CLOUD NOMENCLATURE
SINCE a considerable number of new terms have been suggested in the
foregoing pages, it may be convenient to collect them and tabulate
them, so as to show their relation to those already recognized by the
International system.
In the atlas put forward by the committee, sixteen varieties are
recognized by distinct names, and these are drawn up in tabular form
with appropriate abbreviations for use in making records.
The names are--
Cirrus. Ci.
Cirro-stratus. Ci. S.
Cirro-cumulus. Ci. Cu.
Alto-cumulus. A. Cu.
Alto-stratus. A. S.
Strato-cumulus. S. Cu.
Nimbus. N.
Cumulus. Cu.
Cumulo-nimbus. Cu. N.
Stratus. S.
Fracto-cumulus. Fr. Cu.
Fracto-nimbus. Fr. N.
Fracto-stratus. Fr. S.
Stratus-cumuliformis. S. Cf.
Nimbus-cumuliformis. N. Cf.
Mammato-cumulus. M. Cu.
During our survey of these groups we have found that some of them
include clouds of many shapes, which must be due to very diverse
conditions. It follows that if observations are to be made on the
occurrence of these special kinds, with a view to arriving at a
thorough understanding of the circumstances to which they owe their
forms, it becomes necessary to devise a code of names and symbols
whereby an interchange of ideas and records may be rendered possible.
Specific names have been proposed as each form was considered, and
it only remains to sum them up concisely. Subsequent observation,
particularly in other climates, may show that further additions should
be made; but if the principle of specific names be once admitted, it
will be easy to fill any omission.
GROUP CIRRUS.
Under the general head of cirrus we have found nine distinct forms--
1. _Cirro-nebula_ (Ley) (Plates 2 and 3). Cirrus veil.
Characterized by comparative absence of structure and by the formation
of halo. Ci. Na.
2. _Cirro-filum_ (Ley) (Plate 7). Thread cirrus.
Built up of fine long threads, straight, curved, or crossing, but free
from hazy curling or flocculent structures. Ci. F.
3. _Cirrus excelsus_ (Plate 5). High cirrus.
Characterized by great altitude, thinness, irregular branching
structure. Ci. Ex.
4. _Cirrus ventosus_ (Plate 6). Windy cirrus.
Characterized by curving branches leaning forward in the direction of
movement, and other long curving streamers lagging behind and below.
Fluffy parts are usually present, and mark the origins of the long
curling fibres. Ci. V.
5. _Cirrus nebulosus_ (Plate 9). Hazy cirrus.
Characterized by the absence of sharply defined lines, fibres, or
streamers; all parts of the cloud being hazy, and suggestive of other
varieties of cirrus out of focus. Ci. Neb.
6. _Cirrus caudatus_ (Plate 8). Tailed cirrus.
Characterized by small hazy or fluffy heads behind or below which hang
long streamers, which taper away more or less to a point. The tails are
sharply defined, and so are the edges of the heads. Ci. Ca.
7. _Cirrus vittatus_ (Plates 12 and 13). Ribbon cirrus.
Characterized by formation in long bands of cloud, sometimes made of
parallel long fibres with cirrus haze linking them together, sometimes
consisting of a long bundle of fibres, from which others diverge at an
angle as shown in the plate. Ci. Vt.
8. _Cirrus inconstans_ (Plate 10). Change cirrus.
Characterized by a peculiar ragged, wavy appearance. It is
generally only the beginning or the end of a mass of cirro-stratus
or cirro-cumulus, but occasionally it vanishes shortly after its
appearance, without reaching the further stage. Ci. In.
9. _Cirrus communis_ (Plate 11). Type cirrus or common cirrus.
Characterized by short irregularly curling fibres collected together
in considerable patches. No definite arrangement into any of the forms
already described. Ci. Com.
GROUP CIRRO-STRATUS.
Under this group the cloud usually shows some structure, being
apparently built up from a massing together of detached forms at a
common level. When this is so it should be described by adding the
specific name of the detached form most nearly related.
1. _Cirro-stratus nebulosus_ (Plates 3, 4, and 14). Hazy cirro-stratus.
Characterized by absence of visible structure. Ci. S. Neb.
2. _Cirro-stratus communis_ (Plate 16). Common cirro-stratus.
Characterized by the presence of short curling fibres matted together.
Ci. S. Com.
3. _Cirro-stratus vittatus_ (Plate 57). Ribboned cirro-stratus.
Characterized by being made up of long stripes or bands of cloud. Ci.
S. Vt.
4. _Cirro-stratus cumulosus_ (Plate 17). Flocculent cirro-stratus.
Characterized by an obscurely granular structure. Ci. S. Cu.
Many forms of cirro-stratus are arranged in waves or ripples. This is
indicated by attaching the word undatus, or waved, after the ordinary
specific name, or the letter U after the abbreviation.
GROUP CIRRO-CUMULUS. Divisible into three species.
1. _Cirro-macula_ (Ley) (Plate 23). Speckle cloud.
Characterized by semi-transparency, by the fact that the particles
are frequently whiter and more opaque on their edges. A patch of
cirro-macula always looks like a thin sheet which has curdled. Ci. Ma.
