On The Cloud

Family D1 includes:

Genus cumulus (Cu): HP G62-b27SA BatteryClouds of free convection with clear-cut flat bases and domed tops. Towering cumulus (cumulus congestus) are usually classified as family D2 clouds of considerable vertical development.

Species cumulus fractus (Cu fra): Cumulus clouds broken up into ragged and changing fragments (CL1 or 7) HP G62 Battery.

Species cumulus humilis (Cu hum): Small cumulus clouds usually with just a light-grey shading underneath (CL1).

Species cumulus mediocris (Cu med): Cumulus clouds of moderate size with medium-grey shading underneath (CL2). Cumulus mediocris can produce scattered showers of light intensity. HP G62 Notebook PC Series Battery

Pattern-based variety: Radiatus.

Opacity-based varieties: None.

Precipitation-based supplementary features: Virga, praecipitatio.

Accessory clouds: Pannus (CL7), HP G62t-100 CTO Batterypileus, velum, arcus, tuba.

Mother clouds -genitus: Altocumulus, stratocumulus; -mutatus: Stratocumulus, stratus.

Genus nimbostratus (Ns): A diffuse dark-grey non-convective layer that looks feebly illuminated from the inside (CM2). It normally forms from altostratus along warm fronts and around low-pressure areas and produces widespread steady precipitation that can reach moderate or heavy intensity. HP G62t Battery

Nimbostratus is not divided into species.

Pattern-based varieties: None.

Opacity-based varieties: None.

Precipitation-based supplementary features: Virga, HP G72-101SA Batterypraecipitatio.

Accessory cloud: Pannus (CL7).

Mother clouds -genitus: Cumulus, cumulonimbus; -mutatus: Altocumulus, altostratus, stratocumulus.[26]

[edit]Towering vertical (Family D2) HP G72-102SA Battery

Stages of a cumulonimbus cloud’s life.

These clouds can have strong vertical currents and rise far above their bases, which form anywhere in the low to lower-middle altitude range from near surface to about 10,000 ft (3,000 m). HP G72-105SA Battery Like smaller cumuliform clouds in family D1, these towering giants usually form in the low-altitude range at first, but the bases can rise into the middle range when the moisture content of the air is very low. Unlike families A through D1 that each include a cumuliform and stratiform-category genus, HP G72-100 Batterythe family of towering clouds has instead one distinct cumuliform-category genus, cumulonimbus, and one species of cumulus, a genus otherwise considered a cloud of moderate vertical development. By definition, even very thick stratiform clouds cannot have towering vertical extent or structure, although they may be accompanied by embedded towering cumuliform types. HP G72-110EL Battery [28] As with the moderate vertical clouds, some authorities do not recognize a separate family of towering vertical types, and, instead, classify them as low family C. Others designate vertical clouds separately from low, middle, and high, but consider moderate and towering vertical types to be a single family.[21][29] However, HP G72-110EV Battery the International Civil Aviation Organization (ICAO) distinguishes towering vertical clouds by specifying that these very large family D2 cumuliform types must be identified by genus names or standard abbreviations in all aviation observations (METARS) and forecasts (TAFS) to warn pilots of possible severe weather and turbulanceHP G72-110SA Battery.[35]

Family D2 includes:

Genus cumulonimbus (Cb): Heavy towering masses of free convective cloud with dark-grey to nearly black bases that are associated with thunderstorms and showers. Thunderstorms can produce a range of severe weather that includes hail, HP G72-110SD Battery tornadoes, a variety of other localized strong wind events, several types of lightning, and local very heavy downpours of rain that can cause flash floods, although lightning is the only one of these that requires a thunderstorm to be taking place. In general, cumulonimbus require moistureHP G72-110SO Battery, an unstable air mass, and a lifting force (heat) in order to form. Cumulonimbus typically go through three stages: the developing stage, the mature stage (where the main cloud may reach supercell status in favorable conditions), and the dissipation stage.[36] The average thunderstorm has a 24 km (15 mi) diameter. HP G72-110SW Battery Depending on the conditions present in the atmosphere, these three stages take an average of 30 minutes to go through.[37]

Species cumulonimbus calvus (Cb cal): Cumulonimbus clouds with very high clear-cut domed tops similar to towering cumulus (CL3).

