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    "source_title": "Encyclopaedia Britannica (1926)",
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    "title": "METEOROLOGY",
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    "verified_text": "since 1910 considerable ad- vances in meteorological knowledge have been made both on the observational and the theoretical sides. the upper atmosphere—during the years before the war observations on the temperature and humidity of the air strata were rapidly accumulating, more particularly from a network of stations spread over europe, and since the w. and n. of europe is subject during the winter to the passage of many deep cy- clonic depressions, the conditions of temperature in cyclones and anticyclones up to a height of some 20 km.(123 m.) had become known. the brief tables which were all that were available to cleveland abbe in ro909 had been supplemented by much information, drawn up and arranged for the european results by lt.-col. e. gold (al.o.no. 210e, geophysical memoirs, no. 5), by dr. wegener for the continent (die tem peratur- verheltnisse in der freicn atmos phiire, iii. band, heft 2/3, leipzig, 1909) and for russia by dr. rykatchew (afeteorologische zeit- schrift, jan. 19t1). in 1916 a summary of the information available about the upper air was drawn up for the meteoro- logical office but not published. it quoted freely from gold’s paper but included the results of observations up to 1916. this summary together with certain theoretical matter was published in 1919 under the title “ characteristics of the free atmos- phere”? (m.o. 220c, geophysical memoirs, no. 13), and from it the following abstract summarising our present knowledge of the strata from o to 20 km. is mostly taken. tem peratire.—as the surface of the earth is left the temperature of the air decreases with increasing height, and when the great varia- tions of climate and of the conclitions prevalent in different parts of the earth are considered it is remarkable how uniform is the fall of temperature, now commonly called the lapse rate. the height to which it extends is variable, but in all places in which observations have been made, the lapse rate up to 8 km. has been found close to 6°c. per kilometre. this hoids between 2 and 7 km. not indeed exactly but approximately, for summer and winter and for places as far apart as the equator and the antarctic in lat. 78°s. thus in batavia the lapse rate up to 8 km. is 6-1° per km.; at petrograd it is §-8°. in england in the winter it is 5-8°, in the summer it is 6-0°, these are means, but the rule holds quite well even for the individ- ual case, for if in one part of the 8 km. the lapse rate is small this is usually compensated for by its being large in the other part. the only important exception that has been found so far is in regions and at times where the temperature ts extremely low, as in siberia or canada or the antarctic in the winter. in such instances the bot- tom layer is unduly cold and the lapse rate 1s negative over the first 2 km., so that the rule would make the upper air temperature too low. also it must be remembered that the daily variation of temperature does not extend upward more than one or two km., so that the mean 887 for the day rather than the precise temperature at the moment should represent the surface temperature. this layer, in which temperature falls with increasing height, is called the troposphere. at a certain height, which varies with the latitude, with the barometric conditions, and with the season, the fall of temperature ceases, and the air up to the greatest heights that have been explored remains at a nearly uniform temperature in the vertical direction. this upper part in which there is no lapse rate is called the strato- sphere, the boundary between the two parts is found at about 16 km. near the equator and at 10 km.in northern europe. over england its mean height is 10-5 km., falling to rather below 10 km. in the winter, and rising to over ii km. in the summer, in the centre of a deep cyclone the value may easily fall to 8 km.; in an anticyclone it may exceed 12 km. the temperature of the stratosphere is below 200° a. over the equator and in tropical regions; it isabove 220° a. in northern europe. in canada it seems to be lower in the summer than in the winter. these anomalies are roughly expressed by the rule that the mean tempcrature of the air column taken with regard to height from oo up to 19 km. is approximately the same in all parts of the earth. there is probably a physical reason for this, and it explains the un- expectedly low tempcrature above 14 km. over the equator and the curious reversion of temperature between summer and winter over canada (toronto) where the seasonal range is very large. the annual range of temperature in the troposphere does not differ very greatly from the range at the surface; in island and coastal climates like england it is rather greater in the upper parts than at the surface; in continental climates the surface has the greatest range. in the stratosphere the range is much reduced and, as already stated, appears in canada to be reversed although enough observations are not yet available to make this absolutely certain. whether or not there is any regular diurnal change of temperature above 2 km. height is uncertain; all that can be said is that if there be any its amplitude is certainly less than 1° centigrade. the mean annual temperatures are given in the accompanying table i. in europe the probable error of any value is about 1°c.; for canada and the equator owing to paucity of observations it is greater, especially above 15 km., where it may reach perhaps 3° centigrade. over europe the mean temperature does not change from 14 to 20 km. and does not change much over toronto. ovcr the equator the lowest temperature, which is about 193° a., is not reached under 16 or 17 kilometres, table i. mean atmospheric temperature the absolute scale with the first “2” 273:0° =0° c.