Clouds

Note from the webmaster: To me clouds are not just a product of science; they will forever be intertwined with fantasy. Ever since I was a boy, sailing on our family sailboat, I fondly remember the clouds of all shapes and sizes taking on spectacular shapes, constantly occupying my mind with ever changing characters.

I do not have images of any cloud types, as I have not taken pictures of specific types, for images check links provided below. My intentions are to provide a list of cloud types and the height for which they are found.

National Weather Service -- Cloud Observing Handbook.pdf (4.63Mb)

Luke Howard, the man who named the clouds

In London one evening in December 1802, a pharmacist called Luke Howard presented a paper at a meeting of the Askesian Society, an association of amateur scientists he had himself helped found (in March 1796). The paper was "On the modification of clouds" ('modification' meaning 'classification'), and in this paper Howard proposed some of the cloud names we still use today.
He stated, to quote from the published version of his paper, that "if clouds were the mere result of the condensation of vapour in the masses of atmosphere which they occupy, if their variations were produced by the movements of the atmosphere alone, then indeed might the study of them be deemed an useless pursuit of shadows, an attempt to describe forms which, being the sport of winds, must be ever varying, and therefore not to be defined". "But", he went on, "however the erroneous admission of this opinion may have operated to prevent attention to them, the case is not so with clouds". "They are", he said, "subject to certain distinct modifications, produced by the general causes which effect all the variations of the atmosphere".
Therefore, he proposed, "in order to enable the meteorologist to apply the key of analysis to the experience of others, as well as to record his own with brevity and precision, it may perhaps be allowable to introduce a methodical nomenclature, applicable to the various forms of suspended water, or, in other words, to the modifications of cloud".
Howard chose to use Latin for his nomenclature, saying that "the reasons for having recourse to a dead language for terms to be adopted by the learned of different nations are obvious". In adopting Latin, Howard followed the lead of the Swedish taxonomist Carl von Linné (Linnaeus).
In his original classification, Howard introduced three basic cloud genera:

Cirrus (Latin for a curl of hair), which he described as "parallel, flexuous, or diverging fibres, extensible in any or all directions";
Cumulus (meaning heap), which he described as "convex or conical heaps, increasing upward from a horizontal base";
Stratus (meaning something spread), which he described as "a widely extended, continuous, horizontal sheet, increasing from below".

He combined these names to form four more cloud types, namely:
Cirro-cumulus, which he described as "small, well-defined roundish masses, in close horizontal arrangement";
Cirro-stratus, which he described as "horizontal or slightly inclined masses, attenuated towards a part or the whole of their circumference, bent downward, or undulated, separate, or in groups consisting of small clouds having these characters";
Cumulostratus, which he described as "the cirrostratus blended with the cumulus, and either appearing intermixed with the heaps of the latter, or super-adding a widespread structure to its base";
Cumulo-cirro-stratus or Nimbus, which he called the rain cloud, "a cloud or system of clouds from which rain is falling". He described it as "a horizontal sheet, above which the cirrus spreads, while the cumulus enters it laterally and from beneath".

Howard was not the first to classify clouds. In 1802, the French scientist Jean-Baptiste Lamarck (1744-1829) published, in the third volume of his Annuaires météorologiques, a paper "Sur la forme des nuages" (On the form of clouds). In this, he proposed five main types of cloud, these being:
Nuages en voile (clouds like veils)
Nuages attroupés (massed clouds)
Nuages pommelés (dappled clouds)
Nuages en balayures (clouds like sweepings)
Nuages groupés (grouped clouds)
Unfortunately for Lamarck, his classification attracted little attention, perhaps because it was a little vague, perhaps because it was presented in French, rather than the international language of science (which was Latin). Whatever the reason, Howard's classification was the one adopted and developed.
Before the time of Lamarck and Howard, clouds were described by their colour or their form, especially by farmers and sailors, who used such terms as "mackerel sky", "curl cloud", "mares' tails", "curdly sky", "wool bags", "brassy-coloured clouds" and "inky-looking clouds". Clouds were considered too changeable and short-lived to be classified.

