|WATER AND REFLECTION OF LIGHT
METEOROLOGIST JEFF HABY
An object with a high
albedo reflects a significant amount of the incoming light. An object with a
low albedo does not reflect much light. With an albedo of 100% all incoming radiation is reflected
while it is 0% if it is all absorbed. In almost all cases the albedo will not be perfectly 100%
or 0%. Water has an interesting property in that the amount of reflection depends greatly on
the state (liquid or frozen) and the angle the radiation is striking it.
Liquid water has a higher albedo when the sun angle is low. For example, just after the sun rises the
sun angle will be low and much of the radiation will be reflected by the water. This has important
implication in locations the sun angle is low such as in high latitudes. High latitude locations where
the sun is near the horizon will reflect more solar radiation away than at
low latitude locations. This is one reason that
high latitude locations are colder (with the main reason being that the sun's energy is spread
over a larger surface area in high latitude regions).
When the sun is well above the horizon (30 degrees to directly overhead) then water has a low albedo and
absorbs a great deal of solar radiation. The middle latitude and tropical oceans absorb an enormous amount of
Ice is a good reflector of solar radiation especially if it is a fresh snowfall. The albedo decreases
as the age of snow increases.
Here is a guide to the albedo of water at various states and sun angles:
fresh snow: 80%
sun near the horizon on water: 65%
old or dirty ice: 40%
water with a sun angle 30 degrees or more above the horizon: 8%