Response of Ionospheric E-region Electron Density to Geomagnetic Activity

This work analyzes the response of ionospheric E-region electron density (Ne) to geomagnetic activity. This work primarily utilizes radio occultation (RO) measurements of E-region Ne profiles. The observed responses are compared with simulations from the Specified Dynamics – Whole Atmosphere Community Climate Model with Ionosphere/Thermosphere eXtension (SD-WACCM-X) and the Thermosphere Ionosphere Electrodynamics – General Circulation Model (TIE-GCM).

The work first quantifies the contributions of geomagnetic activity on E-region Ne’s day-to-day variability. This involves performing regression and correlation analysis between E-region Ne and the Kp index. 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. Spire observes depletion in mid-latitude E-region Ne during the day while SD-WACCM-X doesn’t. 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.

Next, this work assesses these enhancements or depletion of E-region Ne during specific geomagnetic storms: the April 2023 storm and the May 2024 storm. Spire RO does indeed observe the enhancement in night-time E-region Ne over the auroral ovals during the storm’s main to recovery phases. Spire RO also observes a depletion in day-time E-region Ne over the mid-latitudes during the storm’s main to recovery phases. These are simulated by the TIE-GCM model. Diagnostics with the model reveal that while the night-time enhancements are primarily tied to enhancements in NO+ ions, the day-time depletions are primarily tied to depletions in O2+ ions.