= 32°f. the values are in omitted. d 3) bo - 3 ~~ ¥ col 5 6 5. oo hee we bd c a os oo fae] <— © ~ 8 hi} ecls!] €] 8/34) 2/ @] e/] 9)/35) 8) 8 3 13/8] 8/5/24) 8) §|8/ 3% (s43) 5] & m | oa] a] ee | oa ee oe gy i4 |23°5|22-0]20-5118-7118-9] 19-1|17-9]19-6|17-7/ 19-1] 12-5] 3-0 13 |23:4/21-8]20-6/19-3)18-7]19°3}17-6)19-6/16-4/19-2]14-0] 11-0 12 $20-7|21-6]20-0/18°3/18-8] 19-5] 16-8] 18-3] 16-1/18-4] 16-2] 19-0 ii |20-0/20-5/20-9/19-2\\19-6!20-2]18-1)18-4/18-5/19-1\\19-3(27-0 io [21-321 -2]23-2|21°9]22:2|24-3|22-3/21-8|22-7|22-2123:2)/35-0 9 |24-4/24-8]28-2|26-8]27-5|30-0| 27-8] 26-9|27-3|27-2/29°3/43-0 8 }29°8/30-2)] 33°8]33-1)33-6 36-9]34-8, 33-6) 33-9/33°4' 35-9) 51-0 7 |37-1|38-0]40-2]40-8]40-7 | 44-3] 42-1/41-2/41-2| 40-7 /43-5]58-0 6 |43-3)45-0]47-0]47-9]/47-8] 51-4) 49-3] 48-8] 49-4) 47:8|50-9]/65-0 5 [49-8/52-0]53°8]54°8}54-8) 58-1£/56-1/55-6|56-2/54:-6/57-7/72-0 4 155°7/58-4]60-4)61 -0)61 -7)64-3)62-4)6t -9)62-9 61-1 )64-1)79-0 3 |61-3/64-0]66-6/66-9/67 -7/69-8168-4] 67 -6|69-2|67-0/69-6]/85-0 2 |66-7|70-3)71-°7171-7|73°2|74°5|73°8173 -0|75-1|72°4|74:8|90-0 i 170:0175'3177°0176°8]78-0178-5/ 78-2177 6180-7 |76-8178-3195-0 pressure and density.—the temperature of the air having been found by observation, the pressure and the density are easily found up to the height to which the observations extend. in the same way the mean pressures and mean densities can be determined from the mean tempcratures without appreciable error provided the mean pressure at the surface is known. in the lower strata the pressure at any particular height is natural- ly most dependent upon the surface pressure, but since the air is lighter, bulk for bulk, when it is warm the pressure decreases less rapidly than usual in a warm area, and the pressure at any given height depends more and more upon the temperature of the under- lying air as that height increases. thus it comes to pass that in the hot regions of the carth, say in the belt included between the two tropics, the pressure at the height of 9 km. is very much greater than it is at the same height over temperate latitudes, and the pressure gradient which causes the prevailing westerly winds of the cirrus level is thus produced. ata height of 20 km. the surface pressure has ceased to have much effect, and it requires a rise of nearly 20 mb.} 1the average pressure of the atmosphere at sea-level being reckoned as 1 bar=r1ooo millibars (mb.). 1 mb.=0-0295306 in. mercury at 32°f. in lat. 45°. 888 in the surface pressure to produce a rise of i mb. at 20km., whereasa change of 1-5°c. in the temperature of the air column will produce that effect. it has been stated that the mean temperature of the air column up to i9 km. is much the same in all parts of the world, and it follows that the same level is one of nearly uniform pressure. the pressures are given in table ii. at various stations for heights up to 20 kilometres. the values for canada and the equator at heights above 15 km. are not very reliable owing to paucity of data. ‘the densities are given in table iii. the variations in the density became of great consequence during the war on account of their influence on the range of projectiles; they depend on the connection which has been found to exist between temperature and pressure. statistical methods.—statistical methods have been much in vogue of late years, and it is necessary to indicate how the method of correlation has been used for forecasting and for elucidating meteorological problems. a large number of cor- relation coefficients have been determined between various meteorological events, and the values of many of them are given in the computer’s handbook, m.o. 223, section v.—tables, published by the meteorological office. the advantage of a correlation coefficient in estimating the connection if any between two events, is that it expresses the connection as a decimal, which must lie between 1 and —1, and meteorology the application of the method of correlation to forecasting can hardly be looked upon as very successful. two highly correlated events are required happening with a definite time interval between them. a correlation coefficient may be high accidentally if it be founded on too small a number of instances, but genuinely high coefhcients between meteorological events occurring with more than a few days’ interva{f between them are hard to find. the most suc- cessful instance is perhaps the forecast of the monsoon rain of india by sir g, t. walker from the correlation between it and sundry other events occurring in the spring of the same year or earlier. in this case the correlation coefficients on which the forecast is based have values of about -50; if values of -80 or -go could be obtained very much greater success would be secured. there are a few coefhicients of from -70 to -80 between the rainfall at various pertods and the subsequent yield of sundry crops. thus in the eastern counties of england if april and may be wet it is a practical cer- tainty that there will be a jarge hay crop, and if the autumn be dry there will almost certainly be a large crop of wheat the next year. mr. r. hw. hooker has calculated a most interesting set of figures relating to the correlation between the weather and the crops, and the problem has been re-analysed by r. a. fisher and w. a. mac- kenzie, quart. jour. r. meteor. soc., july 1922. similar work has been done for the potato crop in america by j. warren smith, and many correlation coefficients relating to agricultural matters are available from sweden and elsewhere. the case is different where correlation is resorted to for the pur- pose of elucidating some physical process in the atmosphere; here a table il. afean pressure of the atmosphere (millibars) height petro manches- england, stras- . . mean for} toron-] equa- ae grad scotland ae berlin ao paris | bourg vienna pavia europe a ie 20 55:0 55-0 55:2 54°8 54°9 56-0 54°7 55°0 54°8 54°9 53 19 64:0 64-2 64-6 64-0 64-1 65-6 64-0 64-4 | 64-0 64-1 63 18 74°5 74°8 754 74°8 75:0 76-6 74:8 75:2 75:0 75:0 75 17 87-0 87-3 88-0 87-4 87-5 89-6 87-6 88-0 876 87:8 go 16 ioi 102 103 103 102 105 {02 103 603 102 me 107 15 118 118 120 120 120 123 120 121 121 120 120 128 14 138 138 140 140 140 143 bar 142 142 140 142 152 13 161 161 164 164 164 167 165 165 165 164 167 178 12 187 187 192 192 192 195 193 193 i94 192 195 209 if 218 219 224 22 22: 228 226 226 227 226 228 pp vel 10 255 256 261 262 261 266 263 263 264 262 266 283 9 297 299 302 305 303 309 307 306 307 305 309 327 8 346 348 352 354 352 357 355 354 356 353 358 376 7 400 402 407 408 407 412 410 409 412 408 413 430 6 46! 