Ionosphere
An ionized layer of Earth's upper atmosphere (~60 km to 1,000 km) where extreme solar UV and X-ray radiation ionize atmospheric gas atoms into free electrons and ions.
Governing formula
Plasma Frequency f_p = (1 / 2π) √(n_e e² / (ε₀ m_e))
SI unit
Electrons/m³ (Electron Density n_e)
In depth
Divided into D, E, and F plasma layers. The ionosphere reflects high-frequency (HF) radio waves back toward Earth, enabling long-distance skywave AM radio communications without satellites.
Examples in the real world
HF shortwave radio broadcasts bouncing off the ionospheric F-layer to travel beyond the horizon.