16:30 〜 16:45
[PEM09-23] Intense ionospheric responses to minor geomagnetic storms in solar minimum conditions by using FORMOSAT-7/COSMIC-2 observations
キーワード：Minor geomagnetic storms, FORMOSAT-7/COSMIC-2, Global Ionospheric Specification, Extreme ionosphere response, Magnetosphere-Ionosphere coupling
Recent studies show that in the deep solar minimum conditions extreme and unexpected positive ionospheric response could occur even during minor geomagnetic disturbances. This study examines the ionospheric response during minor magnetic storms that occurred since August 2019, after the launch of the FORMOSAT-7/COSMIC-2 satellites. The geomagnetic storms that occurred during this period are selected when the disturbance storm-time index (Dst) falls below -30 nT and the southward component of interplanetary magnetic field (IMF) remains below -3 nT for at least 1-hour duration. The ionospheric responses during the selected storms are examined using the Global Ionosphere Specification (GIS) 3D electron density profiles constructed from the slant total electron content obtained from the radio occultation measurements of FORMOSAT-7/COSMIC-2 (F7/C2) constellation and ground-based global navigation satellite system (GNSS) receiver network. A superposed epoch analysis is carried out by using the time of maximum interplanetary electric field (IEFy) as the zero-epoch time. Local-time and latitude variations of the average GIS electron density corresponding to the zero-epoch are examined by using previous 5-day average electron density as the quiet-time reference. The results reveal extreme positive storm response during most of the cases, with an average electron density enhancement of 100-200% over low latitudes in the afternoon period. Maximum electron density response occurs within about 3.5-4 hours after the zero-epoch. In the night sector, the enhancement occurs after 5-12 hours of the zero-epoch. The storm effect persists for about 3-days over the mid- and low-latitudes. The electron density variations during the selected events are compared with the corresponding variations of interplanetary and solar wind parameters and the possible factors that contribute to the observed ionospheric responses are examined.