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METEOROLOGY (Gr. JerEwpa, and hb'yos,...
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See also:METEOROLOGY (Gr. JerEwpa, and hb'yos, i.e. the See also:science of things in the See also:air) , the See also:modern study of all the phenomena of the See also:atmosphere of gases, vapours and dust that surrounds the See also:earth and extends to that unknown See also:outer See also:surface which marks the beginning of the so-called interstellar space. These phenomena may be studied either individually or collectively. The collective study has to do with See also:statistics and See also:general See also:average conditions, sometimes called normal values, and is generally known as Climatology (see See also:CLIMATE, where the whole subject of regional climatology is dealt with). The study of the individual items may be either descriptive, explanatory, See also:physical or theoretical. Physical meteorology is again sub-divided according as we consider either the changes that depend upon the motions of masses of air or those that depend upon the motions of the gaseous molecules; the former belong to See also:hydrodynamics, and the latter are mostly comprised under See also:thermodynamics, See also:optics and See also:electricity.
See also:History.—The See also:historical development of meteorology from the most See also:ancient times is well presented by the quotations from classic authors compiled by See also:Julius See also:Ludwig See also:Ideler (Meteorologia veterum graecorum et romanorum, See also:Berlin, 1832). We owe to the Arabian philosophers some slight advance on the know-ledge of the Greeks and See also:Romans; especially as to the See also:optical phenomena of the atmosphere. The Meteorologia of See also:Aristotle (see See also:Zeller, Phil. der Griechen) accords entirely with the Philosophica of See also: Progress has been due too. the most eminent mathematicians at the following approximate See also:dates: See also:Sir See also:Isaac Newton (167o), Leonhard-See also:Euler (1736), See also:Pierre See also:Simon See also:Laplace (178o), See also:Jean See also:Baptiste See also:Joseph See also:Fourier (1785), Simon See also:Denis See also:Poisson (1815), Sir See also:George See also:Gabriel See also:Stokes (1851), See also:Hermann von See also:Helmholtz (18.57), See also:Lord See also:Kelvin (186o), C. A. Bjerknes (1868), V. Bjerknes (1906), and to their many distinguished followers.
The earliest systematic daily See also:record of See also:local See also:weather
phenomena that has survived is that kept by See also: The history of meteorology is marked by the See also:production of comprehensive See also:treatises embodying the current See also:state of our knowledge. Such were See also: The development of this science has been greatly stimulated by the See also:regular publication of See also:special See also:periodicals such as the Zeitschrifl of the See also:Austrian Meteorological Society, 1866—1885, vol. 21 appearing with vol. 3 of the Meteorologische Zeitschrifl of the German Meteorological Society in 1886, and since that date this See also:journal has been jointly maintained by the two See also:societies. The analogous See also:journals of the Royal Meteorological Society, London, 1850 to date, the Scottish Meteorological Society, 186o to date, the Meteorological Society of See also:France, 1838 to date, the See also:Italian Meteorological Society, and the See also:American Meteorological Journal, 1885—1895, have all played important parts in the history of meteorology. On the other See also:hand, the See also:Annals of the Central Meteorological See also:Office at Paris, the Archie of the Deutsche Seewarte at See also:Hamburg, the Annals and the Repertorium of the Central Physical See also:Observatory at St See also:Peters-See also:burg, the Annales of the Central Meteorological Office at See also:Rome, Bulletin of See also:International Simultaneous Met. Obs. and the Monthly Weather See also:Review of the Weather See also:Bureau at Washington, the Abhandlungen of the Royal Prussian Meteorological See also:Institute at Berlin, the Meteorological Papers of the Meteorological Office, London, and the transactions of numerous scientific societies, have represented the important See also:official contributions of the respective See also:national governments to technical meteorology. The recent international See also:union for aerial exploration by kites and balloons has given rise to two important publications, i.e. the Veroffentlichungen of the International. See also:Commission for Scientific Aerostatics (See also:Strassburg, 1905, et seq.), devoted to records of observations, and the Beitrdge zur Physik der freien Atmosphdre (Strassburg, 1904, et seq.), devoted to See also:research. The See also:necessity of studying the atmosphere as a unit and of securing See also:uniform accuracy in the observations has led to the formation of a permanent International Meteorological See also:Committee (of which in 1909 the secretary was Professor Dr G. Hellmann of Berlin, and the See also:president Dr W. N. See also:Shaw of London). Under its directions conferences and general congresses have been held, beginning with that of 1872 at Leipzig. Its Inter-national Tables, See also:Atlas of Clouds, Codex of Instructions, and Forms for Climatological Publications illustrate the activity and usefulness of this committee.
