While water remains a basic human need, the ability to create a nimbostratus cloud in a lab remains elusive.
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Be honest: How many times have you caught yourself wistfully staring into the stratosphere, dreaming of a future in which you are somehow able to put your parched lips to a wispy nimbostratus cloud and fill your belly with its sweet nectar, as if it were some sort of atmospheric teat?
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Nimbostratus occurs along a warm front or occluded front where the slowly rising warm air mass creates nimbostratus along with shallower stratus clouds producing less rain, these clouds being preceded by higher- level clouds such as cirrostratus and altostratus. Often, when an altostratus cloud thickens and descends into lower altitudes, it will become nimbostratus. Nimbostratus, unlike cumulonimbus, is not associated with thunderstorms, however at an unusually unstable warm front caused as a result of the advancing warm air being hot, humid and unstable, cumulonimbus clouds may be embedded within the usual nimbostratus. Lightning from an embedded cumulonimbus cloud may interact with the nimbostratus but only in the immediate area around it.
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Nimbostratus (V-60) with virga Abbreviation: Ns (V-60) Clouds of the genus nimbostratus tend to bring constant precipitation and low visibility. This cloud type normally forms above from altostratus cloud but tends to thicken into the lower levels during the occurrence of precipitation. The top of a nimbostratus deck is usually in the middle level of the troposphere.
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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.
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Nimbostratus has a diffuse cloud base generally found anywhere from near surface in the low levels to about in the middle level of the troposphere. Although usually dark at its base, it often appears illuminated from within to a surface observer. Nimbostratus usually has a thickness of about 2000 to 4000 m. Though found worldwide, nimbostratus occurs more commonly in the middle latitudes.
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Stratus or stratocumulus usually replace the nimbostratus after the passage of the warm or occluded front.
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Nimbostrati often have very few visual features. Nimbostratus is generally a sign of an approaching warm or occluded front producing steady moderate precipitation, as opposed to the shorter period of typically heavier precipitation released by a cold-frontal cumulonimbus cloud. Precipitation may last for several days, depending on the speed of the frontal system. A nimbostratus virga cloud is the same as normal nimbostratus, but the rain or snow falls as virga which doesn't reach the ground.
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In this situation with lightning and rain occurring it would be hard to tell which type of cloud was producing the rain from the ground, however cumulonimbus tend to produce larger droplets and more intense downpours. The occurrence of cumulonimbus and nimbostratus together is uncommon, and usually only nimbostratus is found at a warm front.
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Downward-growing nimbostratus can have the same vertical extent as most large upward-growing cumulus, but its horizontal extent tends to be even greater.
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Fog City Press, San Francisco. . Frontal cirrostratus is a precursor to rain or snow if it thickens into mid-level altostratus and eventually nimbostratus as the weather front moves closer to the observer.
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Several additional types usually form in the low or middle étages but typically extend into all three altitude levels as clouds with significant vertical extent. These include nimbostratus, towering cumulus congestus, and cumulonimbus.
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Altostratus tends to form ahead of a warm or occluded front, the altostratus gradually thickening into rain bearing nimbostratus. However it can also occur together with cumulus congestus or cumulonimbus at a cold front.
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A nimbostratus cloud is a multi-level, gray, often dark, amorphous, nearly uniform cloud that usually produces continuous rain, snow, or sleet but no lightning or thunder.Cloud in the Columbia Electronic EncyclopediaNimbostratus in the American Heritage DictionaryNimbostratus in the Oxford Dictionaries Online Although it is usually a low-based cloud, it actually forms most commonly in the middle level of the troposphere and then spreads vertically into the low and high levels. Nimbostratus usually produces precipitation over a wide area. Nimbo- is from the Latin word nimbus, which denotes precipitation.
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It was then renamed nimbostratus, and published with the new name in the 1932 edition of the International Atlas of Clouds and of States of the Sky. This left cumulonimbus as the only nimboform type as indicated by its root name.
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In these conditions, the aircraft (if not equipped for IMC flight and flown by a pilot experienced in IMC flight) is likely to enter a graveyard spiral and eventually break up by exceeding the wing load limit. In this situation, the cause of the disintegration of the aircraft is not atmospheric turbulence but is the inability of the pilot to control the aircraft following the loss of visual reference to the ground. In the case of an instrument flight, cumulonimbus can catch a pilot by surprise when embedded in a more benign cloud mass. For example, nimbostratus can originate from the spreading of a cumulonimbus (nimbostratus cumulonimbogenitus), making the presence of active convective cells likely.
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Stratus cumulogenitus clouds occur when the base of cumulus clouds spreads, creating a nebulous sheet of stratiform clouds. This can also occur on nimbostratus clouds (stratus nimbostratogenitus) and on cumulonimbus clouds (stratus cumulonimbogenitus). Stratus fractus clouds can also form under the base of precipitation-bearing clouds and are classified as pannus clouds.
