Cloud Photographs and Information
Mamantus at Sunset
Clouds and More
This hub contains photographs of clouds that have been identified. Clouds included are cumulus humulus, cumulus congestus, stratus, stratocumulus, cumulonimbus, nimbostratus, altocumulus, altostratus, cirrus, cirrostratus, and cirrocumulus.
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Low clouds can form with a base as low as the ground, which is the case for fog. Many low clouds form with a base of just a few hundred feet above the ground. Many of these clouds are, at least in the lower region, composed of liquid water that is above freezing.
Low clouds can be grouped into two main classes, layered and convective. These classes are not mutually disjoint. Convective clouds, or better stated, those that show evidence of turbulence, incorporate the word cumulus into their names, while layer clouds incorporate the word stratus into their names.
Cumulus is the name given to clouds that show some evidence of turbulence, often caused by convection. Low clouds that were caused by turbulence, but show little vertical growth, and little horizontal spreading, are called cumulus humulus. Cumulus humulus often indicate fair weather, but if they occur early in the day, and if the thermal transport of air becomes increasingly strong as the day progresses, they can be the first indication of poor weather conditions that will occur later.
Cumulus humulus clouds are often brilliant white in color, and usually have flat bases. However, their bases can be grayish if the cloud is thick enough and positioned so as to diffuse the light of the sun. In fact, the entire cloud may be gray when the sun is low on the horizon, such as near sunset, or make take on red or purple hues near sunset, depending on the relative position of the sun.
Cumulus congestus clouds are cumulus clouds that have a well developed convective system, with the resulting cloud larger than the typical cumulus humulus. These clouds often show extensive evidence of convection, with an appearance resembling a head of cauliflower. They can be massive, and may be just minutes away from producing precipitation.
The fact that a cloud is convective does not preclude the possibility it may have a layered base. When a low cloud shows both convection and layering, it is named stratocumulus.
Stratocumulus clouds have two distinct appearances, depending on whether they are simply elongated cumulus clouds, or if they spread across much of the sky. Those that are elongated cumulus clouds may be caused by a convection source that the air is passing over, hence it causes a cloud that grows as the cloud moves forward. The stratocumulus clouds covering a large portion of the sky often looks similar to stratus clouds. Sometimes small holes exist that can provide a glimpse of the convective structure of the clouds. Sometimes embedded thunderstorms where the convection is more extensive provide the clue as to the clouds' identification. These features are difficult to capture in photographs, so the clouds often are photographically indistinguishable from stratus.
Often, low clouds extend vertically quite a distance through the troposphere. When they do, it is possible that their tops will glaciate, or contain ice. When this happens, precipitation is expected.
A cloud with a low base that convectively reaches a height sufficient to produce precipitation is called cumulonimbus.
Cumulonimbus clouds may also contain lightning and thunder, produce hail, be accompanied buy strong winds due to rapidly descending air spreading out when it encounters the ground, and tornadoes and water spouts. Certainly, not every cumulonimbus cloud contains all of these phenomena.
This can be a low or middle stratified cloud producing precipitation. The cloud must be layered, and producing.
The very name stratus implies layered. Stratus clouds are low clouds that show little or no convection. When stratus clouds form at the ground, they are called fog.
Normally, stratus clouds cover the entire sky, making them just a sheet of gray with little or no features. In figure 4 this is exactly what is being shown, but in figure 5 the stratus clouds are not covering the entire sky. The clouds in figure 5 more resemble patchy fog just above the ground. The area where the photograph in figure 5 was taken is close to several chemical plants, and the condensation nuclei from these plants often cause low clouds and fog to form in bands. On the day the photograph in figure 5 was taken, the condensation was occurring just above the ground.
Middle clouds form at altitudes where the temperature is often cold enough to be below freezing, but not cold enough to have spontaneous crystallization. In this region the air is often too clean to contain a significant quantity of the nuclei required for freezing. Clouds forming at such heights may contain super-cooled water droplets, which is water below what is normally considered freezing. The freezing point is defined for water with a flat surface, and small, round droplets may exist in the liquid state well below zero degrees Celsius.
The prefix given to middle clouds is alto, and both layer clouds, altostratus, and convective clouds, altocumulus, are possible. If the altostratus clouds acquire a significant amount of ice crystals, precipitation can occur. Stratified clouds causing precipitation are called nimbostratus.
Frequently, some ice forms in altocumulus, and snow virga, precipitation not reaching the ground, occurs. It is not likely this light precipitation, which is all small altocumulus clouds can produce, could reach the ground without subliming or melting and evaporating.
Altocumulus clouds commonly form in roughly aligned puffs, resembling cotton balls. They may appear to be fully rounded, or flat at their bases. Other altocumulus clouds form bands in the sky. However, there are some that look like cumulus humulus. The appearance of a cloud cannot be the only criterion for naming it, rather its composition is what is really important.
Altostratus clouds may appear smooth when viewed from below, may have some features to their bases, or may have the distinct appearance of altocumulus clouds thickening into sheets. They may be thin enough to be translucent, allowing viewing of the solar disk through them, or they may be thick enough to transform into nimbostratus clouds and produce precipitation, provided they have an ice component. The precipitation that falls from middle clouds is always snow. It may melt on the way to the ground, but at the cloud base the precipitation is snow.
High clouds are composed of ice. They form so high in the troposphere that their components are always frozen, usually in the form of elongated ice needles. Because of the extreme low temperatures at which they form, often below -40C, it is unnecessary that they have nuclei normally needed for freezing cloud components. In fact, at the altitudes where they form, there are few impurities in the atmosphere.
Clouds composed primarily of ice are said to be in the cirrus family.
Because there is usually little water vapor in these clouds, cloud components grow at a slow rate. Precipitation does not fall from clouds in the cirrus family. If some ice needles were to grow to sufficient size that they would begin tom descend, the atmosphere below them would quickly evaporate them long before they could reach the ground.
Cloud Identification Chart
Cirrus clouds are ice clouds that form in a cold environment, often near the upper limit of the troposphere. They are generally thin clouds that are swept into long streaks by high winds. Occasionally, these beautiful clouds are obscured by lower clouds, but they may be visible between other clouds, or when there is too little water vapor in the atmosphere below them for other clouds to form.
Cirrocumulus are cirrus clouds that have some evidence of convection. They often resemble altocumulus, except the puffs and rolls are generally smaller. The altitude at which these clouds form makes it difficult to have extensive convection, so the convection occurs on a minute scale.
Cirrocumulus rarely occur alone. They are most likely at the edge of stratified cirrus, cirrostratus, or may blend into cirrus clouds.
When cirrus clouds form in sheets, they are called cirrostratus. These clouds can cover the entire sky. They differ from altostratus and stratus in that they are composed of ice needles, but this is often difficult to determine from the ground. In fact, the altitude of a cloud covering the entire sky is difficult to determine from the ground without proper instrumentation. However, some cirrostratus clouds can sometimes be identified by their fiber texture at the base, and others can be identified by how they refract sunlight.
Virga is the name given to precipitation leaving the ground, but evaporating on the way to the ground, so nothing is observed on the ground.