Impact of Doubled CO ₂ on the Response of the Mesosphere, Thermosphere, and Ionosphere to the 2008–2009 Sudden Stratospheric Warming

We investigate the impact of the 2008–2009 sudden stratospheric warming (SSW) event on the mesosphere, thermosphere, and ionosphere under conditions of doubled carbon dioxide (CO 2 ). Using the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension model, we perform two simulations for the 2008–2009 SSW event—a control run and a run with 2 × CO 2 concentration. Our results indicate that the zonal mean response of the upper atmosphere to the SSW is substantially modulated by 2 × CO 2 . During the SSW, the migrating solar semidiurnal tide (SW2) shows a ∼20% change in the lower thermosphere at around 2 × 10 −5 hPa (∼115 km) under 2 × CO 2 relative to the control. SSW‐driven variations in thermospheric O/N 2 is modified up to ∼3% under the 2 × CO 2 case. In the ionosphere, SSW‐related reduction in zonal mean electron density in the control run at equatorial and low latitudes is further modulated up to ∼8% under 2 × CO 2 conditions.