Data reduction of incoherent scatter plasma line parameters

Abstract. In the ionosphere, a sustained population of suprathermal electrons arises due to photoionization or electron precipitation. The presence of such a population enhances the scattered power in the plasma line spectrum, thus making it possible to detect them. Plasma line measurements improve the accuracy of electron density and temperature estimates. We investigate plasma line enhancements in EISCAT Tromsø UHF radar observations, using two image processing methodologies for detection: a supervised image morphological processing technique and an unsupervised connected component analysis. The supervised methodology detects more plasma lines, demonstrating higher sensitivity. We determine the times and altitudes with enhancements and model the spectrum with a Gaussian function. The radar beam points in the field-aligned direction for 25 % of the total observational time, is directed east for another 25 % and is oriented in the vertical direction for the remaining 50 %. Plasma lines are detected 26 % of the time when the radar is pointed in the field-aligned direction, 5 % of the time in the east direction and 5 % of the time in the vertical direction. Most plasma lines are detected around the F-region altitude where the electron density is maximum, typically between 230–260 km, with a simultaneous increase in the electron density estimates from the ion line. Plasma line intensity is maximum around noon. It decreases as the aspect angle increases. Both detection methodologies' advantages and disadvantages are discussed, and plasma line intensity variations are analyzed as a function of altitude, aspect angle and phase energy.