Characteristics of ion upflow and downflow observed with the European Incoherent Scatter Svalbard radar

Abstract

We have investigated how geomagnetic activity, the solar wind (SW), and the interplanetary magnetic field (IMF) influence the occurrence of the F‐region/topside ionospheric ion upflow and downflow. Occurrence of dayside ion upflow observed with the European Incoherent Scatter Svalbard radar (ESR) at 75.2° magnetic latitude is highly correlated with the SW density, as well as with the strength of the IMF By component. We suggest that this correlation exists because the region where ion upflow occurs is enlarged owing to SW density and IMF By magnitude, but it does not move significantly in geomagnetic latitude. The occurrence frequency of dayside ion upflow displays peaks versus the geomagnetic activity index (Kp), SW velocity, and negative IMF Bz component; that is, ion upflow is less frequently seen at the highest values of these parameters. Dayside ion downflow in the F‐region/topside ionosphere occurs only when the Kp index and/or SW velocity are high or when IMF Bz is largely negative. The ion downflow is likely due to ballistic return of the ion upflow. We suggest that the region of ion upflow not only becomes larger but also moves equatorward with increasing Kp, SW velocity, and negative IMF Bz. The ESR can so be poleward of the upflow region and observe ions convecting poleward and returning ballistically downward.