etage
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A cloud étage is a meteorological term used to delimit any one of three main altitude levels in the troposphere where certain cloud types usually form.{{cite web|url=http://www.eumetcal.org/euromet/glossary/cloudeta.htm |title=Cloud étage |author=World Meteorological Organization |author-link=World Meteorological Organization |publisher=Eumetcal |accessdate=March 28, 2016 |url-status=dead |archiveurl=https://web.archive.org/web/20160412151955/http://www.eumetcal.org/euromet/glossary/cloudeta.htm |archivedate=April 12, 2016 }} The term is derived from the French word which means floor or storey, 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 from Earth's equator to the arctic and antarctic regions at the poles.
Correspondences for étages and cloud genus types
The high étage ranges from altitudes of {{convert|10000|to|25000|ft|abbr=on|disp=flip|-2}} in the polar regions, {{convert|16500|to|40000|ft|abbr=on|disp=flip|-2}} in the temperate regions and {{convert|20000|to|60000|ft|abbr=on|disp=flip|-2}} in the tropical region. The major high-level cloud types comprise cirrus, cirrocumulus, and cirrostratus.{{cite web |url=http://oceanservice.noaa.gov/education/yos/resource/JetStream/synoptic/clouds_max.htm |title=Cloud Classifications |author=JetStream |publisher=National Weather Service |date=5 January 2010 |accessdate=31 January 2011}}
The middle étage extends from {{convert|6500|ft|abbr=on|disp=flip|-2}} above surface at any latitude as high as {{convert|13000|ft|abbr=on|disp=flip|-2}} near the poles, {{convert|23000|ft|abbr=on|disp=flip|-2}} at mid latitudes, and {{convert|25000|ft|abbr=on|disp=flip|-2}} in the tropics. Altocumulus and Altostratus are the main cloud types found in the middle levels of the troposphere.
The low étage is found from surface up to {{convert|6500|ft|abbr=on|disp=flip|-2}} at all latitudes. Principal cloud types found in the low levels of the troposphere include stratocumulus, stratus, and small fair weather cumulus.
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.{{cite book |editor=World Meteorological Organization |title=Étages, International Cloud Atlas |volume=I |year=1975 |url=https://archive.org/details/manualonobservat00worl/page/15 |pages=[https://archive.org/details/manualonobservat00worl/page/15 15–16] |isbn=92-63-10407-7 |accessdate=26 August 2014 |url-access=registration }}