Fractus cloud
Encyclopedia
Fractus clouds are small, ragged cloud
fragments that are usually found under an ambient cloud base
. They form or have broken off from a larger cloud, and are generally sheared by strong wind
s, giving them a jagged, shredded appearance. Fractus have irregular patterns, appearing much like torn pieces of cotton candy
. They change constantly, often forming and dissipating rapidly. They do not have clearly defined base
s. Sometimes they are persistent and form very near the surface. Common kinds include scud and cloud tags.
Fractus are accessory cloud
s, named for the type of cloud from which they were sheared. The two principal forms are cumulus fractus (formerly, fractocumulus) and stratus fractus (formerly, fractostratus). Fractus clouds may develop into cumulus
if the ground heats enough to start convection. Stratus fractus is distinguishable from cumulus fractus by its smaller vertical extent, darker color, and by the greater dispersion of its particles.
Cumulus fractus clouds actually look like ragged cumulus clouds. They may originate from dissipated cumulus clouds, appearing in this case as white ragged clouds located at significant distances from each other. Cumulus fractus in particular form on the leading and trailing edges of summer storms in warm and humid conditions. Observing fractus gives an indication of wind movements under the parent cloud.
Masses of multiple fractus clouds, located under a main cloud, are called pannus.
Fractonimbus are a form of stratus fractus, developing under precipitation clouds due to turbulent air movement. They are dark-gray and ragged in appearance. Fractonimbus exist only under precipitation clouds (such as nimbostratus, altostratus
or cumulonimbus
), and don't produce precipitation themselves. Fractonimbus may eventually merge completely with overlying nimbostratus clouds.
, then the thunderstorm is still developing. Scud are common and are usually insignificant. However, scud precede wall clouds, which often form from rising scud.
In addition to forming in inflow
, fractus also form in outflow
. Scud are very common on the leading edge of a thunderstorm where warm, moist air is lifted by the gust front. Scud are usually found under shelf clouds.
Cloud
A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...
fragments that are usually found under an ambient cloud base
Cloud base
This article refers to meteorology. For the airborne base of the TV series Captain Scarlet and the Mysterons, see Cloudbase.The cloud base is the lowest altitude of the visible portion of the cloud...
. They form or have broken off from a larger cloud, and are generally sheared by strong wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
s, giving them a jagged, shredded appearance. Fractus have irregular patterns, appearing much like torn pieces of cotton candy
Cotton candy
Cotton candy , candy floss or candyfloss or candy buttox , or fairy floss is a form of spun sugar. Since cotton candy is mostly air, a small initial quantity of sugar generates a tremendously greater final volume, causing servings to be physically large and voluminous...
. They change constantly, often forming and dissipating rapidly. They do not have clearly defined base
Cloud base
This article refers to meteorology. For the airborne base of the TV series Captain Scarlet and the Mysterons, see Cloudbase.The cloud base is the lowest altitude of the visible portion of the cloud...
s. Sometimes they are persistent and form very near the surface. Common kinds include scud and cloud tags.
Forms
Accessory cloud
An accessory cloud is a cloud which is dependent on a larger cloud system for its development and continuance. It is often an appendage but also can be adjacent to the parent cloud system...
s, named for the type of cloud from which they were sheared. The two principal forms are cumulus fractus (formerly, fractocumulus) and stratus fractus (formerly, fractostratus). Fractus clouds may develop into cumulus
Cumulus cloud
Cumulus clouds are a type of cloud with noticeable vertical development and clearly defined edges. Cumulus means "heap" or "pile" in Latin. They are often described as "puffy" or "cotton-like" in appearance. Cumulus clouds may appear alone, in lines, or in clusters...
if the ground heats enough to start convection. Stratus fractus is distinguishable from cumulus fractus by its smaller vertical extent, darker color, and by the greater dispersion of its particles.
Cumulus fractus clouds actually look like ragged cumulus clouds. They may originate from dissipated cumulus clouds, appearing in this case as white ragged clouds located at significant distances from each other. Cumulus fractus in particular form on the leading and trailing edges of summer storms in warm and humid conditions. Observing fractus gives an indication of wind movements under the parent cloud.
Masses of multiple fractus clouds, located under a main cloud, are called pannus.
Fractonimbus are a form of stratus fractus, developing under precipitation clouds due to turbulent air movement. They are dark-gray and ragged in appearance. Fractonimbus exist only under precipitation clouds (such as nimbostratus, altostratus
Altostratus cloud
Altostratus is a cloud belonging to a class characterized by a generally uniform gray to bluish-gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus. The sun can be seen through thin altostratus, but thicker layers can be quite opaque...
or cumulonimbus
Cumulonimbus cloud
Cumulonimbus is a towering vertical cloud that is very tall, dense, and involved in thunderstorms and other inclement weather. Cumulonimbus originates from Latin: Cumulus "Heap" and nimbus "rain". It is a result of atmospheric instability. These clouds can form alone, in clusters, or along a cold...
), and don't produce precipitation themselves. Fractonimbus may eventually merge completely with overlying nimbostratus clouds.
Significance in thunderstorms
In rainstorms, scud often form in the updraft area where the air has been cooled by precipitation from the downdraft, thus condensation occurs below the ambient cloud deck. If scud are rising and moving towards the main updraft, sometimes marked by a rain-free base (RFB) or wall cloudWall cloud
A wall cloud is a large, lowering, and rotating base of a cumulonimbus cloud that potentially forms tornadoes. It is typically beneath the rain-free base portion of a deep cumulus cloud , and indicates the area of primary and strongest updraft which condenses into cloud at altitudes lower than...
, then the thunderstorm is still developing. Scud are common and are usually insignificant. However, scud precede wall clouds, which often form from rising scud.
In addition to forming in inflow
Inflow
Inflow may refer to:*Inflow - In hydrology, the source of the water in a body of water*Infiltration/Inflow, inappropriate connection of surface runoff drains into sanitary sewers*Inflow , air that flows inwards to a thunderstorm...
, fractus also form in outflow
Outflow
Outflow may refer to:*Capital outflow - an economic term describing capital flowing out of a particular economy.*Bipolar outflow in astronomy represents two continuous flows of gas from the poles of a star....
. Scud are very common on the leading edge of a thunderstorm where warm, moist air is lifted by the gust front. Scud are usually found under shelf clouds.