Читать книгу Weather For Dummies - John D. Cox - Страница 58

Did you know there are two forms of heat?

One is the kind of heat that you feel on your arm, say, when you exercise or hang out in the sunshine. This they call sensible heat, because you can sense it. (This sounds pretty sensible to me, although I wouldn’t spend too much time out in that sunshine.)

The other kind is latent heat. This is heat that is released or absorbed when things like water change phase, or form, between vapor and liquid and ice. They call it latent because it is stored away, or hidden. (They could have called it insensible, you know, but nobody asked me.)

This idea sounds a little tricky at first, but really it’s no sweat. Look at it this way:

When you perspire, your body is working on getting rid of excess sensible heat. The sweat on your arm evaporates, converts from liquid water to gaseous vapor. This process of conversion from liquid to gas state absorbs heat, and the coolness you feel is the sensible heat being converted to latent heat. The heat that left your body is stored away in the molecules of that little bubble of air that just lifted off from your arm.

Now follow that water vapor off of your arm as it rises up higher and higher into the sky and forms a cloud. When it does this, it converts itself back into liquid, tiny water droplets, and gives the heat it took off your body back to the atmosphere. Oops, things look a little unstable up there. A storm is brewing! Now see what you’ve done!

This invisible long-wave radiation that is given off by the Sun-warmed Earth is more important to weather than direct sunlight. Somebody who has spent the day in the sunshine may find it hard to believe, but a weather scientist will tell you: The energy radiating back up into the atmosphere from the surface of the Earth as long-wave radiation has more direct effect on weather processes than the short-wave energy that comes directly through the atmosphere as sunshine.