First attempt to estimate the ion content over the ionosphere using data from the IAR frequency structure

Abstract

Ionospheric Alfvén resonator (IAR) is located between the lower ionosphere and the transition area from the ionosphere to the plasmasphere (at middle latitudes), or magnetosphere (at high latitudes). Its walls are sharp gradients in plasma concentration below the F2 layer at the bottom and at the height of 0.5-1.5 Earth radii above. The resonator captures Alfvén waves ranging from a fraction of a hertz to about 10 Hz. The dynamic range of the IAR emission has the form of a set of fan-shaped bands with frequency varying in accordance with the change of ionospheric parameters, primarily the plasma concentration in the F2 layer of the ionosphere. In this paper, using the example of spectrograms calculated from the observations of the IAR emissions in the mid-latitudes (Mondy, Eastern Siberia) and in the auroral zone (Sodankylä, Finland), the possibility of obtaining information on the ion composition at altitudes of 2,000 to 6,000 km is shown. The analysis was carried out by comparing the frequency differences Δf between adjacent harmonics measured from spectrograms with the resonator characteristics calculated on the basis of the IRI-2012 model, extrapolated up to a height of 10,000 km. By selecting coefficients in the extrapolation formulae of ion altitude profiles to achieve a minimum discrepancy between the measured Δf frequency and its estimate calculated on the basis of the model the profiles of ion composition in the region above the IRI-2012 model limit height, i.e., higher than 2,000 km, were obtained. As a result, the graphics of height variations in relative and absolute concentrations of the three types of ions: oxygen, hydrogen and helium were obtained; changes in altitude profiles of these ions during the transition from daytime to night were followed. Comparison of the profiles obtained for the middle and high latitudes showed a significant difference. For example, if over the obs. Mondy relative content of oxygen ions is close to zero in the entire range of heights, then at high latitudes in the early evening hours, it decreases from over 70% at 2000 km to 20% at an altitude of 4000 km and it slowly falls when approaching the night.