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

Glossary of Solar Terrestrial Terms


See Total Electron Content.

Ten Centimetre Flux

The power output of the Sun at a wavelength of 10.7 centimetres, frequently used in place of sunspot number as an indicator of solar activity.


In a HF prediction, this is the location of one of the two transceivers, e.g., Sydney.


See Travelling Ionospheric Disturbance.

T Index

An indicator of the effect of solar activity on HF frequencies. The T index is an indicator of the highest frequencies able to be refracted from regions in the ionosphere. The higher the T index, the higher the frequencies able to be refracted from an ionospheric region.

Total Electron Content

The number of electrons along a wave path measured in electrons/square cm. The TEC is used in determining delay and directional changes of a wave in the ionosphere.

Travelling Ionospheric Disturbance

These are wave-like motions in the ionosphere that cause focusing and defocusing of radio waves. The disturbance usually appears at higher frequencies, gradually affecting lower frequencies. Some are associated with magnetic storms and originate in the auroral zone. These may travel great distances. Others appear to be more localised, originating in the troposphere in local weather.


The lowest layer of the Earth's atmosphere extending up to about 13 km in altitude.

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