Modern meteorology has been See also:developed along two lines of study, based respectively on maps of monthly and See also:annual averages and on daily weather maps. The latter study seems to have been begun by H. W. Brandes in Leipzig, who first, about 1820, compiled maps for 1783 from the data collected in the Ephemerides mannheimensis, and subsequently published maps of the See also:European storms of 182o and 1821. Simultaneously with Brandes we find William C. Redfield in New Yorkcompiling a See also:chart of the See also:hurricane of 1821, which was published in 1831, and was the first of many memoirs by him on hurricanes that completely established their rotary and progressive See also:motion. Soon after this Piddington and Sir William See also:Reid began their great works on the storms of the Orient. About 1825 See also: The destructive See also:storm of the 14th of See also:November 1854, in the See also:Crimea gave U. J. J. Le Vervier, at Paris, an opportunity to propose the proper action, and his proposals were immediately adopted by the secretary of See also:war, See also:Marshal Valliant. On the 17th of See also:February 1855 the See also:emperor ordered the director-general of government telegraph lines to co-operate completely with Le Verrier in the organization of a bureau of telegraphic meteorology. The international daily bulletin of the Paris Observatory began to be printed in regular See also:form on the 1st of See also:January 1858, and the daily map of isobars was added to the See also:text in the autumn of 1863. The further development of this bulletin, the inclusion of See also:British and ocean reports in 186r, the addition of special storm warnings it1 1863, the publication of the Atlas See also:des mauvements generaux covering the See also:Atlantic in 1865, the study of local thunderstorms by Hippolyte See also:Marie-See also:Davy, Sonrel, Fron, Peslin, in France, and the work of See also:Fitzroy, See also:Buys-See also:Ballot, See also:Buchan, Glaisher and See also:Thomson in Great See also:Britain, parallel the analogous works of the American students of meteorology and form the beginnings of our modern dynamic meteorology. The details of the historical development of this subject are well given by See also:Hugo See also:Hildebrand-Hildebrandsson and See also:Leon Teisserenc de See also:Bort in their See also:joint work, See also:Les Bases de la meteorologie dynamique (Paris, 1898-1907). The technical material has been collected by Hann in his Lehrbuch. Many of the See also:original memoirs have been reproduced by Brillouin in his Memoires originaux (Paris, 1900), and in See also:Cleveland See also:Abbe's See also:Mechanics of the Earth's Atmosphere (vol. i., 1891; vol. ii., 1909). The publication of daily weather charts and forecasts is now carried on by all civilized nations. The See also:list of government bureaux and their publications is given in See also:Bartholomew's Atlas (vol. iii., London, 1899). Special establishments for the exploration of the upper atmospheric conditions are maintained at Paris, Berlin, See also:Copenhagen, St See also:Petersburg, Washington and Strassburg. The general problems of climatology (1900) are best presented in the Handbook of Dr Julius Hann (2nd ed., Stuttgart, 1897). The general See also:distribution of temperature, winds and pressure over the whole globe was first given by Buchan in charts published by the Royal Society of See also:Edinburgh in 1868, and again greatly revised and improved in the See also:volume of the Challenger reports devoted to meteoro+ logy. The most complete atlas of meteorology is Buchan and Herbertson's vol. iii. of Bartholomew's Atlas (London, 1899). Extensive works of a more special character have been published by the London Meteorological Office, and the Deutsche Seewarte for the Atlantic, Pacific and See also:Indian Oceans. Daily charts of atmospheric conditions of the whole northern hemisphere were published by the U.S. Weather Bureau from 1875 to 1883 inclusive, with monthly charts; the latter were continued through .1889. The physical problems of meteorology were discussed in Ferrel's Recent Advances in Meteorology (Washington, 1885). Mathematical papers on this subject will be found in the author's collection known as The