|the rate at which the sun's energy is received per unit area at the top of the earth's atmosphere when the sun is at its mean distance from the earth and atmospheric absorption has been corrected for. Its value is 1367 watts per square metre|
The average amount of solar radiation received by the Earth's atmosphere, per unit area, when the Earth is at its mean distance from the Sun. It is equal to 1370 watts per square meter. Solar radiation varies with the Earth's distance from the Sun and with the appearance or decay of sunspots.