Cirrus Clouds – Feathery Wisps That Can Foretell The Weather

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cirrus spissatus cloud
Cirrus spissatus cloud

What Are Cirrus Clouds?

Thin, wispy clouds of the Cirrus type are frequently found in the atmosphere. The name derives from the Latin word cirrus, meaning a lock of curly hair because the clouds appear to be locks of hair.

Such a cloud can appear at altitudes between 5,000 and 13,700 m (16,500 and 45,000 ft) above sea level. “Mares’ tails” tufts are sometimes formed when strands of cloud develop into tufts.

At elevations above 5,500 m (18,000 ft) in temperate regions or 6,400 m (21,000 ft) in tropical locales, water vapor sometimes becomes deposited (goes from water vapor directly to ice crystals without the usual intermediate stage of being a liquid) and forms cirrus clouds, which appear white or light grey.

There are three types or shapes of cirrus clouds: tufted, ragged, and filamentary.

Mares tails clouds cirrus
Mares tails

They are also formed from tropical cyclones’ outflows, cumulonimbus anvil clouds, and thunderstorms. They also foretell storm fronts that are associated with deteriorating weather conditions, appearing in advance of them.

These clouds can show precipitation, but they usually create thin ice-crystal ‘fall streaks’ that evaporate as they fall through drier, hotter air (virga).

A jet stream-powered cirrus can extend across continents while staying only a few kilometers deep, resulting in optical phenomena such as sun dogs and halos. The light that interacts with the ice crystals creates them.

The presence of cirrus clouds is said to increase the temperature of the air beneath the main cloud layer by as much as 10 °C (18 °F). When the cloud becomes so large that it blends in with other cirrus clouds, it forms a high cloud layer known as cirrostratus.

Jet stream cirrus clouds
Jet stream cirrus clouds as seen from outer space

Small cloud tufts comprised of supercooled water droplets create the cirrocumulus cloud genus at high altitudes, where convection occurs. Polar stratospheric clouds can mimic Cirrus clouds. Noctilucent clouds are typically structured like Cirrus clouds.

On Mars, Jupiter, Saturn, Neptune, and Uranus, cirrus clouds can also form in the atmosphere, and they have been seen on Titan, a large moon of Saturn.

Ammonia or methane ice are thought to form part of these extraterrestrial cirrus clouds, just as they do terrestrial water ice. (Cirrus clouds are also known as interstellar clouds composed of sub-micrometer-sized dust grains.

10 Facts About Cirrus Clouds

  1. Cirrus clouds are made of ice crystals.
  2. They form at high altitudes, typically between 16,500 and 45,000 feet.
  3. They have a wispy and feathery appearance.
  4. They are the highest type of clouds.
  5. They are usually found in the troposphere.
  6. Their appearance can identify them, often appearing as horse’s tails, castle turrets, or tufts of wool.
  7. Their transparency depends on the degree of separation of the ice crystals.
  8. They may veil or obscure the sun’s light when exceptionally thick.
  9. Cirrus clouds are typically white or light gray in color.
  10. When they cross the sun’s disk, they hardly diminish its brightness.

Types of Cirrus Clouds

Cirrus clouds are one of the four main types of clouds and belong to the cirro-form category. They are identified by their wispy, hair-like appearance and are composed of ice crystals, which makes them appear whitish.

Cirrus clouds are typically found at high altitudes and appear short and detached from one another. There are several variations of cirrus clouds based on species and varieties, including

  • Cirrus spissatus
  • Cirrus fibratus radiatus
  • Cirrus uncinus
  • and Cirrus fibratus.

These variations differ in their shape and appearance, with some having the traditional mares tail appearance and others having long, fibrous, and curved shapes with no tufts or curls at the ends.

How Do Cirrus Clouds Form?

At high altitudes, water vapor is deposited and forms cirrus clouds. The atmospheric pressure ranges from 600 mBar at 4,000 m (13,000 ft) to 200 mBar at 12,000 m (39,000 ft) beyond sea level. A warm front is usually the first stage of a front.

The ice crystals that compose cirrus clouds are formed from supercooled water droplets that freeze at temperatures below -20 °C or -30 °C. Because humidity is low at such high altitudes, this type is usually quite thin. Cirrus clouds form in fair weather in zones in which the air temperature is below -20 °C or -30 °C.

Turbulence and wind shear, or convection in the upper troposphere, can cause these clouds to form. They are named after and resemble Mammatus clouds, swollen balls that flatten from the top of a dying cumulonimbus.

