cloud classification and identification - vortex.plymouth.edu
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Cloud Classification and Identification
Part of Chapter 5
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• Cloud classification is based on:‒ Height‒ Physical appearance
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Types of clouds• Clouds with vertical development• Low clouds‒ base below 2,000 m (6,500 ft)‒ composed of water droplets
• High clouds‒ base generally above 6,000 m (20,000 ft)‒ composed of ice crystals
• Middle clouds‒ in between• Some overlap with high clouds
‒ composed of water droplets • (mixed with ice crystals when T is low enough)
• Unusual clouds
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Cloud namesVertically-Developing(Cu) cumulus(Cb) cumulonimbus
Low High Middle(St) stratus (Ci) cirrus(Ns) nimbostratus (Cs) cirrostratus (As) altostratus(Sc) stratocumulus (Cc) cirrocumulus (Ac) altocumulus
UnusualLenticular, mammatus, billow, contrail, others…
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1. Clouds with vertical development
• Cumulus
• Cumuloniumbus
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• Cumulus‒ Abbreviation Cu‒ White-gray puffy clouds• Cumulus‒ Latin for heap or accumulation
‒ Composition: water droplets‒ Scud (Cumulus Fractus)• Irregular and ragged looking• Sometimes form under precipitating clouds
‒ Cumulus Congestus• Towering cumulus
‒ Commonly form by convection• During warm afternoons
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• Cumulonimbus‒ Thunderstorm cloud• Nimbus ‒ Latin for rain
‒ Abbreviation Cb‒ Dark base, commonly anvil shaped‒ Usually extends to top of troposphere‒ Composition varies with height• Water droplets to mix to ice
‒ Lightning and thunder‒ Heavy precipitation• Showery• Capable of rain, snow, hail
‒ Need unstable environments to form• Normally conditionally unstable environment, since absolutely unstable does not occur too often
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Formation of a cumulus cloud
• As the day progresses, conditionally unstable conditions reach higher levels, allowing the cloud to grow‒ From cumulus humilis (regular, small, puffy cloud), to cumulus congestus, to comulonimbus
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2. Low Clouds‒ base below 2,000 m (6,500 ft)‒ composed of water droplets
• Stratus
• Nimbostratus
• Stratocumulus
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• Stratus‒ Abbreviation St‒ Covers entire sky• Stratus ‒ Latin for layer
‒ Resembles fog above the ground‒ No precipitation‒ Cannot see sun through it
‒ Technically, fog is a stratus cloud on the ground
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• Nimbostratus‒ Abbreviation Ns‒ Steady precipitation• Nimbo ‒ rain• stratus ‒ layer
‒ Commonly accompanied by Scud
‒ Sometimes considered a middle cloud• Since it extends from low to middle levels
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• Stratocumulus‒ Abbreviation Sc‒ Lumpy cloud layer‒ Blue sky visible in between‒ Individual “lumps”• Roughly size of fist when arm extended
‒ Produced by an unstable layer capped by a stable layer• Usually an inversion
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3. High Clouds‒ base generally above 6,000 m (20,000 ft)‒ composed of ice crystals
• Cirrus
• Cirrostratus
• Cirrocumulus
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• Cirrus‒ Abbreviation Ci‒ Thin, wispy, feathery clouds• Cirro ‒ Latin for feather
‒ Associated with fair weather
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• Cirrostratus‒ Abbreviation Cs‒ thin, sheet-like clouds that cover the whole sky‒ Sun easily visible through‒ Can be accompanied by a halo
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• Cirrocumulus‒ Abbreviation Cc‒ Small rounded white puffs‒ Less common than Ci and Cs‒ Can resemble fish scales• Mackerel sky
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4. Middle Clouds‒ in between ‒ 2,000 m to 7,000 m• 6,500 ft to 23,000 ft• Some overlap with high clouds
‒ composed of water droplets • (mixed with ice crystals when T is low enough)
• Altostratus
• Altocumulus
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• Altostratus‒ Abbreviation As‒ Covers entire sky‒ Sun dimly seen though it• No shadows cast
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• Altocumulus‒ Abbreviation Ac‒ Grey/white puffy masses‒ Individual “lumps”• Size of thumbnail when arm extended
All Together!
