Influence of Large-Scale Auroral Inhomogeneities on the Passage of Radio Waves under Moderate Geomagnetic Storm Conditions

We analyze the experimental results of multifrequency oblique radio sounding of the ionosphere on the Norilsk–Irkutsk meridional transauroral radio path during the moderate geomagnetic storm on September 22, 2018, with a maximum value of the disturbance index Kp ~ 5. The Global Dynamic Model of the Ionosphere (GDMI), which takes into account the dynamic state of the basic large-scale structures of the polar ionosphere—the main ionospheric trough (MIT), polar oval, and auroral E layer—is used to demonstrate the overall correspondence of maximum observed frequencies (MOF 1F2) and calculated maximum usable frequencies (MUF 1F2) with variations in the geomagnetic disturbance dynamics. A physical explanation is given for the recorded phenomenon of complete blocking of radio waves transmission in local nighttime conditions (“blackout”). The main factor of this effect is the presence of the auroral E-layer in the ionosphere, generated by precipitating charged particles, which are highly inhomogeneous in the longitudinal section of the radio path. Under daytime conditions, the presence of the auroral component in the E layer leads to a weaker effect of degradation of multiple reflections traces on oblique radio sounding ionograms.