Mechanics of the Earth's Atmosphere; the memoirs by Helmholtz and Von Bezold contained in this. collection have been made, the basis of a most important work by Brillouin (Paris, 1898), entitled Vents contigus et nuages. A general ,See also:summary of our knowledge of the mechanics and physics of the atmosphere is contained in the See also:Report on the International See also:Cloud Work, by F. H. See also:Bigelow (Washing-ton, 1900). The extensive Lehrbuch (Leipzig, 1901; 2nd ed., 1906) by Dr Julius Hann is an authoritative work. The optical phenomena of the atmosphere are well treated by E. Mascart in his Traite d'optique (Paris, 1891-1898), and by J. M. Penter, Meteorologische Optik (1904-1907). Of See also:minor treatises especially adapted to collegiate courses of study we may mention those by Sprung (Berlin, 1885) ; W. Ferrel (New See also:York, 1890) ; Angot (Paris, 1898) ; W. M.See also:Davis, (See also:Boston, 1893) ; See also:Waldo (New York, 1898) ; See also:Van Bebber (Stuttgart, 189o) ; See also:Moore (London, 1893) ; T. See also:Russell (New York), 1895. The brilliant volume by Svante See also:Arrhenius, Kosmische Physik (Leipzig, 1900) contains a See also:section by Sandstrom on meteorology, in which the new hydrodynamic methods of Bjerknes are developed. I.—FUNDAMENTAL PHYSICAL DATA There can be no proper study of meteorology without a See also:consideration of the various physical properties of the atmospheric gases and vapours, each of which plays an See also:independent See also:part, and yet also reacts upon its neighbours. Atmospheric air is a mixture of nitrogen, oxygen, aqueous vapour, carbonic acid gas (See also:carbon dioxide), See also:ammonia, argon, neon, See also:helium, with slight traces of See also:free See also:hydrogen and hydro-carbons. The proportions in which these gases are See also:present are quite See also:constant, except that the percentage of aqueous vapour is subject to large See also:variations. In an atmosphere that is saturated at the temperature of 90° F., as may occur in such a climate as that of See also:Calcutta, the water may be 240A of the whole weight of any given volume of air. When this aqueous vapour is entirely abstracted, the remaining dry gas is found to have a very uniform constitution in all regions and at all altitudes where examination has been carried out. In this so-called dry atmosphere the relative weights are about as follows: Oxygen, 23.16; nitrogen and argon, 76.77; carbonic acid, o•o4; ammonia and all other gases, less than o•oi in the See also:lower See also:half of the atmosphere but probably in larger percentages at great altitudes. Of still greater rarity are the highly volatile gases, argon (q.v.), neon, krypton and helium (q.v.). Outer Limit.—These exceedingly volatile components of the atmosphere cannot apparently be held down to the earth by the attraction of See also:gravitation, but are continually diffusing through the atmosphere outwards into interstellar space, and possibly also from that region back into the atmosphere. There are doubtless other volatile gases filling interstellar space and occasionally entering into the atmosphere of the various See also:planets as well as of the See also:sun itself ; possibly the hydrogen and hydro-carbons that See also:escape from the earth into the lower atmosphere ascend to regions inaccessible to See also:man and slowly diffuse into the outer space. The laws of See also:diffusion show that for each gas there is an See also:altitude at which as many molecules diffuse inwards as outwards in a unit of See also:time. This See also:condition defines the outer limit of each particular gaseous atmosphere, so that we must not imagine the atmosphere of the earth to have any general boundary. The only intimation we have as to the presence of gases far above the surface of the globe come from the phenomena of the See also:Aurora, the See also:refraction of See also:light, the See also:morning and evening twilight, and especially from the See also:shooting stars which suddenly become luminous when they pass into what we See also:call our atmosphere. (See C. C. See also:Trowbridge, ' On Luminous See also:Meteor Trains " and " On Movements of the Atmosphere at Very Great Heights," Monthly Weather Review, See also:Sept. 1907.)