Mammatus clouds
Mammatus clouds over nebraska after a tornado. Photographer by jorn c. Olsen

What Do Cirrus Clouds Look Like?

Cirrus clouds comprise ice crystals of assorted sizes and shapes. In addition to solid columns, hollow columns, plates, rosettes, and other forms, ice crystals can be shaped in numerous ways. The temperature of the air, the atmospheric pressure, and the degree of supersaturation with ice determine the shape of the ice crystals.

A Cirrus cloud comprises ice crystals ranging from 0.25 millimeters to 4.9 meters (1,500 to 26,000 meters). The thickness of a Cirrus cloud ranges from 100 meters (330 feet) to 8,000 meters (26,000 feet). Even though their lengths vary from as little as 0.01 millimeters to as much as several millimeters, these ice crystals are normally around 0.25 millimeters long.

Contrails are created when hot jet exhaust collides with ice-cold upper-atmosphere air, creating tiny ice crystals. These crystals are 0.001 to 0.1 millimeters in length. Temperatures in cirrus clouds vary from −20 °C to −30 °C.

Cirrus clouds weather

In temperate zones, the clouds are typically divided into two types: the columns and plates are near the bottom, while the rosettes and conglomerations are near the top.

The only types of crystals in the northern Arctic region are plates, columns, and conglomerations. These crystals are four times bigger than the smallest ones. In Antarctica, the only type of cirrus cloud comprises only columns, which are considerably longer than usual.

Many applications have been used to study Cirrus’s characteristics. LiDAR provides precise measurements of the cloud’s altitude, length, and width.

Although balloons carry them, cirrus cloud hygrometers do not give sufficient information on the cloud’s thickness. Radar units provide altitudes and cirrus cloud thicknesses.

The Stratospheric Aerosol and Gas Experiment (SAGE) program provides information from satellites monitoring infrared radiation. CIRRUS clouds are detected by observing where infrared radiation is absorbed in the atmosphere.

The MODIS instrument on the NASA Terra and Aqua satellites measures the spectral signatures of reflected infrared radiation from cirrus clouds during the day. It detects night infrared emissions from the Earth to determine the amount of cirrus coverage.

Satellites can detect the “shadow” this cloud casts into space by looking at the cloud from space. Additional information about cirrus clouds is provided by aircraft or ground observations.

The cirrus cloud cover was monitored in the United States to determine whether it was affected by the time of day or season. The researchers found that 23% of the United States land area at noon in the summer was covered by cirrus clouds. Around midnight, cirrus cloud cover extended to about 28%.

Cirrus floccus cirrus uncinus x

The cirrus cloud cover did not change much from day to night during the winter. These percentages include clear days and nights as well as days and nights with other cloud types when no cirrus cloud cover is present.

Based on satellite information, Cirrus covers around 20% to 25% of the Earth’s surface when these clouds are present. The average coverage here is 30% to 50%. This cloud covers around 70% of the region’s exterior area in tropical areas.

Virga – Falling Ice Crystals From Cirrus Clouds

Virga cirrus clouds weather
Virga – cirrus clouds where the ice crystals become too heavy and fall and evaporate before they hit the ground

Fall streaks, hair-like filaments produced in cirrus clouds, are composed of heavier ice crystals that descend from the cloud. The wind shear determines the size and shape of fall streaks.

There are four species of Cirrus, namely castellanus, fibratus, spissatus, and uncinus, all of which are subdivided into four varieties: intortus, vertebratus, radiatus, and duplicatus. Because high-altitude convection builds up from the main cloud body, cirrus castellanus has cumuliform tops.

Among the cirrus species, Cirrus fibratus appears striated and appears frequently. Cirrus uncinus clouds appear curved and are commonly referred to as mare’s tails. Among the variations, Cirrus intortus has a particularly convoluted form, and cirrus radiatus has cirrus clouds with large radial zones that spread across the sky.

Vertical wind shear has distorted a type of cirrus intortus known as Kelvin-Helmholtz waves into loops.

Cirrus castellanus clouds
Cirrus-castellanus clouds
Cirrus fibratus clouds
Cirrus fibratus clouds
Cirrus spissatus cloud
Cirrus spissatus cloud
Cirrus uncinus clouds
Cirrus uncinus clouds

Cirrus Clouds In Cyclones, Tropical Storms, and Hurricanes

There are difficulties detecting the eye and rainbands in satellite photos of hurricanes and typhoons because of the extensive shield of Cirrus and cirrostratus that often follows the high-altitude outflow.

