Data reduction of plasma lines in Incoherent Scatter Radar spectrum

In the ionosphere, a sustained population of suprathermal electrons is generated due to photoionization or electron precipitation. At resonance, the phase velocity of the electrons matches the Langmuir phase velocity observed by the Incoherent Scatter Radar (ISR). As a result, the scattered power in the plasma line spectrum is enhanced, thus making it possible to detect them. Plasma lines can be used to improve the accuracy of the estimates of electron density and temperature, study features in the electron velocity distribution of the suprathermal electrons and provide an independent method to calculate ionospheric currents.  

We analyzed the data collected with the EISCAT Tromsø UHF radar on 27 January 2022. We present a novel technique of data reduction to detect plasma lines and extract parameters. We use the method developed by Ivchenko (2017) to determine the times with enhanced plasma lines. For those times, we model the spectrum with a Gaussian function, where the plasma line intensity, frequency and bandwidth correspond to the amplitude, mean and variance, respectively. We observe photoelectron-enhanced plasma lines between 09:16:15 LT – 13:56:15 LT. All the detected plasma lines are field-aligned, except for 11:29:30 LT - 12:51:30 LT, when they are also detected in the vertical direction (i.e. at 11.67° to the magnetic field). The detection of the plasma lines is accompanied by an increase in the electron density estimates from the ion line.