Reaction of the Upper Atmosphere to the 27-d Solar Cycle - Comparison of CTIPe and TIE-GCM Simulations to Observations

Solar EUV radiation is the dominant driver for upper atmosphere ionization. Ionospheric variations that affect radio signal propagation and thus affect technical systems such as satellite-based positioning systems. One significant time scale for the solar variability is the solar 27-day rotation period that causes a corresponding response in ionospheric observables like the height-dependent electron density (Ne) or the integrated total electron content (TEC). To enhance our understanding of the processes within the ionosphere we investigate a combination of observations and physical models, namely the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model and the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM), are analyzed to identify differences in Ne, TEC data and ionized oxygen (O⁺ and O₂⁺). Furthermore, the model results are compared to ground-based ionosonde Ne measurements with regard to the spatial and temporal response of the ionosphere to the 27-day solar rotation period. Modeled Ne correlates strongly with the observed Ne at mid-latitudes, but at low-latitudes the modeled TEC distribution follows the geomagnetic coordinates more strictly when compared to the observational data. Local TEC and F2 layer peak Ne are well represented by CTIPe, whereas TIE-GCM represents the global TEC and F2 layer peak height well.