Cloud
High clouds form at altitudes of in the polar regions, in the temperate regions and in the tropics. All cirriform clouds are classified as high and thus constitute a single genus "cirrus" (Ci). Stratocumuliform and stratiform clouds in the high altitude range carry the prefix "cirro-", yielding the respective genus names "cirrocumulus" (Cc) and "cirrostratus" (Cs). When limited-resolution satellite images of high clouds are analysed without supporting data from direct human observations, it becomes impossible to distinguish between individual forms or genus types, which are then collectively identified as "high-type" (or informally as "cirrus-type" even though not all high clouds are of the cirrus form or genus).Non-vertical clouds in the middle level are prefixed by "alto-", yielding the genus names "altocumulus" (Ac) for stratocumuliform types and "altostratus" (As) for stratiform types. These clouds can form as low as above surface at any latitude, but may be based as high as near the poles, at mid latitudes, and in the tropics. As with high clouds, the main genus types are easily identified by the human eye, but it is not possible to distinguish between them using satellite photography. Without the support of human observations, these clouds are usually collectively identified as "middle-type" on satellite images.
Low clouds are found from near surface up to . Genus types in this level either have no prefix or carry one that refers to a characteristic other than altitude. Clouds that form in the low level of the troposphere are generally of larger structure than those that form in the middle and high levels, so they can usually be identified by their forms and genus types using satellite photography alone.
Cumulus cloud
The species "Cumulus fractus" is ragged in appearance and can form in clear air as a precursor to cumulus humilis and larger cumulus species-types; or it can form in precipitation as the supplementary feature "pannus" (also called scud) which can also include stratus fractus of bad weather. "Cumulus humilis" clouds look like puffy, flattened shapes. "Cumulus mediocris" clouds look similar, except that they have some vertical development. "Cumulus congestus" clouds have a cauliflower-like structure and tower high into the atmosphere, hence their alternate name "towering cumulus". The variety "Cumulus radiatus" forms in radial bands called cloud streets and can comprise any of the four species of cumulus.
Cumulus supplementary features are most commonly seen with the species congestus. "Cumulus virga" clouds are cumulus clouds producing virga (precipitation that evaporates while aloft), and "cumulus praecipitatio" produce precipitation that reaches the Earth's surface. "Cumulus pannus" comprise shredded clouds that normally appear beneath the parent cumulus cloud during precipitation. "Cumulus arcus" clouds have a gust front, and "cumulus tuba" clouds have funnel clouds or tornadoes. "Cumulus pileus" clouds refer to cumulus clouds that have grown so rapidly as to force the formation of pileus over the top of the cloud. "Cumulus velum" clouds have an ice crystal veil over the growing top of the cloud.