Solar Wind Control of Electron Precipitation in the Ionospheric D Region During the 1-year Long IPY Period as Seen by the EISCAT Svalbard Radar

Continuous operation of the EISCAT Svalbard Radar during the International Polar Year (IPY), starting on 1 March 2007 and ending on 29 February 2008 occured during the prolonged solar minimum time which was on the average geophysically very quiet. The ISR experiment used a specially written IPY mode, which was intended to cover the entire altitude range of the ionosphere, from D and lower E regions to the ionospheric F peak, reaching into the topside ionosphere. The low altitude IPY electron density data from backscattered power measurements, with 3 km range resolution and 2.25 km steps, start from the altitude of 45 km. Although the low altitude data is subject to variable sea and/or tropospheric clutter, normally data is usable for altitudes higher than 70 km. This unique set of electron density data from a high-latitude station reveals repeated occurence of short lasting low-altitude ionisation enhancements and thus high-energy electron precipitation events, in spite of the generally geomagnetically quiet conditions. Comparison between riometer data from Svalbard and mainland stations, specially with the IRIS imaging riometer, shows that precipitation is generally very localized and restricted to higher latitudes. We discuss the statistics of this data in terms of precipitating electron spectra and connection to observed variations in the solar wind parameters.