We love clouds. Melanie is a
meteorologist by education, after all. Not only are clouds
themselves fascinating, but their names are mysterious and enigmatic.
We hope to remove some of the mystery from cloud names by providing
their etymologies. Note that we will discuss only scientific names
of clouds in this issue. Folk names for clouds and weather events
are "a whole nother thing" which we may discuss in a future issue.
Today's system of classifying clouds comes
from a system proposed by
Luke Howard in 1803.
Either he was very thorough and/or foresightful, or meteorology hasn't
changed much since 1803! Actually, since Howard was using morphology
(form) to classify clouds, and basic cloud forms are not going to change
over 200 years, his system is still applicable. However,
meteorology and especially forecasting have changed dramatically over
the last 200 years.
Howard used Latin to name cloud types and
characteristics. If you have some knowledge of Latin, you may be
able to figure out what some of the cloud terms mean.
First we should identify the different
cloud classifications. Clouds are classified based on the
1. main characteristics (genera)
2. differences in shape and internal
3. special characteristics of arrangement
and/or transparency (varieties)
4. supplementary features and accessory
There are ten genera:
Cirrus: Latin, "curl,
fringe" - cirrus are curled, wispy or feathery high clouds.
Stratus: "layered, in a sheet" from Latin sternere/stranere
"to spread out, to flatten" - stratus form low grey sheets across the
sky. In ancient Rome, the word stratum was used for many
flat, layered or spread-out objects, including "a bed-covering", " a
horse-blanket" and "pavement". In geology, a stratum is a layer
Cumulus: Latin, "little heap" - the white, fluffy clouds
associated with summer days. We also find the Latin cumulus
in accumulate (literally "to heap up").
nimbus with cumuliform characteristics. Nimbus is Latin for
"cloud" - in meteorology, nimbus means specifically "rain cloud"
- cumulonimbus are large storm clouds, often thunderclouds.
Cirrocumulus: cirrus with small globular elements (instead
of being wispy or sheet-like).
Cirrostratus: stratus-like cirrus (cirrus taking on a
Altocumulus: Latin alto "high" + cumulus - a
high sheet of globular elements that are fairly evenly spaced and of
uniform size. Altitude, of course, is related.
Altostratus: high stratus - a fairly uniform sheet of
cloud at a relatively high altitude (i.e., not extremely low like
Nimbostratus: nimbus with stratiform characteristics - in
meteorology, nimbus means "rain cloud" and nimbostratus appears
as a sheet covering the sky. It is also relatively thick in the vertical
direction. It often produces steady rain which obscures the cloud
shape and extent. Sometimes nimbostratus produces rain that evaporates
before it hits the ground (see virga, below). The ancients
believed that when their gods descended to earth they were surrounded by
a shining cloud of glory - nimbus in Latin. That is why the halo
around a saint's head is still called a nimbus.
Stratocumulus: stratus with cumulus-like properties - this
is stratus that is forming heaps or globules, versus pure stratus, which
appears in a fairly uniform sheet.
There are also two other, rarer clouds,
which occur mostly at very high latitudes: nacreous clouds (from
Latin nacrum "mother of pearl", referring to the iridescence of
the clouds); they are found at altitudes of 15-20 miles and are
identifiable as remaining lit long after cirrus has gone dark (after
sunset). The other rare cloud is the noctilucent cloud,
named from Latin nox "night" and lucere "to shine".
It remains brilliantly lit well after sunset, having an altitude of as
much as 50 miles. These are usually seen only in latitudes above
There are fourteen species that
may be associated with the ten basic genera:
Latin for "fibrous", having a hair-like or filamentous shape.
Uncinus: Latin for "hooked".
Spissatus: Latin for "thickened".
Castellanus: Latin for "castle-like", referring usually to
altocumulus having "turrets" or vertical formations.
Floccus: Latin for "tuft of wool, fluff", said of cirrus,
cirrocumulus and altocumulus that form a patch or sheet of small tufts
with ragged bases.
Stratiform: Latin for "layered" + forma
Nebulosus: Latin for "mist-like, nebulous", a cloud
showing no distinct details or margins. In astronomy, a nebula
is a cloud of interstellar gas. It was also used to mean a cloud made up
of a myriad of stars, though we now tend to call these galaxies
(from the Greek galactos, "milk").
Lenticularis: Latin for "little lentil", it is the
diminutive form of lens "lentil". The name implies
a lens-shaped cloud, not necessarily a lentil-shaped cloud (though our
word lens derives from the shape of the lentil).
Fractus: Latin "broken" (as in fracture,
fraction and fractious), referring to ragged clouds.
humilis: Latin "low, of small size, insignificant", referring to fair
weather (vertically short) cumulus. Humility and humble
Mediocris: Latin "of middle or medium quality", applied to cumulus that are
larger than humilis but smaller than congestus. The obvious
cognate is mediocre.
Congestus: Latin "to pile up, heap up, accumulate",
applied to cumulus whose tops are achieving respectable vertical height
and have a cauliflower-like appearance. English congested
comes from the same Latin source and refers to an "accumulation" of
phlegm (or, originally, blood).