464 468 470 469 473 472 471 474 470 475 491 5 529 532 537 538 538 541 5.40 539 542 538 543 558 4 606 608 613 614 615 617 616 615 618 o14 618 632 3 692 694 698 699 699 701 700 700 703 699 793 713 | 2 787 787 793 795 795 796 794 795 797 794 798 803 i $q6 894 8o8 goo goo | goo goo goo | ol 899 go3 903 table iii. density, grammes per cubic metre canada equator europe | 14 13 12 if boe | om nwa ayn ow thus renders the connections between different pairs of events comparable with each other. the velocity of the wind and the steepness of the barometric gradient may be taken as an example. the actual connection is obvious from the daily weather charts; on some it is well marked, on others badly, but the fact that there is a connection is quite apparent from even two or three charts. the correlation coefficient is about 0-70. small coefficient is just as likely to give information as a large one but the interpretation of the meaning of the coeflicient 1s often difficult, and in many cases the value obtained is quite different from that which most meteorologists would have expected. sir g. t. walker in addition to his statistical work on the mon- soon rain has published several sects of correlation coefficients, and amongst them a set of roo showing the correlation between the sunspot number and the temperature at 100 stations well distributed over the earth’s surface. the correlation is negative and small, but it is large enough to be significant and to prove that during the 40 or so odd years considered the temperature of the earth as a whale was lower at the time of the sunspot maxima than at the time of the minima. it is commonly supposed that the sun is giving out most energy when its surface is most disturbed, and this idea has been confirmed by direct observation of the radiant heat. a per- fectly satisfactory explanation is at present wanting. walker also correlated between sunspots and rainfall, and found the coefficient too small to be significant. hlowever, in none of these cases has the work been wasted, since important conclusions have been established. for high correlation coefficients one must take data relating to the upper air. the relation between pressure and temperature is so remarkable and has such a close relationship to the theory of cyclones and anticyclones that it will be treated separately. the correlation coefficients between the thickness of the troposphere, a height com- monly denoted by ii., the surface pressure, the temperature of the stratosphere and other variables often exceed 0-7o, and the gen- crally high values show quite plainly that there is an ordered se- quence in the processes going on above, which is strikingly absent from the surface phenomena. cyclones and anticyclones.—\\n a cyclone the troposphere is cold and the stratosphere warm, in an anticyclone the reverse is the case; in a cyclone the tropopause is low, in an anticyclone high. thus as an area of low pressure passes across the map the following changes occur in the various air strata above. the deficiency of pressure is about the same from the surface up to some 10 km., meteorology above which it falls off rapidly until the normal value for the height is reached at about 18-20 kilometres. the temperature from about 2 to 8 or 9 km. falls, and from to to 20 km. it rises. the height at which the lapse rate ceases, the timit of the troposphere falls. these statements are based on the very high correlation coefficients that are found to exist between pressure and temperature. i[t will be seen from the accompanying table iv. (which gives the correlation coefficients) that close to the surface the correlation is low, but it is very high from 4 km. to 8 kilometres. there are probably two rea- sons for this. the surface temperature is governed by many consid- erations—the time of day, the state of the sky, the strength and direc- tion of the wind; higher up these disturbances do not apply, for, as has been already stated, the diurnal variation is very shallow and the correlation between the components of the wind and the tempera- ture is surprisingly small above a few km. height. secondly, it may well be that the chief item in determining the temperature is the re- cent vertical motion of the air, and a systematic vertical flow of air either up or down is plainly impossible quite close to the surface. the table iv. height, km... re) i 2 3 4 5 jan.-—march — +02 54 82 “79 86 “85 april-june “14 28 49 79 89 -89 july—sept. —-02 31 -56 -72 75 ‘81 oct.-dec. “33 -56 76 “77 83 87 means. , il “42 66 ‘77 4 85 rise and fall of the tropopause (h.) and the regularity with which it occurs is shown by the high correlation, -84, between it and the pres- sure at 9 km. height. there is hardly a single instance of observa- tions made in europe at a time of really low barometer in which h, has not been found well below its average value. the dependence of the temperature of the stratosphere on the barometric conditions is not so close, the correlation being only -50; but based on some hundreds of observations as these correlation coefficients are, -50 is amply significant. still the importance of a correlation in general depends upon its square rather than upon itself, and the significance of -50 is very different from that of -90 or -85. one noticeable result of this high correlation between pressure and temperature is that the density is not subject to much variation save close to the surface, for a high pressure and a high temperature act upon the density in opposite ways, and since they occur together the density remains comparatively unchanged. (see also below, the meeting of air masses from different climates.) stability for vertical displacements; available energy.