|RADIATION IN THE ATMOSPHERE
METEOROLOGIST JEFF HABY
Energy moves through the atmosphere that comes from the sun, from the earth and features in the
atmosphere. Much of the radiation that comes from the sun is in the visible spectrum. Because of this
humans can sense visible radiation the best. Energy from the earth is mostly in the infrared spectrum. The presence
of clouds or lack of clouds is important in that it changes the radiation energy budget since clouds absorb and
and reflect radiation.
There are a couple of definitions I want to mention and the importance in the atmosphere:
Translucent: This is a substance that lets light for the most part through. An example is a clear day.
Much of the sun's energy will be able to penetrate through the atmosphere and make it to the surface. Of course
there is still significant scattering and absorption in the atmosphere even when it is clear but in a
relative sense a great amount of radiation makes it to the surface. Think of a translucent material as
a window. It lets light in for the most part.
Opaque: This is a substance that does not allow much light through. For example, thick clouds will prevent
a significant amount of radiation from making it to the surface. A great percentage of the solar
radiation striking thick cloud is reflected away or absorbed by the clouds.
Next, there are several definitions I want to mention that can happen to radiation:
Reflection: This is when light reflects at often a 90 degree angle off a substance. An example is
sunlight reflecting off ice.
Transmission: This is light passing through a substance without effecting the light much. An example is
visible light passing through the atmosphere to the surface.
Absorption: This is when a substance takes in the light and does not allow it to pass through. The
substance will gain energy when it absorbs radiation. An example is the ground absorbing solar
radiation and warming up.
Scattering: This is when light bounces off a substance in different directions. The sky is
blue during the day due to the scattering of blue light. Since blue is scattered it looks like
this wavelength of light is coming from all directions in the sky.
An atmospheric window is a term used to describe air that is fairly translucent to radiation in a specific
wavelength. Each gas has wavelengths that are more or less translucent. For example, carbon dioxide and
water vapor absorb certain infrared radiation wavelengths. This would be an example of not being an
atmospheric window for those particular gases and wavelengths.
An absorption band is a wavelength that a particular gas is good at absorbing. An example is ozone's ability
to absorb UV radiation. This absorption is the reason the temperatures warm in the stratosphere.