Activity #7
Comparing Cloud Fraction to Reflected Shortwave Radiation (Nov 1984–Feb 1990)

In this activity, you can view the Earth from the unique perspective of outer space. You will examine monthly snapshots (or global datasets) of our planet’s surface and atmosphere. During this activity, you will investigate complex interaction of the Earth’s cloud cover and the amount of sunlight the planet reflects by looking for patterns and changes over time. You will make connections to global environmental issues.

Background:
Cloud fraction represents the portion of sky in each pixel that is covered by clouds. Satellites can measure cloud fraction over the entire atmosphere and for all types of clouds. Since most clouds reflect incoming sunlight very well and trap heat escaping from the Earth’s surface, cloud fraction is an important parameter in studies of our planet’s radiant energy budget. (Data from International Satellite Cloud Climatology Project [ISCCP]).

A portion of the sunlight that enters the Earth system is reflected back into space by a combination of the clouds, aerosols, and gases in the atmosphere, as well as from the surface. The term “reflected shortwave radiation” refers to the sum total of all the shortwave electromagnetic energy, or sunlight at wavelengths ranging from 0.3 to 5 micrometers, that escapes from the top of the Earth’s atmosphere back into space. The image above is a false-color map showing the amount of shortwave energy (in Watts per square meter) that was reflected by the Earth system for the given month(s). In the image, the brighter, whiter regions show where more sunlight is reflected, while green regions show intermediate values, and blue regions are lower values. Notice that regions that are typically cloudy tend to reflect more shortwave energy, while the land surface reflects less than clouds, and the ocean reflects less than the land. (Data courtesy ERBE Project, NASA LaRC)