—the rate of decrease of tempcrature with height is normally less than the 10°, c. per km. by which clear ascending air is cooled by adiabatic expansion. consequently a small portion of air, if forcibly raised or depressed, usually tends to return to its original level. the periodic time t of its vertical oscillation, if undamped, has been calculated by vaisila (soc. scient. fennica, comm. phys. math. i[., vol. 19, p. 38) to be se {9 i = an|/ — g(y¥o-y) where @, is the absolute temperature of the air in the equilibrium level, g is the acceleration of gravity, y is the actual decrease of temperature per unit increase of height, y. the adiabatic value of y. thus at a height of three km. t is normally about ten min- utes, while in the stratosphere t is about five minutes. any energy that there may occasionally be in a vertical col- umn available for producing thunderstorms or other local dis- turbances has been made conspicuous by sir napier shaw, who has plotted upon a special chart observations of temperature against those of pressure at thesame height, so as to produce, without calculation, the entropy-temperature-diagram familiar to engineers. fig. 1 is a simplified sketch of it showing the ob- servation for benson, oxfordshire, on july 5 1923, 7 p.m. he regards the dry air as the working substance and calls its en- tropy the “‘ realised entropy,” while the moisture he regards as merely a reservoir of latent energy. let aand b be two points where the curve representing the observations cuts the same adiabatic for cloud. if a sphere of unit mass of cloud at a is pushed up it will follow this adiabatic. if we may assume that the surrounding air, in descending to take the place of that which has risen, does so by a very small displacement spread over a large horizontal area, and in such a way that unit mass descends across each level surface, then what has occurred will apparently be indistinguishable, as far as energy changes are concerned, from the passage of a unit mass 889 round the thermodynamic cycle from a via the adiabatic to b and back by the observed curve. then, from the known prop- erties of the entropy-temperature-diagram, the mechanical en- ergy will be proportional to the area enclosed between the curves, and will be consumed or given out according as the observed curve lies below or above the adiabatic. actually two diagrams are employed, in order to represent humidity as well as temperature and pressure.! radiation in the form of electromagnetic waves.—just as a point has no parts and no magnitude, so a single direction con- tains no radiant energy. to mark off a definite flux of energy we must have two areas not in the same plane. for simplicity let us think of two square centimetres placed one metre apart and both normal to the line p q joining their centres p and q. correlation between pressure and temperature 7 9 12 13 84 87 ‘gl ‘bi sor jhe 52\" | regs 2 87 “si “45 20 —-i2 | —-24 83 87 -87 -83 43 ~—-o8 |] —-4! 85 85 86 7 29 see oe 86 86 86 72 2 —-19 | —-36 we are now able to define the “ intensity of radiation ”’ in the direction p to q as being 10‘ times the amount of energy that goes through both square centimetres in the order i to q in one second. the intensity of radiation k,dv in the range of frequencies of vibration between v and y-+dy has been shown to have the fol- lowing value inside a black enclosure at a uniform temperature § absolute centigrade, sy hv kidy= et — jis wherec is the speed of light, 4 =6-55 x10 27 erg sec, k= 1-34 x 10716 erg degreetm!. (planck, vorlesungen iiber die theorie der wedrme- sirahlung, barth, leipzig.) this is known as the “ full” radia- f’ adiabatic for clear air realized entropy per mass temperature } fg. 1.—diagram of “air” entropy. tion. further it was proved by kirchhoff that if a portion of air absorbs a ijraction a oj the energy in a ray of frequency v then that portion emits in the direction of that ray the same fractiona of the full radiation, k,dv, corresponding to its temperature @. through any sphere of one centimeter diameter in the atmos- phere radiations of various frequencies are passing simultane- ously in all directions without blocking each other’s paths. a division at a wave-length of three microns has nearly all the energy of solar origin on the short side of it and nearly all the energy of terrestrial origin on the long side. when a ray passes through a centimetre length of atmosphere its energy is in general divided into three parts. one part, al- most unchanged in wave-length, is turned aside and scattered in most directions. another part is absorbed, that is to say— changed into heat-energy of the air. whatever is left goes straight on unchanged in wave-length. the fraction that is scattered in unit length of path depends on the wave-length and the 1see the report of the meeting of the international commission for the investigation of the upper air, held in london 1925 (m.o. 281 published by h.m. stationery office, london), 890 presence of dust and cloud particles. even air molecules scatter, and more so in the shorter wave-lengths. hence we see a yellow- ish sun in a blue sky (rayleigh). the fraction that is absorbed in unit length of path depends on the wave-lengths and the various gases present; ne, ox, o3, cos, ho, each absorbing strongly characteristic wave-lengths. at the same time each small sphere of atmosphere is sending out, at the expense of its heat energy, long-wave radiations equally in all directions. with such an abundance of processes going on simultaneously the difficulty of the observer has been to separate that one which he wished to observe; and the difficulty of the theorist has been to include them all without making his theory too cumbrous. “tong wave” radiation—w. h. dines (geophysical afem- oirs of the meteorological office, no. 18) has measured the radiation which will not go through a glass plate and which reaches the earth from different zones of the sky. he finds that the intensity of radiation from a thick fog is within a few per cent. of that from a “ full” radiator at the same temperature; whereas the intensity of radiation from a clear zenith sky at sunset ranges from about o-65 of that from a grass meadow in december to 0-74 of it in september. the meadow was practi- cally a full radiator. from the way in which the intensity in- creases as the zenith distance increases, w. h. dines concludes that there must be at least two groups of radiation differently absorbed; one group comprising two-thirds of the energy is half absorbed in passing normally through a horizontal layer of clear air roo millibars thick, the other group, comprising one-third of the energy, is only 1/20 absorbed in this way; whereas 100 millibars of thick fog absorb eight-tenths or nine-tenths of all the incident energy. the sum of the radiations received by a horizontal square centimetre from all parts of the sky amounts to soo gr.