Textbook, chapter 4, p. 100-106
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Transcript of Textbook, chapter 4, p. 100-106
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Textbook, chapter 4, p. 100-106Textbook, chapter 4, p. 100-106
clouds
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Cloud classification
• Originally by Luke Howard (1850’s)• Currently used nomeclature based on Abercromy & Hildebrandsson (1887) • Linnean system (genus, species)• morphological only, not genealogical
Latin Root Translation Examplecumulus heap fair weather cumulus stratus layer altostratuscirrus curl of hair cirrusnimbus rain cumulonimbus
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Cloud subclassification
Further classification identifies clouds by height of cloud base.3 levels
Examples:
the prefix "cirr-" (as in cirrus clouds) refers to high levels, the prefix "alto-" (as in altostratus) refers to middle levels.
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Relative heights vary zonally
0
2,000
4,000
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8,000
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12,000
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20,000m
eter
s ag
l
Tropics Midlatitudes Poles
H M L H M L H M L
tropopause
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Cloud types and relative altitudes
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High clouds
composed of ice crystals
fibrous or filamentous shape
ice crystal concentration generally very small
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Cirrus uncinus (mares’ tails)Height (km): 7-10 km+Falling light snow [fallstreaks], not reaching the ground. distorted by upper-tropospheric wind shear.
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Cirrus uncinus
Cirrus floccus
Cirrus uncinus
Cirrus fibratus vertibratus
Cirrus
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Cirrus
Cirrus spissatus
Cirrus spissatus with virga
Cirrus uncinus
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Cirrostratuscontinuoussun shines thru, no precipitation process: widespread ascent aloft, or old thunderstorm anvil
halo
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Cirrocumulus Cs broken into wavessun shine thru, no precipitation
process: widespread ascent combined with convective overturning in a thin layer.
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Middle clouds
Altostratus clouds occur as uniformly gray or white layers that totally or partiallycover the sky. They are usually so thick that the sun is only dimly visible, as ifviewed through frosted glass.
* occur at altitudes where temperatures range between 0 and -25ºC (32 and -13ºF).
* composed of supercooled water droplets, or are in mixed-phase (supercooled water droplets and ice crystals).
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Altostratus
Height (km): base=2-6 km, can be thick, liquid or ice, no precipitation reaching the ground. Process: widespread stable ascent, often preceding a surface warm front.
Altostratus has a uniform and diffuse coverage
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Iridescent Altostratus (difraction)
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Altocumulusbase=2-6 km, usually thin, usually liquid, no precipitation.
Process: widespread ascent combined with convective overturning aloft (left) or with wave activity (right)
clear regions descending air cloudy regions ascending air
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Altocumulus
Altocumulus castellanus
Altocumulus stratiformis
Sharp cloud boundaries indicate the presence of water droplets ratherthan ice crystals.
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Altocumulus lenticularis
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Low-Level Clouds
* usually at temperatures above -5ºC (23ºF)* composed mostly of water droplets.
geostationarysatellite
precipitation
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Stratus
Base>0.1 km, top<3 km, liquid (or ice), may have drizzle falling. Process: stable ascent, mixing
Fog occurs when stratus meets the ground; when it lifts, it maybreak up into stratocumulus.
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Nimbostratus
steady light precipitation
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StratocumulusShallow, usually liquid, no precipitation Process: forced or spontaneous overturning in a shallow layer
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Marine stratocumulus
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cumulusBuoyantly rising air parcels (thermals) become saturatedCu cloud base … LCLShallow or deep
LCL
Cu humulis
Cu mediocris
Cumulonimbus
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Fair-Weather CumulusWidely separated heap clouds of small vertical development. With flat bottoms and rounded tops, they resemble a flock of sheep grazing in a pasture.
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Cu humilis or mediocris
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Cumulus congestus
Larger and deeper cauliflower appearances to the tops. Base is flattish, representing the LCL. Can produce showers.
Cloud top=5-7 km, above the freezing level but usually still liquid.