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Hints to help remember names
• “cirro”• Means “feather”• Always used for high clouds
• “alto”• Means “tall”• Always used for middle clouds
• “stratus”• Means “layer”• usually cover entire sky
• “cumulus”• Means “accumulation”• Puffy, rounded
• “nimbus”• Means “rain”• Used for precipitating clouds
• Latin origin
Distinguishing between Sc, Ac and Cc
• Refer to notes from class
Distinguishing between St, As and Cs
• Refer to notes from class
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Distinguishing between St and Ns
• Stratus ‒ no rain
• Nimbostratus - rain
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Note about precipitating clouds• By definition, Cb and Ns cause precipitation‒ Cb ‒ showery, potentially intense‒ Ns ‒ steady, light or moderate
• But other cloud types are also capable of producing some precipitation‒ Mostly drizzle or very light rain or snow
‒ The following table shows what kind of precipitation is possible
32• From “The Cloudspotter’s Guide” (2006)‒ (The symbols refer to precip type and not intensity)
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More to Classification
• There is a lot more to cloud classification
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Guide (2006)
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• Cloud ID Handout
• Cloud type list and links from Wikipedia• (they are slowly being filled up)
‒ http://en.wikipedia.org/wiki/Cloud_types
• Cloud Classification information from the glossary of Meteorology‒ http://amsglossary.allenpress.com/glossary/search?id=cloud-classification1
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• Cloud symbols can be added to the station model• http://www.srh.weather.gov/srh/jetstream/synoptic/wxmaps.htm
‒ All cloud symbols• http://www.srh.weather.gov/srh/jetstream/synoptic/clouds_max.htm
» (click on the pictures)
• High clouds• Middle clouds
• Low Clouds
• Cloud base in hundreds of feet
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5. Unusual clouds‒ Note: Unusual clouds can usually be classified into one of the main ten categories
• Lenticular clouds‒ Individual elements look like a lens‒ More often compared to UFOs
• Billow clouds‒ Look like crashing waves
• Contrails‒ Condensation trails from airplanes
• Clouds outside the troposphere‒ Not a lot is known about them
• Other…
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• Lenticular clouds are wave clouds formed when stable air passes over mountains
• Rising air cools and water vapor condenses into cloud droplets
• Sinking air warms and droplets evaporate
‒ Billow clouds form when two layers of air with differing speeds meet. The wave formation is analogous to waves in the ocean• Also called instability clouds • Or KH-clouds‒ Because formed by Kelvin-Helmholtz instability
Clouds Outside the Troposphere
• Nacreous Clouds
• Noctilucent Clouds
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Nacreousclouds
Noctilucentclouds
http://science.nasa.gov/headlines/y2003/19feb_nlc.htm
Thunderstorm Cloud Features• Mammatus• Overshooting Top• Shelf Cloud• Roll Cloud• Wall Cloud• Cap Cloud
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Other Miscellaneous Clouds
• Cap Clouds• Pyrocumulus• “Sonic boom cloud”
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• Relevant Textbook readings‒ Clouds• Classification of Clouds ‒ pp 122-123• Cloud Identification ‒ pp 123-128• Some Unusual Clouds ‒ pp 128-130
‒ Cloud Development (Ch 6)• (formation of lenticular clouds) ‒ p 157• Changing Cloud Forms ‒ pp 158-160
‒ Eddies and “Air Pockets” (Ch 9) ‒ p 229• (for info about billow cloud formation)
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• Relevant Web Content‒ Including clouds in a station model plot• How to read ‘surface’ weather maps
‒ http://www.srh.weather.gov/srh/jetstream/synoptic/wxmaps.htm• Cloud Symbols
‒ http://www.srh.weather.gov/srh/jetstream/synoptic/sfc_plot_symbols.htm#c
‒ Cloud Classification and Identification resources• List of cloud types from Wikipedia
‒ http://en.wikipedia.org/wiki/Cloud_types• Could not find any good online guides ….
• Great Book Resource‒ The Cloudspotter’s Guide: The Science, History and Culture of Clouds (2007)• By Gavin Pretor-Pinney 51
• No extra textbook reading …
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