Cloud

A cloud is a visible mass of condensed water droplets suspended in the atmosphere above Earth's (or another planetary body's) surface.

The condensing water vapor forms small droplets of water (0.012 mm) or ice crystals that, when surrounded with billions of other droplets or crystals, are visible as clouds. Clouds reflect all light and are white, but they can appear grey or even black if they are so thick or dense that sunlight cannot pass through.

Clouds on other planets often consist of material other than water, depending on local atmospheric conditions (what gases are present, and the temperature).

Table of contents

1 Cloud creation 2 Cloud Classification 2.1 High clouds (Family A) 2.2 Middle clouds (Family B) 2.3 Low clouds (Family C) 2.4 Vertical clouds (Family D) 3 See also: 4 External Link

Cloud creation

Clouds form in areas where moist air rises and cools. This can happen

• along warm and cold frontss,
• where air flows up the side of a mountain and cools as it rises higher into the atmosphere (orographic uplift),
• and when warm air blows over a colder surface such as a cool body of water.

The actual form of cloud created depends on the strength of the uplift and on air stability. In unstable conditions convection dominates, creating vertically developed clouds. Stable air produces clouds created through turbulence alone, creating massive bulbous cloud forms. Frontal uplift creates various cloud forms depending on the composition of the front (ana-type or kata-type warm or cold front). Orographic uplift also creates variable cloud forms depending on air stability, although cap cloud and wave clouds are specific to orographic clouds.

Cloud Classification

Clouds are divided into two general categories: sheet-like and layer-like. These are named stratus clouds (or stratiform, the Latin stratus means layer) and cumulus clouds (or cumiloform, cumulus means piled up). These two cloud types are divided into four more groups that distinguish the cloud's altitude.

High clouds (Family A)

These form above 16,500 feet, in the cold region of the troposphere. They are denoted by the prefix cirro- or cirrus. At this altitude water almost always freezes so clouds are composed of ice crystals. The clouds tend to be wispy, and are often transparent.

Clouds in Family A include:

• Cirrus
• Cirrus Uncinus
• Cirrus Kelvin-Helmholtz
• Cirrostratus
• Cirrocumulus
• Cumulonimbus with Mammatus
• Cumulonimbus with Pileus
• Contrail

A contrail is a long thin cloud which develops as the result of the passage of a jet airplane at high altitudes.

Middle clouds (Family B)

These develop between 6,500 and 16,500 feet and are denoted by the prefix alto-. They are made of water droplets, and are frequently supercooled.

Clouds in Family B include:

• Altostratus
• Altostratus Undulatus
• Altocumulus
• Altocumulus Undulatus
• Altocumulus Mackerel Sky
• Altocumulus Castellanus
• Altocumulus Lenticularis

Low clouds (Family C)

These are found up to 6,500 feet and include the stratus (dense and grey). When stratus clouds contact the ground they are called fog.

Coulds in Family C include:

• Stratus
• Cumulus Humilis
• Cumulus Mediocris
• Stratocumulus

Vertical clouds (Family D)

These clouds can have strong upcurrents, rise far above their bases and can form at many heights.

Clouds in Family D include:

• Cumulonimbus (associated with heavy precipitation and thunderstorms)
• Cumulus Congestus
• Pyrocumulus
• Cumulonimbus Incus
• Cumulonimbus Calvus
• Cumulonimbus with Mammatus

See also:

cloud albedo, cloud feedback, fog, cloud forcing, precipitation, cloud base, coalescence, tornado, hurricane, monsoon, thunderstorm

External Link

• Australia Severe Weather: cloud classification system Lots of photos. Click on the thumbnail to get a bigger image.