Effect of Auroral Disturbances on the Propagation of Very Low Frequency Signals from the RSDN-20 Radio Navigation System

Results are presented from analyzing VLF signals of the RSDN-20 radio navigation system recorded at the Lovozero, Verkhnetulomsky (both on the Kola Peninsula), and Barentsburg (Svålbard Archipelago) observatories. Events are found of an unusual drop in the amplitude of the horizontal magnetic field under nighttime ionospheric conditions that occurred during substorms at AL indices below −500 nT. Cases are considered where optical observations according to which auroral precipitation were recorded were available during the substorm. The observed effect could be related to local fluctuations in the electron density profile of the lower ionosphere caused by auroral precipitations during a substorm.