The response of the lower ionosphere to the solar flares that occurred in March 2012 is considered. Measurements of the propagation velocity and wave impedance of ELF electromagnetic pulses (atmospherics) performed at Lovozero and Barentsburg high-latitude observatories were used to estimate this response. It was shown that the daily average propagation velocity of atmospherics decreased by 20–30 thousand km/s under disturbed heliogeophysical conditions as compared to the velocity measured under quiet conditions. This is related to a decrease in the effective waveguide height that results from the change in the ionospheric conductivity profile during a solar flare. It was detected that pronounced bursts of wave impedance, the maximums of which exceed the impedance average value by a factor of more than 2, are observed during strong heliogeophysical disturbances. This fact cannot be explained in the scope of a spherically layered model; consequently, such deviations indicate an increase in the D-layer conductivity inhomogeneities.