-cal. per day on the average for clear skies, or 700 for fully clouded skies, while at 10°c. a full radiator gives out 711 of these units. a similar but not identical account is given by a. angstrem (oquar. jour. roy. meteor. soc., april 1924). he divides the energy sent out bya full radiator into three groups of wave- lengths comprising one-fourth, one-half, one-fourth of the whole energy. for the first group a clear moist atmosphere is almost perfectly transparent. the second group is almost totally ab- sorbed in the first 30 metres above ground when the vapour pressure is 10 mm. of mercury. the third group has a variable absorption chiefly dependent on the amount of water- vapour present. “ short wave” radiation of solar origin.—a square centi- metre placed outside the atmosphere normal to the sun’s rays would receive, according to the extensive researches of abbot, 1-94 gr.-cal. per minute. the question of natural fluctua- tions about this mean is still in debate (vide the monthly weather review, july and aug. 1925). when the sun is in the zenith of a clear sky a unit of incident energy is divided roughly as follows: o:78 comes to earth in the direct beam, 0-06 is scattered to space, 0-06 is scattered to earth and o-10 is absorbed, warming the air. when the sun is nearer the horizon the scattering and absorp- tion are much greater relative to the transmission. abbot states that clouds reflect about 0-65 of the solar radiation falling upon them. much further information will be found in the smithsonian publications, in l. v. king’s paper in the pail. trans. roy. soc., a, vol. 212 (1913), and tn recent papers in the meteorologische zeitschrift. the absorption by ozone is now being studied by dobson and harrison (quar. jour. roy. meteor. soc., 1925). turbulence and diffusion—a statement that the wind has a velocity of so many metres per second customarily refers to some mean value taken over say 10 minutes or more. actually portions of air are moving faster or slower than the mean, as well as up and down and horizontally to and fro across the mean track. these deviations are well shown on the records of pres- sure-tube anemometers. the wandering portions carry qualities with them. thus fragments coming from a rapid, damp, hot, smoky current into an adjacent slow, dry, cool, clear layer would bring with them some of the momentum, moisture, potential meteorology temperature and dust characteristic of the layer in which they had previously journeyed. the motion of such fragments is too intricate to be analysed in detail; but its general effect can be summed up by a statistical coefficient representing the average rate of transfer of the quantities mentioned. the theory of diffusion, originally worked out by fourier for the diffusion of heat in metals, and applied by fick to the diffusion of salts in liquids, has been extended to eddy-diffusion in the atmosphere by akerblim, g. i. taylor (london roy. soc. phil. trans., a, vol. 215, pp. 1 to 26), hesselberg and sverdrup, and w. schmidt and others. if x be the concentration of the dust or other diffusing sub- stance it has become customary to assume that the changes pro- ceed in accordance with an equation of fick’s type such as 3? 2 3? xox ox ox\" —_. ox 1 ix 1 ax | ox _ ( ox at tale? ay ies ay? az? where x, v, z, / are rectangular co-ordinates and time; #, 7 and & are the components of the mean velocity, and k is the diffusivity. this view of the process has led to k being observed under a variety of circumstances, by the increase of wind aloft, by the rate at which water vapour finds its way upward to the clouds, by the scattering of smoke or of balloons or of volcano ash. it has thus become known that k is of the same order of magnitude whether the diffusing substance be momentum, dust, moisture or potential-heat. it has further appeared that in the first three kilometres k is roughly proportional to the speed of the mean wind, and is decreased when the static stability of the atmosphere increases. but the variation of k which overwhelms all others is that dependent on the size of the portion of atmosphere which is observed. thus if the air is confined to a capillary tube, k is about 0-2 cm.? sec. 4, if the portion is a few metres across k is of the order of 10°, if a few hundred metres k is about 10%, if a thousand kilometres across k is of the order of ro! in the same units (defant). we may explain this by saying that diffusivity is a compensation for neglect of detail, and that the amount of compensation increases as the things neglected include in suc- cession molecular motion, gusts, squalls and cyclones. in other words, the mean-velocity %, 7 and @ takes on a new sense when- ever the size of the portion of the atmosphere under observation is enlarged, and this enormously affects k. sce a paper by l. f. richardson in the roy. soc. proc., a, 1926. a vertical gradient of mean wind tends to produce eddies, stat- ical stability tends to damp out eddies. the condition in which these effects just balance has been formulated by l. f. richard- son (phil. mag., jan. 1925). rayleigh’s theory of unstable tem- perature gradients has been brought into meteorology by d. brunt (meteor. magazine, v. 60, 1925, p.1). the heat balance of the atmosphere-—gold (lond. roy. soc. proc., a, vol. 82, 1909, and simultaneously humphreys (a siro- phys. journ., vol. 29, 1909, p. 14) showed that the existence of the stratosphere could be explained if it were in radiative equilibrium. the discussion as to the atmosphere generally has been continued by emden (silz.