Textbook, chapter 4, p clouds

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 Example cumulus heap fair weather cumulus stratus layer altostratus cirrus curl of hair cirrus nimbus rain cumulonimbus

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.

Relative heights vary zonally Tropics Midlatitudes Poles H M L tropopause

Cloud types and relative altitudes

High clouds composed of ice crystals fibrous or filamentous shape ice crystal concentration generally very small

Cirrus uncinus (mares’ tails) Height (km): 7-10 km+ Falling light snow [fallstreaks], not reaching the ground. distorted by upper-tropospheric wind shear.

Cirrus uncinus Cirrus floccus Cirrus uncinus Cirrus fibratus vertibratus Cirrus

Cirrus spissatus Cirrus spissatus with virga Cirrus uncinus

Cirrostratus continuous sun shines thru, no precipitation process: widespread ascent aloft, or old thunderstorm anvil halo

Cirrocumulus Cs broken into waves sun shine thru, no precipitation process: widespread ascent combined with convective overturning in a thin layer.

Middle clouds Altostratus clouds occur as uniformly gray or white layers that totally or partially cover the sky. They are usually so thick that the sun is only dimly visible, as if viewed 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).

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

Iridescent Altostratus (difraction)

Altocumulus base=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

Altocumulus Altocumulus castellanus Altocumulus stratiformis Sharp cloud boundaries indicate the presence of water droplets rather than ice crystals.

Altocumulus lenticularis

Low-Level Clouds * usually at temperatures above -5ºC (23ºF) * composed mostly of water droplets. geostationary satellite precipitation

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 may break up into stratocumulus.

Nimbostratus steady light precipitation

Stratocumulus Shallow, usually liquid, no precipitation Process: forced or spontaneous overturning in a shallow layer

Marine stratocumulus

cumulus Buoyantly rising air parcels (thermals) become saturated Cu cloud base … LCL Shallow or deep LCL  Cu humulis Cu mediocris Cumulonimbus

Fair-Weather Cumulus Widely separated heap clouds of small vertical development. With flat bottoms and rounded tops, they resemble a flock of sheep grazing in a pasture.

Cu humilis or mediocris

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.

Cumulonimbus Look at this animation

12 June 2004, Hastings NE. Photo by Doug Raflik

Cumulonimbus: the most active member of the cumulus family Convective family over the South China Sea

Cumulonimbus

Pop quizzes: cloud identification n A: cirrus n B: cirrostratus n C: cirrocumulus n D: altostratus n E: altocumulus n F: stratus n G: stratocumulus n H: cumulus humilis n I: cumulus congestus n J: cumulonimbus n J: nimbostratus

a mid-level cloud in the lee of mountain ranges n cirrus n cirrostratus n cirrocumulus n altostratus n altocumulus n stratus n stratocumulus n cumulus humilis n cumulus congestus n cumulonimbus n nimbostratus

n cirrus n cirrostratus n cirrocumulus n altostratus n altocumulus n stratus n stratocumulus n cumulus humilis n cumulus congestus n cumulonimbus n nimbostratus

n cirrus n cirrostratus n cirrocumulus n altostratus n altocumulus n stratus n stratocumulus n cumulus humilis n cumulus congestus n cumulonimbus n nimbostratus

Hint: it is overcast, but not raining n cirrus n cirrostratus n cirrocumulus n altostratus n altocumulus n stratus n stratocumulus n cumulus humilis n cumulus congestus n cumulonimbus n nimbostratus

n cirrus n cirrostratus n cirrocumulus n altostratus n altocumulus n stratus n stratocumulus n cumulus humilis n cumulus congestus n cumulonimbus n nimbostratus

n cirrus n cirrostratus n cirrocumulus n altostratus n altocumulus n stratus n stratocumulus n cumulus humilis n cumulus congestus n cumulonimbus n nimbostratus

Hint: this cloud layer is low n cirrus n cirrostratus n cirrocumulus n altostratus n altocumulus n stratus n stratocumulus n cumulus humilis n cumulus congestus n cumulonimbus n nimbostratus

Hint: this cloud layer is high n cirrus n cirrostratus n cirrocumulus n altostratus n altocumulus n stratus n stratocumulus n cumulus humilis n cumulus congestus n cumulonimbus n nimbostratus

this is a halo n cirrus n cirrostratus n cirrocumulus n altostratus n altocumulus n stratus n stratocumulus n cumulus humilis n cumulus congestus n cumulonimbus n nimbostratus

Hint: it is raining n cirrus n cirrostratus n cirrocumulus n altostratus n altocumulus n stratus n stratocumulus n cumulus humilis n cumulus congestus n cumulonimbus n nimbostratus

A few other cloud visual clues 1. anvil development process: buoyant ascent lightning usual (lightning is rare over the oceans) much precip evaporates if LCL is high view this animation

Cumulonimbus: Severe weather lightning, thunder, heavy rains, hail, strong winds, and tornadoes … Model simulations: Typical thunderstorm Severe thunderstorm

Cumulonimbus: Shelf clouds We 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.

Cumulonimbus: Mammatus clouds pockets of negatively-buoyant air, filled with snow suspended from the anvil base

Mesoscale Convective Complexes Radar animation

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

Altocumulus lenticularis

Lenticular clouds Altocumulus lenticularis are the "mountain-wave clouds." As strong horizontal winds encounter a mountain range, gravity waves propagate upwards, and leeward. Mountain waves are stationary.

Ac lenticularis elsewhere RH stratification may yield a ‘stack of pancakes’ Plymouth, NH, 3 Dec ‘96 Which one is liquid which one ice ?

Unusual AC lenticularis

Mountain-wave turbulence Föhn wall cloud, Rockies turbulent rotor cloud in Owens Valley, CA, downwind of the Sierras.

Mountain-wave turbulence : Banner clouds

Banner cloud or lenticular cloud ? (same mountain)

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)

Kevin-Helmholtz instability

Breaking billows – an aviation hazard

 Kelvin-Helmholtz waves on Jupiter. Colors indicate the clouds' altitudes: blue is lowest through red as highest.

Cap clouds Pileus, Latin for "skullcap," is a smooth cloud that forms when a stable, humid layer aloft forced to rise by a penetrating Thunderstorm cell.  cap cloud on a Cb Pileus cloud attached to the top of a cumuliform cloud.

“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

Air rises and condenses at the leading edge, and evaporates behind

These cigar-shaped clouds also occur in the US, mainly in spring

note the stably stratified layer below, and the more turbulent one above