During the 19th century, Howard's system of cloud classification was modified and expanded, notably by the Swedish meteorologist Hugo Hildebrand Hildebrandsson (1838-1920) and the British meteorologist Ralph Abercromby (1842-1897). At an international conference held in 1891, meteorologists agreed the system of cloud genera, species and varieties used today. Three years later, at another international conference, definitions of the various cloud forms were approved.
In 1896, the first edition of The International Cloud Atlas was published. Astonishingly, there was no mention of Howard in this work, an omission pointed out by Dr Robert Barnes in The Quarterly Journal of the Royal Meteorological Society (1897, Vol.23, p.62). "Surely if ever a man deserved recognition in connection with this subject [cloud classification], it is this famous scientist and noble philanthropist [Luke Howard]. No-one can examine this atlas or study the subject [clouds] without seeing that the foundation was laid by Luke Howard. It is the old tale, Sic vos non vobis nidificatis … Alter tulit honores" (which means, very roughly translated, that Howard built the nest but others gained the credit).1

Main Components
Latin Origins	Translations	Examples
cumulus	heap	fair weather cumulus
stratus	layer	altostratus
cirrus	curl of hair	cirrus
altum	height, upper air	altocumulus
nimbus	rain	altocumulus

Cloud Genus (PL. Genera)
Genus	ABBR.	Obs. Symbol	Description / Translation	Height
Stratus	St	See Below	Essentially featureless, grey layer clouds at low level	Low
Stratocumulus	Sc	See Below	Heaps or rolls of clouds, with distinct gaps and heavy shading at low levels	Low
Nimbostratus	Ns	See Below	Dark grey clouds at middle levels, frequently extending down towards surface, and giving prolonged precipitation	Low to middle
Cumulus	Cu	See Below	Rounded heaps of clouds at low levels	Low
Cumulonimbus	Cb	See Below	Large towering clouds extending to great heights, with ragged base and heavy precipitation	Low to High
Altocumulus	Ac	See Below	Heaps or rolls of clouds, showing distinct shading, and with clear gaps between them, in a layer at middle levels	middle
Altostratus	As	See Below	Sheet of featureless, white or grey cloud at middle levels	middle
Cirrus	Ci	See Below	Fibrous wisps of clouds at high levels	high
Cirrocumulus	Cc	See Below	Tiny heaps of clouds with no shading, with clear gaps, in a layer at high levels	high
Cirrostratus	Cs	See Below	Essentially featureless sheets of thin clouds at high levels	high

Cloud Species
Fourteen terms to describe cloud shape and structure: three letter abbreviations.
Species	ABBR.	Example	Description / Translation	Genera
calvus	cal	status calvus	Tops of rising cells lose their hard appearance adn become smooth	Cb
capillatus	cap	cumulus capillatus	Tops of rising cells become distinctly fibrous or straited; obvious cirrus may appear	Cb
castellanus	cas	altocumulus castellanus	Distinct turrets rising from an extended base	Sc, Ac, Cc, Ci
congestus	con	cumulus congestus	Great vertical extent; obviously growing vigorously, with hard, 'caulifower-like' tops	Cu
fibratus	fib	cirrostratus fibratus	Fibrous appearance, normally straight or uniformly curved; no distinct hooks	Ci, Cs
floccus	flo	cirrus floccus	Individual tufts of clouds, with ragged bases, sometimes with distinct virga	Ac, Cc, Ci
fractus	fra	cirrostratus fractus	Broken cloud with ragged edges and base	Cu, St
humilis	hum	cumulus humilis	Cloud of restricted vertical extent; lenght much greater than height	Cu
lenticularis	len	altocumulus lenticularis	Lens- or almond-shaped clouds, stationary in the sky	Sc, Ac, Cc
Mediocris	med	cumulus mediocris	Cloud of moderate vertical extent, growing upwards	Cu
nebulosus	neb	stratus nebulosus	Featureless sheet of cloud, with no structure	St, Cs
spissatus	spi	cirrus spissatus	Dense cloud, appearing grey when viewed towards the Sun	Ci
stratiformis	str	altocumulus stratiformis	Clouds in an extensive sheet or layer	Sc, Ac, Cc
uncinus	unc	cirrus uncinus	Distinctly hooked, often without a visible generating heat	Ci
mammatus cloud	mam	mammatus	sagging pouch-like structures;Mammatus are pouch-like cloud structures and a rare example of clouds in sinking air. Sometimes very ominous in appearance, mammatus clouds are harmless and do not mean that a tornado is about to form; a commonly held misconception. In fact, mammatus are usually seen after the worst of a thunderstorm has passed.	Cb
billow cloud		billow	Billow clouds are created from instability associated with air flows having marked vertical shear and weak thermal stratification. The common name for this instability is Kelvin-Helmholtz instability. These instabilities are often visualized as a row of horizontal eddies aligned within this layer of vertical shear.
contrail cloud		contrails	A contrail, also known as a condensation trail, is a cirrus-like trail of condensed water vapor often resembling the tail of a kite. Contrails are produced at high altitudes where extremely cold temperatures freeze water droplets in a matter of seconds before they can evaporate.	Ci
pileous cloud		pileous	smooth capping clouds; Pileus (Latin for "skullcap") is a smooth cloud found attached to either a mountain top or growing cumulus tower