Species cumulonimbus capillatus (Cb cap): HP G72-120EG Battery Cumulonimbus clouds with very high tops that have become fibrous due to the presence of ice crystals (CL9).

Opacity-based varieties: None.

Pattern-based varieties: NoneHP G72-120EP Battery.

Precipitation-based supplementary features: Virga, praecipitatio.

Accessory clouds: Pannus (CL7), incus, mamma, pileus, velum, arcus, tuba.

Mother clouds -genitus: Altocumulus, HP G72-120EV Batteryaltostratus, nimbostratus, stratocumulus, cumulus; -mutatus: Cumulus.

Genus cumulus (Cu)[26]

Species cumulus congestus (WMO: Cu Con/ICAO: TCu): Towering cumulus clouds of great vertical size, usually with dark-grey bases, HP G72-120EW Battery and capable of producing severe turbulence and showers of moderate to heavy intensity (CL2).

Opacity-based variety: None.

Pattern-based variety: Radiatus.

Precipitation-based supplementary features: Virga, HP G72-120SD Battery praecipitatio.

Accessory clouds: Pannus (CL7), pileus, velum, arcus, tuba.

Mother clouds -genitus: Altocumulus, stratocumulus; -mutatus: Stratocumulus, stratus.[26]

Non-WMO variant

Pyrocumulus (No official abbreviation): Cumulus clouds associated with volcanic eruptions and large-scale fires. HP G72-120SG BatteryPyrocumulus is not recognized by the WMO as a distinct genus or species, but is, in essence, cumulus congestus formed under special circumstances that can also cause severe turbulance.[26]

[edit]Polar stratosphericHP G72-120SO Battery

[edit]Very high

nacreous: Nacreous clouds occur occasionally in polar regions of the stratosphere where moisture is very scarce. They are found at altitudes of about 15,000–25,000 m (49,200–82,000 ft) during the winter when that part of the atmosphere is coldest and has the best chance of triggering condensationHP G72-130 Battery. Also known as mother of pearl clouds, they are typically very thin with a cirriform appearance.[38] Nacreous clouds are sub-classified alpha-numerically based on chemical makeup rather than variations in physical appearance.

Type 1: Nacreous containing supercooled nitric acid and water dropletsHP G72-130ED Battery.

Subtypes

1A: Nacreous containing crystals of water and nitric acid.

1B: Also contains supercooled sulfuric acid in ternary solution.

Type 2: Nacreous consisting of water crystals only.

[edit]Polar mesosphericHP G72-130EG Battery

[edit]Extremely high

Noctilucent: The polar air in the mesosphere is coldest during the summer so it is mostly at this time of year that noctilucent clouds are seen.[39] They can occasionally be seen illuminated by the sun during deep twilight at ground level. HP G72-130EV Battery Noctilucent clouds are the highest in the atmosphere and occur mostly at altitudes of 80 to 85 kilometers (50 to 53 mi),[40] in the mesosphere. An alpha-numeric sub-classification is used to identify variations in physical appearanceHP G72-130SA Battery.

Type 1: Very tenuous noctilucent resembling cirrus fibratus.

Type 2: Bands; noctilucent in the form of long streaks, often in groups or interwoven at small angles, similar to cirrus intortus.

Subtypes

2A: Noctilucent streaks with diffuse, blurred edges.

2B: Streaks with sharply defined edges. HP G72-130SF Battery

Type 3: Billows; noctilucent in the form of short streaks that are clearly spaced and roughly parallel.

Subtypes

3A: Noctilucent in the form of short, HP G72-140ED Battery straight, narrow streaks.

3B: Wave-like streaks similar to cirrus undulatus.

Type 4: Whirls; noctilucent in the form of partial or rarely complete rings with dark centers.

Subtypes

4A: Noctilucent whirls of small angular radius having a similar appearance to surface water ripples. HP G72-150EF Battery

4B: Simple curve of medium angular radius with one or more bands.

4C: Whirls with large-scale ring structure.

[edit]Throughout the homosphere

[edit]ColorationHP G72-251XX Battery

An occurrence of altocumulus and cirrocumulus cloud iridescence

Sunset reflecting shades of pink onto grey stratocumulus clouds.

