The atmosphere attenuates both longwave and shortwave radiation and reduces the amount of sunlight that reaches the surface and the amount of longwave radiation that leaves the top of atmosphere. Below is a graph showing the solar radiation incident at the top of atmosphere (1) and the amount at the top of the troposphere (2) and surface. For longwave, click here.

The probability, Pa, that a photon
will be absorbed along the path is expressed as the negative exponential
of the optical depth, t, through which the radiation passes. That is:
Pa = exp(-t This is Beer's Law.
Important atmospheric windows (where absorption is small) include: 0.3 to 0.7 micrometers which accounts for the large proportion of visible radiation that reaches the surface. |