Cloud Varieties
Nine terms that describe cloud transparency and the arrangement of cloud elements: two-letter abbreviations. Any given cloud may exhibit the characteritics of more than one variety-often several may be present simultaneously.
Variety	ABBR.	Example	Description / Translation	Genera
duplicatus	du		Two or more layers	Sc, Ac, Cc, Cs
intortus	in		Tangled or irregularly curved	Ci
lacunosus	la		Thin cloud with regularly spaced holes, appearing like a net	Ac, Cc, Sc
opacus	op		Thick cloud that completely hides the Sun or Moon	St, Sc, Ac, As
perlucidus	pe		Extensive layer with gaps, through which blue sky, the Sun or Moon are visible	Sc, Ac
radiatus	ra		Appearing to radiate from one point in the sky	Cu, Sc, Ac, As, Ci
translucidus	tr		Translucent cloud, through which the position of the Sun or Moon is readily visible	St, Sc, Ac, As
undalatus	un		Layer or patch of cloud with distinct undulations	St, Sc, Ac, As, Cc, Cs
vertebratus	ve		Lines of cloud looking like ribs, vertebrae or fish bones	Ci

Cloud Accessory
Three forms that occur only in conjunction with one of the 10 main genera: three-letter abbreviations.
Name	ABBR.	Example	Description / Translation	Genera
pannus	pan		Ragged shred of cloud beneath main cloud mass	Cu, Cb, As, Ns
pileus	pil		Hood or cap of clouds above rising cells	Cu, Cb
velum	vel		Thin, extensive sheet of clouds, through which the most vigorous cells my penetrate	Cu, Cb

Cloud Supplementary Features
Six particular form (some common, others quite rare) that particular genera or species may adopt: three-letter abbreviations.
Features	ABBR.	Example	Description / Translation	Genera
arcus	arc		Arch or roll of cloud	Cb, Cu
incus	inc		Anvil cloud	Cb
mamma	mam		Bulges or pouches beneath higher cloud	Cb, Ci, Cc, Ac, As, Sc
praecipitatio	pre		Precipitation that reaches the surface	Cb, Cu, Ns
tuba	tub		Funnel cloud of any type	Cb, Cu
virga	vir		Fallstreaks; trails of precipitation that do not reach the surface	Ac, As, Cc, Cb, Cu, Ns, Sc, (Ci)

Additional

Further classification identifies clouds by height of cloud base. For example, cloud names containing the prefix "cirr-", as in cirrus clouds, are located at high levels while cloud names with the prefix "alto-", as in altostratus, are found at middle levels. This module introduces several cloud groups. The first three groups are identified based upon their height above the ground. The fourth group consists of vertically developed clouds, while the final group consists of a collection of miscellaneous cloud types.

Two additional terms are used occationally. These are the suffixes '-genitus' and '-mutatus' -- abbreviated 'gen' and 'mut', respectively-- which are added to a particular cloud genus to indicate the type from which are added to a particular cloud genus to indictate the type from which a currently observed cloud has been derived. The first implies that a considerable amount of the parent cloud is still present; the second that essentially all the parent cloud has been altered.

Source: http://www.meteo.psu.edu/~verlinde/meteo437/atlas.html and http://www.rmets.org/education/howard.php

NWS - Cloud Classification
Clouds are classified into 27 different categories that use Latin words to describe the appearance of clouds as seen by an observer on the ground. Additionally, further classification identifies clouds by height of cloud base. For example:

Cirro is the prefix given to high clouds, those with bases above 20,000 feet (6,000 m), composed of ice crystals. High-level clouds are typically thin and white in appearance, but can appear in a magnificent array of colors when the sun is low on the horizon.

Alto is the prefix given to mid-level clouds, those between 6,000 and 20,000 feet (1,800 to 6,000 m). They are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are low enough.

Strato is the prefix given for low clouds, those with bases below 6,000 feet (1,800 m). These low clouds are of mostly composed of water droplets.

Nimbo added to the beginning, or nimbus added to the end of a cloud name means the cloud is producing precipitation.
Following is a cloud chart showing the different categories, codes and symbols for each type. (click images to enlarge).

