Highlights • Oblique high latitude ionograms were analyzed during the storm of March 17–19, 2015. • Observed ionograms were characterized by appearance of intense sporadic layers. • Loss of multihop reflections from sporadic layers was a result of absorption growth. • Real and IRI-based distance–frequency characteristics were compared. • Parameters of movement of disturbance front were estimated.

Abstract The ionospheric phenomena which significantly influenced radio propagation during March 17–19, 2015 are considered in the study. The data of oblique ionospheric sounding (OIS) were analyzed at six radio paths. These paths are located in the zone of North Siberia in Russia and have different lengths: from 1000 to 5000km. The results are the following. The magnetic storm drastically changed the character of radio propagation at all the considered paths: in most cases the reflections from the ionospheric F2-layer were changed by the reflections only from the sporadic Es-layer. The parameters of movement of the disturbance front were estimated on the basis of OIS data of the paths. The average velocity of the front movements from east to west was about V =440m/s. Even the moderate growth of riometer absorption within the region of radio paths’ locations, resulted in loss of multihop modes in the signal reflections from sporadic layers. It also resulted in a sharp decrease of signal strength at the paths. Real distance–frequency characteristics (DFC) of the paths were compared to DFC calculated on the basis of International Reference Ionosphere (IRI) model. It was revealed that on a quiet day of March, 15th, the real and the calculated DFC are similar or coincide in the majority of cases. During the disturbed days of March, 17–19, most commonly observed are the significant differences between the calculated and the experimental data. The most pronounced difference is revealed while estimating the character of OIS signals’ reflections from Es-layers.