Cirrus clouds and cyclones hurricanes weather
Satellite image of cirrus clouds emanating out of a tropical disturbance

Thunderstorms and Cirrus Clouds

A cumulonimbus thunderstorm cloud can produce thick Cirrus at its summit. As the cumulonimbus cloud rises vertically, the liquid water droplets freeze as the air temperature approaches freezing.

Because the tropopause temperature inversion prevents the warm, moist air that creates the thunderstorm from rising any higher, the anvil cloud appears as a flat top.

Copious quantities of Cirrus are rarely produced from the anvils of these thunderstorms in the tropics. This dense mat of high-altitude winds is pushed out into an anvil frame that extends downwind for several kilometers.

A cumulonimbus cloud’s anvil can produce individual cirrus clouds as it dissipates or dies. The mat of cirrus in the anvil remains when the rising column of cumulonimbus clouds has disappeared or evaporated.

Cumulo nimbus with anvil cirrus
Cumulonimbus (thunderstorm) with anvil cirrus

Contrails

Persisting, jet-engine-produced clouds of ice crystals and water vapor, known as contrails, are formed when hot jet exhaust mixes with cold upper-atmosphere air.

A jet engine’s exhaust produces water vapor, which freezes on dust and other air particles to form artificial cirrus clouds called contrails. Whether the air surrounding a jet engine’s exhaust or the exhaust itself produces particles, water vapor from its exhaust freezes on them and forms a visible track.

Exhausts can also provide ice nuclei, causing cirrus formations when the atmosphere is inadequately stocked with naturally-occurring ice accumulation.

Increased air traffic has been connected to the increase in Cirrus in Earth’s atmosphere, which is thought to be caused by the formation of contrails. Cirrus are formed when water vapor in the air condenses onto ice crystals, which are produced when water vapor in the air comes into contact with ice crystals.

Are Cirrus clouds a sign of bad weather?

Irregular, isolated Cirrus clouds are of little significance. The presence of a large number of cirrus clouds may foreshadow a frontal system or upper air disturbance. If a cirrus castellanus is present, there may be significant instability at high altitude levels. This suggests that weather change is imminent and storms will soon be prevalent.

When cirrus clouds radiatus or fibratus expand and disperse, an incoming weather front is usually signified. If it is a warm front, the cirrus clouds transform into cirrostratus, which also thickens and lowers into altocumulus and altostratus.

The nimbostratus clouds are the ones that bring rainfall. When cirrus clouds accompany a cold front, squall line, or multicellular thunderstorm, they are dislodged from the anvil. The cumulonimbus clouds are the next to appear. Kelvin-Helmholtz waves indicate extreme wind shear at high altitudes.

Forecasters and meteorologists in the tropics were able to foretell the arrival of a tropical cyclone 36 hours before the center passage by noting the advance of a veil of white cirrus clouds from the cyclone’s direction. These clouds were noted in the late 19th century.

Father Benito Viñes formed the first hurricane forecasting system at Belén College in Havana, Cuba, in the early 1870s. He based his predictions on the clouds’ movements.

Viñes began collecting data on hurricanes in the West Indies and studying their patterns after spending hours observing clouds. He subsequently recorded his findings in his book Apuntes Relativos a los Huracanes de las Antilles.

Cirrus castellanus cloud
Cirrus castellanus cloud

Effects on climate

Thin and translucent cirrus clouds cover 0% to 25% of the Earth (up to 70% in the tropics). They contribute to global warming by absorbing infrared radiation while only marginally reflecting incoming sunlight. When cirrus clouds are 100 meters (330 feet) deep, they reflect only about 9% of the incoming sunlight.

Most clouds still block almost 50% of the outgoing infrared radiation from leaving, thus raising the temperature of the atmosphere below the clouds by an average of 10 °C (18 °F), a process known as the greenhouse effect. Globally, cloud formation occurs due to a temperature loss of 5 °C (9 °F) at the earth’s surface, mainly due to stratocumulus clouds.

Scientists have theorized that global warming may be partially caused by thin cirrus clouds, which have warming effects. Global warming may be caused by high thin cloud cover, resulting in higher temperatures and humidity.

