The region of the earth's upper atmosphere containing a small percentage of free electrons and ions produced by photoioniza- tion of the constituents of the atmosphere by solar ultraviolet radiation at very short wavelengths (l.t.1000 angstroms). The ionosphere significantly influences radiowave propagation of fre- quencies less than about 30 MHz.

» อภิธานศัพท์ฟิสิกส์ (อวกาศ)