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CumulonimbusLook at this animation
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12 June 2004, Hastings NE. Photo by Doug Raflik
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Cumulonimbus: the most active member of the cumulus family
Convective family over the South China Sea
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Cumulonimbus
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Pop quizzes: cloud identification
A: cirrusA: cirrus B: cirrostratusB: cirrostratus C: cirrocumulusC: cirrocumulus D: altostratusD: altostratus E: altocumulusE: altocumulus F: stratusF: stratus G: stratocumulusG: stratocumulus
H: cumulus humilisH: cumulus humilis I: cumulus congestusI: cumulus congestus J: cumulonimbusJ: cumulonimbus J: nimbostratusJ: nimbostratus
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a mid-level cloud in the lee of mountain ranges
cirruscirrus cirrostratuscirrostratus cirrocumuluscirrocumulus altostratusaltostratus altocumulusaltocumulus stratusstratus stratocumulusstratocumulus cumulus humiliscumulus humilis cumulus congestuscumulus congestus cumulonimbuscumulonimbus nimbostratusnimbostratus
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cirruscirrus cirrostratuscirrostratus cirrocumuluscirrocumulus altostratusaltostratus altocumulusaltocumulus stratusstratus stratocumulusstratocumulus cumulus humiliscumulus humilis cumulus congestuscumulus congestus cumulonimbuscumulonimbus nimbostratusnimbostratus
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cirruscirrus cirrostratuscirrostratus cirrocumuluscirrocumulus altostratusaltostratus altocumulusaltocumulus stratusstratus stratocumulusstratocumulus cumulus humiliscumulus humilis cumulus congestuscumulus congestus cumulonimbuscumulonimbus nimbostratusnimbostratus
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Hint: it is overcast, but not raining
cirruscirrus cirrostratuscirrostratus cirrocumuluscirrocumulus altostratusaltostratus altocumulusaltocumulus stratusstratus stratocumulusstratocumulus cumulus humiliscumulus humilis cumulus congestuscumulus congestus cumulonimbuscumulonimbus nimbostratusnimbostratus
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cirruscirrus cirrostratuscirrostratus cirrocumuluscirrocumulus altostratusaltostratus altocumulusaltocumulus stratusstratus stratocumulusstratocumulus cumulus humiliscumulus humilis cumulus congestuscumulus congestus cumulonimbuscumulonimbus nimbostratusnimbostratus
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cirruscirrus cirrostratuscirrostratus cirrocumuluscirrocumulus altostratusaltostratus altocumulusaltocumulus stratusstratus stratocumulusstratocumulus cumulus humiliscumulus humilis cumulus congestuscumulus congestus cumulonimbuscumulonimbus nimbostratusnimbostratus
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Hint: this cloud layer is low
cirruscirrus cirrostratuscirrostratus cirrocumuluscirrocumulus altostratusaltostratus altocumulusaltocumulus stratusstratus stratocumulusstratocumulus cumulus humiliscumulus humilis cumulus congestuscumulus congestus cumulonimbuscumulonimbus nimbostratusnimbostratus
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Hint: this cloud layer is high
cirruscirrus cirrostratuscirrostratus cirrocumuluscirrocumulus altostratusaltostratus altocumulusaltocumulus stratusstratus stratocumulusstratocumulus cumulus humiliscumulus humilis cumulus congestuscumulus congestus cumulonimbuscumulonimbus nimbostratusnimbostratus
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this is a halo
cirruscirrus cirrostratuscirrostratus cirrocumuluscirrocumulus altostratusaltostratus altocumulusaltocumulus stratusstratus stratocumulusstratocumulus cumulus humiliscumulus humilis cumulus congestuscumulus congestus cumulonimbuscumulonimbus nimbostratusnimbostratus
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Hint:it is raining
cirruscirrus cirrostratuscirrostratus cirrocumuluscirrocumulus altostratusaltostratus altocumulusaltocumulus stratusstratus stratocumulusstratocumulus cumulus humiliscumulus humilis cumulus congestuscumulus congestus cumulonimbuscumulonimbus nimbostratusnimbostratus
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A few other cloud visual clues 1. anvil development
process: buoyant ascentlightning usual(lightning is rare over the oceans)much precip evaporates if LCL is high
view this animation
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Cumulonimbus: Severe weather
lightning, thunder, heavy rains, hail, strong winds, and tornadoes …
Model simulations:
Typical thunderstorm
Severe thunderstorm
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Cumulonimbus: Shelf cloudsWe are just ahead of a severe thunderstorm. Dewpoints are in the mid-70s.
Winds gust to over 40 mph with the passage of this shelf cloud. Evaporatively cooled air is pushed out of the precipitation area by the
downdraft, warm air slides up and over the gust front forming the concave-shaped shelf cloud.
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Cumulonimbus: Mammatus cloudspockets of negatively-buoyant air, filled with snowsuspended from the anvil base
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Mesoscale Convective Complexes
Radar animation
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Orographic and wave clouds
Orographic clouds are produced by the flow of air interacting with mountainous terrain. They often indicate areas of clear air turbulence.
mountain wave
lee wave
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Altocumulus lenticularis
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Lenticular clouds
Altocumulus lenticularis are the"mountain-wave clouds." As strong horizontal winds encountera mountain range, gravity wavespropagate upwards, and leeward.
Mountain waves are stationary.
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Ac lenticularis elsewhere
RH stratification may yield a ‘stack of pancakes’
Plymouth, NH, 3 Dec ‘96 Which one is liquidwhich one ice ?
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Unusual AC lenticularis
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Mountain-wave turbulence
Föhn wall cloud, Rockies
turbulent rotor cloud in Owens Valley, CA, downwind of the Sierras.
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Mountain-wave turbulence :Banner clouds
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Banner cloud or lenticular cloud ? (same mountain)
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Kelvin-Helmholtz waves and KH billows
KH waves form when strong wind shear overturns a stable layer (i.e., an inversion).
They are usually invisible!(CAT)
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Kevin-Helmholtz instability
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Breaking billows – an aviation hazard
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Kelvin-Helmholtzwaves onJupiter. Colors indicate the clouds' altitudes: blue is lowestthrough red as highest.
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Cap clouds
Pileus, Latin for "skullcap,"is a smooth cloud that forms when a stable, humid layer aloft forced to rise by a penetratingThunderstorm cell.
cap cloud on a Cb
Pileus cloud attached to the top of a cumuliform cloud.
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“Morning glory” roll clouds
These occur when a deep stable layer overruns a shallower stable layer. Gravity waves ahead of the deep layer result in roll clouds, and may cause severe turbulence.
~1000 km
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Air rises and condenses at the leading edge, and evaporates behind
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These cigar-shaped clouds also occur in the US, mainly in spring
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note the stably stratified layer below, and the more turbulent one above