	1	2	3	4	5	6	7	8	9
High clouds
Mid Clouds
Low Clouds

Clouds are typically identified based upon your observation point. From sea-level, you might observe stratus clouds enveloping the top of a mountain. However, if you were on the mountain top and in that same cloud, you would observe and report fog. The exception to this is cumulus clouds over a mountain. Even though cumulus clouds typically have bases under 6,000 feet (1,800 m), if you were to observe them over a mountain top, their base might be 12,000 feet (3,600 m) or higher relative to your location closer to sea-level. However, you would still call it a cumulus cloud.

Low-level Clouds or Low-Etage Clouds
Low clouds are of mostly composed of water droplets since their bases generally lie below 6,500 feet (2,000 meters). However, when temperatures are cold enough, these clouds may also contain ice particles and snow.

POLAR REGIONS
Surface - 6,500 ft
Surface - 1,981 m

TEMPERATE REGIONS
Surface - 6,500 ft
Surface - 1,981 m

TROPICAL REGIONS
Surface - 6,500 ft
Surface - 1,981 m

Mid-Level Clouds or Middle-Etage Clouds
The bases of mid-level clouds typically appear between 6,500 to 20,000 feet (2,000 to 6,000 meters). Because of their lower altitudes, they are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are cold enough.

POLAR REGIONS
6,500 - 13,000 ft
1,981 - 3,962 m

TEMPERATE REGIONS
6,500 - 23,000 ft
1,981 - 7,010 m

TROPICAL REGIONS
6,500 - 25,000 ft
1,981 - 7,620 m

High-Level Clouds
High-level clouds form above 20,000 feet (6,000 meters) and since the temperatures are so cold at such high elevations, these clouds are primarily composed of ice crystals. High-level clouds are typically thin and white in appearance, but can appear in a magnificent array of colors when the sun is low on the horizon.

POLAR REGIONS
10,000 - 25,000 ft
3,048 - 7,620 m

TEMPERATE REGIONS
16,500 - 45,000 ft
5,029 - 13,716 m

TROPICAL REGIONS
20,000 - 60,000 ft
6,096 - 18,288 m

Vertically Developed Clouds
Probably the most familiar of the classified clouds is the cumulus cloud. Generated most commonly through either thermal convection or frontal lifting, these clouds can grow to heights in excess of 39,000 feet (12,000 meters), releasing incredible amounts of energy through the condensation of water vapor within the cloud itself.

Source: WW2010: University of Illinois

How Climate Researchers Classify Clouds
Classifying clouds into different cloud types is the first step in analyzing clouds. Recently scientists have suggested an alternative method of classifyng clouds into the traditional groups. This new method classifies clouds based upon how optically thick they are and how high they are in the sky.

The following chart shows how this method classifies clouds based on their optical thickness and cloud top pressure:

source: Goddard Institute for Space Studies (New York, New York)

Cloud Enthusiast!
Cloud Appreciation Society http://www.cloudappreciationsociety.org/	Clouds R Us.com http://www.rcn27.dial.pipex.com/cloudsrus/features.html
Observations and Plotting: Cloud abbr http://www.weathergraphics.com/dl/wxchart.pdf	http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld /home.rxml http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr /cld/home.rxml
Wikipedia.com - Clouds http://en.wikipedia.org/wiki/Cloud	Weather Wiz Kid http://www.weatherwizkids.com/cloud.htm
Wild Wild Weather http://www.wildwildweather.com/clouds.htm	USA Today http://www.usatoday.com/weather/wcloud0.htm
Austrialian Severe Weather - Clouds http://australiasevereweather.com /techniques/moreadv/class.htm#Top	Texas A & M Cloud Classification http://www.met.tamu.edu/class/Metr304/Exer10dir/ classification.html
CCRC http://www.ccrc.sr.unh.edu/~stm/AS/Weather_Toolbox /Cloud_Classification.html	Cloud Classification Kids project http://asd-www.larc.nasa.gov/edu_act/class_cloud_type.html
More on clouds http://vortex.plymouth.edu/clouds.html/	NWS - Jetstream -- clouds http://www.srh.noaa.gov/jetstream/synoptic/clouds_max.htm
NWS - Jetstream :: Online learning of weather http://www.srh.noaa.gov/jetstream/synoptic/clouds.htm#skywatcher	Navy AG module - Cloud Classification http://www.tpub.com/content/aerographer/14312/ css/14312_140.htm