Shortwave and longwave radiation
Topic: Solar Radiation, Heat Balance and Temperature · NCERT: Class 11, Ch 8 "Solar Radiation, Heat Balance and Temperature"; Class 11, Ch 11 "World Climate and Climate Change"
Meaning
The Sun is very hot, so it sends energy mostly as short waves, mainly visible light. Most of this short-wave radiation passes straight through the atmosphere and heats the ground. The warmed Earth then gives off long-wave (infrared) radiation, called terrestrial radiation. Water vapour, carbon dioxide and other greenhouse gases absorb much of these long waves. This is why the air is heated mainly from below, not directly by the Sun.
Example
In the Thar Desert of Rajasthan, short-wave sunlight heats the sand strongly by day. On clear nights the sand quickly loses its heat as long waves. There are few clouds or little water vapour to trap this heat, so nights become cold.
Don't confuse with
- Ultraviolet radiation: it is also short-wave, but it is even shorter than visible light. Ozone high in the atmosphere absorbs most of it. Greenhouse gases near the ground do not.