Such observations are supposed to show that there is an appreciable quantity of gas at the height of, See also:loo m., where it may have a See also:density of a millionth part of that which prevails at the earth's surface. Such See also:matter is not a gas in the ordinary use of that See also:term, but is a collection of particles moving independently of each other under those influences that emanate from sun and earth, which we call radiant See also:energy. According to Stormer this radiant energy is that of electrons from the sun, and their movements in the magnetic See also: Chamberlin in the Amer. Geol. Jour., published memoirs in which they argued that a variation of several per cent. in the proportion of carbonic acid gas is quite consistent with the existence of See also:animal and See also:vegetable See also:life and may explain the variations of climate during See also:geological periods. But the specific absorption of this gas for See also:solar radiations is too small (C. G. See also: (Berlin, 1900) has deduced from See also:balloon observations the following formula for the free air over Europe log a=log eo—h(I+k/20000)/6000. He has also computed the specific moisture of the atmosphere or the mixing ratio, or the number of grams of moisture mixed with I kilogram of dry air for which he finds the formula log m=log mo-h(i+3h/4o)/9000. The relative humidity varies with altitude so irregularly that it cannot be expressed by any simple formula. The computed values of e and m are as given in the following table: Altitude Relative , Metres. Vapour Pressure. Relative h. a/eo. Specific Moisture. m/mo. O See also:I000 I0o0 m 665 26 759 2000 oo 6 555 3000 158 264 4000 91 172 5000 5o Io8 6000 27 65 7000 14 38 8000 In addition to the gases and vapours in the atmosphere, the motes of dust and the aqueous particles that constitute cloud, See also:fog and haze are also important. As all these See also:float in the air, slowly descending, but resisted by the viscosity of the atmosphere, their whole weight is added to the atmosphere and becomes a part of thebarometric record. When the air is cooled to the See also:dew-point and condensation of the vapour begins, it takes See also:place first upon the atoms of dust as nuclei; consequently, air that is free from dust is scarcely to be found except within a See also:mass of cloud or fog. Mass.—According to a calculation published in the U.S. Monthly Weather Review for February 1899, the See also:total mass of the atmosphere is 1/1,See also:I25,000 of the mass of the earth itself but, according to Professor R. S. See also:Woodward (see Science for See also:Jan. 1900), See also:celestial See also:dynamics shows that there may possibly be a gaseous envelope whose weight is not See also:felt at the earth's surface, since it is held in dynamic See also:equilibrium above the atmosphere; the mass of this outer atmosphere cannot exceed 216ath of the mass of the earth, and is probably far less, if indeed it be at all appreciable. Conductivity.—Dry air is a poor conductor of See also:heat, its co-efficient of See also:conduction being expressed by the formula: o•000 0568 (1-+-0.00190 t) where the temperature (t) is expressed in centigrade degrees. This formula states the fact that a See also:plate of air i centimetre thick can conduct through its substance for every square centimetre of its See also:area, in one second of time, when the difference of temperature between two faces of the plate is I° C., enough heat to warm i See also:gram of water 0.000 0568° C., or I gram of air o•000 239° C., or a cubic centimetre of air o. 1850° C., if that air is at the See also:standard density for 76o millimetres of pressure and 0° C. The figure 0.1850° C. is the thermometric coefficient as distinguished from the first or calorimetric coefficient (o.000 0568° C.), and shows what great effect on the air itself its poor conductivity may have. Diathermancy.—Dry air is extremely diathcrmanous or transparent., to the transmission of radiant heat. For the whole moist atmosphere the general coefficient of transmission increases as the waves become longer: and for a zenithal sun it is about 0.4 at the See also:violet end of the spectrum and about o•8 at the red. By specific absorption many specific See also:wave-lengths- are entirely cut off by the vapours and gases, so that in general the atmosphere may appearto be more transparent to the See also:short wave-lengths or violet end of the spectrum, but this is not really so. When the zenithal sun's rays fall upon a station whose barometric pressure is 76o mm., then only from 5o to 8o% of the total heat reaches the earth's surface, and thus the general coefficient of transmission for the thickness of one atmosphere is usually estimated at about 6o %. Of course when the rays are more oblique, or when haze, dust or cloud interfere, the transmission is still further diminished. In general one half of the heat received from the sun by the illuminated terrestrial hemisphere is absorbed by the clearest atmosphere, leaving the other half to reach the surface of the ground, provided there be no intercepting clouds. The thermal conditions actually observed at the immediate surface of the globe during hazy and cloudy weather are therefore of minor importance in the mechanism of the whole atmosphere, as compared with the See also:influence of the heat retained within its mass. The transmission of solar See also:radiation through the earth's atmosphere is the fundamental problem of meteorology, and has been the subject of many studies, beginning with J. H. See also:Lambert and P. See also:Bouguer. The pyrheliometer of C. S. M. Pouillet gave us our first See also:idea of the thermal See also:equivalent of solar radiation outside of our atmosphere or the so-called " solar constant," the value of which has been variously placed at from 2 to 4 calories per sq. cm. per See also:minute. At present the weight of the argument is in favour of 2.1, with a See also:fair presumption that both the intensity and the quality of the solar radiation as it strikes the upper layers of our atmosphere are slightly variable. It is also likely that this " constant " does not represent the sun proper, but the remaining energy after the sunbeam has sifted through masses of matter between the sun and our upper atmosphere, so that it may thus come to have appreciable variations. The coefficients of absorption for specific wave-lengths were first determined by L. E. Jewell, of Johns See also:Hopkins University, for numerous vapour lines in 1892 (see W. B. Bulletin, No. i6). In 1904 C. G. Abbot published a table based on bolograph work at Washington showing the coefficient of atmospheric transmission for solar rays passing through a unit mass of air-namely, from the See also:zenith to the ground. He showed that this coefficient increased with the wave-length; hence any See also:change in the quality of the solar radiation will affect the general coefficient of transmission. The following table gives his averages for the respective wave-lengths, as deduced from ten clear days in 1901-1902 and nine clear days in 1903:- Wave Length. Coefficient of Atmospheric Transmission (Abbot). 1901-1902. 1903. Mean by Weights.
