94 MONTHLY WEATHER REVIEW. FEBRUARY, 1914
at scattered places, the Mercator projection may be rec- ommended for these synoptic charts, with the possible addition of supplementary maps in polar projection for special occasions. In any case there will surely be no one to prefer the who11 unsuitable pro'ection adopted,
greatest dwtortion occurs in the Tenipcrate Zones, the ver region of which we know the most. &om the theoretical viewpoint the one daily siniul- taneous observation may be made a t any hour; practi- cally Greenwich noon would probably be the best time, since then the 1at.e afternoon and the early morning hours, which are the most difficult to secure in simultaneous observations, almost without esception will fall to the lot of the Pacific stnations where tahese hours offer no coii-
siderable ciifficulties to observers on shipboard. It i.; evi- dent that such cstensivc! synoptic charts will further u
more comprehensive knowledge of the dynamic enoni-
tage in tho forcca9tmg of weather and storms; t,Iius it. would not be necessary to niake special provision for this latter work. I doubt not that this view will find warm supporters amon the inembers of this congress, but if i t is to enierge froni t B e realm of siniple desire where so many unanimous resolves of former meteorological congresses still abide, then this Chicago congress must also consider the means for executing such a resolution. Perhaps, indeed, such
- arrangement-s have already been perfected very niuch as
when at Vienna Brig. Gen. Albert J. Myer init.iatec1 the system of simultaneous observations over the Nort.liern Hemisphere, undertaken and published by the TJnited States Signal Service, whose chef he then was. [See the following extracts from the official protocol of the Vienna con 89s.-c. A.]
#the United States of North America, in its former enerous manner, shdl guarantee the means for collecting, shiiig these pro )oset1 new siniulta- %mussing? and publi- neous observations for t,he whole glo e, it niay be safely assumed that no nation will withliold its cooperation in organizing the simultaneous observations in its own ter- ritory for this mutually beneficial work. Rut since it is scarcely to be expected that a single nation will again make so .great a sacrifice for the int~ernationnl wclfarc., the proposed undertaking can only be realized by assiei- ing its execution to an international meteorolo ical bu-
The establishment of such an international bureau, but. for other pur oses, was discussed at the Internat,ional
to the International Meteorological Committee for further considera.tion. The cougress at. Chicago night themfore request the latter comnlittee to consider the present ques- tion AS an additional task for such an international mete- orological bureau.
for exam le, for the C z art of Annual k ainfdl in Ber- ghaus' P 1 ysikalisches Atlas, 1887 edition, wherein the
ena of our atmosphere, and be of great prttctica Yh advan-
b
reau founded and maintained a t the expense of a1 f nations.
Meteorologic af Conference at Munich in 1891, and referred
[Extracts from Bericht Uber dle'Verhsndlungeo des Intarnstiooslen Meteomlopen-Con- greasas~u Wlen,2.-16. September, 1873. ProtokolleuodBeilageo. Wien. 1Ri3. vi., 114p. .I".]
PROTOCOL OF THE SEVENTH SESSION, SEPTEMBER 12, 1573, 10:!?0 S . M.
Chairman: Mr. Scorn. After the minutee of the Sixth plenary session were read and ap-
roved, the chairman read the written ropoaition, published aa $irst Ap endu .to pIotoc01 No. 7, from .D~%ypte General Myer, con- cerning %e mst~tut~on of at leeet one dady auunltaneous observation, and announcedathat the d i e d o n of this proposal had been aesigned to the next semen. (Pp. 23-24.)
1. BEILAQE ZUM PROTOKOLL DER VIITEN SITZUNQ. LETTER OF
GENERAL ALBERT J. MYER TO THE CONGRESS.
METEOROLOGICAL CONGRESS,
Vienna, 8eptember 11, 1873.
To the Congress.
