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Cirrocumulus cloud
Cirrocumulus cloud
Cirrocumulus cloud
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Cirrocumulus cloud
Cirrocumulus floccus
AbbreviationCc[1]
GenusCirro- (curl)
-cumulus (heaped)
Species
  • Castellanus
  • Floccus
  • Lenticularis
  • Stratiformis
Variety
  • Lacunosus
  • Undulatus
Altitude6,096–15,000 m
(20,000–49,000 ft)
ClassificationFamily A (High-level)
AppearanceSmall, flakey, and white high-altitude cumulus patches.
PrecipitationOccasionally virga.[2] May form ahead of a frontal system, especially together with other cirriform clouds meaning rain in around 10 hours.

Cirrocumulus is one of the three main genus types of high-altitude tropospheric clouds, the other two being cirrus and cirrostratus.[3] They usually occur at an altitude of 5 to 12 km (16,000 to 39,000 ft), however they can occur as low as 10,000 ft (3.0 km) in the arctic and weather reporting standards such as the Canadian MANOBS suggests heights of 29,000 ft (8.8 km) in summer and 26,000 ft (7.9 km) in winter.[4] Like lower-altitude cumuliform and stratocumuliform clouds, cirrocumulus signifies convection. Unlike other high-altitude tropospheric clouds like cirrus and cirrostratus, cirrocumulus includes a small amount of liquid water droplets, although these are in a supercooled state. Ice crystals are the predominant component, and typically, the ice crystals cause the supercooled water drops in the cloud to rapidly freeze, transforming the cirrocumulus into cirrostratus. This process can also produce precipitation in the form of a virga consisting of ice or snow. Thus, cirrocumulus clouds are usually short-lived.[5] They usually only form as part of a short-lived transitional phase within an area of cirrus clouds and can also form briefly as a result of the breaking up of part of a cumulonimbus anvil.

Properly, the term cirrocumulus refers to each cloud, but is typically also used to refer to an entire patch of cirrocumulus. When used in this way, each cirrocumulus element is referred to as a "cloudlet".[6]

Appearance

[edit]
High cloud weather map symbols

Cirrocumulus is a cloud of the stratocumuliform physical category that shows both stratiform and cumuliform characteristics and typically appears as white, patchy sheets with ripples or tufts without gray shading.[7] Each cloudlet appears no larger than a finger held at arm's length.[5] These often are organized in rows like other cumuliform and stratocumuliform clouds, but since they are so small, cirrocumulus patches take on a finer appearance, sometimes also referred to colloquially as "herringbone" or as a "mackerel sky".[1] Cirrocumulus is coded CH9 for the main genus-type and all subforms.

Cirrocumulus is distinguished from altocumulus in several ways, although the two stratocumuliform genus types can occasionally occur together with no clear demarcation between them. Cirrocumulus generally occur at higher altitudes than altocumulus, thus the "cloudlets" appear smaller, as they are more distant from observation at ground level. They are also colder. Cirrocumulus clouds never cast self-shadows and are translucent to a certain degree. They are also typically found amongst other cirrus clouds in the sky and are usually themselves seen to be transforming into these other types of cirrus.[5] This often occurs at the leading edge of a warm front, where many types of cirriform clouds can be present.

Cirrocumulus clouds on a summer afternoon

Cirrocumulus clouds tend to reflect the red and yellow colours during a sunset and sunrise, so they have been referred to as "one of the most beautiful clouds".[1][8] This occurs because they reflect the unscattered rays of light from the early morning or evening sun, and those rays are yellow, orange, red, and sometimes purple.[9]

Forecasting

[edit]

Cirrocumulus usually only forms in patches. If it forms in patches with cirrus or cirrostratus and the clouds spread across the sky, it usually means rain in 8–10 hours (can be more if the front is slow-moving). Only small patches of cirrocumulus and perhaps some wisps of cirrus usually mean a continuation of good weather (although this may also be seen in conjunction with showers and thunderstorms). If it is seen after rain, it usually means improving the weather.

