Meteorology is the interdisciplinary study of the atmosphere either on a short time scale or long, that affects the weather. Under meteorology a cloud is described as a visible mass of liquid droplets or frozen particles of water that are suspended in the air above a planetary body.
The branch of meteorology or atmospheric sciences that focus’ on the study of clouds is referred to cloud physics, this is the directed examination of physical process’ that lead to the growth, formation and precipitation of clouds. Clouds can be differentiated into categories of warm, that consist of microscopic droplets liquid water and cold that is made up of frozen droplets, however there are also mixed phase clouds that contain both elements. All types of clouds are formed by the condensation of water vapour. A number of different types of cloud can be formed dependant on the pressure and temperature that has caused condensation, these can sit at various altitudes.
Cloud level and Cloud type
High clouds (CH) Base usually 20,000 ft or above, over land
Cirrus – Latin word meaning ringlet or curling lock of hair
A cirrus cloud can be characterised by thin wispy layers that are usually white or light grey in colour. These clouds can often indicate a change in weather conditions, suggest precipitation will follow suit. Cirrus clouds do not precipitate as such, although they do release ice crystals that evaporate before reaching land.
Cirrocumulus – cirro (curl of hair) – cumulus (heaped)
These clouds are often short lived, they usually form due to the break up of the Cumulonimbus (CL) or as a transitionary phase within and area of Cirrus clouds (CH). As seen below the Cirrocumulus clouds are often found in clusters predominantly white and fluffy in appearance, almost resembling a small ball of cotton wool. Although the name refers to each individual cloud it is also used to refer to an entire area in which they have formed. The Cirrocumulus never creates a shadow as it is near translucent.
The Cirrostratus cloud can be characterised by it’s very thin and consistent appearance. Due to the thinness of the cloud itself it can be extremely difficult to detect and can sometimes create a ‘halo’ around the sun when it takes form of the cirrostratus nebulosus (featureless and uniform).
There are two most common forms of the cirrostratus:
Cirrostratus Nebulosus – Latin Meaning, full of vapour, foggy, cloudy
Cirrostratus Fibratus – Latin Meaning, fibrous
These are formed by strong winds that continue to blow at high altitudes, causing them to accommodate a large area of the sky. Like the cirrocumulus the cirrostratus also does not produce precipitation itself but often indicates imminent rain.
Medium clouds (CM) Base usually between 6,500 and 20,000 ft over land
Altocumulus - Alto (middle) – culmus (heaped)
Altocumulus often appear in a cluster or sheet of grey/white bundles or rolls that can be conjoined, these are however regularly hidden by lower clouds. This cloud species can take many forms and again can be a pre-warning to a change in weather. Towering altocumulus, known as altocumulus castellanus, frequently signals the development of thunderstorms later in the day, as it shows instability and convection in the middle levels of the troposphere, the area where towering cumulus clouds can turn into cumulonimbus (CL). Satalite images have shown that the altocumulus has the abilities to create formations for thousands of square miles.
Altostratus – Alto (middle) – stratus (layered)
The Altostratus can be characterised by it’s grey/blue appearance, often forming in a thick sheet although the sun can usually be seen through it. This cloud can precipitate in the form of virga, a type of rain that can be seen in streaks but dissolves before reaching the ground. If the precipitation becomes heavier or intensify this cloud has the abilities to fall lower and become a nimbostratus (see below).
Like the altostratus this mid level cloud also produces precipitation, often appears darker at its base. This cloud usually occurs due to advancing hot air that is humid and unstable, this itself is not associated with thunderstorms, however, the cumulonimbus and nimbostratus can occasionally interact. This phenomenon happens very rarely, when they meet they will only interact with the immediate area surrounding the cloud. The nimbostratus can be a sign of steady to moderate rain that could perhaps last for a number of days depending on the speed of the occluded front (when cold and hot air passes).
Low clouds (CL) Base usually below 6,500 ft over land
The stratocumulus cloud can be identified by their large dark appearance, occurring in a round mass, commonly featuring in groups, lines or waves across the sky. These low formation clouds are created by weak convective currents that create layers due to the stable air above preventing progressive vertical development. Stratocumulus tend not to precipitate if they do they have the capabilities to release light rain or snow. These clouds are however often seen before or after bad weather, therefore they can be an indication of thunderstorms or heavy downpours.
Stratus - latin strato meaning ‘layer’
Stratus clouds are recognised through their solid flat base and horizontal sheet-like platforms. These types of clouds generally cause light drizzle or a limited supply of snow. They form through the slow rise of morning fog or due to cold air travelling at a small elevation over land, hence why they are sometimes referred to as ‘high fog’. Although they produce a small amount of precipitation, this does not necessarily mean they have any effect on the atmosphere.
Cumulus – latin Cumulo meaning heaped
Cumulus clouds are generally flat based although the tops are often labelled as resembling cotton. These clouds have a distinguishing vertical buildup that have a definitive perimeter whilst appearing in clusters. Cumulus can indicate the arrival of other cloud formations like the cumulonimbus, normally they do not precipitate and if so it will be very little, but depending on the surround atmosphere factors such as moisture or a change in temperature can cause these to morph into the cumulonimbus that do precipitate. These clouds have the capability to cool the earth by reflecting incoming solar rays.
Cumulonimbus – latin meaning cumulus (heaped) and nimbus (rainstorm)
Cumulonimbus are generally thick, soaring vertical cloud formations identified with thunderstorms and atmospheric activity. They are formed from water vapour being carried upwards by powerful air streams. These clouds can be created singularly or in groups, and are able to generate many types of serious weather, such as: lightning, hail and tornadoes. The base of these clouds can expand over a number of miles and may be active within both low and medium range forming a mushroom shape.
Understanding how clouds affect the climate has been a difficult proposition. What controls the makeup of the low clouds that cool the atmosphere or the high ones that trap heat underneath?
Clouds need tiny particles called aerosols that rise in the atmosphere, in order to form. These aerosols – natural ones like sea salt or dust, or such human-made ones as soot – form nuclei around which the cloud droplets condense. In relatively clean environments, clouds can only grow as large as the amount of aerosols in the atmosphere allows: They will be the limiting factor in cloud formation.