Meteorology: Understanding the Atmosphere            Ackerman and Knox



  The planetary averaged albedo is a key climate variable as it, combined with the solar constant determines the radiative energy input to the planet. The global annual averaged albedo is approximately 0.30 (or 30%). The albedo varies quite markedly with geographic region and time of year. Oceans have a low albedo, snow a high albedo. While the Northern Hemisphere has more land the Southern Hemisphere, the annual average albedo of the two hemispheres is nearly the same, demonstrating the important influence of clouds in determining the albedo.

Notice the high albedo off the west coast of South America. This is a region of persistent low level clouds -- stratus clouds. Can you find other regions of oceanic stratus?

Can you explain why Greenland has a very high albedo compared to its surroundings?

Notice the strong dependence of albedo on season, the annual cycle of the albedo follows the annual cycle of the position of the sun. Also notice that cloud free ocean regions have low albedos while deserts generally have high albedos.

In the tropical regions the albedo variation is influenced primarily by weather disturbances and their associated cloud distributions. In the polar regions, seasonal variations in albedo are due to the distribution of major ice sheets and the decreasing mean solar elevation angle with latitude.