Subtypes

[edit]
  • Species: Cirrocumulus stratiformis (Cc str) is one of four species and appears in the form of relatively flat stratocumuliform sheets or patches. The species Cirrocumulus 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 Cirrocumulus floccus (Cc flo).[10] Cirrocumulus with castellanus buildups can show some vertical extent, but are not usually classified as vertical or multi-étage clouds.
    • 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.[11]
      • Precipitation-based supplementary feature: Cirrocumulus occasionally produces virga, precipitation that evaporates before reaching the ground.
      • Cloud-based supplementary feature: Mamma in the form of downward forming bubbles is infrequently seen as a cloud-based supplementary feature.[12]
      • 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 stratocumuli form 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.
Cirrocumulus undulatus clouds

References

[edit]
[edit]
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Cirrocumulus cloud

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from Grokipedia
Cirrocumulus clouds are high-level clouds composed primarily of ice crystals, appearing as small, white, rippled patches or layers that often resemble a honeycomb or fish scales, known as a "mackerel sky." They form at altitudes of 20,000 to 40,000 feet (6 to 12 kilometers) in the upper troposphere, where temperatures are cold enough for ice crystal development. These clouds are relatively rare and short-lived, typically emerging from turbulent vertical air currents interacting with existing cirrus layers or from spreading aircraft contrails. Cirrocumulus clouds exhibit a thin, patchy, sheet-like structure with individual elements smaller than one degree in width—roughly the span of a at arm's length—lacking any significant shading or depth. They can appear in various species, including stratiformis (flat sheets), lenticularis (lens-shaped), floccus (tufted), and castellanus (towering), which highlight their diverse formations driven by . Although they do not produce that reaches the ground due to their high and composition, cirrocumulus often signals fair but cold , though in tropical regions, they may precede approaching hurricanes or stormy conditions. Frequently observed alongside cirrus or cirrostratus clouds, cirrocumulus contributes to the dynamic visual spectacle of high-altitude cloud systems, reflecting subtle waves in the upper atmosphere.

Definition and Characteristics

Definition

Cirrocumulus clouds are defined by the (WMO) as a high-level cloud type consisting of thin, white patches, sheets, or layers composed of very small elements in the form of grains, ripples, or waves, without any shading, and often merged or separate. These clouds form part of the high cloud family, which also includes cirrus and cirrostratus, and are typically found at altitudes of 5,000 to 13,000 meters (16,500 to 43,000 feet) within the . In contrast to low- or middle-level clouds, which are mainly composed of water droplets, cirrocumulus clouds are almost exclusively made up of ice crystals, with any supercooled water droplets quickly transforming into ice due to the frigid temperatures at these elevations. The name "cirrocumulus" derives from the Latin "cirrus," meaning a curl or lock of hair, and "cumulus," meaning a heap or pile, capturing their characteristic small, heaped, and rippled appearance. This compound term was introduced by English and Luke Howard in his seminal 1803 essay "On the Modification of ," which established the foundational system for classifying cloud types still used today.

Physical Properties

Cirrocumulus clouds are primarily composed of ice crystals, with supercooled droplets occasionally present in the cloudlets at temperatures below 0°C but above approximately -40°C, where the remains despite the cold environment. These supercooled droplets are typically short-lived, as they rapidly freeze upon contact with ice crystals, leading to a predominantly icy . The clouds exhibit low , typically around 0.025 g/m³ or less, which contributes to their thin optical thickness and high transparency, preventing the casting of on the ground. This low opacity arises from the sparse distribution of particles in the upper , allowing to pass through with minimal . Cirrocumulus clouds form at high altitudes, generally between 5 and 13 km in mid-latitudes, though this range varies regionally: 3 to 8 km in polar areas and 6 to 18 km in tropical regions. Associated temperatures span -20°C to -60°C, conditions that favor the formation and persistence of ice crystals over liquid water. The individual cloudlets, or elements, of cirrocumulus are small, with diameters of 1 km or less, and are spaced several kilometers apart, often 1 to 3 km, creating a patterned arrangement in the . This scale reflects the convective instability at cirrus levels, where the high altitude classifies them as part of the upper cloud tier.