Striking cloud colorations can be seen at many altitudes in the homosphere, which includes the troposphere, stratosphere, HP G72-260US Battery and mesophere. The first recorded colored cloud was seen by Nathan Ingleton in 1651, he wrote the event in his diary but the records were destroyed in 1666, in the Great Fire of London. The color of a cloud, as seen from Earth, tells much about what is going on inside the cloud.

In the troposphere, dense, HP G72-a10SA Batterydeep clouds exhibit a high reflectance (70% to 95%) throughout the visible spectrum. Tiny particles of water are densely packed and sunlight cannot penetrate far into the cloud before it is reflected out, giving a cloud its characteristic white color, especially when viewed from the top.[41] Cloud droplets tend to scatter light efficiently, HP G72-a20SA Battery so that the intensity of the solar radiation decreases with depth into the gases. As a result, the cloud base can vary from a very light to very-dark-grey depending on the cloud’s thickness and how much light is being reflected or transmitted back to the observer. Thin clouds may look white or appear to have acquired the color of their environment or background. HP G72-a30SA Battery High tropospheric clouds appear mostly white if composed entirely of ice crystals or supercooled water droplets.

As a tropospheric cloud matures, the dense water droplets may combine to produce larger droplets. HP G72-a40SA Battery If the droplets become too large and heavy to be kept aloft by the air circulation, they will fall from the cloud as rain. By this process of accumulation, the space between droplets becomes increasingly larger, permitting light to penetrate farther into the cloud. If the cloud is sufficiently large and the droplets within are spaced far enough apart, HP G72-b01EA Battery a percentage of the light that enters the cloud is not reflected back out but is absorbed giving the cloud a darker look. A simple example of this is one’s being able to see farther in heavy rain than in heavy fog. This process of reflection/absorption is what causes the range of cloud color from white to black.[42]

Other colors occur naturally in tropospheric clouds. HP G72-b01SA Battery Bluish-grey is the result of light scattering within the cloud. In the visible spectrum, blue and green are at the short end of light’s visible wavelengths, whereas red and yellow are at the long end. The short rays are more easily scattered by water droplets, and the long rays are more likely to be absorbed. HP G72-b02SA Battery The bluish color is evidence that such scattering is being produced by rain-size droplets in the cloud. A cumulonimbus cloud that appears to have a greenish/bluish tint is a sign that it contains extremely high amounts of water; hail or rain. Supercell type storms are more likely to be characterized by this but any storm can appear this way. HP G72-b10SA BatteryColoration such as this does not directly indicate that it is a severe thunderstorm, it only confirms its potential. Since a green/blue tint signifies copious amounts of water, a strong updraft to support it, high winds from the storm raining out, and wet hail; all elements that improve the chance for it to become severe, can all be inferred from this.HP G72-b15SA Battery In addition, the stronger the updraft is, the more likely the storm is to undergo tornadogenesis and to produce large hail and high winds.[43] Yellowish clouds may occur in the late spring through early fall months during forest fire season. The yellow color is due to the presence of pollutants in the smoke. HP G72-b20SA BatteryYellowish clouds caused by the presence of nitrogen dioxide are sometimes seen in urban areas with high air pollution levels.[44]

Within the troposphere, red, orange, and pink clouds occur almost entirely at sunrise/sunset and are the result of the scattering of sunlight by the atmosphere. HP G72 Battery When the angle between the sun and the horizon is less than 10 percent, as it is just after sunrise or just prior to sunset, sunlight becomes too red due to refraction for any colors other than those with a reddish hue to be seen.[45] The clouds do not become that color; they are reflecting long and unscattered rays of sunlight, which are predominant at those hours. HP G72 Notebook PC Series BatteryThe effect is much like if one were to shine a red spotlight on a white sheet. In combination with large, mature thunderheads, this can produce blood-red clouds. Clouds look darker in the near-infrared because water absorbs solar radiation at those wavelengths.

In high latitude regions of the stratosphereHP G72T-200 CTO Battery, nacreous clouds occasionally found there during the polar winter tend to display quite striking displays of mother-of-pearl colorations due to the refraction and diffusion of the sun’s rays through thin ice crystal clouds that often contain compounds other than water. At still higher altitudes up in the mesospere, HP G72t Batterynoctilucent clouds sometimes seen in polar regions in the summer usually appear a silvery white that can resemble brightly illuminated cirrus.