GENTLEMEN: I have the honor to submit the following propositiun: 1
That it is desirable that with a view to their exchange at least one uniform observation of such character aa to be suitable for the prepara- tion of synoptic charta be taken and recorded daily and simultaneously at aa many stations as practicable throu hout the world." I am, gentlemen, very respectfufy,
(Syd) ALBERT J. MYER, Brigadier aeml, Chief Signal Oficer, U. S . A .
PROTOCOL OF TEE EIGHTH SESSION, SEPTEMBER 13, AT 10.35 A. Y.
* * * Next came the discussion of the proposal made by Gen. A. Myer (introduction of simultaneous observahom over the whole Northern Hemisphere, ap endk 1 to protocol of the seventh session). F h t , Mr. M er stated ttat hewas commiesioned by the War Depart- ment of the &ted State8 of North America to wure the cougrese of the deep interest taken by the department in all that concerns advance in the system of storm wnriungs and ita desire that the exchange of internahonal telegraphic weather reports shall find the greatest possible distribution. Turning then to hW p r o p d , M!. Myer sta-ted. that it seemed superfluous to argue for the actual estabhshment of it aince the importance of Simultaneous observations would undoubtedly be at once conceded by all. The pro osal was supported on several sides. Mr. Hoffmeyer an- nounced tEat he could support it only in case no ve great practical difficulties were present, because it could not be h e l d k t the scientific results would justify any very great sacrifice for their sake. Mr. Buys-Ballot drew attention to his own "Su stions," wherein he had pointed out simultaneous meteorologiraf?bservatims as a
desirable ob'ect After Mr. &er had again emphasized the fact that hia proposal only called for a declaration by the congrear that Simultaneous observations over the whole earth were a desirable consummation, the redotion was unanimously adopted. * * * (P. 27.)
A CLASSIFICATION OF THE METHODS OF TRANSITION FROX RAIN TO BLUE SKY.
By Prof. WILLIS I. MILHAM.
[Dated Wllliama college, WlUIamstowo, Mass., Feb. 20,19t4.]
INTRODUCTION.
The occurrence of rain or snow and also of most of the thundershowers of summer is due, as is well known, in nearly every instance to the passage of an estratropical c.yclone or area of low baronietric pressure near the place in uestion. Rdn or snow now and then result from a
cloud, or from the action of a barrier, or from the con- densation of moisture from a purely loca! source, and summer thundershowers are also sometiines due to purely local conditions, but these cases are too few in coniparison with the whole number to nierit further con- sideration. In wint,er, a passing low is generall attended by a continuous. fall of rain or snow for some iours. In summer, warm, sultry weather with thundershowers, particularly in ita southern quadrants, is the usual accom- paniment of a paasin low.
perature, pressure, wind, moisture, cloud, precipitation) about an area of low pressure has been much studied by
inany observem, and the statistical method has been the usual way of studying these formations. Most of the books on meteorology contain in more or less detail the generalizations from these statistics, which may be
V-s R aped depression, or from an overgrown cuniulus
The distribution o B the meteorological elements (tem-
I Adopted at the Vmth Session, Sept. 13,1873 (p. 68.)
FEBRUARY, 1914. MONTHLY WEATHER REVIEW. 95
expressed as laws, in tables, or by means of diagrams (1).
"he distribution of the nieteorological elements about a
low is not exactly the same for all countries or for all arts of the same country and there is also a difference
. Thus the geo aphical and gepending upon the seasons seasonal chan es ought to be studied as we as the dis-
low is very much the same formation the world around. The sequence of cloud forms before, during the inter- vals between, and after rains has also been much studied. The work of the Blue Hill Observatory near Boston is particularly worthy of mention, and an artide by Clayton rn the Annals 01 the Harvard Colle e Observatory,
distribution of the meteorological' elements about a low, but the change in cloud forms and their direction of motion, the occurrence of rain or snow, and the direction of the wind are the factors which can be observed without instruments and are the most conspicuous and interesting in the sequence of events which accompany the passing of a low. It is the distribution of the elements about a normal
or typical low and the normal or usual sequence of cloud forms which is determined by these statistical investi- gations. If every low were normal, the se uence of
be the same. An observer of weather changes knows that this is not t E e case, and the reason is t.hnt lows almost never conform exactly to the nornial or t.ype form. The question treated in this pa ,er is u-Iiethcr
classified in different ways, so that by stating 111 which group a low belongs, its characteristics are at oiicc ap- parent to anyone familiar with the various t,gpes.
