Relative Contributions of Lower‐Atmosphere Tidal and Solar‐Magnetospheric Forcings to the Day‐to‐Day Variability of F‐Region Electron Density

Abstract We use Thermosphere Ionosphere Electrodynamics General Circulation Model simulations nudged to realistic tides and their statistical day‐to‐day variabilities (DTDVs), derived from Michelson Interferometer for Global High‐Resolution Thermospheric Imaging/Ionospheric Connection Explorer observations, to estimate the relative importance of tidal and solar‐geomagnetic (solar and magnetospheric (SM)) forcings in driving F‐region electron density (Ne) variability. Ne is decomposed into mean and tidal components for diagnosis. The simulations show excellent agreements with COSMIC‐2 observations in reproducing 2–35‐day Ne DTDVs, proving that the dominant sources for DTDVs are realistically captured. Under solar minimum conditions (F10.7 = 70), tides contribute ∼56% of the absolute Ne DTDVs across all components, while SM forcing contributes ∼33%. As solar activity rises (F10.7 = 80–110), the tidal contribution decreases to ∼37%, while the SM contribution increases to ∼49%. Their summed contributions of less than one suggest a role of nonlinear dynamics in dictating the overall variability. The tidal and SM contributions to relative DTDVs (absolute DTDVs divided by background Ne) are ∼77% and ∼58%, respectively, indicating the stronger role of tides in determining short‐term relative fluctuations. The increased SM contribution with rising solar activity, combined with the dominant role of tides in relative DTDVs, implies that part of the SM contribution to absolute DTDVs stems from modifying the background Ne. The relative importance of tidal and SM forcings varies significantly by component: tides consistently dominate DE3 and SW2, while SM dominates DW1; for the Ne mean, the dominant driver changes as solar activity changes. These observationally constrained and validated simulations enable more realistic quantifications of the forcing contributions from above and below, providing valuable guidance for advancing Ionosphere‐Thermosphere predictability.