The atmosphere and the Weather

Clouds

A Cloud is a visible assemblage of small water droplets or ice crystals suspended in the air. A cloud might contain about 3,000 droplets per cubic inch of air. Cloud droplets sizes range from microscopic to 0.002 inches.

Clouds are important for other than aesthetic reasons. As they form, vast quantities of heat are released into the atmosphere. Clouds regulate the earth's energy balance by regulating the amount of solar radiation reflected back to space and by absorbing the earth's infrared energy.

But clouds are also important because they visually indicate the physical processes taking place in the atmosphere.

In the atmosphere, three processes act to create water droplets or ice crystals. These three processes are:

• Condensation - water moving from a vapor to a liquid state.
• Freezing - water moving from a liquid to a solid state.
• Deposition - water moving from a vapor to a solid state.

The formation of water droplets and ice crystals takes place when the water in the atmosphere is cooled. As air containing water vapor cools, the relative humidity of the air parcel increases until the dew or frost point is reached. At dew point (relative humidity = 100%) water begins to condense into droplets. If 100% relative humidity is reached below 0°C deposition occurs and ice crystals form.

Formation of water droplets and ice crystals also requires a surface for condensation, freezing, or deposition. In the atmosphere, these surfaces are microscopic particles of dust, smoke, and salt commonly called condensation nuclei.

The following two links will take you to explore Cloud Formation Processes and Cloud Classification

And finally, how do clouds look from space?. And another satellite imagery web page.