A Study of Observations of Ionospheric Upwelling Made by the EISCAT Svalbard Radar During the International Polar Year Campaign of 2007

Abstract

We have used EISCAT Svalbard Radar data, obtained during the International Polar Year 2007 campaign, to study ionospheric upflow events with fluxes exceeding 1013 m 2 s 1 . In this study, we have classified the upflow events into low, medium, and high flux upflows, and we report on the incidence and seasonal distribution of these different classes. It is observed that high upflow fluxes are comparatively rare and low flux upflow events are a frequent phenomenon. Analysis shows that occurrence peaks around local noon at 31%, 16%, and 2% for low, medium, and high-flux upflow, respectively, during geomagnetically disturbed periods. In agreement with previous studies on vertical and field-aligned flows, ion upflow is observed to take place over a wide range of geomagnetic conditions, with downflow flux occurrence being lower than upflow occurrence. In contrast to previous observations, however, the upflow occurrence is greater around noon during highly disturbed geomagnetic conditions than for moderate geomagnetic conditions. Analysis of the seasonal distribution reveals that, while high-flux upflow has its peak around local noon in the summer, with its occurrence being driven predominantly by high geomagnetic disturbance, the occurrence of low-flux upflow is broadly distributed across all seasons, geomagnetic activity conditions, and times of day. The medium-flux upflow events, although distributed across all seasons, show an occurrence peak strongly related to high Kp. Furthermore, during highly disturbed conditions, the low-flux and medium-flux upflow events show a minimum occurrence during the winter, whereas minimum occurrence for the high-flux upflow events occurs in autumn.