SEPTEMBER, 1920. MONTHLY WEATHER REVIEW. S 13
weather would be improved if writers were given some training in the observations of weather forms and pos- sessed some knowledge of weather causes. I f writers will use, as needs they must, weather in amounts ranging from a modicum to a moiety in every outdoor scene, it is not improper to sug est seriously that mcteoroloe,
the curriculum of belles-lettres.
. Let no one be deceived by the notion that any meteor- ologist desires literary descri tions in the form of cate-
that good literature shall not be permeated b bad
proved by the use of weather that simulates Nature- weather that a peals to him who knows what weathers are made up of. March winds are not always “raw,” nor sunset skies always “imbued with a lurid’ low.’’
have been occasionally witnessed by most persons and would be recognized if well described. Again, meteorological metaphors are not undesirable,
which is the science o P weather, should have a place in
goncal scientific facts. The B esire is rather otherwise-
weather but that, on the other hand, i t shall l? e im-
There are many phases of weather which, even i f rare,
but, on the other hand, often facilitate the painting of a
word icture in the most concise manner possible.
o ened up and the windows of Heaven were opened.” &is tells briefly a story which would require many ad- jectives for an adequate description in a matter-03-fact way. Who has not beon impressed with Nature’s denr in the thunderstorm, when “with whipcor s of lightning she drives the storm on.” Here the metaphor is not strictly accurate, since in reality the storm gener- ates the 1igh.tning; but the object of the metaphor is to create a true picture in the mind of the reader, and suc- cess is attained in a measure as the picture appears clean cut and correct, and the vehicle of the metaphor is for otten. f n the use of better-defined weather types, accurate detail where detail is needed, and good metaphor where it will serve, as also in other ways, there are still oppor- tunities for those who write to utilize weather descrip- tions that are not altogether trite and yet do no violence to Nature.
In le oah’s flood “ the fountains of the great deep were
r-
CLOUD NOMENCLATURE.’
By CHARLES F. BROOKS, Meteorologist.
Weather Bureau, Waglungton, D. C., Nw. 8,1020.1
SYNOp818.
Cloud names closely defined are ossectial not onlv for the cloud observer but also for the cloud invwtigator. Since heights and the atmospheric rocease3 responsible for particular clouds are not. always known, the gest basis for a nomenclature for neral uae is cloud appeafance. The aupec’t of a cloud may he dmwrrigd in terms of form, coamenes9, and density; and rather complcte records can be made by recognizing the seven principal types of form, three degrees of coamenem, or apparent angular size, and five degrees of densit . Such a system of keeping cloud observations is to be rc?comrnendeion!y for those who have lenty of time and whg wish to have great detail in them cloud
The eneml needs of meteorologist,s were recognized many e m ago,
as evitfencerl in the adopt.ion of nn International Clmi&ation of Clouds in 1848. This classification waa sim le and included aspects of form, coBrBeneiw, and density. Altliougl! the original clmifica- tion waa revieed in 1905, the distinctions between several of the cloud
forms were not closely drawn, and pract.ically no provision wm made for iiniformitv i n detrtlled cloud records. As doud fornls occur in geat variety the lack of names to indicate adequately the appearance of the eky I= made cloud observations. in geneJrrl: the least complete xnd the least accurate of any rerords of the important weather elements. Pending further interimticma1 revision nn attempt is here made to provide for stricter differenthtion of cloud lorms, with the aid of a
guide to identification. Particular emphask is placed on the desir- ability of confining the name drro-cumulus to ice rloiirls in order to prevent its present, indkriruinate application to both the t n e , high cirro-rumulns and the appreciably lower, t l ~n alto-cumulus. Diifer- ent.iation of thin alto-ptratus from cirro-stratus, and of nimbus from other min clouds iR aleo discussed. Revised wordin of parts of the International descriptions are si1 ted for consifktion. Photo- graplls * are not presented, for it is =red to place emphasis on the Fact that the delinitiom form t.he ultimate baeis for diffcrentiation of forms. The addition of 14 generally applirable suhclames, sereral of which already are widely used, tn the prezent,. simple International Clamifi- cation is urged aa an aid to greater detail and gcater wcumy.
INTRODUCTION.
mor K s.
Cloud names are as necessary in the work of the me- teorologist as rock names in that of the geologist or plant names in that of the botanist. To be widely serviceable,
a system should invariably use the same name for the same kind of cloud and offer a sufficient variety of names adequately to describe the appearance of the sky. Inter- national agreement has already provided a fundamental
1 Revised from aper presented at the meeting of the Ametiesn Meteomlogical Society,
*A chart with aZ cfoud hoto raphs with legends conforming with thls discussion washington, D. E l . A ril a. ism.
will soon be h i d by the 6.8. #eather Bureau.
nomenclature. As now used, however, different observers have various conce tions of the given types; and there is
cloud forms accurately. no uniformity in a f ding adjectives for describing certain
TInter-
CLOUD-APPEARANCE THE BASIS FOR CLASSIFICATION.
As a background for a discussion of the existi national Classification let us consider how cloud o serva- tions might be recorded were there no existent nomen- clature and were there ample time a t an observer’s dis- posal. We are interested primarily in clouds as indica- tors of winds aloft, of atmospheric processes, and of future weather, and in clouds as sky cover affecting incoming and outgoing radiation. Horizontal movement and sky cover are recorded separately and are only in a minor de me involved.in cloud form. Rut the name
atmospheric processes probab responsible for it, and also provide at least a partia basis for local forecast studies. It would appear, then, that our classification cf clouds should be based on cloud-forming processes. But how is one to know what processes are involved without being acquainted ,with the actual conditions in and about a particular cloud? A howled e of meteorology,
not provide unmistakable evidenpe of why there is a cloud and why it has such an a pearance. Therefore,
especially since all observers do .not study clouds with equal care nor interpret clouds ahke, and since it should be possible to make a record without protracted observa- tion. This leaves a pearmce, with, of course, all its in- dications as to heig t t and ori in, as the only safe and universal basis for cloud classiftoation.
F m , coarseness, and den&ty.--Cloud appearance may be described in terms of form, coarseness, and denmty. Since coarseness, or the apparent size of the elements and markings of a cloud, and density are matters of degree on1 , the primary differentiation of clouds must be
b
of a cloud s fl ould, if possible, ive some indication of the
coupled with close observation of a c f oud, may or may
a classification by origin would B e on an unsafe basis,
based on P om. The principal types of form to be seen
514 MONTHLY WEATHER REVIEW. SEPTEMBER, 1920
individually or in combination in clouds may be con- venientl grouped in seven divisions, as follows:
rain as seen from a distance.
