Hemisphere-Asymmetric Responses of the Ionosphere to Geomagnetic Storms as Observed by GNSS and AMPERE

To characterize global ionosphere-thermosphere (IT) system responses during geomagnetic storms, we use electron density (Ne) and Total Electron Content (TEC) observations from space and ground for multiple storms, occurring in the boreal and austral summer months, as well as equinoctial month. The storm-induced Ne response in the summer and winter hemispheres appears to be different and asymmetric. The summer hemisphere shows a stronger response compared to the winter hemisphere. On the other hand, the response during the equinoctial month storm is more symmetric. The global 3D view from GNSS Radio Occultation (RO) Ne observation captures enhancements and uplifting of Ne structures at high latitudes during the initial and main phases. A clear time lag is evident in the storm-induced perturbation at high latitudes between the summer and winter hemispheres. Subsequently, Ne depletions occur at high latitudes. Time lag between high and mid latitudes is also evident, as the storm reaches its recovery phase. The observed hemispheric asymmetry in the ionospheric response appears to be consistent with AMPERE Field-Aligned Current (FAC) measurements. The integrated FACs in the summer hemisphere is a 4 - 5 MA higher than the winter hemisphere during these storms.