THE NATURAL ENVIRONMENT
Geography 101 Online
Cloud watching, from children looking for animals in cloud shapes to the meteorologist studying weather patterns in satellite images, is an international pastime. Both observations, the whimsical and the analytical, try to interpret one of nature's most complex phenomena.
Even a basic classification of these continuously shifting shapes eluded humanity for millennia until about 200 years ago when amateur meteorologist Luke Howard proposed one. His basic cloud designations are still in use.
Most clouds can be classified combinations of just five words: cirrus (referring to high-altitude, and sometimes wispy), alto (referring to mid-altitude), cumulus (individual puffy), stratus (continuous layer), and nimbus (meaning precipitating). Look at the chart below and see how these words are used by themselves and in combination to describe ten basic cloud types. Notice the difference in the Sun's appearance seen though cirrostratus and altostratus clouds: cirrostratus often produces a circular halo. You may see this halo at night around a full moon when cirrostratus clouds are present. Also note that the huge, thunderstorm-producing cumulonimbus clouds can fill the entire depth of the troposphere and range from liquid water at the bottom to ice crystals at the top.
The altitude designations represent the different states of water in the atmosphere. Below about 2 km (1.2 mi), clouds consist mostly of liquid water droplets. Above about 6 km (4 mi), cirrus clouds consist mostly of ice crystals, and in between alto clouds are a mixture of both ice and liquid water.
Altocumulus (mid-altitude puffy) clouds sometimes form a fish-scale pattern called a mackerel sky, shown at left. And if you see a flying saucer floating over a tall Hawaiian mountain, don't be alarmed; it's just a lenticular cloud, such as this one over Mauna Kea. These form at mountain tops under very stable conditions with high winds. Air squeezes over the summit and creates these eerily distinct clouds.
Fog is simply a cloud that touches the ground. Fog forms in many ways, including:
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