Calvus: Latin "bald" or "bare", referring to a
cumulonimbus which has reached a stage in its development such that its
top is starting to lose its cumuliform (cauliflower) shape due to
high-speed winds at the altitude of the cloud top. English
callow is thought to be related. It means "immature" or
"inexperienced". Considering that men tend to go bald as they age, this
may seem a strange derivation, but callow was applied to baby
birds who had no feathers, and the sense of "inexperienced" and
"immature" developed from there.
Capillatus: Latin "having hair", referring to a
cumulonimbus whose top is growing fibrous or striated, often taking the
shape of an anvil. This stage of development suggests that the
cloud was or is producing rain and possibly lightning and hail.
The tiny blood vessels knows as capillaries are so named because
they are as thin as a hair.
There are nine varieties which
refer to cloud arrangements and transparency:
turned", referring to cirrus filaments that seem entangled.
Related words are distort and the legal term tort
Vertebratus: Latin for "in the form of vertebrae", used mainly
for cirrus that have a fish-skeleton appearance.
Undulatus: Latin for "having waves", said of
sheets or patches of clouds that have visible undulations.
Undus, Latin for "wave", is related to the verb undare ("to
flow") which gave us inundate - literally "to flood".
Latin for "radiating", clouds that appear to be radiating from one
or two "radiation points". Other words deriving from radium
are radial, radio (which is an abbreviation for
radio-telegraphy), radioactive ("radiating ionizing
radiation") and there is, of course, radium, the first known
Lacunosus: Latin for "having holes or
furrow", a honeycombing effect in a cloud patch, sheet. Old
manuscripts sometimes have lacunae - gaps in the text.
Duplicatus: Latin for "doubled", cloud
patches, sheets or layers that occur at slightly different levels,
sometimes merging (and so appearing to be "doubled"). Duplicate
derives from the Latin word.
Translucidus: Latin for "translucent", said
of clouds that are thin enough to allow the shape of the sun or moon to
be seen through them. Translucent is related.
Perlucidus: Latin for "allowing light to
pass through", for a large cloud patch or sheet that has distinct,
though often very small, clear patches between the elements, allowing
sky or overlying clouds to be seen.
Opacus: Latin for "shady, shadowy, dark", opaque clouds that
do not allow the sun or moon to be seen at all. Opaque, of
course, comes from the same source.
Finally, there are nine supplementary
features and accessory clouds:
Incus: Latin for "anvil", for
the anvil-shape that cumulonimbus often acquire to their tops due to
high-speed winds in the upper levels of the atmosphere.
There is a tiny anvil-shaped bone in the inner ear called the incus.
Latin for "udder" or "breast", these pendulous formations appear on the
undersides of clouds, especially cumulonimbus, and are an indicator of
turbulence. They are sometimes an indicator of severe weather, but
Virga: Latin for "rod, stick, branch", virga is a shaft or trail of
precipitation which is visible coming from the base of the cloud but
does not reach the ground. In the U.S., this is most often seen in
the West, where the air near the surface is very dry, allowing falling
rain to evaporate when it hits the dry boundary. A striking
example of virga occasionally occurs in the Himalayas where snow
falls to within a few feet of the ground and then disappears. The
Tibetans call this lha'i metog ("flowers of the gods") and
consider it highly auspicious.
Praecipitatio: Latin for "a fall", ultimately from
prae "before" and caput "head" - "a headlong fall". It refers, of course, to
precipitation that is falling from a cloud .
Arcus: Latin for "bow, arch", a horizontal roll formation on the
front of certain clouds, it can often look like an architectural arch.
Tuba: Latin for "trumpet" or "tube", this is simply the Latin term
for a tornado, waterspout, or funnel cloud. The instrument called a
tuba takes its name from the same Latin word.
Pileus: Latin for "cap", the pileus is a small cloud which forms a
cap on the top of a cumuliform
Velum: Latin for "ship's sail" or "tent flap", a velum is a
horizontal, veil-like cloud which a cumuliform cloud may pierce.
The vellum which means "parchment" is not related (and derives
from vel, French for "veal").
Pannus: this is the Latin word for what we often call scud
(because they scud, or move quickly), shreds of cloud moving beneath a
main cloud, but sometimes also part of the main cloud.
These accessory clouds do not have
Latin names but are sometimes included in the above group:
Wall cloud: this is English,
of course, referring to an obvious lowering of a portion of the base of
a large cumulonimbus cloud. Rotation is often visible within the
wall cloud, and wall clouds can produce tornadoes. This feature
was named by Dr. Theodore Fujita because of its appearance - a "wall of
cloud". Dr. Fujita is the inventor of the Fujita Scale which measures
the strength/destructive power of tornadoes on a scale of F1 (weakest)
to F5 (strongest).
Flanking line: again, this
is English, and refers to towers of cumulus which grow beside and as a
part of a main cumulonimbus cloud. These grow and then dissipate,
and more towers build further down the line, causing the thunderstorm
activity to shift down that line.
Now that you know something about cloud
classifications, the following table may be helpful in applying species
and varieties to the proper genera:
Note that in meteorology, only the
singular form of the Latin terms is used, for example, multiple
cirrus are called cirrus and not cirri.
We've just had a fall of snow here, so
we're off to find a patch to play in!