Formation and Appearance

Formation Mechanisms

Cirrocumulus clouds form in the upper primarily through atmospheric instabilities that perturb existing cirrus or cirrostratus layers, leading to adiabatic cooling and development in air, where temperatures typically range from -20°C to -60°C. As air ascends due to synoptic-scale lifting or convective processes, it expands and cools at a rate of approximately 9.8°C per kilometer in dry conditions or slower in moist air, leading to with respect to . This triggers heterogeneous of on atmospheric aerosols such as mineral dust or particles, initiating formation; homogeneous can also occur at temperatures below -38°C when sufficient relative is reached. Atmospheric instabilities and wave motions play a key role in shaping cirrocumulus structures, often perturbing existing cirrus or cirrostratus layers to produce the characteristic rippled appearance. Kelvin-Helmholtz instability arises from between layers of differing velocities, generating wave-like undulations or breaking waves (fluctus) on the upper surface of high-level clouds, which promote localized cooling and growth. These instabilities are common in regions of strong vertical , such as near jet streams. Additionally, cirrocumulus can develop from the spreading or degradation of cirrus clouds or from the transformation of altocumulus elements (altocumulomutatus), where or turbulent vertical currents interact with a preexisting layer to create small, puffy elements. Cirrocumulus can also form from the spreading and evolution of persistent aircraft contrails (homogenitus) under upper-level . Upper-level fronts and jet stream perturbations provide the necessary lift for cirrocumulus development by forcing air ascent along isentropic surfaces in the mid- to upper . Warm fronts or troughs associated with s induce large-scale rising motion, cooling the air and fostering ice supersaturation, particularly in regions of divergent flow at the jet entrance or exit. Cirrocumulus often emerges in these dynamic environments as a transient feature.

Visual Characteristics

Cirrocumulus clouds present as small, rounded white cloudlets arranged in patches or thin layers, evoking a sense of delicate, high-altitude . These elements, often smaller than the width of a at arm's length, form regular patterns such as rows, waves, or honeycomb-like ripples across the sky. A distinctive "" arises when cirrocumulus cloudlets densely populate much of the sky, their uniform spacing mimicking the scales of a mackerel fish. This rippled, dappled texture results from the clouds' lack of self-shading or shadows, as their thin ice-crystal composition allows to pass through translucently. Typically fleeting and transient, cirrocumulus formations appear in patchy sheets that seldom dominate the entire sky, dissolving quickly due to upper-level winds. Their colors remain predominantly pure white against clear blue backgrounds, though they may appear light gray in denser arrangements or adopt warm red and yellow hues near sunrise or sunset. This fine, distant appearance stems from their high-altitude perch, rendering the cloudlets sharp yet remote to ground observers.

Classification

Species

The species of cirrocumulus clouds are defined by their primary structural forms, as outlined in the (WMO) . These species—stratiformis, lenticularis, floccus, and castellanus—distinguish the clouds based on their arrangement, shape, and internal organization, while maintaining the genus's characteristic thin, white appearance without shading. Cirrocumulus stratiformis (abbreviated Cc str) appears as a relatively extensive horizontal sheet or layer composed of small elements, such as grains or ripples, which may be merged or separate and sometimes interrupted by breaks. This species is identified by its broad, layered arrangement with low opacity, allowing the sky to be visible through the cloudlets. Cirrocumulus lenticularis (Cc len) consists of isolated, lens- or almond-shaped patches that are often elongated with well-defined outlines. The arrangement is typically in more or less discrete formations, emphasizing the species's distinct, rounded contours and uniform thinness across the elements. Cirrocumulus floccus (Cc flo) consists of very small cumuliform tufts, the lower parts of which are more or less ragged, with the apparent width of each tuft always less than one degree. This species often shows a tufted appearance with frayed edges. Cirrocumulus castellanus (Cc cas) features elements that are vertically developed into small turrets or protuberances rising from a common horizontal base, giving a crenellated or turret-like structure to portions of the cloud. Diagnostic identification relies on the presence of these cumuliform upper extensions amid the otherwise flat arrangement, with the overall opacity remaining translucent. Among these, cirrocumulus stratiformis is the most prevalent , forming widespread layers, while lenticularis is rarer and more localized in occurrence. In meteorological coding, the are denoted by WMO abbreviations (str for stratiformis, len for lenticularis, flo for floccus, cas for castellanus) within the cirrocumulus genus code (Cc), facilitating precise observation and reporting based on opacity (thin and non-shading) and spatial arrangement (sheet-like, lens-shaped, tufted, or turreted).