An increased cirrus cloud cover would result from this theory, resulting in a ripple effect or a more extensive impact from a smaller one. According to this theory, the Cirrus clouds would rise higher as temperatures increased, resulting in more air volume beneath the clouds and more infrared radiation bounced back down to Earth.

The notion postulates that the temperature rise might cause cirrus clouds to expand, thus equalizing the reflection of solar and terrestrial infrared radiation.

Richard Lindzen has proposed a similar iris hypothesis in which an increase in tropical sea surface temperatures causes fewer cirrus clouds, resulting in more infrared radiation being emitted into space.

Weather and Optical Phenomena – Halos

Sun halo cirrus clouds weather
Sun halo caused by cirrus clouds.

Cirrus clouds can produce various optical effects, such as halos around the sun and moon. Halos are created when light interacts with hexagonal ice crystals that are already in the clouds, resulting in a wide range of white and colored rings, arcs, and spots in the sky. The 22° halo, the circumzenithal arc, sun dogs, and the circum horizontal arc (also known as fire rainbows) are all well-known halo varieties.

Fire rainbows
Fire rainbows – weather phenomena

Cirrus clouds produce brighter and more colorful halos than those produced by cirrostratus.

Cirrus clouds are occasionally capable of producing glories, a type of cloud that is normally composed of liquid water. Glory is a set of concentric, pale rings that form around the observer’s shadow and can be best seen from a distance or in the air.

Only when forming ice crystals are aspherical do cirrus clouds produce glories. According to researchers, ice crystals must be between 0.009 and 0.015 millimeters in length to produce glories.

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Relation to Other Clouds

High-étage clouds (5,000 m [16,500 ft] and higher) are one of three types of high-étage clouds. Cirrus clouds are one of three high-étage clouds appearing in temperate regions. The other two types are cirrocumulus and cirrostratus clouds.

The mid-étage clouds, which exist between 2,000 and 7,000 m (6,500 and 23,000 ft) in temperate regions, are divided into two or three categories depending on the classification method used. According to the WMO classification, these clouds are nimbostratus. They are composed of ice crystals, supercooled water droplets, or liquid water droplets.

Stratus and stratocumulus clouds are the two types of low-étage clouds, which are located at elevations less than 2,000 m (6,500 feet). These clouds are composed of water droplets, except those made of supercooled water droplets or ice crystals when the temperature at the cloud level is subfreezing.

Cumulus and cumulonimbus clouds, which are two distinct genera, usually begin in the low elevation range. However, they may be positioned at higher levels if the humidity is extremely low. Nimbostratus is often grouped with cumulus and cumulonimbus as clouds of vertical development, mainly when their tops are composed of supercooled water droplets or ice crystals.

Cirrus clouds, which are high-level clouds, vary significantly in height with latitude. At the poles, they measure 3,000 m (10,000 feet) in height or less, while at the equator, they rise as high as 7,600 m (25,000 feet). In tropical regions, the height varies from about 6,100 m (20,000 feet) to about 18,000 m (60,000 feet).

At latitudes below the Arctic Circle, they range from 5,000 m (16,500 ft) to 14,000 m (45,000 ft) in height—contrasting with low-étage clouds, which do not change altitude with latitude.

The family of high clouds consists of three main types: cirrus, cirrocumulus, and cirrostratus. Because cirrostratus clouds are composed almost exclusively of ice crystals, they are responsible for halos. Cirrocumulus and cirrostratus are occasionally called “cirriform clouds” because of their association with Cirrus.

Though cirrocumulus clouds are classified as cumuliform, their structure is more relevant to their altitude range than their physical structure. For example, the Altostratus and deeper-based sheet clouds are stratiform, and the cirrocumulus clouds are cumuliform.

Cirrocumulus

Cirrocumulus
Cirrocumulus

Cirrocumulus clouds are composed of sheets or patches of uniform, rippling patterns or rows of clouds with clear areas. They are formed through convective processes, just as other cumuliform classes.

We may expect unsettled weather when cirrocumulus clouds develop large patches at high altitudes. The ice crystals in the bottoms of these clouds tend to be hexagonal cylinders. The stepped funnels develop from the ends rather than being solid.

The ice crystals near the summit of these clouds clump together to form Cirrus clouds. Since the upward convection of water vapor continues to accumulate on the crystals as the cloud ascends, it ultimately begins to fall and evaporate, resulting in a Cirrus cloud.

There are four types of cirrocumulus clouds: stratiformis, lenticularis, floccus, and castellanus. When the supercooled water droplets are of equal size, they appear iridescent.

