A cloud étage is a

meteorological Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agriculture ...

term used to delimit any one of three main

altitude Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum (geodesy), datum and a point or object. The exact definition and reference datum varies according to the context (e.g., aviation, geometr ...

levels in the

troposphere The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the Atmosphere, planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the ...

where certain cloud types usually form. The term is derived from the French word which means ''

floor A floor is the bottom surface of a room or vehicle. Floors vary from wikt:hovel, simple dirt in a cave to many layered surfaces made with modern technology. Floors may be stone, wood, bamboo, metal or any other material that can support the ex ...

'' or ''

storey A storey (English in the Commonwealth of Nations, Commonwealth English) or story (American English), is any level part of a building with a floor that could be used by people (for living, work, storage, recreation, etc.). Plurals for the wor ...

'', as in the floor of a multi-storey building. With the exception of the low étage, the altitude range of each level varies according to

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

to the

arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

and

antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

regions at the poles.

Correspondences for étages and cloud genus types

The high étage ranges from altitudes of in the

polar region The polar regions, also called the frigid zones or polar zones, of Earth are Earth's polar ice caps, the regions of the planet that surround its geographical poles (the North and South Poles), lying within the polar circles. These high latitu ...

s, in the

temperate regions In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...

and in the tropical region. The major high-level cloud types comprise cirrus,

cirrocumulus Cirrocumulus is one of the three main genus types of high-altitude tropospheric clouds, the other two being cirrus and cirrostratus. They usually occur at an altitude of , however they can occur as low as in the arctic and weather reporting sta ...

, and

cirrostratus Cirrostratus () is a high-altitude, very thin, and generally uniform stratiform genus-type of cloud. It is composed of ice crystals, which are particles of frozen water. Cirrostratus is difficult to see and can produce halos. These optical e ...

. The middle étage extends from above surface at any latitude as high as near the poles, at mid latitudes, and in the tropics.

Altocumulus Altocumulus () is a middle-altitude cloud genus that belongs mainly to the physical category, characterized by globular masses or rolls in layers or patchesthe individual elements being larger and darker than those of cirrocumulus and smaller t ...

and

Altostratus Altostratus is a middle-altitude cloud genus made up of water droplets, ice crystals, or a mixture of the two. Altostratus clouds are formed when large masses of warm, moist air rise, causing water vapor to condense. Altostratus clouds are usual ...

are the main cloud types found in the middle levels of the troposphere. The low étage is found from surface up to at all latitudes. Principal cloud types found in the low levels of the troposphere include

stratocumulus A stratocumulus cloud, 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 ...

, stratus, and small fair weather

cumulus Cumulus clouds are clouds that have flat bases and are often described as puffy, cotton-like, or fluffy in appearance. Their name derives from the Latin , meaning "heap" or "pile". Cumulus clouds are low-level clouds, generally less than in a ...

. 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 Cumulus congestus or towering cumulus clouds are a species of cumulus that can be based in the low- to middle-height ranges. They achieve considerable vertical development in areas of deep, moist convection. They are an intermediate stage between ...

, and

cumulonimbus Cumulonimbus () is a dense, towering, vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. Above the lower portions of the cumulonimbus the water va ...

References

Clouds {{Cloud-stub fr:Nuage#Classification troposphérique