microns. - 0.484 -
0.40 violet
0.45 - 0.557 -
o•50 0.765 0.627 0.700
o•6o 0.769 0.692 0.730
0.70 0.857 0.753 0.808
0.80 red 0.897 0.797 0.847
0.90 0.910 0.825 0.856
1.00 0.921 0.847 0.884
I.20 0.933 0.874 0.903
1.6o 0.930 0.909 0.920
2.00 0.950 0.912 0.919
Any variation in the energy that the atmosphere receives from the sun will have a corresponding influence on meteorological phenomena. Such variations were simultaneously announced in 1903 by See also: See also:Coll., xlv. 78 and xlvii. 403, 1905) :-
Date. Abbot. Fowle.
Calories. Calories.
1902 Oct. 9 2.19 2' 19
„ 15 2.19 -
22 2.16
1903 Feb . 19 2.28 2.27
„ 19 2.25 -
See also: 27 - 2.02
„ Feb. 11 - 2.26
„ May 28 - 2.09
„ Oct. 5 - 2.32
„ Nov. 16 1.98
If the relative accuracy of these figures is i %, as estimated by Abbot, then they demonstrate irregular fluctations of 5 %. But different observers and localities vary so much that Abbot estimates the reliability of the mean value, 2.12, to be about io%. The causes of this variation apparently See also:lie above our lower atmosphere and move slowly eastward from day to day, and as the variability is comparable with that of other atmospheric data, therefore conservative meteorologists at present confine their See also:attention to the explanation of terrestrial phenomena under the See also:assumption of a constant solar radiation. The large local changes of weather and climate are not due to changes in the sun, but to the See also:mechanical and thermodynamic interactions of earth and ocean and atmosphere. Excellent illustrations of this principle are found in the studies of See also:Blanford, See also:Eliot and See also: This coefficient holds See also:good, strictly speaking, between the temperatures-30° and +io° C., and there is a very slight diminution for higher temperatures up to 200°. The specific heat of moist air is larger than that of dry air, and is given by the expression C5" = (0.2375 + 0'4805 x) where x is the number of kilograms of vapour associated with I kilogram of dry air. As x does not exceed 0.030 (or 30 grams) the value of C,,", may increase up to 0.2519. The latent heat evolved in the condensation of this moisture is a matter of great importance in the formation of cloud and See also:rain. Radiating Power.-The radiating power of clean dry air is so small that it cannot be measured quantitatively, but the spectroscope and bolometer demonstrate its existence. The coefficient of radiation of the moisture diffused in the atmosphere is combined with that of the particles of dust and cloud, and is nearly equal to that of an equal surface of See also:lamp-black. From the normal diurnal change in temperature at high and low stations, it should be possible to deter-mine the general coefficient of atmospheric radiation for the average condition of the air in so far as this is not obscured by the influence of the winds. This was first done by J. See also:Maurer in 1885, who obtained a result in calories that may be expressed as follows: the total radiation in twenty-four See also:hours of a unit mass of average dusty'and moist air towards an enclosure whose temperature is 1 ° lower is sufficient to lower the temperature of the radiating air by 3.31 ° C. in twenty-four hours. This very small quantity was confirmed by the studies of Trabert, published in 1892, who found that 1 gram of air at 278° See also:absolute temperature radiates 0.1655 calories per minute toward a black surface at the absolute zero. The See also:direct observations of C. C. Hutchins on dry dusty air, as published in 189o, gave a much larger value-evidently too large. Slight changes in water, vapour and carbon dioxide affect the radiation greatly. The investigation of this subject prosecuted by Professor F. W. Very at the See also:Allegheny Observatory, and published as " Bulletin G of the U.S. Weather Bureau, shows the character and amount of the radiation of several gases, and especially the details of the See also:process going on under normal conditions in the atmosphere. Density.-The absolute density or mass of a cubic centimetre of dry air at the standard pressure, 76o millimetres, and temperature 0° C., is 0.001 29305 grams; that of a cubic See also:metre is 1.29305 kilograms; that of a cubic See also:foot is o.o8o7i lb See also:avoirdupois. The variations of this density with pressure, temperature, moisture and gravity are given in the Smithsonian meteorological tables, and give rise to all the movements of the atmosphere; they are, therefore,.of fundamental importance to dynamic meteorology. Expansion.-The air expands with heat, and the expansion of aqueous vapour is so nearly the same as that of -dry air that the same coefficient may be used for the complex atmosphere itself. The change of volume may be expressed in centigrade degrees by the formula V=V0 (i+o•000 3665t), or in See also:Fahrenheit degrees V=Vo (1+0.000 237t). See also:Elasticity.