐mean Kzzis lower in magnitude than the suggested global‐mean Kzzfrom Qian et al. (2009) that can model the observed AO and SAO in the ionosphere/thermosphere (IT) region. However, our estimated global‐mean Kzzis similar in magnitude with recent suggestions of global‐mean Kzzin models with explicit gravity wave parameterization. Our work therefore concludes that global‐mean Kzzfrom global‐mean CO2profiles cannot model the observed AO and SAO in the IT region because our estimated global‐mean Kzzmay only be representing eddy diffusion due to gravity wave breaking. The difference between our estimated global‐mean Kzzand the global‐mean Kzzfrom 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. Global‐mean CO2has annual and semiannual oscillationsSeasonal variation of global‐mean Kzzestimated from global‐mean CO2Global‐mean Kzzfrom CO2alone cannot reproduce annual and semiannual oscillations in IT region