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.