Читать книгу Weather For Dummies - John D. Cox - Страница 55

Some sunshine is missing. Nobody leave the room.

About half of the solar energy that reaches Earth’s atmosphere ends up getting absorbed at the surface. There it gets converted into invisible long-wave radiation. When it re-enters the atmosphere sooner or later, it helps make weather. Another 20 percent gets absorbed by the atmosphere and clouds on the way down.

So what happens to the other 30 percent of the sunshine? People who have been put on the case say it gets lost to scattering, when sunlight rays collide with air molecules or tiny dust particles are reflected back off of bright surfaces. The brighter the surface, the more light it reflects (and the less it absorbs). This is why a white shirt is cooler than a dark one on a summer day. The percentage of light that a surface reflects back, rather than absorbs, is a property that scientists call albedo.

Albedo is a big deal. For example, 20 percent of the incoming sunshine bounces right off the bright white cloud tops and heads back toward space. About 4 percent is reflected back from Earth, but there are big differences in the albedo of different surfaces. It ranges anywhere from 95 percent for fresh snow to 2 percent for calm water.