-ber. d. akad. wissensch. wen, 1913, pp. 55) w. h. dines (quar. jour. r. meteor. soc., april 1917), w. schmidt (akad. wiss., wien, mat-nat. kl., 127-75, 1918), chap- man (ouar. jour. r. mcteor. soc., april 1925) and others, and has joined with theories of radiative equilibrium in stars. (sce e. a. milnc, phil. mag., nov. 1922. it is, however, doubtful whether the horizontal transport of heat can be neglected in comparison with that in the vertical. | there are seemingly four methods by which an appreciable vertical flux of heat energy is produced in the atmosphere: (1) convection, which carries heat upwards from the earth’s sur- face; its action does not extend beyond the first few kilometres. (2) the latent heat set free by the condensation of aqueous vapour, which carries upwards to the regions where clouds are formed the solar heat which has evaporated the water from the sea or wet land surface; this acts in just the same region as con- vection. (3) radiation, which mostly carries heat upwards from a lower to a higher stratum. these three methods present no difficulty, but it must be pointed out that “convection” here meteorology means local convection, t.e., heat carried by an ascending cur- rent that is produced by local warmth, not heat carried by an air current or by eddy motion due to the general circulation. this distinction, however, is difficult to maintain, because even frictional eddies behave as thermodynamic engines. (4) stirring by eddies in the wind /.e., turbulence. w. schmidt has made an estimate which shows that the amount of heat carried down- wards across the 2 km.-level in europe by this cause to be 50 gm. calories per sq. cm. per day. an important conclusion follows. since above the region of the formation of heavy clouds neither convection nor the supply of latent heat by condensation is efficacious, the actual lapse-rate there must represent the balance of two opposing tendencies, one radiation, tending toward an isothermal condition, and the other mixing, tending to an adiabatic lapse rate. dynamics of wind—in the upper air it has been shown by gold that the wind velocity approximates to the ideal “ geo- strophic wind ” which is imagined as blowing parallel to the isobars with a speed v given by v.2wwp sin @ = dp/dx where w is the earth’s angular speed, p is the air density, d is the latitude, p is the pressure, and x is horizontal distance normal to the isobars. in the first kilometre this simplicity is modified by eddy-viscosity. elaborate theories on the dynamics of wind continue to develop.! the meeting of air-masses from different climates——dr. j. bjerknes writes as follows:— cold currents in the temperate zone can be traced back, more or less directly, to polar regions; in winter also to cold continents. on their way they are heated by contact with the ground and become unstable, provided that no adequate heating takes place in higher layers. polar currents in temperate latitudes therefore frequently have cumulus or even cumulo nimbus with showery weather, warm currents in the temperate zone can be traced back to sub- tropical regions; in summer also to warm continents. on their way northward they are cooled in contact with the ground and become stable. if the cooling continues to the dewpoint then stratus clouds or fogs are formed. where cold and warm currents border each other, in typical de- pressions or elsewhere, precipitation is usually formed. in cases where the warm current gains terrain (warm front) it climbs upwards on a gently inclined wedge, say 1/100, formed by the underlying cold current. impervious cloud-sheets are formed in the climbing warm current, low clouds close to the warm front and higher clouds farther forward. precipitation is usually falling from the whole extensive cloud system, but that falling from the higher parts evaporates be- fore reaching the ground. in cases where the cold current displaces the warm (cold front) the precipitating clouds are likewise formed in the rising warm air. the advancing cold wedges are frequently so steep that violent ascending motion and correspondingly strong pre- cipitation results. on the other hand, such precipitation is mostly confined to a narrow belt along the cold front. extratropical cyclones examined individually show a great variety of types. usually the young cyclones consist of two oppositcly directed currents, one cold occupying a little more than the half of the area and one warm current covering the remaining area—the ‘warm sector.’’ during the development of the cyclone, air from the warm sector ascends and is replaced at the ground by the cold air. this motion transforms potential energy into kinetic energy, which appears in the increasing windsand deepening of the depression. after a couple of days all the air from the original warm sector is lifted off the ground, but can still be found aloft (occluded cyclone). during the ascension the warm air is cooled adiabatically, and finally it reaches a level where it finds surrounding air of its own temperature, so that the buoyancy can lift it no farther. having reached this stage the cyclone is maintained merely by the inertia of the circulat- ing air masses. if no new energy is supplied the cyclone decays grad- ually. original papers on this subject will be found in oslo, geofys- iske publikationer, and elsewhere. for the relation between the source of air and its temperature see c. k. m. douglas, quart. jour. r. meteor. soc., july 1925. antarctic meteorology —great additions to our knowledge of the meteorology of the antarctic regions were made by the publi- cation of the results of scott’s antarctic expedition of 1910 to 1912. the observations were taken mostly by dr. simpson, who 1see papers by j. bjerknes, oslo, geofysiske publikationer; brunt, phil. mag., feb. 1926; jeffreys, quar. jour, r. afeteor. soc., jan. 1926; and books by exner, richardson and shaw. sq i has worked them up and discussed various problems left in a more or less uncertain condition by previous expeditions. he has greatly extended our knowledge both from the observational and theoretical sides. amongst other matters dr. simpson has established the anticyclonic character of the weather in the ross sea area, and has shown that the blizzards are not parts of the circulation about the centres of cyclones moving from west to east over the antarctic ocean. new methods of observation upper wind was observed dur- ing the war (1) at night by pilot balloons carrying candles, (2) by shell bursts observed by two mirrors, (3) by sound-ranging eg) * ve str qo zf “0a stn : <——< sisareon . se ni2worm gir=== ni sses cold air iramennnmmeie cold air nn wl 0g 23 trum est is) hae wh bd edd dd: uy lte art te a eer hes 4 os =e a u - “cold att 2 = 5 warmair =e a ‘it : ld air <4 warm air \"a eee == al cold air voto oo t tot wa etop a rlpellelgpoillcaaty sll ll iddildididit ype ca7okm co200hm ca300km ca 500 km fic. 2.