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They mostly appear under the precipitation of major rain-bearing clouds; these are the nimbostratus clouds, and the cumulonimbus clouds, and are classified as pannus clouds. Stratus fractus can also form beside mountain slopes, without the presence of nimbus clouds (clouds that precipitate), and their color can be from dark grey to almost white.
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They comprise two or three genera depending on the system of height classification being used: altostratus, altocumulus, and, according to WMO classification, nimbostratus. These clouds are formed from ice crystals, supercooled water droplets, or liquid water droplets. Low-étage clouds form at less than . The two genera that are strictly low-étage are stratus, and stratocumulus.
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Consequently, it is assumed that there are no anthropic clouds of these two genera. However, what can occur is enhancing existing Nimbostratus or Altostratus due to the additional water vapor or condensation nuclei emitted by a thermal power plant, for instance. The only anthropic clouds existing in the middle region of the troposphere are Altocumulus homogenitus (Aca) from contrails at this region.
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Low stratus fractus partly obscuring nimbostratus over Deccan Plateau, India Tropospheric classification is based on a hierarchy of categories with physical forms and altitude levels at the top. These are cross-classified into a total of ten genus types, most of which can be divided into species and further subdivided into varieties which are at the bottom of the hierarchy.
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Of the non-convective stratiform group, high-level cirrostratus comprises two species. Cirrostratus nebulosus has a rather diffuse appearance lacking in structural detail. Cirrostratus fibratus is a species made of semi-merged filaments that are transitional to or from cirrus. Mid-level altostratus and multi-level nimbostratus always have a flat or diffuse appearance and are therefore not subdivided into species.
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A stratus cloud can form from stratocumulus spreading out under an inversion, indicating a continuation of prolonged cloudy weather with drizzle for several hours and then an improvement as it breaks into stratocumulus. Stratus clouds can persist for days in anticyclone conditions. It is common for a stratus to form on a weak warm front, rather than the usual nimbostratus.
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A nimbostratus cloud in the background with a stratus fractus in the middle of the upper half of the image. Fractus are accessory clouds, 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.
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The intermediate layers of the troposphere are the regions with less influence of human activity. This region is far enough from the surface for not being affected by the surface emissions. Additionally, commercial and military flights only cross this region during ascending or descending maneuvers. Moreover, in this region there exist two types of clouds with a large horizontal extension: Nimbostratus and Altostratus, which cannot originate from human activity.
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Altostratus translucidus (V-49) near top of photo merging into altostratus opacus (V-50) near bottom Abbreviation: As Stratiform clouds of the genus altostratus form when a large convectively stable airmass is lifted to condensation in the middle level of the troposphere, usually along a frontal system. Altostratus can bring light rain or snow. If the precipitation becomes continuous, it may thicken into nimbostratus which can bring precipitation of moderate to heavy intensity.
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If the cloud is a cirrus castellanus, there might be instability at the high altitude level. When the clouds deepen and spread, especially when they are of the cirrus radiatus variety or cirrus fibratus species, this usually indicates an approaching weather front. If it is a warm front, the cirrus clouds spread out into cirrostratus, which then thicken and lower into altocumulus and altostratus. The next set of clouds are the rain- bearing nimbostratus clouds.
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Of the latter, upward-growing cumulus mediocris produces only isolated light showers, while downward growing nimbostratus is capable of heavier, more extensive precipitation. Towering vertical clouds have the greatest ability to produce intense precipitation events, but these tend to be localized unless organized along fast-moving cold fronts. Showers of moderate to heavy intensity can fall from cumulus congestus clouds. Cumulonimbus, the largest of all cloud genera, has the capacity to produce very heavy showers.
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It can produce light precipitation, often in the form of virga. If the precipitation increases in persistence and intensity, the altostratus cloud may thicken into nimbostratus. Altostratus most often takes the form of a featureless sheet of cloud but can be wavy (undulatus) as a result of wind shear through the cloud. It can also be fragmented (fibratus) with clear sky visible, which often precedes the approach of a weakened or upper level warm front.
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Multi-level nimbostratus is physically related to other stratiform genus-types by way of being non-convective in nature. However, the other sheet-like clouds usually each occupy only one or two levels at the same time. Stratus clouds are low-level and form from near ground level to at all latitudes. In the middle level are the altostratus clouds that form from to in polar areas, in temperate areas, and in tropical areas.
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Pannus, or scud clouds, is a type of fractus cloud at low height above ground, detached, and of irregular form, found beneath nimbostratus or cumulonimbus clouds. These clouds are often ragged or wispy in appearance. When caught in the outflow (downdraft) beneath a thunderstorm, scud clouds will often move faster than the storm clouds themselves. When in an inflow (updraft) area, scud clouds tend to rise and may exhibit lateral movement ranging from very little to substantial.
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Altostratus is a middle altitude cloud genus belonging to the stratiform physical category characterized by a generally uniform gray to bluish-green sheet or layer. It is lighter in color than nimbostratus and darker than high cirrostratus. The sun can be seen through thin altostratus, but thicker layers can be quite opaque. Altostratus undulatus Altostratus is formed by the lifting of a large mostly stable air mass that causes invisible water vapor to condense into cloud.
