VLF noise during Forbush decreases of cosmic rays

The VLF-noise amplitude variations in Yakutsk during Forbush decreases of cosmic rays are considered by the. epoch superposition method. Nighttime VLF-noise amplitudes reflect mainly the activity of their thunderstorm source in the equatorial region (Africa): summer daytime amplitudes, local thunderstorms activity. Two effect phases can generally be distinguished with respect to the Forbush decrease onset. The VLF noise amplitude decreases by day 0 or -1 during the first phase and increases by day +1 or +2 in the second phase, exceeding the initial undisturbed amplitude on days -5 or -4.