—diagram of idealised cyclone (young). (from “life cycle of cyclones, and the polar front theory of atmospheric circulation.” j. bjeranes and h, solberg, geofysiske publtkationer, vol. r11., no, 1.) on a balloon that exploded. subsequently a method has been developed for observing wind above fog by shooting spheres up- ward. particulars of such things will be found in the computers’ tandbook or the professional notes of the meteorological office. clouds can be photographed by moonlight (oslo, geofysiske publikationer, vol. 3, no. 12). the amount of water in thin clouds can be measured (quart. jour. roy. meteor. soc., jan. 1925). the upgradient of temperature near the ground can be measured by thermocouples (p/il. afag., jan. 1925) and by an optical method (quar. jour. roy. meteor. soc., april 1925). upper air temperature is regularly measured from aeroplanes, and can also be observed by balloons that explode at a pre- arranged temperature (m.o. prof. note 19). for radiation in- struments see dictionary of applied physics, vol. 3. weather forecasts forecasts for one or more days ahead continue to be made by the process of drawing a map to repre- sent weather observations reccived by telegraph from an area some thousands of km. in diameter. the accumulated and classi- fied experience of what usually does follow such a distribution of pressure, temperature, cloud and wind is then employed to form the forecast. the smithsonian institution is progressing in its studies looking toward weather forecasts based on solar radiation observations. organisations.—the international meteorological committee and its subcommissions in 1925 reattained their fully interna- tional character, which was destroyed by the war. a post-war restricted organisation known as the international union for geodesy and geophysics has a section for meteorology which is active. bibliography.—sir w. n. shaw, forecasting weather: the air and its ways (1923); willits l. moore, descriptive meteorology (i911); c. j. p. cave, the structure of the aimosphere in clear 8q2 weather (1912); dr. julius v. hann, handbuch der klimatologie (ard ed., 3 vol., 1911); lehrbuch der meteorologie (3rd. ed., 1915); v. bjerknes and others, dynamische meteorologie und hydrogra- phie (carnegie institute of washington, 1912); ii. n. dickson, climate and weather (1912); dr. alfred wegener, thermodynamik der atmosphdre (1911); m. w. campbell hepworth, national ant- arctic expedition 1901-1904 (london, roy. soc., 1913); ice observa- tion, meteorology, and oceanography in the north atlantic ocean, report on the work carried out by the s. s. “ scotia ” (1913); c. g. abbot, f. e. fowle and l. b. aldrich, ‘’ new evidence on the intensity of solar radiation outside the atmosphere,” smithsonian miscellaneous collections, vol. 65, no. 4; sir gilbert j. watker, * correlations in seasonal variations of weather,” femoirs of the indian meteorological department, vol. 20 and 21; anders ang- strem, “ a study of the radiation of the atmosphere,” smithsonian miscellaneous collections, vol. 65, no. 3 (1915); g. c. simpson, british antarctic [ixpedition 1910-1913, meteorology, 3 vol.; w. j. humphreys, paysics of the atr, franklin inst. (1920); f. m. exner, dynamische meteorologie, 2nd ed. (1925); r. g. k. lempfert, afeteor- ology (1920); i. f. richardson, weather prediction by numerical process (1922) (the geophysical memoirs, pub. by the meteorological office); the afeteorological glossary (fourth issue, m.o. 225.11, the meteorological office); the dictionary of applied physics, vol. 3. for original papers see the bibliography issued by the royal meteorological society, the bibliography published monthly in the monthly weather review (washington), also references in text. cw. h,. die. ers meter: electric and gas (sce 18.291).—-meters are used to measure the amount of electricity or gas supplied to the customers of the company concerned. in the case of electric meters these register the number of units supplied for light, heat or power. i. electric meters these meters include induction-motor, mercury-motor and commutator meters, which register the revolutions of a disk or other armature caused to revolve, by the action of the current, at a speed proportional to the amperes or watts passing through the meter, and electrolytic meters in which the current or a shunted fraction of it passes through an electrolyte and decom- poses it, the rate of decomposition being proportional to the current employed. induction-motor type.—in the ferranti alternating current watt-hour meter, a series coil of a few turns of thick wire carrying the main current is arranged below, and a shunt coil of many turns of fine wire is arranged above a horizontal rotary disk of aluminium. this disk is situated in the gap between the poles of a permanent magnet and the lower bearing of its vertical spindle is a sapphire carefully selected to reduce friction toa minimum. the magnetic fields due to the shunt and series windings produce a resultant rotating or shifting field which interacts with eddy currents, induced in the disk so as to exert a driving torque proportional to the watts. a retarding torque is produced by the action of the permanent magnet also caus- ing the speed of the disk to be proportional to the watts. a worm on the spindle drives the registering train; the registering dials are of the clock pattern, or of the cyclometer pattern. to read the meter is a simple operation. in the clock pattern, starting from left to right, the figure last passed by the thousands pointer in its revolution is written down