Quantifying geomagnetic activity's contribution to the Global E-region Electron density's day‐to‐day variability using Spire Radio Occultation observations

Using the unprecedented sampling of the Spire Radio Occultation (RO) data set, this paper statistically estimates geomagnetic dependencies of the global E‐region Electron Density's (Ne) day‐to‐day variability. To assesses how much Spire RO‐observed variabilities are consistent with known Physics, comparison is made with the Specified Dynamics–Whole Atmosphere Community Climate Model with Ionosphere/Thermosphere eXtension (SD‐WACCM‐X), a first principles Physics‐based model. Results show that the largest geomagnetic dependency on Spire and SD‐WACCM‐X E‐region Ne occurs at night over the auroral latitudes with coefficients of determination at around 49% and 80%, respectively. Their regression coefficients are both between +10%/Kp index to +16%/Kp index. On the other hand, Spire and SD‐WACCM‐X substantially disagree on the geomagnetic dependencies during day‐time. These results suggest that Spire RO's observations of E‐region Ne geomagnetic dependencies may only be substantially explained by known physics at night and not during the day.