Cirrostratus

Cirrostratus fibratus undulatus halo x
Cirrostratus clouds

The sun or moon may be seen through a milky sheen in the sky or a striated layer of cirrostratus clouds. Cirrostratus clouds may be altostratus or cirrostratus, with the former being distinguishable from the latter because altostratus is usually either opaque or semitransparent, whereas cirrostratus is usually transparent.

There are two species of cirrostratus clouds, fibratus, and nebulosus. The crystals in these clouds vary in size depending on the elevation. The crystals are hexagonal, six-sided columns at the base, where temperatures are about −35 to −45 °C (−31 to −49 °F).

At temperatures of about −47 to −52 °C (−53 to −62 °F), the dominant crystal types near the top of the cloud are hexagonal deep plates and short, solid, hexagonal columns. These clouds usually produce halos; occasionally, the corona is the only indication that they are present.

Warm fronts cause the clouds to become thicker and lower in altitude, creating altostratus clouds. Cirrostratus clouds become thicker and descend when a front approaches, signaling rain. It usually begins raining 12 to 24 hours later.

Cirrus Clouds On Other Planets

Cirrus clouds have been observed in numerous other worlds. The Martian Lander Phoenix captured a time-lapse photograph of a flock of cirrus clouds moving across the Martian sky using LiDAR on September 18, 2008.

Phoenix had observed thin clouds near the north pole of Mars shortly before the end of its mission. They thickened, sank, and then began to snow. The total water content or precipitation was only a few thousandths of a millimeter. James Whiteway from York University states that “precipitation is a component of the Martian hydrologic cycle.”

At ground level, these clouds formed one layer around 4,000 m (13,000 ft) above ground during Martian night. They lasted through the early morning before being cooked away by the sun.

These ice clouds had crystals that were produced at a temperature of −65 °C (−85 °F) and shaped like irregular ellipsoids 0.127 millimeters long and 0.042 millimeters wide.

Cirrus clouds on Jupiter are made of ammonia. According to Glenn Orten, the disappearance of Jupiter’s South Equatorial Belt was concealed from view by a large quantity of ammonia cirrus clouds.

Cassini discovered Cirrus clouds made of water ice on Saturn’s satellite Titan and thin Cirrus clouds on Saturn. Cirrus clouds consisting of methane ice exist on Uranus. On Neptune, wispy, thin clouds that may be Cirrus were observed over the Great Dark Spot. Like those on Uranus, these clouds are presumably made of methane crystals.

These cirrus clouds are composed of dust grains measuring less than a micrometer. As a result, they do not consist of ice crystals or other frozen liquids, which are real cirrus clouds. They may span anywhere from a few light-years to dozens of light-years.

Despite being dust clouds rather than cirrus clouds, they are called “cirrus” since they resemble Earth’s clouds. The dust clouds also reflect infrared radiation like cirrus clouds on Earth reflect heat radiated outward into space.

Sol clouds color
Curiosity rover captures cirrus-type clouds on the planet mars

People Also Ask

What Are Cirrus Clouds a Sign Of?

The presence of cirrus clouds may signify diverse weather patterns, depending on the type of clouds present. These clouds may signal fine and mild weather, or they might foretell unsettled or stormy weather, or even cyclones and hurricanes.

Do Cirrus Clouds Bring Rain?

The presence of cirrus clouds may signify diverse weather patterns, depending on the type of clouds present. These clouds may signal fine and mild weather, or they might foretell unsettled or stormy weather, or even cyclones and hurricanes.

Why Are Cirrus Clouds So Thin?

The thin cirrus clouds that form at such high elevations are caused by the freezing of supercooled raindrops, which freeze when the air temperature is -20 °C or -30 °C. Someone standing on the ground might think these clouds are thin, but they are actually kilometers high and long.

What Causes Cirrus Clouds To Form?

When dry air rises and water vapor is displaced into ice (turning from a gas into a solid), cirrus clouds are created. Cirrus clouds are composed solely of ice crystals, resulting in their white color and diverse forms and sizes.

Why cirrus clouds do not rain?

Cirrus clouds do not typically produce rain as they are made of small ice crystals that usually sublimate prior to reaching the ground. Instead, precipitation from cirrus clouds usually forms falling ice that has broken up but is not enough to reach the ground as rain. Although isolated cirrus clouds do not bring rain, large amounts of cirrus can indicate an approaching storm system, which may eventually lead to rain.

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