Cloud Physics - Cloud Classification

Cloud Classification

Clouds are classified according to the height at which they are found, and their shape or appearance. There are three basic categories based on physical structure and process of formation. Stratiform clouds appear as extensive layers, ranging from thin to moderately thick with some vertical development. They are mostly the product of large scale lift of stable air. Cumuliform clouds are formed mostly into localized heaps, rolls and/or ripples ranging from very small cloudlets of limited convection in slightly unstable air to very large towering free convective buildups when the airmass is very unstable. Cirriform clouds are high, thin and wispy, and are seen most extensively along the leading edges of organized weather disturbances.

Stratus and limited convection stratocumulus clouds are seen at low altitudes of around 2 kilometres or lower. Clouds of similar shape in the topmost region of the troposphere have the prefix "cirro" added to their names ("cirrostratus" and "cirrocumulus"), appearing as light brush strokes in the blue sky. Stratiform clouds and cumuliform clouds of limited convection found at intermediate heights have the prefix "alto" added to their names ("altostratus" and "altocumulus"). All cirriform clouds are classified as high and therefore constitute a single cloud type or genus "cirrus".

Vertically developed nimbostratus, cumulus, and cumulonimbus may form anywhere from near surface to intermediates heights of around 3 kilometres and therefore, like the low clouds, have no height related prefixes. However, those capable of producing heavy precipitation or stormy weather carry a "nimbo" or "nimbus" designation. Of the vertically developed clouds, the "cumulonimbus" type is the largest and can virtually span the entire troposphere from a few hundred metres above the ground up to the tropopause. The cumulonimbus is the cloud responsible for thunderstorms.