Varieties

In the classification of cirrocumulus clouds according to the (WMO), varieties represent supplementary features that modify the arrangement, pattern, or transparency of the cloud's primary species without altering the high-level cirrocumulus genus. These features enhance observational detail and are identified through visual patterns in the sky, often combining with species like stratiformis for precise nomenclature. The undulatus variety exhibits wavy or undulating patterns across the cloud layer, where elements form regular, wave-like ridges perpendicular to the wind direction. This appearance arises from , in which differing wind speeds at adjacent altitudes create instabilities that ripple the thin ice crystal sheets. Such formations are common in cirrocumulus and indicate dynamic upper-atmospheric conditions without implying changes to the cloud's overall structure. The lacunosus variety is distinguished by circular or tear-like holes within the cloud sheet, giving a net-like or perforated texture as if the cloud has been "torn" apart. These openings form through the mixing of a cooler overlying air layer with warmer air below, which promotes localized evaporative cooling and sublimation of ice crystals, leading to rapid clearing in those patches. In cirrocumulus, this variety often appears transiently, highlighting instability at high altitudes around 5–13 km. Identification of these varieties in cirrocumulus relies on observing the dominant macroscopic arrangement or from the ground, allowing multiple varieties to coexist; they supplement but do not redefine the .

Meteorological Significance

Weather Associations

Cirrocumulus clouds are typically associated with stable, fair weather conditions in mid-latitudes, often appearing under high-pressure systems where limits significant vertical development. These clouds indicate clear skies with minimal surface impacts, though their presence can sometimes precede convective activity from lower levels. In synoptic settings, cirrocumulus may occur in the warm sectors of mid-latitude cyclones or ahead of cold fronts, signaling the presence of upper-level moisture and potential . High clouds like cirrocumulus often form through gradual uplift in these environments, providing an early indicator of approaching weather changes without immediate . Due to their high altitude and composition of thin ice crystals, cirrocumulus clouds rarely produce direct that reaches the surface, as any evaporates well before ground level. However, they can evolve into denser forms such as cirrostratus or contribute to the development of lower-altitude clouds if moisture increases. Cirrocumulus clouds exhibit seasonal patterns, appearing more frequently in winter in mid-latitudes. This winter preference aligns with enhanced stability and in extratropical regions during colder months. Globally, cirrocumulus are common in temperate zones, occurring above 5 km (16,500 ft), but less prevalent in tropical regions where they occur above 6 km (20,000 ft) due to higher levels that shift their formation thresholds. In polar areas, they occur above 3 km (10,000 ft), reflecting latitudinal variations in atmospheric structure.

Forecasting Implications

Cirrocumulus clouds serve as indicators of potential weather changes when their coverage thickens or increases, possibly preceding such as or within 12–24 hours in association with approaching systems. This predictive value stems from their association with upper-level moisture advection ahead of advancing systems, where initial sparse formations may evolve into denser layers as mid-level instability builds. In contexts, cirrocumulus clouds, particularly the standing lenticular variety (CCSL), signal potential associated with atmospheric waves, such as those induced by mountainous terrain. Pilots are advised to avoid these formations due to the risk of moderate to severe , and such conditions may prompt the issuance of warnings for en-route hazards above typical flight levels. Satellite and radar detection plays a key role in monitoring cirrocumulus for , as these thin high-level clouds appear as subtle, cold signatures—often bright white pixels—in due to their elevated, icy composition. In geostationary observations like those from GOES, they manifest as patchy, high-top reflectors with low brightness temperatures, aiding in the identification of upper-tropospheric dynamics, though conventional radars detect them weakly owing to minimal content. Historically, meteorologists have utilized cirrocumulus observations since the for front analysis, incorporating cloud type symbols into synoptic charts to track approaching pressure systems and moisture influx. Luke Howard's 1803 cloud classification system formalized their recognition, enabling early forecasters to sequence high-cloud progressions as precursors to barometric shifts and events. In modern applications, cirrocumulus features are integrated into models like the ECMWF Integrated Forecasting System for upper-air diagnostics, where high-cloud parameterizations help validate moisture and stability profiles in the . These models employ diagnostic schemes to simulate cirrocumulus evolution, improving forecasts of interactions and frontal passages by assimilating satellite-derived data into ensemble predictions.