-The air is compressed nearly in proportion to the pressure that confines it. The pressure, temperature and volume of the ideal gas are connected by the See also:equation pv = RT, where T is the absolute temperature or 273° plus the centigrade temperature p is the barometric pressure in millimetres and v the volume of a unit mass of gas, or the reciprocal of the density of the gas. The constant R is 29.272 for dry atmospheric air when the centimetre, the gram, the second and the centigrade degrees are adopted as units of measure, and differs for each gas. For aqueous vapour in a gaseous state and not near the point of condensation R has the value 47.061. For ordinary air in which x is the mass of the aqueous vapour that is mixed with the unit mass of dry air, the above equation becomes pv=(29.272+47.061x) T. This equation is sometimes known as the equation of condition See also:peculiar to the gaseous state. It may also be properly called the equation of elasticity or the elastic equation for gases, as expressing the fact that the elastic pressure p depends upon the temperature and the volume. The mose exact equations given by Van der Waals, See also:Clausius, Thiesen, are not needed by us for the pressures that occur in meteorology. Diffusion.—In comparison with the convective actions of the winds, it may be said that it is difficult for aqueous vapour to diffuse in the air. In fact, the distribution of moisture is carried on principally by the See also:horizontal convection due to the wind and the See also:vertical convection due to ascending and descending currents. Diffusion proper, however, comes into See also:play in the first moments of the process of evaporation. The coefficient of diffusion for aqueous vapour from a pure water surface into the atmosphere is 0.18 according to Stefan, or 0.1980 according to See also:Winkelmann; that is to say, for a unit surface of 1 sq. centimetre, and a unit gradient of vapour pressure of one atmosphere per centimetre, as we proceed from the water surface into the still dry air, at the standard pressure and temperature, and quantity of moisture diffused is 0.198o grams per second. This coefficient increases with the temperature, and is 0.2827 at 49.5° C. But the gradient. of vapour pressure, and therefore See also:rate of diffusion, diminishes very rapidly at a small distance from the free surface of the water, so that the most important condition facilitating evaporation is the action of the wind. Viscosity.—When the atmosphere is in motion each layer is a See also:drag upon the adjacent one that moves a little faster than it does. This drag is the so-called molecular or See also:internal See also:friction or viscosity. The coefficient of viscosity in gases increases with the absolute temperature, and its value is given by an equation like the following; 0.000 248 (1+o•ooe 6651) which is the formula given by Carl Barus (See also:Ann. Phvs., 1889, See also:xxxvi.). This expression implies that for air whose temperature is the absolute zero there is no viscosity, but that at a temperature (t) of 0° C., or 2730 on the absolute See also:scale, a force of 0.000 248 grams is required in See also:order to push or pull a layer of air t centimetre square past another layer distant from it by 1 centimetre at a uniform rate oft centimetre per second. Friction.—The general motions of the atmosphere are opposed by the viscosity of the air as a resisting force, but this is an exceedingly feeble resistance as compared with the obstacles encountered on the earth's surface and the inertia of the rising and falling masses of warm and See also:cold air. The coefficient of friction used in meteorology is deduced from the observations of the winds and results essentially not from viscosity, but from the resistances of all kinds to which the motion of the atmosphere is subjected. The greater part of these resistances consists essentially in a dissipation of the energy of the moving masses by their See also:division into smaller masses which penetrate the quiet air in all directions. The loss of energy due to this process and the See also:conversion of kinetic into potential energy or pressure, if it must be called friction, should perhaps be called convective friction, or, more properly, convective-resistance. The coefficient of resistance for the free air was determined by Mohn and Ferrel by the following considerations. When the winds, temperatures and barometric .pressures are steady for a considerable time, as in the See also:trade winds, monsoons and stationary cyclones, it is the barometric gradient that overcomes the resistances, while the resulting wind is deflected to the right (in the northern hemisphere) by the influence of the centrifugal force of the diurnal rotation (co) of the earth. The wind, therefore, makes a constant See also:angle (a) with the direction of the gradient (G). There is also a slight centrifugal force to be considered if the winds, are circulating with velocity v and See also:radius (r) about a storm centre, but neglecting this we have approximately for the See also:latitude G See also:sin a = 2ccv sin G See also:cos a = Kv, where (K) is the coefficient connecting the wind-velocity (v) with the component of the gradient pressure in the direction of the wind. These relations give K = 2w sin 0/tan a. The values of a and v as read off from the map of winds and isotherms at sea level give us the data for computing the coefficients for oceanic and See also:continental surfaces respectively, expressed in the same units as those used for G and v. The extreme values of this coefficient of friction were found by Guldberg and Mohn to be 0.00002 for the free ocean and 0.00012 for the irregular surface of the land. For See also:Norwegian land stations Mohn found = 61° a = 56.5° K = 0.0000845. For the interior of North America See also:Elias Loomis found ¢ = 37.5° a = 42.2 ° = o•00008o3. Gravity.