Glossary of Solar Terrestrial Termsskip terms menu
The strongest spectral line in the solar spectrum. The wavelength is 656.3 nm. H-alpha radiation is formed in the chromosphere and its intensity increases during solar flares. It is the spectral line used for world wide surveillance of solar flares.
The variation of a parameter, e.g., electron density with height.
See High Frequency.
The virtual height of the F2 layer. At night when the F2 and F1 regions merge to form the F region, h'F is measured. Similar heights are obtained for the E and F1 layers.
That part of the electromagnetic spectrum between 3 and 30 MHz.
That geographic region of the Earth that lies between about 60 and 90 degrees.
In HF sky wave communications, this refers to a radio wave travelling up to the ionosphere, being refracted and then returning to Earth.
The distance across the ground a radio wave travels with one refraction from the ionosphere. The distance will depend on the antenna elevation angle and the height of the reflecting layer.