Fluids: Liquids and Gases - Computer Animation: Algorithms and Techniques - page 262

FIGURE 8.10
An example of cirrus and cirrostratus clouds at sunset. (Copyright 1998 David S. Ebert.)
form relatively quickly and can appear threatening in a manner of minutes. Complex atmospheric pro-
cesses form clouds. These processes can be modeled and animated to show the formation of storms,
hurricanes, and inclement weather (see Figures 8.10 and 8.11 ).
Clouds are naturally occurring atmospheric phenomena. They are composed of visible water drop-
lets or ice crystals suspended in air, and are formed by moisture droplets adhering to dust particles.
When moisture is added to the air and/or the temperature of the air decreases, clouds can form. In either
case, moisture in the air condenses into droplets because the air cannot transparently hold that amount
of water at that temperature. Clouds occur at a variety of altitudes. Some clouds can be found at 60,000
feet while others can be as low as ground level. Although typically one thinks of clouds as high in the
sky, fog phenomena are just very low-level clouds. In addition, a single cloud formation can start near
the surface and extend upward as much as 10,000 feet.
Anatomy of clouds and cloud formation
Clouds are categorized according to their altitude, their general shape, and whether they carry moisture
(e.g., see [ 23 ] ). The naming convention combines a standard set of terms that describe the altitude,
shape, and moisture of the cloud.