EARTH SCIENCE > SUN-EARTH INTERACTIONS > SOLAR ACTIVITY
Any change in the sun's appearance or behavior. The sun's activity
is described as being very low, low, moderate, high or very high.
Solar activity changes over a period of, on average, 11 years. At
solar maximum, the solar activity is high and so too the Extreme
Ultraviolet (EUV) radiation output which affects the ionosphere. At solar
minimum, the opposite is true.
Reference: An Extended Glossary of Solar-Terrestrial Terms from the IPS Radio
and Space Services: http://www.ips.oz.au/background/richard/glossary.html