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A weather front is the boundary of two air masses Frontal precipitation is the result of frontal systems surrounding extratropical cyclones or lows, which form when warm and tropical air meets cooler air. Frontal precipitation typically falls out of nimbostratus clouds. When masses of air with different densities (moisture and temperature characteristics) meet, the less dense warmer air overrides the more dense colder air. The warmer air is forced to rise and, if conditions are right, creates an effect of saturation, causing precipitation.
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Nonconvective stratiform clouds appear in stable airmass conditions and, in general, have flat, sheet-like structures that can form at any altitude in the troposphere. The stratiform group is divided by altitude range into the genera cirrostratus (high-level), altostratus (mid-level), stratus (low-level), and nimbostratus (multi-level). Fog is commonly considered a surface-based cloud layer. The fog may form at surface level in clear air or it may be the result of a very low stratus cloud subsiding to ground or sea level.
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Although altostratus forms mostly in the middle level of the troposphere, strong frontal lift can push it into the lower part of the high- level. The main high-level stratiform cloud is cirrostratus which is composed of ice crystals that often produce halo effects around the sun. Cirrostratus forms at altitudes of in high latitudes, in temperate latitudes, and in low, tropical latitudes. Of the non-stratiform clouds, cumulonimbus and cumulus congestus are the most closely related to nimbostratus because of their vertical extent and ability to produce moderate to heavy precipitation.
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These clouds are composed of water droplets, except during winter when they are formed of supercooled waterdroplets or ice crystals if the temperature at cloud level is below freezing. Two additional genera usually form in the low altitude range, but may be based at higher levels under conditions of very low humidity. They comprise the genera cumulus, and cumulonimbus, which along with nimbostratus, are often classified separately as clouds of vertical development, especially when their tops are high enough to be composed of super-cooled water droplets or ice crystals. The altitudes of high-étage clouds like cirrus vary considerably with latitude.
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One group of supplementary features are not actual cloud formations, but precipitation that falls when water droplets or ice crystals that make up visible clouds have grown too heavy to remain aloft. Virga is a feature seen with clouds producing precipitation that evaporates before reaching the ground, these being of the genera cirrocumulus, altocumulus, altostratus, nimbostratus, stratocumulus, cumulus, and cumulonimbus. When the precipitation reaches the ground without completely evaporating, it is designated as the feature praecipitatio. This normally occurs with altostratus opacus, which can produce widespread but usually light precipitation, and with thicker clouds that show significant vertical development.
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Supplementary cloud formations detached from the main cloud are known as accessory clouds. The heavier precipitating clouds, nimbostratus, towering cumulus (cumulus congestus), and cumulonimbus typically see the formation in precipitation of the pannus feature, low ragged clouds of the genera and species cumulus fractus or stratus fractus. A group of accessory clouds comprise formations that are associated mainly with upward-growing cumuliform and cumulonimbiform clouds of free convection. Pileus is a cap cloud that can form over a cumulonimbus or large cumulus cloud, whereas a velum feature is a thin horizontal sheet that sometimes forms like an apron around the middle or in front of the parent cloud.
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An approaching weather front often brings mid level clouds such as altostratus or altocumulus which usually stop any cumulus from reaching the congestus stage by reducing the Sun's heat or acting as a layer of stable air through which the cumulus cannot rise through. Occasionally, however, particularly if the air below the mid level cloud is very warm or unstable, some of the cumuli may become congestus and the tops of them may rise above the mid level cloud layer, sometimes resulting in showers ahead of the main rainband. This is often a sign the approaching front contains at least a few cumulonimbi amongst the nimbostratus rain clouds and therefore any rain may be accompanied by thunderstorms.
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The first clouds that indicate an approaching warm front tend to be mostly high cirrus at first, changing to cirrostratus as the front approaches. However, if cirrocumulus also appears, there is greater airmass instability approaching ahead of the front. When these high clouds progressively invade the sky and the barometric pressure begins to fall, precipitation associated with the disturbance is likely about 6 to 8 hours away. A thickening and lowering of these high clouds into middle-stage altostratus or altocumulus is a good sign the warm front or low has moved closer and precipitation may begin within less than six hours. Once the clouds have thickened to from the earth’s surface, precipitation can begin to fall from heavy nimbostratus.
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Any cloud type with significant vertical extent that can occupy more than one étage is coded as low (cumulus and cumulonimbus) or middle (nimbostratus) depending on the altitude level or étage where it normally initially forms aside from any vertical growth that takes place. The symbol used on the map for each of these étages at a particular observation time is for the genus, species, variety, mutation, or cloud motion that is considered most important according to criteria set out by the World Meteorological Organization (WMO). If these elements for any étage at the time of observation are deemed to be of equal importance, then the type which is predominant in amount is coded by the observer and plotted on the weather map using the appropriate symbol. Special weather maps in aviation show areas of icing and turbulence.
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