Propagation atten uation rates for frequencies below 1 kcls in t he ELF region (30 cis to 3,000 cis) were calculated from t he spectra of atmospherics observed at widely-spaced stations. D ata are presented for east to west propagation under sunset app roaching t he eastern station. Un der t hese conditions, t he attenu ation rates are about 1 db l1,000 km at 75 cis and increase with increasing frequ ency, attaining about 3 dbl l ,OOO km at 200 cis. The attenuation rates observed seem to be co nsistent with a two-layered ionosphere model with its lower region 90 km above t he eart h.

Attenuation rates for ELF radio waves below 1 kcls are consistent with a two-layered ionosphere model, with a lower region 90 km above the Earth's surface.

Observed attenuation rate of ELF radio waves

Key Takeaway: Attenuation rates for ELF radio waves below 1 kcls are consistent with a two-layered ionosphere model, with a lower region 90 km above the Earth's surface.