Cloud - Tropospheric Class - Summary of Families, Genera, Species, Varieties, Supplementary Features, Mother Clouds, and Associat - High Cirriform, Stratocumuliform, and Stratiform

High Cirriform, Stratocumuliform, and Stratiform

• Genus cirrus (Ci):

These are mostly fibrous wisps of delicate white cirriform ice crystal cloud that show up clearly against the blue sky. Cirrus clouds are generally non-convective except castellanus and floccus species which show limited convection. They often form along a high altitude jetstream and at the very leading edge of a frontal or low pressure disturbance where they may merge into cirrostratus.

• Species: This genus is divided into five species which are grouped to form the basis of reporting cirrus in the SYNOP code. Cirrus fibratus (Ci fib) consists of thin fibrous streaks with no tufts or hooks. Cirrus uncinus (Ci unc) is similar except that the filaments are hooked at the ends. Both species are coded C_H1. Cirrus spissatus (Ci spi) consists of patchy dense high cloud. The castellanus species (Ci cas) has convective buildups that give the cloud a partly or mainly turreted appearance, especially when viewed from the side. Cirrus with a tufted appearance is designated cirrus floccus (Ci flo). All three of these dense cirrus species are coded C_H2.

• Varieties: Certain cirrus species can sometimes be divided into pattern-based varieties. The filaments of cirrus fibratus intortus are twisted into irregular patterns. Cirrus fibratus vertebratus sees the filaments arranged in a pattern that resembles the backbone of a fish. Another pattern-based variety can be found with fibratus and uncinus species. Cirrus radiatus consists of parallel bands that appear to converge at the horizon. This pattern is often seen when the high clouds are invading the sky or increasing in amount. It is then reported on the SYNOP observation code as C_H4, or as C_H5 or 6 (depending on how much of the sky is covered) if accompanied by cirrostratus. Cirrus duplicatus is observable when the fibratus or uncinus filaments are arranged in closely spaced layers, one above the other. Pattern-based varieties are not commonly associated with the species spissatus, castellanus, or floccus. Opacity-based varieties are not associated with cirrus of any types because the wispy or fibrous species are always translucent while the more dense species are inherently opaque.

• Precipitation-based supplementary features: These are not associated with cirrus clouds because they do not produce any precipitation.
• Accessory cloud: Mamma is cloud-based supplementary feature that can be seen with with cirrus spissatus cumulonimbogenitus (C_H3). It appears as bubble-like downward protuberances from the cloud base and is caused by localized downdrafts in the cloud.
• Genitus mother clouds: Apart from the aforementioned cumulonimbus mother cloud, cirrus fibratus cirrocumulogenitus or altocumulogenitus can form when cirrocumulus or very high altocumulus mother clouds lose some of their stratocumuliform structure and take on a more wispy or fibrous appearance.
• Mutatus mother cloud: Cirrus fibratus cirrostratomutatus forms from a cirrostratus mother cloud when mostly continuous sheets of high cloud break up into more detached wispy or fibrous streaks.

• Genus cirrocumulus (Cc):

This is a pure white stratocumuliform cloud layer of limited convection. It is composed of ice crystals or supercooled water droplets appearing as small unshaded round masses or flakes in groups or lines with ripples like sand on a beach . Cc occasionally form alongside cirrus or cirrostratus clouds at the very leading edge of an active weather system. It is coded C_H9 for all species.

• Species: Cirrocumulus stratiformis (Cc str) is one of four species and appears in the form of relatively flat stratocumuliform sheets or patches. The species lenticularis (Cc len) takes its name from the lens-shaped structure of this cloud which is tapered at each end. Cirrocumulus castellanus (Cc cas) has cumuliform buildups that give the cloud a partly or mainly turreted appearance. When the cumuliform parts have more of a tufted appearance, it is given the species name floccus (Cc flo)

• Varieties: This genus type is always translucent and so has no opacity-based varieties. However, like cirrus, certain cirrocumulus species can sometimes be divided into pattern-based varieties. The undulatus variety has a wavy undulating base and is seen mostly with the stratiformis and lenticularis species types. The lacunosus variety contains circular holes caused by downdrafts in the cloud and is associated mainly with the species stratiformis, castellanus and floccus.

• Precipitation-based supplementary feature: Cirrocumlus occasionally produces virga, precipitation that evaporates before reaching the ground..
• Accessory cloud: Mamma in the form of downward forming bubbles is infrequently seen as a cloud-based supplementary feature.
• Mother clouds: This genus type has no recognized genitus mother clouds. However cirrocumulus stratiformis cirromutatus or cirrostratomutatus can result from sheets or filaments of high cloud taking on a stratocumuliform structure as a result of high altitude convection. A high layer of white or light grey altocumulus of a particular species can thin out into pure white cirrocumulus altocumulomutatus of the same species.

• Genus cirrostratus (Cs):

Cirrostratus is a thin non-convective stratiform ice crystal veil that typically gives rise to halos caused by refraction of the sun's rays. The sun and moon are visible in clear outline. Cirrostratus typically thickens into altostratus ahead of a warm front or low-pressure area.

• Species: Cirrostratus fibratus (Cs fib) is a high fibrous sheet similar to cirrus but with less detached semi-merged filaments. It is reported in the SYNOP code as C_H8 or as C_H5 or 6 (depending on the amount of sky covered) if increasing in amount. If the high cloud covers the entire sky and takes on the form of a featureless veil, it is classified as cirrostratus of the species nebulosus (Cs neb) and is coded C_H7.

• Varieties: Cirrostratus species have no opacity-based varieties as they are always translucent. Two pattern-based varieties are sometimes seen with the species fibratus. These are the closely spaced duplicatus and wavy undulatus types similar to those seen with cirrus fibratus. Pattern-based varieties are not commonly associated with the species nebulosus due to its lack of features.

• Supplementary features: Cirrostratus produces no precipitation or virga, and is not accompanied by any accessory clouds.
• Genitus mother clouds: Cirrostratus fibratus cirrocumulogenitus sometimes appears as the latter cloud flattens and loses some of its stratocumuliform structure. Cirrostratus fibratus cumulonimbogenitus may form if the cirriform top of a mature thundercloud spreads and flattens sufficiently to become a high stratiform cloud..
• Mutatus mother clouds: Cirrostratus fibratus cirromutatus or cirrocumulomutatus are the result of a complete transformation from cirrus and cirrocumulus genus types. Cirrostratus nebulosis altostratomutatus results when a high grey nebulous altostratus layer thins out into a whitish layer of featureless high cloud.