2. Smooth, characteristic of sAe4tZiike clouds, especially when‘low, and when snow or rain is falling rather uni- formly. 3. FZocmZen.t, scaly, ice-cake like, or disk like, cloud elements in ups, which as wholes usually have smooth, cumin o u g e s , which may be called le..ntidd, more
are markedly developel and the clouds have the form of detached convex lenses, they are called “lenticular.”
4. Wmed or in rolls, characteristic of wape movenfents a t or near horizon tal boundaries between diff epng wlnds, or near the ground, and of lines where the wind at any level shifts to a new direction.
5. Round-top, characteristic of the sununits of locally
1. Fi B TOW, characteristic of streaks of falling snow or
or less f ens- or lentil-sha ed. When these curved outlines
rising air mass&.
6. Down-bdqed or round-?hoZed, cliarac teristic of local- ized down-currents.
cloud in a turbulent wind.
its dements and markings, ?ay, in such. terms as cocme,
medium, andjne, and when its density in such terms as
transparent, semitran.spnrent, medium, dense, and very den.se, are noted. Thus, with seven names for form, with three degrees of coarseness, and five of density, we have an easily applied, compact, and, may I say, coni- plete, basis for recordin cloud appearance. Ezperiment with clod-recording in great detail.Cuch
8 method cf recording cloud observations was tried for
50 days, and was then abandoned, because. (1) it was very bme-consuming, even though requirmg little thought or judgment; (2) the records were comparable only with difficulty,, even though the mass of detail was in orderly form and in a relatively small compass; ancl (3) such a eat number of combinations (about 3,000)
were possibe that it was hopeless to. deqise satisfactory names for distinguishing oiie combination of detailed characteristics from another As this strictly rational lan is impracticable for general use, let us consider the fnternational Classification with the hope of modifying it to meet the need for greater explicitness and more detail, yet without departing from its fundaniental and necessary simplicity.
7. Rag@, characteristic of forming or evaporating
Any cloud defined in terms of form will have its as rather fully recorded, when the apparent size of
THE INTERNATIONAL CLASSIFICATION.
Histoly.-The following account cloud nomenclature in eneral use from (p. 317) in%. Helm Clayton’s exhaustive a “Historical sketch of cloud nomenclature.”
Notwithstanding the numerou8 proposed systems of cloud nomencla- ture, none has to any extent displaced thc system of Howard [ltX).?], which gradually came into general use. Here a name like .frmfo-
cumdus hrta been borrowed from Poey Il8f‘&79], there the name of mammato-cumulus has been taken from Ley [1870-!33], and r u t d o - nimbrts from Weilbach [ISfWl; but in tne nmin the qytcm of 1Iow:wd has remained unchan ed except by natural growth. lhe International system of Hildebran&so~ ind Abercromby [181371 is, as etakd by n e
authors, only an adaptahon for peneral use of the cloud mimes whlch had already come into use in d1fCerent places by gradual and slight changes in the sptem of Howard. Kaemtz [1531-36] added the name
8bato-ani.dW, thus dbtingiiqhinp: a cloud forni recorded bv other ob- servers with [as] cumulo-stratus. Renou Ibefore 18771 added the name
2 “Dlscu9sion of the cloud observat!ons,” Ann. Astr. Ob. Harvard Coll., 1896, vol. 30, pt. 4 p. 271-600.17 pl. 4to. Hlstoncsl chapter, p. 279-381. Cf. summary of inter- && lpmgth in 15m. detsl four., JW, W, 11: L
nlto-mniulm to dietingukh the law form of cirro-cumulus! or a cloud intermediate between rirro-cumulus and strato-cumulus. Tn Portu.gal the name stmto-cirr!is came into use to describe t.he lowest form of rirro- stmtiis, or rather a lower hliiish or grayish sheet which had previously been recorded aa cirro-stratus. It appears to correspond to Po6y’~ pallio- cirrus, and was given the name dtr~-rbstzis probably by TIildehmndeson [ lSS7J.‘
The International Classification of Clouds was formed largely from the most widely used cloud n m e s and defi- nitions a t the time of its compilation some 30 years ago. It was, necesswily , m agglomeration and a compromise. Clayton quotes an account of how Abercromb ob-
went to ITpsda to see Hildebrandsson. Of this confer- ence Abercromby himself, writes:
Y y primary idea-in which Prof. Hildebrandsson entirely con- curred-wm that the name of a cloud is oE iar less im ortance than that the same name should be ‘applied to the same cloii$ by all observers; and also that the existing names should be retained, only that the Iorm they are applied to should be more precisely defined.*
Existing cloud schemes, of which there ‘were many in use in cliff erent countries, were worked over. Abercromby continues:
Eventually, we agreed that ‘10 terms, all compounded ol €Toward’s
4 fundamental type-crirnts, stratus, cwniulus, ndmbic+would fully nieet the requirements of pmtica.1 meteorology. with the least disturb- ance of esisting systems * * *.
Hildebrandsson’s statement about this syst.em is quoted
(p. 300) as follows:
If one wishes to study the connection between cloud forms and the phenomena of the atmosphere, or to use these forms for prngnostication, le must hare a detailed terminology. * * * According to my view the nest most importaut parpose of cloud observations is to determine the wind dirertions at diKerent heights of the stuioapliere. For that purpose it is not necessry to di&ngui& so many Corms.
An atlas based on t.he Hildebrmdsson-Abercromby sys- ten1 was published. The Inteinat.iona1 Meterological Congress at Munich, in M I , adopted this system as the lnternrttional Classification.
tnined photographs of clouds all over the world an B then
Or,flbic qf t h Iiitrrn~i.tioiid Cia.wiAmtioi~, rdopierl in 1891.0-
(a! Detached clouds with rounded upper outlines (most frequent in drv weather). .. . ~. .~~- . .
(a’) Clouds of great horizontal extent su,wstinga layer or sheet (sug- gestion 01 wet weather). A. ITpper Clouds: Average altitude, 9.OOO metres (30,000 feet).
((1 ) 1. Cirrus. (b’) 3. Cirro-stmtfl. R. Intermediate Ulourls: Behveen 3,OOO metres and 7,000 metres
(I ) !. c‘irro-cumulus.
( {d. .\lto-cumulus. (h ) 5. .-Ilto-stratus. C.’ Lower Clouds: Below 2,000 metres I7,Olx) feet;.
(a) 6. Strato-cumulus.
(a) 7. Nimbus. D. Clouds of diurnal ascending currents.