2. _Cirro-cumulus nebulosus_ (Plates 20 and 21). Hazy cirro-cumulus.
Characterized as rounded balls of semi-transparent cloud, but
ill-defined and hazy. No shadows. Ci. Cu. Neb.
3. _Cirro-cumulus_ (Plates 18 and 19).
Characterized as opaque rounded balls clearly defined, but showing no
shadows on their under sides. Ci. Cu. Com.
Wave forms again are indicated by the addition of the word undatus.
GROUP ALTO CLOUDS. Divisible into nine species.
1. _Alto-stratus._ High stratus.
A uniform veil of cloud showing no details of structure except local
variation in density in patches. Rarely dense enough to completely hide
the sun, or even the full moon. A. S.
2. _Alto-stratus maculosus_ (Plate 30). Mackerel sky.
Characterized as numerous nearly equal and small lenticular patches
ranged on a level and about equi-distant from each other. A. S. Mac.
3. _Alto-stratus fractus_ (Plate 34).
Patches and bits of cloud of irregular shape, but resembling broken
bits of a level sheet. A. S. Fr.
4. _Alto-strato-cumulus_ (Plate 32).
Intermediate between alto-stratus and alto-cumulus. A. S. Cu.
5. _Alto-cumulus informis_ (Plate 25).
Characterized as more or less rounded cloudlets interspersed with
ragged bits of cloud and occasionally with streaks of cirrus, the
cloudlets showing no clear-cut outlines, but having distinct shadows.
A. Cu. In.
6. _Alto-cumulus nebulosus_ (Plate 26).
Hazy alto-cumulus. A. Cu. Neb.
7. _Alto-cumulus castellatus_ (Plate 28). Turret cloud.
A high cloud resembling a number of tall narrow cumulus clouds on a
very diminutive scale. The cloudlets show distinct shadows, are very
opaque, and their upper margins are sharply defined. Vertical axes
longer than the horizontal ones. A. Cu. Ca.
8. _Alto-cumulus glomeratus_ (Plate 29).
Characterized by the roundness and regularity of the cloudlets, which
have sharp margins, cast distinct shadows, and have their axes about
equal in all directions. A. Cu. Gl.
9. _Alto-cumulus communis._
Small high cumulus of the ordinary pyramidal pattern. A. Cu. Com.
10. _Alto-cumulus stratiformis_ (Plate 27).
Flattened cloudlets gathering into small detached sheets. A. Cu. S.
Lower clouds. GROUP STRATUS.
1. _Stratus communis_ (Plates 37 and 41).
In its most typical state, stratus consists of a sheet of cloud of
approximately uniform thickness. The most common form, however, does
vary considerably, though usually dense enough to hide the sun.
Portions of such a sheet would take the same specific name, unless the
portions are very small and ragged, which would be expressed by adding
the word fractus. S. Com.
2. _Stratus maculosus_ (Plate 40).
Formed either by the appearance of cloud in lumps, which are always
lenticular in shape, and ultimately join together to form a stratus, or
by the break up of the typical stratus. S. Mac.
3. _Stratus radius_ (Plate 42). Roll cloud.
Formed during the break up of a low stratus, which separates up into a
number of parallel lines of cloud. S. R.
4. _Stratus lenticularis_ (Plate 47). Fall cloud.
Formed by the collapse of cumulus or strato-cumulus. A cloud of
evening, easily recognized as lenticular patches. S. L.
5. _Strato-cumulus_ (Plates 38 and 39).
A term applied to either a stratus which has thickened every here and
there into cumulus, or a number of cumulus which have joined together
so as to show a nearly continuous common base. S. Cu.
GROUP CUMULUS.
1. _Cumulus minor_ (Plate 43). Small cumulus.
Cumulus clouds so small as to present the appearance of rounded lumps,
no definite pyramidal form or flattened base. Cu. Mi.
2. _Cumulus major_ (Plates 44 and 45). Large cumulus.
Characterized by a flattened base and rounded clear-cut upper surfaces.
Cu. Ma.
3. _Cumulo-nimbus_ (Plates 49 to 52). Storm cloud.
Characterized by the expanded, anvil-shaped, or disc-shaped top,
cirrifying at its edges.
GENERAL TERMS
_Nimbus_, a term applied to a cloud from which rain is falling. When
the form of the cloud is visible, the term should be attached to that
belonging to the cloud. It may, however, be used as a substantive alone
when there is nothing to show from what sort of cloud, or combination
of clouds, the rain is falling (Plates 35 and 36).
Nimbus is either heavy stratus, massive strato-cumulus, or a
combination of these with stratiform clouds above, and possibly ragged
masses of fracto-cumulus below. N. either alone or after the sign of
the cloud.
_Fracto-_ is a term placed as a prefix before the name of a cloud to
indicate that the cloud has ragged irregular margins, as if it had been
more or less torn to pieces. It is sometimes less awkward to append the
word fractus after the name of the cloud.
A convenient abbreviation would be to write F. after the name of the
cloud.
_Undatus_, or waved, should always be added to the name of any cloud
which shows the arrangement so described.