Cloud type is measured using a standardized system based on visual observation and classification criteria established by the World Meteorological Organization (WMO). The process involves identifying characteristic shapes, altitudes, and associated weather patterns. This contrasts with measuring cloud cover, which uses the okta scale.
The Okta Scale: Measuring Cloud Cover, Not Type
While not directly measuring type, the okta scale is crucial in weather reporting. It quantifies the fraction of the sky covered by clouds:
- 0 oktas: A completely clear sky, no clouds present.
- 1 okta: Cloud cover of 1 eighth or less.
- 7 oktas: Cloud cover of 7 eighths or more, but not completely overcast.
These observations, combined with visual identification, contribute to a comprehensive weather report. Satellite imagery can also assist in assessing cloud cover. Wikipedia's article on Okta offers further details.
Identifying Cloud Types: Visual Observation and Classification
Human observers, trained in cloud identification, are essential. They categorize clouds based on their appearance and altitude, employing the WMO's international classification system. This system groups clouds into various genera, species, and varieties, allowing for precise identification. For example, cumulus clouds are puffy and typically associated with fair weather, while stratus clouds are layered and often indicate overcast conditions. The Met Office provides a guide on observing clouds.
Technological Aids: Ceilometers and Lidar
Technology complements visual observation. Ceilometers, a type of lidar, measure cloud base height using light beams. They project a beam of light upward, and the time it takes for the beam to reflect back from the cloud base is used to calculate the cloud's height. This technology doesn't directly identify cloud type but provides crucial information about cloud altitude which aids in classification. Windy.app's article on cloud height explains this method.
In Summary
Cloud type is primarily measured through visual identification using the WMO classification system, supported by instrumental measurements of cloud height (e.g., ceilometers) and observation of cloud cover (oktas).