(a) 8. Cumulus: top, 1,800 metres (6,000 feet); base, 1,400 metre.
(a) 9. Cumulo-nimbus: top, 3,000 metres to 8,000 metres (10,000 feet
E. High Fogs under 1,000 metres (3,300 feet).
N. B.-The equivalehta in feet of the heighta given in metres are only roughly approximate.
The definitions and descriptiuns of each form as adopt,ed were translated into English in 1$94, and were published
(10,OOO feet and 33,OOO feet).
(1,500 feet).
to 36,000 feet); base, 1,400 metres (4,500 feet).
10. stratus.
The use ofallo-sfrofus was bmdcncd hi 1% enough to include the nonfibrous sheet- clouds at intermediate hcights althou h these are not speclflcall mentioned.
4 y; elt., p. 299: Abercromb , R., kuggestlons fnr an interna&mal nomenclature of clou s Quart. Jour. Roy. Mrt’fSoc 1SS7, 13: 154-162 discussion 182-166, plate. Thls and an earlier paper ihid p 140-1& contalu an illu~inatinp discussion of the way in which descriptlvendrnes &cPduds becime associated with considerations ofaltitade and attendant weather phenomena.
J Quart. Jour. Roy. Meteorological Soc., Apr., 1887, pp. 1.18-162: quoted rn Clayton, op eit p 299. ;Q&t!d from “Cloud forms scrordin to the International Clas.+llcation.yJ British Meteorological Office, London, NIS, Y. 8.?33,10 pp., 17 pl. [from photogrephs by Q. A. Clarkel
SEPTEMBER, 19u). MONTHLY WEATHER REVIEW. ‘515
in the h t edition of the International Cloud Atlas in 1595. Slight revisions were made at the International Meteorolo ‘cal Conference at Imbruck, in 1905, and pub-
in 1910.1 General rem.arks on cloud obse&ng qcnder Me Intar-
national CZami$catioia .-Mos t meteorologist~s have at one time or another made cloud records. Some have tried to use them. In making cloud records it. is seldom easy to decide on the ap ropnate cloud names for the appearance of the sky; nncf when the decision is made, one feels almost invariably that mother observer might have made
a different record. Anyone who thinks of using these cloud records recognizes that, unless made with special reference to certain features, they c m be relied on only in a very general way as data in nnr investigation. This situation IS not necessarily the fau t of the observer, for in spite of careful study, perhhps memorization of the definitions of the 10 cloud forms, one c m not describe the sky by using these 10 names without elaborating remarks, and, since only tin enthusiast would be espected to miike such elaborating remarks, the observer is likely t.0 con- sider the attainment of accuracy in cloud observation as well-nigh hopeless and, therefore, not worth more thnn n
minute or two during the limited observation When a given cloud might be called anv one o three names, few care to split hairs in d6ciding which it shall be. This situation may be improved, however, for, once ranted that the 10 names are to cover an observed cloud forms, we are faced merely with the duty of defining where the dividing line shall be placed between the forms where they converge. To be sure, if some changes in the wordings of definitions a.nd descriptions will remove am- biguity and mrtke them inclusive to their limits, the
presentation ‘of such modifications is justifiable. Any such attempts to clarify, however, should rest on ideas rather generally held among cloud observers, as indicated
by remarks on this subject published in various countries. !&e following definitions and descriptions, quoted from the International Cloud Atlas, secoiid edition: are a - poached, therefore, with the idea of delimiting the appH- cation of each name in accordance with accepted usage, and for some, to suggest such broadening or altering of definitions as appear to remove ambiguities and to make them inclusive yet explicit:
1. Cirrus (Ci.).-Detached elorids of delicate and fibrous appeamnce, o ten slrouring a feather-like siriicture, genmally o a whitish colour. Cirrus c ouds take the most vaned shapes, such as is0 $. ted tufts, thin filaments on a blue sky, threads spreading out in the form of feathers, curved
lished in t % e International Cloud Atlas, second edition,
period
_-- Important cloud atlases publlihed since l9iO are as rbllowi: Lolsel Julien Atlas hotographique des nuages. Paris, 1911. 20 ver good photo- graphs. ’ [A revkw by f Vincent, 1912, loc. rit states that this atlas is 07 reat service t o new men and that it imposes on olTicial orgaiizations, international or o&erwise,the revision ot the clouds of the Intermediate level.] Taffara Luigi Lonubi. Part I Testo: 67 pp. diagrs., ills. PartII,.Atlaate p pls.] R. UtRcid Cent+ di [Com rises d w x s d o f cloud photogrn h a histdry of rloud nomenrlatke, and a new dehled classiDcatlan by the author, a% $pes of whirh are illustratcd in the plates lar 1 from the author’s hotographs See review by R. DeC. Ward In Grogr. R t i : Occ TWO, 10 :!2713, and by 5. Brunt in Quart. Jour. Roy. MeteorologicdSoc., Julp,1919, vnl. 45. nn. 2sR-239.1
eteorol. e beodiamica, home 1917. 14 by @ inches
. -.. .., cc. ___ [Clarke 0 A N h meteorolo cai servire rloud atlas Prrpared by H Urographlc Departmint‘ Aamlralty under $a su crintmdenre oI‘ Rear Admiral J! F. Parry pndon] l9h. p. 1,14 &.plates. 48+ t!y 39 rm. . [Large. colorrd prints ofoil paintings rrf3 A FIa&.r “J
-. --. “-....,.A
8 The booklet, M. 0. 233, loc. Pit.. -tams another set of dehitions, now in omcial use b British o!xmvers. The following note ex lalns: ,#Tie translation into English has been alterdin certain respeeta from that whim s r ja the English version of the +odurtion t:,the Intarnational Cloud Atlas in er to represent mom clos$y the origmal Fmnrh. Wnce the Engllsh version in the Intarnational Cloud Atlas is otEclal there 888111s to be no call for American ohervers to use a translatinn of the French version. At any rate the British Meteor01 ical Office translation of the French version does not diffd appreciably from that% the Internatid Cloud Atlas.
[or straight] filamenta ending in tufta, sometimes called h uncinw,
etc.; they are sometimes arranged in parallel belta which QOBS a por- tion of the sky in a great circle, and by an effect of mpective ap ear towsrds a point on the hodron, or, if sul#ciently exten&l, :z q s T e opposite point also. ((3.-St. and Ci.-Cu., etc., amale0 sometunes arranged in Qmilar bands.)
