page_title: Glossary of meteorology
section_title: C
hierarchical_section_title: Glossary of meteorology / C
caption_attribution_description: English: A beautifully-formed low-pressure system swirls off the southwestern coast of Iceland, illustrating the maxim that "nature abhors a vacuum." The vacuum in this case would be a region of low atmospheric pressure. In order to fill this void, air from a nearby high-pressure system moves in, in this case bringing clouds along for the ride. And because this low-pressure system occurred in the Northern Hemisphere, the winds spun in toward the center of the low-pressure system in a counter-clockwise direction; a phenomenon known as the Coriolis force (in the Southern Hemisphere, the Coriolis force would be manifested in a clockwise direction of movement). The clouds in the image resembled pulled cotton and lace as they spun in a lazy hurricane-like pattern. This huge system swirled over the Denmark Strait in between Greenland and Iceland. Español: Imagen satelital que muestra una depresión centrada en el estrecho de Dinamarca entre Islandia y Groenlandia. Los vientos, atraídos por la zona de baja presión en el centro, doble bajan el efecto de la fuerza de Coriolis, que dan la apariencia de caracol desde el espacio. Français&#160;: Image satellite montrant une dépression centrée sur le détroit du Danemark, entre l'Islande et le Groenland. Les vents, attirés par la zone de basses pressions au centre, se courbent sous l'effet de la force de coriolis, ce qui donne l'aspect spiralé observé ici.
context_page_description: This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.
context_section_description: Canadian Meteorological and Oceanographic Society (CMOS)
  The national society of individuals and organizations dedicated to advancing atmospheric and oceanic sciences and related environmental disciplines in Canada, officially constituted in 1967.
  Canadian Meteorological Centre (CMC)
  capping inversion
  castellanus
  A cloud species that displays at least in its upper part cumuliform protuberances resembling the turrets of a castle, giving a crenellated aspect.
  ceiling
  A measure of the height above the Earth's surface of the base of the lowest layer of clouds or obscuring phenomena that covers more than half of the sky (more than four oktas). An "unlimited" ceiling means either that the sky is mostly free of cloud cover or that the clouds are sufficiently high so as not to impede aircraft operation by visual flight rules.
  ceiling balloon
  ceiling projector
  ceilometer
  An instrument that uses a laser or other light source to determine the height of a cloud ceiling or cloud base or to measure the concentration of aerosols within the atmosphere.
  Center for Analysis and Prediction of Storms (CAPS)
  central dense overcast (CDO)
  The large, centralized, contiguous area of thunderstorms surrounding the rotational center of a strong tropical or subtropical cyclone. When a cyclone reaches sufficient intensity, a distinguishable eye may develop within the CDO. The strongest winds and heaviest rainfall are usually found beneath the coldest cloud tops in the CDO.
  chinook wind
  cirrocumulus
  cirrostratus
  cirrus (Ci)
  A genus of cloud characterized by thin, wispy, feather-like strands that appear white or light grey in color and form at very high altitudes, usually between 5 and 13.7 km (16,000 and 45,000 ft) above sea level. Cirrus clouds often develop from the outflow of cumulonimbus clouds in advance of fronts or thunderstorms, and therefore may indicate the imminent arrival of precipitation.
  clear ice
  A type of solid precipitation which forms when relatively large drops of water are supercooled into a dense, transparent coating of ice without air or other impurities. It is similar to glaze and hard rime and, when formed on the ground, is often called black ice.
  clear-air turbulence
  climate
  The statistics of weather in a given region over long periods of time, measured by assessing long-term patterns of variation in temperature, atmospheric pressure, humidity, wind, precipitation, and other meteorological variables. The climate of a particular location is generated by the interactions of the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere and strongly influenced by latitude, altitude, and local topography. Climates are often classified according to the averages or typical ranges of different variables, most commonly temperature and precipitation.
  climatology
  A branch of the atmospheric sciences that studies climate, defined as weather conditions averaged over an extended to indefinite period of time. Climatology incorporates aspects of oceanography, geology, biogeochemistry, and the related field of meteorology to understand the long-term dynamics of climate-influencing phenomena and to produce climate models which can be used to estimate past climates and predict future climates.
  cloud
  An aerosol consisting of a visible mass of minute liquid droplets, frozen crystals or other particles suspended in the atmosphere. Water or various other chemicals may compose the droplets and crystals. On Earth, clouds are formed as a result of the saturation of an air mass when it is cooled to its dew point or when it gains sufficient moisture (usually in the form of water vapor) from an adjacent source to raise the dew point to the ambient temperature. There are many different types of clouds, which are classified and named according to their shape and altitude.
  cloud atlas
  A pictorial key to the classification and nomenclature of clouds.
  cloud base
  The lowest altitude of the visible portion of a cloud.
  cloud cover
  The obscuration of all or part of the sky by clouds as observed from a particular location, or the specific fraction of the sky 
caption: Very large air masses (and the clouds within them) spiral counterclockwise around a strong center of low atmospheric pressure in this extratropical cyclone over Iceland
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