In meteorology, air currents are concentrated areas of winds. They are mainly due to differences in atmospheric pressure or temperature. They are divided into horizontal and vertical currents; both are present at mesoscale while horizontal ones dominate at synoptic scale. Air currents are not only found in the troposphere, but extend to the stratosphere and mesosphere.
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👉 Air current in the context of Atmosphere of Earth
The atmosphere of Earth consists of a layer of mixed gas (commonly referred to as air) that is retained by gravity, surrounding the Earth's surface. It contains variable quantities of suspended aerosols and particulates that create weather features such as clouds and hazes. The atmosphere serves as a protective buffer between the Earth's surface and outer space. It shields the surface from most meteoroids and ultraviolet solar radiation, reduces diurnal temperature variation – the temperature extremes between day and night, and keeps it warm through heat retention via the greenhouse effect. The atmosphere redistributes heat and moisture among different regions via air currents, and provides the chemical and climate conditions that allow life to exist and evolve on Earth.
By mole fraction (i.e., by quantity of molecules), dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other trace gases (see Composition below for more detail). Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.
In this Dossier
Air current in the context of Fan (machine)
A fan is a powered machine that creates airflow. A fan consists of rotating vanes or blades, generally made of wood, plastic, or metal, which act on the air. The rotating assembly of blades and hub is known as an impeller, rotor, or runner. Usually, it is contained within some form of housing, or case. This may direct the airflow, or increase safety by preventing objects from contacting the fan blades. Most fans are powered by electric motors, but other sources of power may be used, including hydraulic motors, handcranks, and internal combustion engines.
Mechanically, a fan can be any revolving vane, or vanes used for producing currents of air. Fans produce air flows with high volume and low pressure (although higher than ambient pressure), as opposed to compressors which produce high pressures at a comparatively low volume. A fan blade will often rotate when exposed to an air-fluid stream, and devices that take advantage of this, such as anemometers and wind turbines, often have designs similar to that of a fan.
Air current in the context of Downdraft
In meteorology, an updraft (British English: up-draught) is a small-scale current of rising air, often within a cloud.
Air current in the context of Stratocumulus cloud
A stratocumulus cloud [Kämtz 1840], occasionally called a cumulostratus, belongs to a genus-type of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumulus, and the whole being at a lower height, usually below 2,000 metres (6,600 ft). Weak convective currents create shallow cloud layers (see also: sea of clouds) because of drier, stable air above preventing continued vertical development. Historically, in English, this type of cloud has been referred to as a twain cloud for being a combination of two types of clouds.