The distinguishin characteristics of Cirrus am that i t clouds are usually not involved in iYJibrowr and detache 5 . Althou high, the actual or apparent differentiating Ci. from other
2. Cirro-stratus (Ci.-%).-A thin, ruhitiah s k t of e2oLcrb Bometimes covering the sk complete1 and givmg it only a milky appearance
$t is then callex Ckronebd), at other times reaenting, more or lees istinctly, a formation like a tangled web. T&s sheet often produces haloa around the sun and moon.
Cirro-stratus is generally distinguishable from alto- stratus and stratus by its thinness, whiteness, and by halos when present. Difficulty arises, however, in differentiatin Ci.St.g from thin A.St. or thin St. when the
within an angular distance of 90’ of the luminary. Under such conditions slow change of form and density and, usually, relative1 slow movement, characteristic
Ci.St. Thus, while Ci.St. is “a thin, whitish sheet of
c Z d s ,” all thin, whitish sheets are not Ci.St. Althou h the 10 forms are classified in an introductory. section ofthe International Cloud Atlas according to then average heights,l0 should we allow hei ht to be a trite-
winter weather a nebulous white sheet at a low eleva- tion, perha even reaching the ground, may produce brilliant hxs. Should it not be called Ci.St.? It cer- tainl fits the definition of no other form. Furthermore on b ustery days with the temperature near freezing and ragged St.Cu. covering much of the sky,
of snow-fallin from these St.Cu.-which shuts out the
The snowflakes are too irregular and too varied in orien- tation to produce halos. There is a “thin, whitish sheet of clouds” undoubtedly composed of ice particles, as all cirriform clouds are; surely it is not the foglike stratus nor a forming nor evaporating alto-stratus (“a
thick skeet of a grey or bluish colour”), therefore it must be called Ci.St. if any name at all is applied to it. And if it is not named or otherwise mentioned, an important feature of the s as ct is omitted from the cloud record.
national dejinition of cloud forms.
latter are bri fi iantly illuminated by the sun or moon and
of high clouds, identi i? es a thin, white cloud sheet as
rion on which to base records of clou % form? In cold,
what with shou hea. d we call the thin, more or less irregular veil
clear bluenesg o K the sky between the dense cloud masses?
7
It is fortunate kg- t at r eight is not stipulated in the Inter-
3. Cirro-cumulus (Ci.-Cu.), Mackerel S k y .4 m u l l globular ma6se.a
01 ulhitejhkes taiUIout shadows, 01 slwmhtg very slight shadows, arranged in groups and often in lima.
Although some critics claim that cirro-cumulus clouds are neither cirrus nor cumulus, this comment is a relic of the time when cirro-ciimzdzi.e included both our resent Ci.Cu. and A.Cu. Clayton (pp. 293-294) quotes 8ement Ley as follows:
They are, in fact, neither in appearance, nor in mode of physical for- mation, either compounds of cirrus with cumulus, or hybrids between cirrus and cuniulus. Therefore, in practice, the use of the word ‘‘cirro- cumulus” has led to alar e number of cloudsof no great elevation being classed amongst the cirrikrms; a result which was of little consequence when the laws regulating the u per currents of the atmos here had re- ceived no examination, but w\xh must prove absolute$ fatal to a
@ In U. 8. Weather Bureau practice. hyphens are omitted from the cloud-name abbrevhtims. It would be still simpler, and more saving of time and spsce to use the old SIgm Corps abbreviations: C for cirrus: IE for cumulus: N for nimbus. and 8 for stratu8.- Oencral Instructiond to Ohscrilrrs o the Slrnnl Serakc, 1@i, pp. ,5356. These abbrevb tions are still in use at Rluo HIIl dbservatory.
10 See outline quoted on p. 514, above.
616 MONTHLY WEATHER REVIEW. SEPTEMBER, 1920
acheme based .upon t h w laws, according ta which new and most valua- ble results. m!1 be attained. The name “cirro-shtus” is almost equally ob~ectionsble, and for similar reasons.
Meteorologists soon sought to escape this trouhle hy givhg the names nlto-curnuhis and a.Bo-rrtmtus, res ec-
“cirro-cumulus” and “cirro-stratus.” In doing so, how-
ever, it was deemed sufficient merely to define Ci.Cu. as “small lobular masses,” etc., to distinguish it from
etc. Unfortunatel for the value of this distinction, however, forming kCu. often satifies esactly evew oint in the definition of Ci.Cu., and, therefore, is called &Cu. We now know, what was apparently not known then, that the higher, true Ci.Cu. are invariably formed of ice, while the lower grou , for which the name A.Cu. was esclu- sively intendedj are usually composed in large art, at least,of water droplets. Distinguished on the gasis of icecrystal or water-droplet, Ci.Cu. and A.Cu. are not likely to be confused.; the former can make no diffraction colors, corona, or insation, in. the vicinity of the sun or moon,11 whde-the latter es ecially when so thin as to be
structure (suggestive of great height), will produce bril- liant diffrwhon colors. The fact that halos are not seen in Ci.Cu. is not a valid objection to the claim that they
are of ice crystals?’ for the lack of lido phenomena is a consequence of the turbulence and unequal
vertical motions and the process of condensation respou-
tirely, to the lower forms of the clouds formerly c s led
A.Cu. w % ich was defined as “Largish globular masses,”
commonly rmstaken for e i.Cu: on account of its fine
size necessa% of t e crystals attending, respectively, the diverse
sible for the Ci.Cu. Ci.Cu. is defined as “small.” What should we call the
rounded tops on cirrus tufta when of medium or la. ge size which top the CiSt. and fibrous ASt. clouds ove- flowin from an intense cyclone ? Although these are of
tion of A.Cu. In view of these considerations, it would. seem advis- able to have the definition and description of Ci.Cu. read: Cirro-cumulus (Ci.Cu.). --SmaZZ wh,ite. $dies or tmuous globular masses which odzrce n o difractm colors near the
groups and often in lines, suggestive of one or more sets of small wavBg. Ci.Cu. being composed of ice particles, are uaually bright, in spite of their tenuit , and do not have the solid appearance cha-acteristic of fquid-d. oplet, A.Cu. clouds. At times the to s of cirrus tufts or of
or bluish coloiu, some-
At other times the s eet is thin, resembling thick Ci.-St., and through it the Sun or the Moon may tm seen dimly gleaming aa through ground glsas. This form exhibits all c h a y peculiar to (3.-St., but from measurements ita average altitude is ound to be about one half that of 6.-St.