Tl tribution itse i? . But the differences are not large as a
Volume XXX, treats this uestion in % etail. This, to be sure, is only one phase o 8 the general question of the
events in passing from rain to blue sky wou 7 d always
the methods of transition from rain t.o h !I ue sky ran be
one passes t %r ough the southern quadrants, t,here is a
J. GRADUAL SHIFT VERSUS RAPID SHIFT.
The h t eat difference between lows is whether, as
gradual veering of the wind from sonic emtedp qiiartcr into t.he northwest, or whether t.he chai~ge IS alniost instantanaous. In the first case the sequence of eT-enbs is usually as follows: At first. the wind begins t.0 blow gently from the east, the pressure decreases slightly, cirrus clouds make their appearance, and the tempera- ture and moisture begin to increase. Nest., the barom- eter dro s a little more, the wind direction changes to
the cirrus clouds thicken to cirro-stratus or cirro-cuniulus, and the temperature and moisture continue to rise. Jn the wintertime, as the PO ular phrase goes, the wcnther
has begun to moderate. P n the summertime it is the b e g i m of a period of sultriness. The ressure now
the cirriform clouds go through their regular transitZion into nimbus, and the temperature and nioisture are high and increasmg. Now comes a period of rain or snow',
with barometer still dropping and finally reaching its lowest. The wind, meantime, has slsckened somewhat and veered a little, and is perhaps now blowing fiom the south or southwest. The temperature and moisture still continue high. The wind now veers rat,her uickly into the southwest, then west, nitd finally nor?hwest,. The barometer begins to rise, the precipitation grows less, and the temperature and moisture decrease. Soon the nimbus clouds break up into fracto-nimbus, perhaps disclosing an upper cloud area. The fracto-nimbus then chahges into strato-cumulus, and finally cumulus or
the sout Yl east and the velocity becomes a lit.t.le grea,t,er,
drops st8 more, the wind veers a little and E lows harder,
fracto-cumulus, with a clear sky a t night. In the mean- time the wind blows froni the nort.hwest with increasing velocity, the barometer is rising, and the temperature drops rapidly. The air also becomes niuch drier. In the sunliner the dry, cool, northwest wind has re laced the oppressive sultriiiess of a few days before. f n the winter t,he thaw or warm spell has been replaced by a
cold snap. If, on t.he other hand, the windshift iY very sudden, the low possesses what may be called a wind-shift line, and the sequence of events is then soniowhat different. The coming of the rain or snow is just as before, but the wind ceases to veer and remains froni the south or
some southerly quarter. The rain or snow usually ceases for a time, and t,he lower ninibus cloud layer usually breaks in places or entirely disap ears, leamng an upper layer of cirriforni or alto clou 9 s. The tem- erature a.iicl nioisture reniain hi h; Soon the black
horizon ancl then niounts hi her and figher. In a
with considerable velocity. A squall of snow or a heavy fall of rain, perhaps with thunder and lightning, commences, and the temperature dro s as if by magic. Soon the preci itabion ceases, the f ower cloud layer
In the United States about one low in seven is accom- anied by bhis sharp wind shift. In Euro e it is said to !e niuch more common. Its cause is pro \ ably the way in which the weather control is transferred from t,he ],:wing low to the coming high. A coming high has on Its front Iiinsses of cold R;ir from the northwest.. These either overrun or underrun the. warm, moisture-laden air of the low and t.hus cause a rolling of the air about a long, horizontal axis, and to this is due the sudden wind shift). If the replacement of the warm, moist air hy the colder air froni the northwest is a more gradual process, a low of the first kind is the result. The two accompanying diagrams (Fi . 1 and 2) show the dist,ributinn of t,he meteorologic ai? elements about t.hese two 1;inds of lows. The solid lines are Lobars, or
linrs of e ual pressure; the dashed lines are isotherms,
re1ocit.y are indicat.ed by the direction and length of the arrows. The cloud forms on the east are h t cirrus, their the transition clouds, and finally nimbus, which
brenks up on the went usually into strato-cumulus. By nim-inp these diagrams slowly from left to right, so that
n. place ~~~s s e s through their southern quadrants, the se- quence of met,eorological events due to the passage of such lows becomes a t once evident.