and the same procedure is followed for the hundreds, tens and units pointers in succession, the tenths registered on the small lower dial being read only when testing the meter. in the cyclometer pattern, the figures are written down just as they uae on the register. the cyclometer figure wheels are actuated by a falling weight; thus, the changing of the figure whecls does not throw any extra load on the meter. mercury-motor meters—in the chamberlain and hookham direct current ampere-hour meter, a copper disk is caused, by the action of the current, to rotate in a mercury chamber subject to the influence of a magnetic field due to a large permanent mag- net. the vertical spindle of the disk, arranged to rotate with the minimum friction, is connected to the registering train with its series of clock dials. the peripheral wall of the mercury chamber is formed by a leather-lined metal band which is read - ily removable to permit inspection and refilling with mercury. commutator meters—commutator meters have a wound ar- mature connected in parallel with a shunt and arranged to rotate in the field of a permanent magnet. electrolytic meters——in the reason syphon-tube meter, a meter: electric and gas solution of a mercury salt is hermetically sealed in a container, at the top of which are arranged a mercury anode and a cathode. during the operation of the meter, mercury is liberated at the cathode and collects in a syphon tube in the container; this tube, when full of mercury, discharges into the lower part of the con- tainer. close to the right limb of the syphon tube is a vertical scale which registers the mercury level; in one form of the meter, this scale reads from o to 200 units. below the scale is another which registers the level of the lower mercury column; this scale may read from o to 4,000 units. when reading the meter, both scales are read and the sum of the readings is taken. the reason single-tube meter has one vertical mercury tube, which is read like a thermometer. in both forms, the mercury can be used repeatedly, the meters being re-set by tilting; the container is llexibly mounted to facilitate this operation. in the bastian electrolytic meter, acidulated water is decom- posed by the action of the current, and the amount of water decomposed is read off on a vertical scale. il. gas meters there are two main types of gas meters, viz., wet meters and dry meters. a wet gas meter has a strong iron case containing water, which is normally at a definite level called the “ water line.” inside the case is a rotary drum divided into compartments and mounted on a horizontal spindle geared to a vertical spindle operating the registering train. the drum its rotated by the un- balanced elastic pressure of the gas admitted to each compart- ment in turn on the surface of the water. after leaving the drum, the gas passes to an outlet pipe which delivers it to the burners. in order to maintain the level of the water, when lass occurs through evaporation or other causes, most wet meters are pro- vided with means for automatically making good the loss; these are called compensating meters. in most of them, the water to make good the loss is delivered from a water reservoir within the meter case and communicating with the main body of water. dry meters.—in an ordinary dry gas meter, the upper part of the meter case forms the registering chamber in which are situ- ated the registering train and the valve box, which is shut off from the registering chamber and contains gas inlet and gas outlet valves. the registering chamber is separated by a horizontal partition from a lower and larger chamber, which is divided by a vertical partition into two equal chambers. in each of these a bellows of concertina shape, with flexible leather sides, works to and fro horizontally; the vertical partition forms the oe eee oivision ss <0, cubic fic. 1.—diagram illustrating the registering dials of a 1o-light dry gas meter. fixed base of each bellows. arrangements of levers and cranks transmit the motions of the bellows to the valves in the valve box and also to the registering train. when the meter is in operation, gas from the main supply pipe enters one of the bellows and inflates it, while the gas in the corresponding chamber is expelled through a delivery pipe to the burners; at the same time, gas is being expelled from the other bellows by the pressure of gas admitted into its bellows chamber. working in this way, the meter supplies gas continuously to the burners, and the valves in the valve box are opened and closed at the proper times required by the flow of the gas. at the same time the registering train is operated continuously. methodism automatic or prepayment meters —prepayment gas meters are fitted with a box containing mechanism which operates when a coin is passed through a slot in the box and controls the supply of gas to the meter. the value of the inserted coin or token determines the automatic cutting-off of the gas supply. reading a gas meter is a simple operation. fig. 1 represents the registering dials of a 1o-light dry gas meter. the registering train is geared so that the hundreds pointer revolves io times while the thousands pointer revolves once, the thousands pointer revolves 10 times while the tens of thousands pointer revolves once, and so on; also, adjacent pointers revolve in opposite directions. starting from right to left, the figure last passed by the hundreds of thousands pointer in its revolution is written down and the same procedure is followed for the tens of thousands, the thousands and the hundreds pointers in succession; thus the reading in fig. § is 1,459 hundreds. assuming that this was the reading at michaelmas and that 1,356 hundreds was the reading at the preceding midsummer, then the amount of gas consumed during the summer quarter would be 145,900 minus 135,600 or 10,300 cubic feet. the small upper dial is not usually read. it records the flow of small quantities of gas and can therefore be used for ascertaining whether all pipes and gas fittings are gas-tight, or what amount of gas is consumed by any of the burners. ces, bs)",
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