A&. from CiSt. presents the same
just discussed. Although the name alto-stratus was in- vented for the purpose of differentiating the lower sec- tion of the old cirro-stratus oup from the upper, the
adequately for this. Like A.Cu., it is described as a
snow d akes, like Ci.Cu., they seem to fit better the defini-
mn OT won. The c r oud units are usually arranged in
Ci.St. sheets a: e capped with Ci. e u,”
timee forming a c o m r t masw of dark grey co P our and fibrous structure. 4. Alto-stratus (A.-St.).-A thick sheet ofa
Differentiatin diffculties as t i? e distinction between A.Cu. and Ci.Cu
International definition and r escription fails to provide
..-,
11 The twoparta$such aststement as the following.are inrompatibl6: “They [Ci. Cu’ am all corn osed of ice dust or crystal.9 and ma he riamatically colored when near the tam IrlastLn) ”-A G W Howard “The 8Iod,” on back of AUK. lea0 issue of -~m s t e o ;p l o s ~~~~~o f t h ~~~~~~a n Seaa uhliehedh Brit.het. 66. For dbo on of thla question of optics sea p. 538-537 In g. J. Hump%sys Physlca of the Ah,” Philadelphia 1920.
u CL ‘’It would ap that true oirro-cumulua is not corn osed of ioe artiden for hrloa are not -n in tEclouda .”-C. J. P. Caw,. Tge fo- of r%u& Q&rt.
Too?. Roy. Ibeteooological8ffi, 1917, VbL 43, pp. Ol-82,27 flga. (Quotation from i. 65.)
heavier cloud, which at times looks Like its higher coun- terpart. In addition, however, the lower altitude of ASt. is mentioned. Thin A&. is very commonly mistaken for CiSt., and in much the same way that A.Cu. is mistaken for Ci.Cu.; the thin ASt. satisfies every oint in the definition of CiSt. Here, as in the
fied by its more or less smoky appearance when more than 90’ from the sun, and, often, by the changeable form and density of particular sections of the sheet, and by its production of coronas. The fibrous A&., which is
ot snow, as is CiSt., is merely a dense cloud, which if thinner would be CiSt. Thus, fibrous A&. is to be distinguished from Ci.St. by greyness, and, in case a halo has previously been seen with thickening CiSt., by the ’
disappearance of the halo (on account of the weakening of the light passing through the cloud, not because of any decreased refraction). - Other cloud observers haTe complained about the inadequacy of the definition of ASt. to meet the original intention of dividing the old “ cirro-stratus” into upper and lower sections-the new Ci.St. and A.St. Thus, J. Vincent’s objects to the incompleteness of the A.St. definition arising from the omission of any mention of nonfibrous ASt. and of those features of it, such as undu- lations and mammato forms, so commonly observed. Would not some such definition and description of A&. as the following be more serviceable than the present International one ?
Alto-stratus (A.St.1.-A sh.ed qf q r q or b1u.M rolm, either’ generally fibrous or present.ing a smooth, undu- lated, mammato, or fraved-hole appearance. Through the fibrous (snow-crystal) A&. the sun or the moon may at times be seen dimly gleaming as through ground g h s . On thin parts of the other (water droplet) kind diffraction colors appear in the vicinity of the sun or moon. Steady rain or snow may fall for hours from ASt.“
5. Alto-cumulus (A.-Cu.), Qreat Waves.-Largkh lobular maim,
whits or gr&h, partially shaded, arranged in groiips or !inas, and often so closely parked that their edges appear confused. The detached masses are generally largerand more compact (resembling St.-Cu.) at the center of the group, but the thickness of the layer varies. At times the masses
a read themselves out and assume the appearance of small waves or tkn sli htly curved plates. At the margin they form into finer flakes (resemfiing Ci.-Cu.). They often spread themaelves out in lines in one or two directions.
A.Cu., especially when just forming and when higher clouds are absent, may apparently satisfy every point in the definition of Ci.Cu. Such A.Cu., however, usually has a solid appearance, not characteristic of Ci.Cu., and presents brilliant diffraction of colors in the vicinity of the sun or moon. Furthermore, thicker, shadowy parts of the same formation are usually present in ot-her parts of the sky or develop within an hour or two. In view of what. so often presents itself as undouhtedly A.Cu., why not reword the definition and description as follows:
‘‘ Alto-cumulus (A.Cu.) .--Globrcla.r, scaly, or wave-like
masses, white or greyish, partially sh.Cracd, usually arranged in groups or lines, and often so closely picked that their edges appear confused. In the vicinit of the sun or
tops of large cirrus tufts or of Ci.St. or ASt. masses are capped with rounded domes of A.Cu., too large to be called Ci.Cu.”
case o P A.Cu. versus Ci.Cu., the lower form cah be identi-
moon diffraction colors are usually visib P e. At times the
13 h e . cit. (footnote 7 above), p. 206.
14 J. Vincent eitrs tie omission of a mention of this fart as a reasonfor the widespread
Cla on gave thename aZro-nimbus to A. St. from wbkh rain or snow i s falling; and tbls
use of the synonym raln-rlouds I’ for ‘I nimbus ’I (ibid.1. .
is st& use at Blue €Ull Observatary (Massachusetts).
SEPTEMBER, 19u). MONTHLY WEATHER REVIEW. 617
The more or less confusin descriptive matter ob the International text can then 6 e omitted. A comparison with the definitions of St.Cu. and Ci.Cu. would be suffi- cient to reveal the facta that large, dense A.Cu. borders on the smaller St.Cu., and that thin, small A.Cu. must resemble Ci.Cu. in most respects.
6. Strato-cumulus (St.-Cu. .-Large globular maasm or ~011% of dark elovde often covering h who 1 e sky, mpecially in winter. Generally St.-Cu. preeenta the a pearance of a grey lager irregularly broken up into ma- of which &e ed ie often formed of smaller maasee, often of waw appearance reeemging A.-Cu. Sometimes this cloud-form rwenta the characteristic appearance of great rolls arranged in parallel Enee and d cloee up inst one another. In their centres these rolls are ora dark colour. F u e sk may be seen through the interven- ing spaces which me of a much ~J t e r colour. (Roll-cumulus in E=- land, Wulat-cumulus in Germany.) St.-Cu. clouds may be dietin- uished from Nb. by their lobular or rolled appearance, and by the Lct that they are not genenby aseociated with rain.
