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

Abstract

This work estimates global‐mean Kzz using Sounding of the Atmosphere using Broadband Emission Radiometry/Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics monthly global‐mean CO2 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 CO2 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 CO2 are then modeled by AO and SAO in global‐mean Kzz. It is then shown that our estimated global‐mean Kzz is lower in magnitude than the suggested global‐mean Kzz from Qian et al. (2009) that can model the observed AO and SAO in the ionosphere/thermosphere (IT) region. However, our estimated global‐mean Kzz is similar in magnitude with recent suggestions of global‐mean Kzz in models with explicit gravity wave parameterization. Our work therefore concludes that global‐mean Kzz from global‐mean CO2 profiles cannot model the observed AO and SAO in the IT region because our estimated global‐mean Kzz may only be representing eddy diffusion due to gravity wave breaking. The difference between our estimated global‐mean Kzz and the global‐mean Kzz 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.

Middle atmosphere dynamical sources of the semiannual oscillation in the thermosphere and ionosphere

“…The standard TIME‐GCM simulation also agrees well with observations, demonstrating that this model is capable of producing a realistic global T‐I SAO from first principles. The globally averaged K z z in Figure c from the standard TIME‐GCM simulation shows a much smaller SAO than the Qian et al [] K z z variation but is consistent with the small K z z variation derived by Salinas et al [] from SABER CO 2 observations. Without gravity waves TIME‐GCM still produces a reasonable T‐I SAO, which strongly suggests that seasonally varying K z z driven by breaking gravity waves (the K z z hypothesis) is not the primary driver of this phenomenon.…”

“…IAVs in (a) globally averaged mass density at 400 km and (b) TEC in % relative to their global and annual averages. (c) Globally averaged normalized K z z from the NCAR TGCMs and Salinas et al [] as a function of day of year at the TIE‐GCM lower boundary of 5.483 × 10 −4 mbar (∼97 km) and at 98 km, respectively. Shown are TIME‐GCM simulations that include both gravity waves and GSWM‐09 tides (“Standard,” black‐plus signs), only GSMW‐09 tides (orange asterisks), and neither gravity waves nor GSWM‐09 tides (purple triangles); TIE‐GCM results with the Qian et al [] seasonally varying K z z (blue squares); empirical mass density and TEC models (red Xs) developed by Emmert [] and Emmert et al []; and Salinas et al [] SABER CO 2 ‐based K z z at 98 km (green diamonds).…”

“…However, K z z values derived by Salinas et al [] from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) CO 2 measurements indicate a much weaker IAV than the K z z variation inferred Qian et al []. Furthermore, the TIE‐GCM lower boundary condition for O (at ∼97 km) is not directly forced by mesospheric IAVs, whereas satellite observations of O have revealed a strong SAO in the upper mesosphere [e.g., Smith et al , ].…”

Seasonal variations of thermospheric mass density at dawn/dusk from GOCE observations

“…Recently, Calabia et al (2016) investigated the thermospheric mass density variations from GRACE data for the period 2003-2016 by using the principal component analysis (PCA) method, and discussed the annual variation for different local solar times (LSTs) and solar activities. Moreover, Salinas et al (2016) found that the monthly global-mean CO 2 profiles from TIMED/SABER have annual and semiannual oscillations (AO and SAO), but cannot explain the observed AO and SAO in the thermosphere. However, Jones et al (2017) reported that simulations from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM) demonstrated that the intra-annually varying eddy diffusion by the breaking gravity waves may not be the primary driver of the SAO in the thermosphere.…”

Observations and Simulations of Eddy Diffusion and Tidal Effects on the Semiannual Oscillation in the Ionosphere

“…Then, they reduced the constant K zz by a factor of 5 and obtained a larger SAO in the ionosphere, which is comparable to the standard GSWM (global scale wave model) run of TIEGCM with a standard constant K zz . Salinas et al () used K zz based on SABER CO 2 observation ( K zzC ) to drive the TIEGCM; the K zzC is smaller than that from Q09 with a smaller SAO. Their TIEGCM simulation with K zzC produced smaller SAO in the ionosphere compared to the observations and Q09.…”