page_title: List of cloud types
section_title: Extreme-level stratiform, stratocumuliform, and cirriform
hierarchical_section_title: List of cloud types / Polar mesospheric cloud identification and classification / Extreme-level stratiform, stratocumuliform, and cirriform
caption_attribution_description: Eesti: Helkivad ööpilved. Soomaa Kuresoo raba English: Noctilucent clouds, Kuresoo bog, Soomaa National Park, Estonia. Français&#160;: Des nuages noctulescents. Tourbière de Kuresoo, Parc national de Soomaa, Estonie. Español: es:Parque nacional de Soomaa Deutsch: Leuchtende Nachtwolken, Kuresoo bog, Nationalpark Soomaa, Estland
context_page_description: The list of cloud types groups the main genera as high, middle, multi-level, and low according to the altitude level or levels at which each cloud is normally found. Small cumulus are commonly grouped with the low clouds because they do not show significant vertical extent. Of the multi-level genus-types, those with the greatest convective activity are often grouped separately as towering vertical. The genus types all have Latin names.
  The genera are also grouped into five physical forms. These are, in approximate ascending order of instability or convective activity: stratiform sheets; cirriform wisps and patches; stratocumuliform patches, rolls, and ripples; cumuliform heaps, and cumulonimbiform towers that often have complex structures. Most genera are divided into species with Latin names, some of which are common to more than one genus. Most genera and species can be subdivided into varieties, also with Latin names, some of which are common to more than one genus or species.
context_section_description: Noctilucent clouds are thin clouds that come in a variety of forms based from about 80 to 85 kilometres (262,000–279,000 ft) and occasionally seen in deep twilight after sunset and before sunrise.
  Type 1
  Veils, very tenuous stratiform; resembles cirrostratus or poorly defined cirrus.
  Type 2
  Long stratocumuliform bands, often in parallel groups or interwoven at small angles. More widely spaced than cirrocumulus bands.
  Subtypes
  2A
  Bands with diffuse, blurred edges.
  2B
  Bands with sharply defined edges.
  Type 3
  Billows. Clearly spaced, fibrous cirriform, roughly parallel short streaks.
  Subtypes
  3A
  Short, straight, narrow streaks.
  3B
  Wave-like structures with undulations.
  Type 4
  Whirls. Partial (or, more rarely, complete) cirriform rings with dark centers.
  Subtypes
  4A
  Whirls possessing a small angular radius of curvature, sometimes resembling light ripples on a water surface.
  4B
  Simple curve of medium angular radius with one or more streaks.
  4C
  Whirls with large-scale ring structures.
caption: Noctilucent cloud over Estonia
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