Ionospheric Upflow Around the Polar Region During a Solar Minimum

EISCAT Svalbard Radar data, obtained during the International Polar Year 2007 campaign, has been used to study ionospheric upflow events with a threshold of 10¹³ m^-2 s^-1. This study reports the incidence and seasonal variability of ion upflow events classified into low, medium, and high-flux upflows. It is observed that high upflow fluxes are comparatively rare and low flux upflow events are a frequent phenomenon. These classes of ion upflows from the high latitude of Svalbard (78°N) show that occurrence peaks around local noon at 31%, 16%, and 2% for low, medium, and high-flux upflow, respectively, during geomagnetically disturbed periods. Analysis shows that in agreement with previous studies on upflow fluxes, ion upflow occurs over a wide range of geomagnetic conditions, with upflow flux occurrence being greater than downflow occurrence. In contrast to previous observations, however, the upflow occurrence is greater around noon during highly disturbed geomagnetic conditions than for moderate geomagnetic conditions. Moreover, the seasonal distribution shows a high-flux upflow that is peaked around local noon in the summer, a low-flux upflow that is broadly distributed across all seasons at any geomagnetic activity conditions, and a medium-flux upflow showing occurrence peak driven by high Kp across all seasons.