Eank of cloud begins t,o appear 3 1 don the w-&ern
moment the wind snaps into t B e nort,hwest and blows
breaks up, ancl t $ e sequence of events is as before.
or lines o 9 equal temperature. The wind direction and
11. THE THREE TYPES OF GRADUAL WIND SHIFT.
In the first of the preceding cases, when the wind veers gradually and continuously from some easterly direction until it finally reaches the northwest, it is of importance to note the direction of the cloud motion as compared with that of the surface wind. While it is rainin both clouds and wind usually come from the same easterk or perhaps southerly quarter. When the wind nall reaches the northwest and blue sk has
as well. During the shifting, however, the cloud direc- tion and the wind direction may not coincide. The direction of cloud motion may shift with the wind, it may be ahead of it (that is, come from a more westerly quarter), or it may be behind it. There are thus three ossibilities.
If diagrams (Annals of the Haryprd College ($bservatov,
appeared, t K e clouds generally come from the nor tTl west
96 MONTHLY WEATHER REVIEW. FEBRUARY, 1 9 14
Vol. showing the distribution of the meteoro- logical elements about a low at various levels above the earth’s surface are examined, it will be seen that normally the cloud niotion should be ahead of (more westerly than) t,he wind direction. Theory also shows that this is the expected result. Stat,ist,ic.s will show that this is true in about six cases out of ten. I n perhaps two cases the direction will be coincident and in pe,rha s two cases i t will lag behind. The reason is twofolcf In the first Illace, the niasses of c.ooler nir accompanying t,he advanc- ing hi h and coming from the nort,hwest either overrun,
prtnyinq the tlepitrt,m low and coming from a more
wind lnll shift before the clouds; if i t overruns, t,he clouds will shift ahead of the wind; if there is mixture, it is doubtful just which case might cesult. In the
or unc f errun, or mingle with t,he moist, warm air acconi-
souther y direction. B f the air underruns, the surface
FIO. l.--Conditions attending a gradual slow change of wind and weathcr.
second place the axis of a low leans backward or west ward. By the axis is meant a line joining the successive centers of
lowest pressure a t various heights above the earth’s surface. At first thought one would expect t,his to be perpendicular to the earth’s surface, but the unequnl temperature distribution on the two sides of a low causes the axis to lean backward or westwarcl. I t is well known that on a hi h mountain the center of a low
surface. As leaning back of the axis will also influence the relation between the wind direction and the direction of cloud motion. The amount of the leaning is not the same for all lows, but depends on the temperature distribution about the low in question.
sometimes asses an f our or so later than at the earth’s
111. ONE OLOUD LAYER OR MORE THAN ONE.
When the lower cloud layer finall breaks though
Sometimes more than one It consists usually of cirriform or alto
and discloses the blue sky, an upper c T oud layer may be
seen or there may be none. layer is glimpsed.
clouds which move from a more southerly direction than the lower clouds and usually disappear in a few hours. According to the Blue Hill observations, in 110 cases u per layers were seen 71 times. The ordinary observer
is not constantly on the lookout for the merest trace of tin upper layer will not see as many. He will be of the opinion that not more than one low in three or four
his an upler layer. The up er layer is perhaps more
which the wind veers gradunlly.
