FORECAST SOL: Moderate yellow MAG: Normal green ION: Normal green
Space Weather

Glossary of Solar Terrestrial Terms


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.

Height Profile

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.

High Frequency

That part of the electromagnetic spectrum between 3 and 30 MHz.

High Latitude

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.

Hop Length

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.

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