Features of ionospheric responses to geomagnetic storms of low solar activity period

<p>During low solar activity periods, geomagnetic disturbances still occur and impact the Earth’s ionosphere. In such conditions, even comparatively weak disturbances can lead to a noticeable ionospheric response. In particular during the extended solar minimum of the 23<sup>rd</sup> solar cycle, the October 11, 2008 geomagnetic storm of moderate intensity (Dst = -50 nT, maximum Kp=6) caused strong positive ionospheric disturbances. At midlatitudes, the storm-induced enhancement in total electron contain (TEC) exceeded by two times the normal quite time day-to-day variability and the strong density enhancement was registered in the topside ionosphere.</p><p>Using a combination of the ground-based and low-Earth-orbit (LEO) observations (ground-based GNSS networks, LEO RO COSMIC, in-situ and onboard GPS CHAMP and Swarm measurements, space-based optical observations), we examined features of ionospheric responses to several weak-to-moderate geomagnetic storms occurred at low solar activity periods of the 23rd and 24th solar cycles (2008 and 2019 years respectively). The ionospheric response was analyzed in terms of the storm-time TEC changes, large and medium scale travelling ionospheric disturbances generation, and auroral plasma irregularities intensity and location. The prominent features obtained were an intensification of ionospheric irregularities occurrence at sub-auroral latitudes and an equatorward expansion of the auroral irregularities oval, differences of TEC variations from quite-time variability, response of the topside ionosphere, and TIDs generation.</p><p>The first-principle TIEGCM simulations with a comprehensive data-model comparison was carried out to specify the main drivers responsible for the observed ionospheric responses.</p><p>This work is supported by the NASA LWS grant NNX15AB83G.</p>