Properties of Ion Upflows in the Low‐Altitude Polar Ionosphere During CIR‐ and CME‐ Driven Magnetic Storms Based on Long‐Term EISCAT Observations

Abstract We have investigated the effects of Corotating Interaction Region‐ (CIR‐) and Coronal Mass Ejection‐ (CME‐) driven magnetic storms on the characteristics and mechanisms of ion upflow in the low‐altitude ionosphere (250–350 km). Our analysis was based on observations from the European Incoherent Scatter (EISCAT) radars at Tromsø (ILAT = ∼66N) and Svalbard (∼75N) from 1996 to 2015. The ion upflows (defined by the averaged upward ion velocity of >10 m/s) in the low‐altitude ionosphere were mainly detected in the MLT sectors of 03–09 (dawnside) and 21‐03 (nightside) at Tromsø during both CIR‐ and CME‐driven magnetic storms. The ion upflows at Svalbard were not enhanced on the nightside but were remarkable on the dawnside during CIR‐driven storms and were also observed on the nightside during CME‐driven large storms. On the duskside (15–21 MLT), the low‐altitude ion upflows were only detected at Tromsø during CME‐driven large storms. Dayside (09–15 MLT) ion upflows were not detected in the low‐altitude ionosphere. To investigate the generation mechanisms of low‐altitude ion upflows, we compared the convection electric field, ion temperature, and electron temperature between the pre‐storm time and after storm onset. The results indicate that frictional heating (Type 1 ion upflow) is dominant at Tromsø during CME‐driven large storms in all MLT sectors except the dayside. Conversely, particle precipitation (Type 2 ion upflow) is dominant at Tromsø on the nightside during all magnetic storms except CME‐driven large storms. Both mechanisms contribute to ion upflow during CIR‐driven small storms on the dawnside of Svalbard.