w K o does not make niany observations at night and who
common a ’f ter it rapid wind-s&ft low than after one in
after the normal time. slowly, or it may remain totnly 9
IV. THE RAPIDITY OF CLEARING OFF.
After the rain ceases, the blue sky may nppear quick1 ,
I /n -
FIG. ? -renditions attending n sudden c h x ~g ~ of wind and weather.
c.luucly until it rtiins upniii. The nornit11 time iiitervd between the ending of the rain c t n d the first blue sky is perhaps four or five hours. Sonietimes it may appear
111 iin hour or two, in w1iic.h c a w it has c1e;iretl very quickly. The clouds mtiv last 12 hours or R whole tl:ty, in wli~ch case i t hiis cleniwl very slowly. There are
n few ciihes where it will remain totally cloudy until it rains again. The secontl rain iiiust occur, however,
at, least 24 hours after the stopping of the first to be considered iin iiitlepenclent, separate storm.
V. FURTHER CLASSIFICATIONS.
If simple instruments, such as a thermometer and ba- ronieter, are available, a few additional but perha s less
west. Lows may be classified as wind in the southwest, windamore easterly,:orLmore,westerly when the pressure
interesting classifications ma be made. The P owest pressure usually occurs when t i e wind is from the south-
FEBBUABY, 1914. MONTHLY WEATHER REVIEW. 97
is lowest. The temperature drop after the rain ceases and the blue sky comes ma. also be noted. This can be classified as small, normat or large. The rapidity or rise of the barometer may also be classified as rapid, normal, or slow.
VI. LIMITATIONS.
This classification of the sequence of events in passing from rain to blue sky applies geographically to New England or the Middle Atlantic States. This normal dis- tribution of the meteorological e1ement.s about a low is, however, but sli htly different for any part of this country and not very % fierent for the Atlantic Ocean or for Europe. Furthermore, it has always been a low which so moves that an observer passes through its southern quadrants, that has been considered. Now for the northwest,ern part of the United States this is nearly always the case. A wind that backs instead of veers is very unusual except possibl near the seacoast and in the extreme northern part. %‘he sequence of events would be entirely different? and this has not been considered. Furthermore, it is the winter type of storm with steadily falling rain or snow which has been considered rather than the summer t y e with the sultry weather and thunder- showers. The g est way to characterize the difference be- tween the summer and winter type is to liken i t to a
machine. In the winter type the machine runs smoothly. In the summer type the machine clogs and stops and then by a thundershower is jerked forward to where it ought to be. The sequence of events goes forward by jerks rather than smoothly. It would require ten ears of careful observation to do t.his,
fication. For example, it makes little difference whether about one low in seven has a sharp wind-shift line or it. is finally found that for a definite place for a definite period of ten years it is exactly I7 per cent. This chsaification is based upon two or three years of casual observ. a t t.’ 1011
and one year o€ critical observation to test, the clnssifira- tion at Williamstown, Mass.
Furthermore, esact figures have not been given.
and but little woul B be gained. The value is in t,he clnssi-
VII. SUMMARY.
As was stated at the beginning, the 1)urpose uf t.his article is to attempt a classification of t.he various methods of transition from rain to blue sky. For esample, i t niay be said of a certain passing low which caused the rain, that the wind veered steadily instead of changint sudc1en~- ;
that the direction of the cloud motion was a ead of t c
wind direction; that an upper cloud lttyer was seen for a
short time; that the time required for showin was normal. It might also have been state % that sky t,he lowest pressure came with the wind from the southwest, that the temperature drop was normal, and that the pressure increase was rapid. It will thus be seen that this classification would give to an one familiar with the
characteristics of the passin storm. Itwilfalsoa,dd much pleasurf, to watching this o B t occurring transition to know the vanous wa s in which it may take place and the one
various methods of transition, a (9 t3finit.e icture of the
in progress in t Tl e instance under obsemation.