It is well, perhaps, to oint out that some St.&., unless .in very large units, wo J d be called A.Cu. if viewed from
a depth of, say, 2 kilometers helow the earth’s surface. Correspondinoly, a cloud formation which might 1)e called A.Cu. %y an observer in a valley, map be called St.Cu. by one on a mountain I! km. higher. For malip cloud observers, St.Cu. forms a convenient catch-all for
any dense cloud that can not readily be classified other- wise. It should be recognized, however, that there is no more justification for calling such a cloud St..Cu. than for calling it soniething else, unless its character- istics are more nearly like those of St.Cu. as defined than like those of any other form. Since the word “globul~r” carries the implication of
I hericity, it might be better to use the words “disk-
detached St.Cu. with its generally tlat tops and Cu. with its dome-shaped tops would be more obvious.
7. Nimbus (Nb.), Rain Clouds.-A thick layer ofdark clouds, with-
out sha and with ragged edges, from which steady rain or snow usually falls. Through the openings in these clouds an upper layer of Ci.-St
in a strong wind into shreds, or if small loose clouds are visib e floating underneath a la Nb., the cloud may be described aa Fracto-nimbus
edness and density of Nb. differentiates it
and even those clouds from which a steady rain or snow is falling are not, nimbw unless ra ged ed es are visible. Furthermore, there may be “rainfess nim%us. With regard to the wordin of the definition and description,
observers the implication that a rain clouds are Nb. (if not Cu.Nb.l. The first sentence ivcs the correct conce tioii, t.herefore, I think the wor& ‘ ‘Rain clouds” shod$ he omitted. The last sentence, describing k’r.Nb. seems unnecessary, and it detracts from the strength of the definition of Nb. It is somewhat incongruous to have nimbus as “A thick lajer of dark clouds, without shape and with ragged ed es,” and then to describe (thin) separated wisps as “fracto-nimbus. ” ‘Fracto” has the implication of heina broken or ragged: and since nimbus is a rag ed cloud, fPracto-nimbus is thus a ragged ragged cloud. St is probal>le that no rain (except per- haps a light drizzle) ever fdlsfrom a yioce of scud-the rain f d s throug7z it. There are, perhaps, three subtypes of nimbus. One occurs with moderate to brisk, converging southerly winds. Long Lines of cloud arallel to the wind direction ow and grow from rag e{, though nearly horizontal, fmes near the ground an 3 lean forward aloft. The tops
li !i e or scaly” instead. Then the distinction between
or A.-St. may be seen almost invariably. If a layer of Nb. ae P““te8”
(F’r.-Nb.) (“ScuF of sailors).
from The the ’”$ s oetlike St. All rain clouds are not nimbus,
the words‘ ‘Rain clou d s” at the be inning, carry to many
E
Cf. chmt Ley: cloudlend, p. 108
1
of these convectional clouds are probabl rounded,. but the are not often seen from elow. The
are visible the clouds may be called lvimbus eumuZformis. A second (uncommon) type of nimbus develope from heavy fibrous -4.St., with a rather coarse mammato structure, which, by the time rain falls devdo s into very
A third type of nimbus may best be described as the dense, formless clouds characteristic of showery spring or summer days; usually with some thunderstorms (in Cu.Nb.). illthou h many observers claim that there should he
as a substantive, (d. Ley, loc. cit., p. 74) I am strongly in favor of its retention, for it comprises a rather definite tvpe of cloud which otherwise would mere11 make worse the present potpourri St.Cu.
8. Cumulus (Cu.), Wool pack Clouds.--Thiek cloudamof which the uppr muface ia domc-shaped and ezhibita pmtwbemncea whsle the bass is honzontal. These clouda appear to be formed by a diurnal wen- sional movement which is almost always noticeable. When the cloud is o posite the Sun, the surfaces facin the observer have a brilhnce than the margins of the protu!erancee. Then the l i g r & aslant, as ia usually the case, these clouds throw dee shadows; when, on the contrary, the clouds are pn the same side of $e observer BS the Sun, they ap ear dark with b True cumuka haa well definzu per and lower limita, but in strong winds a broken cloud resembling 8umulua is o h seen in which the detached rtions unde continual change. This form may be dia- tinguisheaoby the name% acto-ncmulua (Fr.du.).
Cu. is easily recognizable by the frtct that it is domed
and detached. This ap lies to clouds even when rain
k?%% the name C’umulm nitnbiformirs. WIen the Cu. clouds, such as me characteristic of clearing weather with a northerly wind on a bright morning after rain has fallen, reach a level of littlo or no la se-rate, or pos
flatten, and sometimes spread16 the clouds then are to
be cdled St.Cu. Under such conditions, the newly formino clouds have the domed tops, and are Cu., while tho olzer ones have becomo St.Cu.
9. Cumulo-nimbus (Cu.-Nb.), The Thunder-Cloud; Shower- Cloud.-Heaiy masses of cloud Fiaing in the fm of wunmtaina, turn& or anvils. genwall surwwunted by a sheet or screen of $e appclrmnas Else h) am! having at its base a maas of cloud aamalar to nsmbua. m the base local showers of rain or snow (occasiody.of hail or soft hail) usually fall. Sometimes the upper edges assume the com- pact form of cumulus, and form massive peaka round which delicate “false Cirrus” floata. At other times the edgea themselveu se arate
into 8 fringe of filamenta similar to cirrus clouds. ~h i a b t ?m ie particularly common in s ring showers. The front of thunder-ctuds of wide extent frequently pmenta the form of a large arc spread over a portion of a uniformly bnghter sky.
Cu.Nh., in bricf, is the massive, . composite cloud, 11suttll~+7 with a fibrous [snowl, spreading top. While it
usually harbors a thunderstorm, the occ~irrence of thun- der and li htning within it is not an essential characteris- tic. In t f e matter quoted from the International Atlas there seems to be no need for the introdiict0r.y characteri- zations, ‘ ‘The Thunder-Cloud ; Shower-Cloud.” The descriptive matter covers this fact. Just as with nimbus,
the isolated a pearance of these descriptive names im- plies to some o g serveru that all shower clouds are cumulo- nimbus. Therefore, I believe that ‘ ‘The Thiinder-Cloud;
Shower-Cloud,” should be omitted. In view of the erroneous and ambiguous impression conveyed by the
lnternational At 9 as says that when such rounded tops
large ragged masses with curved lines still pre T; ominating.
no such c 7 oucl as PJb. and that “nimbus” be used merely
h t edgea.
from them. $ he International Atlas rovides
sibly an inversion of temperature, and t I! eir domed tops
IcThe-spread top sheet in such a formation is still called curnulosiroh8 b msn
17 Cave would &e it %Iw&~: I&. m.
European observers, although this name was eliminated froom the IntfmatioXIal%k3Bd cstion becnuse of the liklihood of confusion with St.Cu. Cf. A. de QIm’V&I, BeitrHge
6W Wolkenkunde Met. Zdltsehr lm ZS (rei. to p. 435).
