Interhemispheric Asymmetries in Ionospheric Electron Density Responses During Geomagnetic Storms: A Study Using Space-Based and Ground-Based GNSS and AMPERE Observations

We utilize Total Electron Content (TEC) measurements and electron density (Ne) retrieval profiles from Global Navigation Satellite System (GNSS) receivers onboard multiple Low Earth Orbit (LEO) satellites to characterize large-scale ionosphere-thermosphere system responses during geomagnetic storms. We also analyze TEC measurements from GNSS receivers in a worldwide ground-based network. Measurements from four storms during June and July 2012 (boreal summer months), December 2015 (austral summer month), and March 2015 (equinoctial month) are analyzed to study global ionospheric responses and the interhemispheric asymmetry of these responses. We find that the space-based and ground-based TECs and their responses are consistent in all four geomagnetic storms. The global 3D view from GNSS-Radio Occultation (RO) Ne observations captures enhancements and the uplifting of Ne structures at high latitudes during the initial and main phases. Subsequently, Ne depletion occurs at high latitudes and starts progressing into midlatitude and low latitude as the storm reaches its recovery phase. A clear time lag is evident in the storm-induced Ne perturbations at high latitudes between the summer and winter hemispheres. The interhemispheric asymmetry in TEC and Ne appears to be consistent with the magnitudes of the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) high latitude integrated field-aligned currents (FACs), which are 3–4 MA higher in the summer hemisphere than in the winter hemisphere during these storms. The ionospheric TEC and Ne responses combined with the AMPERE-observed FACs indicate that summer preconditioning in the ionosphere-thermosphere system plays a key role in the interhemispheric asymmetric storm responses.