REFERENCES.
(1) See: Annals of Harvard College Observato Ham, Julius. Lehrbuch der Meteorologic. Zipzig, 1901; 2ded., V?1. XXX.
1905; 3 ed., 1914. 4O.
Hanzlik, Stauislav. Die riiumliche Verteilung der meteomlogiachen Elemente in den Antizyklonen. Wien, 1898. 94 p. fa. Hanzlik, Stsnislav. Die riiumliche Verteilung der meteorologinchen Elementa in den Z klonen. Wien, 1912. 62 fa. Meteorologische &tachrift, Brawhwe‘ . f h i , 1903. v. 20. p. 307. Milham, Willis I. Meteorology. New ?orb, 1912. 8”.
. -. -.
.I d :, ,, 2- .; ; 5-CJ7- -:.2 -7
SQUALLS AND TIDE PREDICTION OF TORNADOES.
By E. DURAND-GRBVILLE.
[Dated Park, Mar. 30,1913. Tr?nslatnd for the Monthly Weather Revlew.]
INTRODUCTORY NOTE.
The International Conference of Directors of Meteorological Obeerva- tories, which met at Innsbruck, Austria, in September, 1905, listened to an enthusiastic paper on the henomena of squalls by M. 4. Durand-Gdville. After his addreas%rof. H. Hildebraneson s u w t e d that the conference app“‘“t a commkion on squalls, its functions to be ando us to those o the International Commission on Clouds a - pointed r y the International Meteorological Committee. Favorabfe action by the Conference resulted in the ap ointment of such a Com- mission composed of MM. Hildebrandeaon bpslla), Shaw (London), and Durand-GrCville (Paris). henom- ena, and this REVIEW has alread published an exposition o f his din- coveriea in this branch of meteorofogy . The ublication of the preaent paper hae been delayed by administrative c&nges that were impend- mgat the time of its receipt. The Editor regrets to announce the
death of it,a author on January 20. 1914.
M. Durand-GGville was long an active student of squall
SQUALLS.
What has come to be known as the “law of squalls” did not. present, it,self to my mind at one time.’ Several years previous to 1890, being intrusted with the meteor- ological articles in the Grande Encyclo Bdie, I had first made myself acquainted with the carter works, or a t least with the greater number of them, notably with t,hose bf Ciro Ferrari, who, according to the expression of Hildebrandsson, was “ the one who had done the most” for the knowledge of thunderstorms; also, of course, the works of MariB-Davy, written under the direction of Id I’errier. The latter had given the simplest possible definition of
n t.liunders torni, VIZ, “ any disruptive electrical discharge in the atmosphere.” The definition had become com- licnted lit,tle by little, in proportion as the details had !ern studied and various brusque changes at the time of the thunderstorm had been observed, such as rise of the bttrometcr; iiicrease in force and change of direction of the wind; fall of temperature; increase of relative humid- ity, et.c. I shall tell you why i t seems necessary to revert to t,he original definition of the thunderstorm and to rest,ore to the squall its personality, the s uall serving
at the mommt when it arrives froin a distance on large cuniuli previously formed. In studying attentively the thunderstorm isochrones of Marie-Davy and more ea ecially those of Ferrari, I
getween two “thunderstorm spots” not, too far distant from one another and that, in certain cases, the isochrones of the two “spots” could easily be connected. If one
sought to verify what took lace between, the two
squall, of a barometric “hook” (crochet), etc. This work of verification was done slowly and fragmenta- lily, but in the end I was persuaded-mthout, however, havin any very tangible proof of it-that the isochronous
without evoking a t understorm, would continue ita
only-as occasional c a u s e t o rouse up the t % understorm
erc.eived t,hat there appeare B to be a real correspondence
‘ispots,” one would discover t R e existence of 8 wind
line o P a Golent squall assing over a place in the morning
R