Searching for an alternative method of the ionosphere monitoring

The ionosphere monitoring is an important task because it allows us to adjust the forecasts of radio wave propagation, specify the environment models, and follow the changes of space weather. Currently sounding of the ionosphere is produced by the HF radio waves from the Earth's surface using ionosondes, as well as by raying signals from satellites. Our goal is to draw attention to the possibility of the diagnosis of the ionospheric parameters by detecting ultra-low frequency (ULF) electromagnetic emission generated in the so-called Ionospheric Alfvén Resonator (IAR). To do this, we offer the observations of the IAR emission made the first time simultaneously at three stations using identical induction magnetometers. The stations are located along the same meridian, two of them are mid-latitudinal; the third one is situated in the auroral zone. We compare the main features of the observed multi-band emission (frequency, amplitude, and frequency difference between adjacent harmonics) with ionospheric parameters measured at the stations using ionosondes and GPS-observations. Diurnal variations of the ionospheric and ULF emission characteristics are also compared. The results show that there is quite a reliable connection between the resonant frequencies of the resonator bands and the critical frequency of the F2 layer of the ionosphere, namely, the frequency of the IAR emission varies inversely as the critical frequency of the ionosphere. This is due to the fact that the frequency of oscillation captured in the resonator is primarily determined by the Alfvén velocity (which depends on the plasma density) in the ionospheric F2 layer. The correlation varies at different stations; at the high latitudes it is smaller, but is generally well observed along the whole meridian. This gives hope for the opportunity to develop a method for evaluating the critical frequency of the F2 layer of the ionosphere according to ULF observations in the 0.5-10 Hz frequency range. This method is particularly in demand for the high latitudes, as there is often not possible to measure the critical frequency by conventional methods due to significant disturbances.