618 MONTHLY WEATHER REVIEW. SEPTEMBER, lSa0
Lenticuldd Flocculent ............
Rolled ................ Undulated
Rouncl-top ............
DowIl-bUlged..
Ragged ....... f
DENSITY.
words “false cirrus” ap died in the first instance to clouds that are real Ci. or Ci. !4 t., tmd in the second, to ASt. or Ci.St. scarfs, 1 believe that they should be oinitted from the quoted matter above.‘8 hrthermore, the definition and the sentence mentioning the occurrence of recipi-
The last three sentences of the first ptlragra h seem to
tion. If this definition of cumulo-nimbus is to be followed, it is obvious from the following considerations that except under unusual circumstances the number of tenths of the sky covered by cumulo-nimbus can not be more than 3 or 4. When a Cu.Nb. cloud with a s reading
Cu.N%. 2, etc., till it covers the sky as Cu.Nb. 108 If
so, the reader of the record, would have no idea of tho a pearance of the clouds except a t the very start. On
Cu.Nb. 2, shifts to ASt. 4 and Nb. 1, we get an indica- tion of what the clouds looked like, although unless we happen to find a record of thunder and lightiiin , or
ing that the Cu.Nb. cloud has disappeared.
10. Stratus (St.).-A rcnifbrm laym of clozui resembting a fog but 7wt rating on tlrc p u n d . When this sheet is broken up into irregular rhreda in a mnd, or by the summits of mountains, i t may be dis- tinguished by the name Fracto-stratus (*.-St.).
tation are sufficient to indicate what ti Cu.Nb. c Y oud is.
be estraneous and weaken the explicitness o P the defini-
top a. proaches the observer, is he to record, cp u.Nb. 1,
t E e other hand, if the observer after recording, say,
some explanatory notes, we may be misled into t i? ink-
Of Stratus, Abercromby says:’@
We now come to the eecond variety of clouds, to which the name of stratue is applied, becauee it always lies in a thin horizontal layer, like a stratum of rock or clay. Pure stratus haa no sign of an hairy or threadlike structure except at the edges, for a stratum whiclshows much markiq would be cimtratue, and has quite a different own. Pure stratus is essentially a fine-weather cloud, and is especially
chsracteristic of antityclonea. One very beautiful variety is often a fine night, then the cloud forms thin broken flakes, ze&s?ike mackerel sky, from which, however, it is really quite distinct. In Howard’s ong~nal work on clouds, “stratus” was applied to ground mist, but that idea is now entirely discarded by all meteom
hP--
Stratus is the layer-cloud that closely hems in the sky. It is not necessarily uniform, however, and this characteristic, when resent, is useless for differentiating St. from A.St. and b.Sk20 Neither do all St. clouds resemble a fog, as is evident from the Abercromby yotation, above. At times, St. forming by misture on t e nearly horizontnlunder-boundary of arelatively warm wind will presont amammillated or undulated appearance,
Ish. le tm-v%i% I )c. clt.,gi\.es. on pp. 44243, an I~storieslaccxmt of “FalseCirris,” rscwmtlally as follows: I
................................................... (*) ................ (*) “(*) I (*) I [fpm c (*) (*) ........ fmr
(*) (*) ....... (*) ......... x P) P) ....... (*I .................................................... (*) (*) ....... .’-...
(*) (5 ) f (*) [fl“m[C’] C .... d C (*I
...................................................................
............................................... c .... c ....
[Uacdlyall bright.] [(lray or shadow#, at lrwl lOmll#.]
or, if condensation takes place in the lower as well as in the upper wind, an aspect not unlike a ra ged, inverted,
is evident from the visible motion within the cloud, and the usual rapid progress across the sky. Thin St. forms coronas about sun or moon, and at more than 90’
from the sun or moon looks mqre or less smoky. Lm-
ness and $alness are the essential chnracteristics of St., therefore, why not define it as “A low layer of cloud”? and add, “St. is distinguishable from ASt. only by whether or not i t appears to be lower than 1,000 meters above t,he surface.”
111 the sentence about VrSt,., the words “in a wind, or by the summits of nioiintains ” are not, only UiinecessaTy, but, preclude considering as FrSt. ragged evaporating remnants or first-forming wisps of n St. cloud when there is raotically 110 wind. Er.St. is indistinguishable from Fr.Cu., and Fr.Nh.’ esccpt by its associat,ions. In view of the fact that forms other than Cu., St., nncl Nb. have ra.gged aspects at. times, it. woulcl seem best to abttiicloii the limitation of “Fracto” to only three and recognize it as applicable t.0 any cloud type.
choppy sea. The low he’ ht by which t a in St. may be differentiated in questiona ’% le ca.ses from ASt. or CiSt.
TABULAR GZTJDE TO CLOU1) II)ENTlYICATION .la
Bearing in mind the considerations brou lit forth in
identificat,ion has been constructed. This guide is serv- iceuble whenever an observer can describe a c.loud or group of clouds a t the same level in terms of forin, coarseness and density.
this discussion, the following tabular p i c 7 e to cloud
International cloud forms.
Characteristics.
Fibrous ............... x
Sheetlike.. ........... ......... Bmooth ............... (*) .......
__. a Fibrous only when like morn or less interlaced fibrous bark cloth. 7 Dhtinguiihable from A.Cu. by lowness and sheebllke aspects of the formation as a
21 The omlssion of “lowR.’ from the hiternstional deflnitioq is deplored by A. de Qwrvsin in his rcvbw of the International Atlas (Met Zcltschr 191’ p :I There is “A guide to the identlficstion of cloud for&,”fubli&d igd ‘h e Observer’s Handbook ‘I Metl. OB London, 1915, pp. XXXIV-MXv. t is arranged aftar the manne; of organlzahon charts:’ There are three “Clouds sfan mostly in elevfpa or praa8,” e and “Low clouds .seen in plan 0r.elevation
whole.
189-1W).
oups, headed “Clouds seen mostly In pla?.
eaordlng to clrcumste3lces.
SEPTEBEBER, 1920. MONTHLY WEATHER REVIEW. 519
USING THE INTERNATIONAL CLASSIFJCATJON FOR DE-
TAILED OBSERVATIONS.