—The weight of the atmosphere depends primarily upon the action of gravity, which gives a downward pressure to every particle. Owing to the elastic compressibility of the air, this downward pressure is converted at once into an elastic oressurein all directions. The force of gravity varies with the latitude and the altitude, and in any exact work its variations must be taken into See also:account. Its value is well represented by the formula due to Helmert, g = 980.6 (1 — o•0026 cos 2¢) X (1 — fh), where 4 represents the latitude of the station and h the altitude. The coefficient f is small and has a different value according as the station is raised above the earth's surface by a See also:continent, as, for instance, on a See also:mountain See also:top, or by the ocean, as on a See also:ship sailing over the sea, or in the free air, as in a balloon. Its different values are sufficiently well known for meteorological needs, and are utilized most discreetly in the elaborate discussion of the hypsometric formula published by Angot in 1899 in the memoirs of the Central Meteorological Bureau of France. Temperature at Sea-Level.—The temperature of the air at the surfaces of the earth and ocean and throughout the atmosphere is the fundamental See also:element of dynamic meteorology. It is best exhibited by means of isotherms or lines of equal temperature See also:drawn on charts of the globe for a series of level surfaces at or above sea-level. It can also be expressed analytically by spherical See also:harmonic functions, as was first done by Schoch. The normal distribution of atmospheric temperature for each See also:month of the year over the whole globe was first given by Buchan in his charts of 1868 and of 1888 (see also the U.S. Weather Bureau " Bulletin A," of 1893, and Buchan's edition of Bartholomew's Physical Atlas, London, 1899). The temperatures, as thus charted, have been corrected so as to represent a uniform special set of years and the conditions at sea-level, in order to constitute a homogeneous system. The actual temperature near the ground at any altitude on a continent or See also:island may be obtained from these charts by subtracting 0.5°C. for each too metres of See also:elevation of the ground above sea-level, or 1° F. for 35o ft. This reduction, however, applies specifically to temperatures observed near the surface of the ground, and cannot be used with any confidence to determine the temperature of points in the free air at any distance above the land or ocean. On all such charts the reader will See also:notice the high temperatures near the ground in the interior of each of the continents in the summer See also:season and the low temperatures in the winter season. In February the average temperatures in the northern hemisphere are not lowest near the North See also:Pole, but in the interiors of See also:Siberia and North America; in the See also:southern hemisphere they are at the same time highest in See also:Australia, and See also:Africa and See also:South America. In See also:August the average temperatures are unexpectedly high in the interior of See also:Asia and North America, but low in Australia and Africa. Temperature at Upper Levels.—The vertical distribution of temperature and moisture in the free air must be studied in detail in order to understand both the general and the special systems of circulation that characterize the earth's atmosphere. Many observations on mountains and in balloons were made during the 19th See also:century in order to ascertain the facts with regard to the decrease of temperature as we ascend in the atmosphere; but it is now recognized that these observations were largely affected by local influences due to the insufficient See also:ventilation of the thermometers and the nearness of the ground and the balloon. Strenuous efforts are being directed to the elimination of these disturbing elements, and to the continuous recording of the temperature of the free air by means of delicate thermographs carried up to great heights by small free "See also:sounding balloons," and to lesser heights by means of kites. Many international balloon ascents have been made since 189o, and a large amount of See also:information has been secured. The development of See also:kite-work in the United States began in See also:October 1893, at the See also:World's Columbian See also:Congress at See also:Chicago, when Professor M. W. See also:Harrington ordered Professor C. F. Marvin of the Weather Bureau to take up the development of the Hargrave or See also:box kite for meteorological work. At that time W. A. Eddy of See also:Bayonne, New See also:Jersey, was applying his " See also:Malay kite to raising and displaying heavy See also:objects, and in August 1894 (at the See also:suggestion of Professor Cleveland Abbe) he visited the private observatory of A. L. Rotch at See also:Blue See also:
from the ground up to the respective altitudes.
