Plasma line observations from the EISCAT Svalbard Radar during the International Polar Year

Abstract. Photo-electrons and secondary electrons from particle precipitation enhance the incoherent scatter plasma line to levels sufficient for detection. When detectable the plasma line gives accurate measure of the electron density and can potentially be used to constrain incoherent scatter estimates of electron temperature. We investigate the statistical occurrence of plasma line enhancements with data from the high-latitude EISCAT Svalbard Radar obtained during the International Polar Year (IPY, 2007–2008). A computationally fast method was implemented to recover the range-frequency dependence of the plasma line. Plasma line backscatter strength strongly depends on time of day, season, altitude, and geomagnetic activity, and the backscatter is detectable in 22.6 % of the total measurements during the IPY. As expected, maximum detection is achieved when photo-electrons due to the Sun's EUV radiation are present. During summer daytime hours the occurrence of detectable plasma lines at altitudes below the F-region peak is up to 90 %. During wintertime the occurrence is a few percent. Electron density profiles recovered from the plasma line show great detail of density variations in height and time. For example, effects of inertial gravity waves on the electron density are observed.