Is there not a way of using the Intermtional Classifica- tion so a.s to show details of cloud appea.rance to any extent needed ? H. H. Clavton’s detailed system hns not been widely used because of its unwieldy Latin n~inies.~~ The most important of his subclasses; and a few new ones, however, can be iven descri t,ive English adjec-
designated in cloud records by es Ionentiit1 1ett.ers w1iic.h
’ (ragged), t (thin), n (rain or snow fa.lling from cloud, w ether or not preci it.at.ion reaches the ground), K
( art of, or derived rom, thunderst.orni cloud), r (roll
to width), I (lenticuloid, i. e., with part or all hounding lines like the smooth curves of a lens),:4 m (mammillated),
zi. (undulated), b (in hands or st.renks), 2 (in zigzags, or with marked angles in lines-fibrous clouds only), d (det.aclied unit.s--no t needed with Ci. and Ck. 1. Thus, St‘ represents frnct.o-st,rn.t,us: i1.Cht disk-like, or ice-cake form, alto-cumulus: A.St.”” smoot,h alto-st,ratus from which ra.in or snow is falling. The use of one, two, or three of the int,ernat.ional names for different part.s of the same cloud sheet, adds greatly to the ossibility of expressing adequately the appearance of t : e clouds.
t.ives or otherwise brig ti y describecf and these can be
a.re in many cases ident.ica1 with t \ lose used by Clnyt.on:
l
c P oud), s (smooth), q (very fine t,esture), c (td1 relative P
CONCLUSJONS.
1. Cloud-records to be comparable should be based on the appearance of the c.louds R.S seen from the ground. If (as we can not) we could always know the origin of a
cloud, a classification on the basis of origin would be preferable. The elements of cloud appearance mu.y .be rec,orded without naming cloud types; but for discussion names are necessary.
8. International agreement ha.s provided a set of 10
cloud names to cover all cloud forms; but the definitions of these 10 do not include all cloud forms, nor do they differentia.te them adequate1 . The chief sources of
A.Cu., Ci.St. and A.St.., Nb. and other rain clouds, and, perhaps, St.Cu. and St. or A.St. If Ci.Cu. 8s defined is confined to ice-clouds, the frequent misnaming of A.Cu. will be eliminated. If i t ’ i s generally understood that A.St. may be either a more or less clense fibro.us, mam- d a t e d or smooth cloud of snowflakes, or a smooth, undulated, or mammilated water-droplet cloud, which is sometimes as thin and white RS CiSt., our difficulties on its score will be largely removed. If it is recognized that ~n,imbus is the name of a cloud form, axid not a syno- nym for the occurrence of prec.ipit,ation, much further
trouble are as between t,he P ollowing pa.irs: Ci.Cu. and
~
Op cit pp. 332-349, ch. 2 ‘*A new detailed nomenrlature of clouds founded ou the Iutkdionql nomenelatu&.” C1oyton:s reaso~!~ for prop0sin.g thed new details were: That they were needed for exact scientific ntudies, !or descriptions of Y clal occur-
renm for meteorolog~cal observatories where ohwrvations are made aufior the u8e of spe6iallst.a His baais waa form altitude and origin a8 compared with Howard’s basis of form only, and the Intmdtional b$is of !oTm ,&d altitude lA.Cu. vn. Ci.Cu., A&. vs. Ci.St.). Although Clayton mentions drrgin m the cases of Cu. and Yt., ?le offrrs ne change in names in consequence. “As the knowledge oftho mwes of sperm1 doud formations @cnurses. however jnmessillg wrjfiht wlU no douht he given tn cloud origin m determinmg classification hnd nomenclature.” With this, the chsslficatlon becomes one of lorm and altitude, therefore,, much of the rhapter,is,devoted tu cloud altitudes. He evolvea a detailed system wvhlch may serve the spclslst who has pledy of time in which to apply it, but the lar e numller of sperlal forms and their Latin name8 will always caiw it t? he avoided by ab but a very few enthusblsts:
41 Not usually ap licanle to CI., Ci.Cu., A.Cu., St.Cu., Nh., Cu., or Cu.Nb. The USB
of the word l r n t i c d r with Ci.Cu. and A.Cu. a.common, in spite of the fact that most lomticular clouds are -4.M. (cf. J. Vincent, loc. cit.).
trouble will he prevented. Finally, if St.Cu. is plwa thought of as strato-cumtiis, there will be less of t F e
indiscriminate misnaming of irregular St. and A.St. Wit.h these and other difficulties removed it is possible to construct a tabular ppide whic.h will indicate which one of the 10 names to apply to any cloud that an ob- server can describe.
3. A vocabulary .of 10 words, is, however, rather limited for recording and discussing the manifold aspects of the sky. The inadequacy of the langua-e of some African tribes has contributed in no smalf de ee to holding theni a t the bottom of the culture s c z . On
the other hand, the wide range of expression and shades of meanin allow-ed by the English lan age has been a
peoples to their present pcsition in the world. Let us adopt a set of standard characteristick, such as: Mam- millated, ragged, undulated, etc. :If, in addition, we make separate notmation of deilsity and actual, computed, or probable height, our cloud records will give a real iiiclication of the aspect of the sky, and will thus complete the weather-picture rovicled by instruments, meteoro-
decidedly F- avorable factor in the rise of % nglish speaking
graphs, ant1 pilot! ha1 ip oons.
ACKNOWLEDGMENT.
Far months Mr. S. P. Fergusson hau been giving me the benefit of his years of familiarit with the
observing of clouds at Blue Hill Observatory. I wish to acknowledge gratefully his many suggestions, espe- cially his service in checking tendencies to deviate too far from well-tried practice. ’
How to make and reduce detailed cloud observations and the use of a new form for cloud records will be pre- sented in a later paper.
of thc Int,ernational Classification an J with the etaled
LAYER MEASUREMENTS OF SNOW ON GROUND NEAR SUMMIT, CALIF.
By H. F. ALPS and 0. H. HAMMONDS.
[Weather Bureau, Reno, Nev., Oct. 8,1920.1
The layer measurements w-ere made in the open park, about one-fourth mile in a southeasterly direction from the railroad station a t Summit, in the same place and in the same manner as during the preceding season. From our experience in this work dunng the past four seasons, it is believed that this ark affords an ideal
Only four trips to the Summit were made, on account of the long interval between the first and second general stonns in the mountains. The first measurement of the snow cover was macle on December 31, 1919. At that time, the de th of the snow was 39 inches, and the
E e r of the snow was slight y granular, due to surface melting. As the snowfall was light in Jdnuary and the first half of February, the second trip was made on March 5, 1920, when the-depth of snow on the round
crust which would support any ordinary vehicle. This
location for la>yer measurements o P the snow cover.
s
und was F rozen to a de th cf one inch. The top
~7 a s 6s inches. The old snow, the eater part o B which fell in 4ecember, was 35 inches in T epth with a 10-inch