|
|
How do clouds form?
Surface Heating - What's next?
The vertical growth of clouds is dependent upon the rising air within the
cloud being warmer than its surroundings. Once the rising air is cooler than
its surroundings, it is also more dense and the upward motion of the air will
cease. This can happen by either rising air cooling or by the surrounding air
warming.
In the first case, the rising air incorporates relatively cool and dry air into the cloud. How does this happen? First, clouds are surrounded by large areas of descending air that has been displaced by the rising air in the clouds. The sinking air is dry and cool.
In cloud edges, there is a lot of mixing and churning going on, and the sinking air can get mixed into the cloud. This process is called entrainment. During entrainment, dry air enters the cloud and evaporates cloud droplets. The overall effect of entrainment is to increase the rate at which the rising air cools by the injection of cold, outside air and by evaporation.
In the second case, the surrounding air can warm up if the rising air encounters a stable layer - where the temperature in the atmosphere begins to increase (or stay the same) with height (for example, temperature increases with height in the stratosphere).
Next page -> mountains
Links and resources
Surface Heating - What's next?
The vertical growth of clouds is dependent upon the rising air within the
cloud being warmer than its surroundings. Once the rising air is cooler than
its surroundings, it is also more dense and the upward motion of the air will
cease. This can happen by either rising air cooling or by the surrounding air
warming. In the first case, the rising air incorporates relatively cool and dry air into the cloud. How does this happen? First, clouds are surrounded by large areas of descending air that has been displaced by the rising air in the clouds. The sinking air is dry and cool.
In cloud edges, there is a lot of mixing and churning going on, and the sinking air can get mixed into the cloud. This process is called entrainment. During entrainment, dry air enters the cloud and evaporates cloud droplets. The overall effect of entrainment is to increase the rate at which the rising air cools by the injection of cold, outside air and by evaporation.
In the second case, the surrounding air can warm up if the rising air encounters a stable layer - where the temperature in the atmosphere begins to increase (or stay the same) with height (for example, temperature increases with height in the stratosphere).
Next page -> mountains
Links and resources