References

  1. https://weather.metoffice.gov.uk/learn-about/weather/types-of-weather/clouds/high-clouds/cirrocumulus
  2. https://www.noaa.gov/jetstream/clouds/ten-basic-clouds
  3. https://www.nesdis.noaa.gov/about/k-12-education/atmosphere/types-of-clouds
  4. https://cloudatlas.wmo.int/cirrocumulus-cc.html
  5. https://cloudatlas.wmo.int/some-useful-concepts-levels.html
  6. https://cloudatlas.wmo.int/en/observation-of-clouds-from-aircraft-descriptions-cirrocumulus.html
  7. https://www.rmets.org/cloud-identification
  8. https://cloudatlas.wmo.int/en/cirrocumulus.html
  9. https://journals.ametsoc.org/view/journals/apme/29/9/1520-0450_1990_029_0970_asotpp_2_0_co_2.xml
  10. https://journals.ametsoc.org/view/journals/amsm/58/1/amsmonographs-d-16-0010.1.xml
  11. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2004JD004803
  12. https://www.weather.gov/source/zhu/ZHU_Training_Page/clouds/cloud_development/clouds.htm
  13. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/cirrus-clouds
  14. https://cloudatlas.wmo.int/clouds-supplementary-features-fluctus.html
  15. https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/clouds/high-clouds/cirrocumulus
  16. https://cloudatlas.wmo.int/cirrocumulus-homogenitus.html
  17. https://commons.erau.edu/cgi/viewcontent.cgi?article=1009&context=mcnair
  18. https://scied.ucar.edu/image/cirrocumulus-clouds
  19. https://scool.larc.nasa.gov/tutorial/clouds/cloudtypes_transcript.html
  20. https://cloudatlas.wmo.int/species-cirrocumulus-stratiformis-cc-str.html
  21. https://cloudatlas.wmo.int/clouds-species-stratiformis.html
  22. https://cloudatlas.wmo.int/species-cirrocumulus-lenticularis-cc-len.html
  23. https://cloudatlas.wmo.int/clouds-species-lenticularis.html
  24. https://cloudatlas.wmo.int/species-cirrocumulus-floccus-cc-flo.html
  25. https://cloudatlas.wmo.int/clouds-species-floccus.html
  26. https://cloudatlas.wmo.int/species-cirrocumulus-castellanus-cc-cas.html
  27. https://cloudatlas.wmo.int/clouds-species-castellanus.html
  28. https://cloudatlas.wmo.int/abbr-and-symbols-of-clouds-table-genera-species.html
  29. https://cloudatlas.wmo.int/clouds-varieties.html
  30. https://cloudatlas.wmo.int/cloud-classification-summary.html
  31. https://www.eoas.ubc.ca/books/Practical_Meteorology/prmet/Ch06-Clouds.pdf
  32. https://www.weatherbriefing.com/weather-blog/2019/9/29/cirrocumulus-lacunosis-clouds
  33. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/cirrocumulus-clouds
  34. https://www.weatherwizkids.com/weather-clouds.htm
  35. https://cloudatlas.wmo.int/observation-of-clouds-from-aircraft-descriptions-cirrocumulus.html
  36. https://www.weather.gov/fgz/CloudsContrails
  37. https://www.weather.gov/source/zhu/ZHU_Training_Page/turbulence_stuff/turbulence/turbulence.htm
  38. https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap7_section_1.html
  39. https://cimss.ssec.wisc.edu/satmet/modules/4_clouds/clouds-3.html
  40. https://journals.ametsoc.org/view/journals/bams/100/12/bams-d-19-0071.1.xml
  41. https://journals.ametsoc.org/view/journals/mwre/130/2/1520-0493_2002_130_0257_aotemc_2.0.co_2.xml
  42. https://www.ecmwf.int/sites/default/files/elibrary/2015/17326-skill-ecmwf-cloudiness-forecasts.pdf
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