[edit]Effects on climate

See also: Cloud cover and Cloud feedbackHP Pavilion dm4-1000 Battery

Global cloud cover, averaged over the month of October 2009. NASA composite satellite image; larger image available here.

The role of tropospheric clouds in regulating weather and climate remains a leading source of uncertainty in projections of global warming.HP Pavilion dm4-1001tu Battery [46] This uncertainty arises because of the delicate balance of processes related to clouds, spanning scales from millimeters to planetary. Hence, interactions between the large-scale (synoptic meteorology) and clouds becomes difficult to represent in global models. The complexity and diversity of clouds, HP Pavilion dm4-1001tx Battery as outlined above, adds to the problem. On the one hand, white-colored cloud tops promote cooling of Earth’s surface by reflecting shortwave radiation from the sun. Most of the sunlight that reaches the ground is absorbed, warming the surface, which emits radiation upward at longer, infrared, wavelengths. At these wavelengths,HP Pavilion dm4-1002tu Batteryhowever, water in the clouds acts as an efficient absorber. The water reacts by radiating, also in the infrared, both upward and downward, and the downward radiation results in a net warming at the surface. This is analogous to the greenhouse effect of greenhouse gases and water vapor.

High tropospheric clouds, HP Pavilion dm4-1003xx Battery such as cirrus, particularly show this duality with both shortwave albedo cooling and longwave greenhouse warming effects that nearly cancel or slightly favor net warming with increasing cloud cover. The shortwave effect is dominant with middle and low clouds like altocumulus and stratocumulus, which results in a net cooling with almost no longwave effect. HP Pavilion dm4-1004tu Battery As a consequence, much research has focused on the response of low clouds to a changing climate. Leading global models can produce quite different results, however, with some showing increasing low-level clouds and others showing decreases.[47][48]

Polar stratospheric and mesospheric clouds are not common or widespread enough to have a significant effect on climate. HP Pavilion dm4-1004xx Battery However an increasing frequency of occurrence of noctilucent clouds since the 19th century may be the result of climate change.[49]

[edit]Global brightening

New research indicates a global brightening trend.[50] The details are not fully understood, HP Pavilion dm4-1006tu Battery but much of the global dimming (and subsequent reversal) is thought to be a consequence of changes in aerosol loading in the atmosphere, especially sulfur-based aerosol associated with biomass burning and urban pollution. Changes in aerosol burden can have indirect effects on clouds by changing the droplet size distribution[51] or the lifetime and precipitation characteristics of clouds. HP Pavilion dm4-1006tx Battery [52]

[edit]Rainmaking bacteria

Bioprecipitation, the concept of rain-making bacteria, was proposed by David Sands from Montana State University. Such microbes – called ice nucleators – are found in rain, snow, HP Pavilion dm4-1008tu Battery and hail throughout the world. These bacteria may be part of a constant feedback between terrestrial ecosystems and clouds and may even have evolved the ability to promote rainstorms as a means of dispersal. They may rely on the rainfall to spread to new habitats, much as some plants rely on windblown pollen grainsHP Pavilion dm4-1008tx Battery.[53][54]

[edit]Extraterrestrial

Main article: Extraterrestrial atmospheres

Within our Solar System, any planet or moon with an atmosphere also has clouds. Venus’s thick clouds are composed of sulfur dioxide. HP Pavilion dm4-1009tx Battery Mars has high, thin clouds of water ice. Both Jupiter and Saturn have an outer cloud deck composed of ammonia clouds, an intermediate deck of ammonium hydrosulfide clouds and an inner deck of water cloudsHP Pavilion dm4-1010eg Battery.[55][56] Saturn’s moon Titan has clouds believed to be composed largely of methane.[57] The Cassini–Huygens Saturn mission uncovered evidence of a fluid cycle on Titan, including lakes near the poles and fluvial channels on the surface of the moon. Uranus and Neptune have cloudy atmospheres dominated by water vapor and methane gas. HP Pavilion dm4-1010tx Battery [58][59]