When the ultraviolet rays from the Sun hit the Earths atmosphere the energy they possess work to knock electrons off of the atoms and molecules that the atmosphere is made up of. These free electrons make up a region of the atmosphere known as the Ionosphere. The region is strongest on the daytime side of the earth since it is dependant on the energy from the solar ultra violet rays.
VERY LOW FREQUENCY (VLF) RADIO STATIONS
Station Station Frequency Radiated
Site ID (kHz) Power
Cutler, ME NAA 24.0 1000
Jim Creek, WA NLK 24.8 250
Lualualei, HI NPM 21.4 566
LaMoure, ND NML 25.2 500