Stations. Il000 1500 2000 3000 4000 5000 6000
ft. ft. ft. ft. ft. ft. ft.
0 0 0 0 0 0 0
Washington, D.C. . . 5.6 4.4 4'0 3.5 3.2 3'0 3.1
See also:Cairo, See also:Ill. . . . 9.7 6.6 6•o 4.9 4.7 4.3 -
See also:Cincinnati, O. . . . 13.0 6.3 6.9 5'8 5'6 4.7 4'2
Fort See also: . . 8.4 6.2 6.6 5'4 5'0 - - See also:Memphis, Tenn. . . 7.8 6.8 5.0 3.8 3'7 3.5 See also:Springfield, Ill. . . . 7.6 5.7 5•I 4.4 4.0 3.7 3.6 Cleveland, O. . . . 5'7 4.1 3.6 3'5 4.1 4'I 4.3 See also:Duluth, Minn. . . . 5'2 4.8 4.6 4'6 4.3 3.8 4.6 See also:Lansing, Mich. . . 7.5 6•o 4.7 4.1 3.9 3'8 - Sault Ste Marie, Mich. . 6.6 6.2 5.2 4'5 3'9 3'0 - See also:Dodge, Kans. . . . 6.3 5.2 4.8 3.7 3.1 3.2 3.2 See also:Dubuque, See also:Iowa . . 6.9 5.9 4.6 3'5 3.2 3.3 - North See also:Platte, Neb. . . 6.8 6.5 5.9 5'2 4'4 4.7 5.4 See also:Omaha, Neb. . . . - 5.4 4.9 3'6 3.2 3'5 3.8 Pierre, S. Dak. . . . 5.9 5.1 4'8 4.3 3'7 4.4 4.0 See also:Topeka, Kans. . . . 7.4 6.2 4.9 4.0 3.8 3.9 4.5 Average . . . . 7.4 5.8 5'2 4'4 4.0 3'8 4.1 Stations Altitude. Temperature. Feet. Gradient. Reduction. °F. °F. Washington 210 -3.00 -15.2 Cairo 315 -4'30 -25.6 Cincinnati 940 -5'15 -27.5 Fort Smith 527 ? ? Knoxville 990 -5'00 -21.5 Memphis 319 -3.50 -17'3 Springfield 684 -3'85 -17'7 Cleveland 705 -4.10 -18.8 Duluth 1197 -4'30 -17.6 Lansing 869 -3'85 -17.0 Sault Ste Marie 722 -3'45 -15'7 Dodge 2473 -4'10 -11.6 North Platte 2891I -5.40 -13.3 Omaha I241 -3.20 -12.9 Topeka 977 192 -33.'8 3 3 -16.4 5 In this table the second See also:column gives the altitude of the ground at the See also:reel on which the kite See also:wire was See also:wound. The third column shows the average gradient in degrees Fahrenheit. per moo ft. between the reel at the respective stations, and a uniform altitude 528o ft. above sea-level. The See also:fourth column shows the total reduction to be applied to the temperature at the reel in order to obtain the temperature at the 1 m. level above sea. These gradients and reductions are based upon observations made only during the six warm months from May to October 1898. The kite-work at the Blue Hill Observatory has been published in full in the successive Annals of the Harvard College Observatory, beginning with 1897, vol. xlii. It has been discussed especially by H. H. See also:Clayton with reference to special meteorological phenomena, such as areas of high and low pressure, fair and cloudy weather, the winds and their velocities at different elevations, insolation, radiation, &c., and has served as a stimulus and See also:model for European meteorologists. Kite-work has also been successfully prosecuted at Trappes, Hamburg, Berlin, St Petersburg, and many other European stations. The highest flights that have been attained have been about 8000 metres. The great work of L. Teisserenc de Bort began with 1897, when he founded his private observatory at Trappes near Paris devoted to the problems of dynamic meteorology. His results are published in full in the Memoirs of the Central Meteorological Bureau of France for 1897 and subsequent years. Beginning with the sounding balloons devised by Hermite, he subsequently added kite work as supplementary to these. In the See also:Corn pies rendus (1904), he gives the mean temperatures as they result from five years of work, 1899-1903, at Trappes. Out of 581 ascensions of sounding balloons there were 141 that attained 14 km. or more, and the following table gives the average temperatures recorded in these ascensions. It will be seen that there is a slow decrease in temperate up to 2 km.; a rapid decrease thence up to to km., and a slow decrease, almost a stationary temperature, between11 and 14 km.; this is the " thermal See also:zone " as discovered and so called by him. Altitude. Winter. Spring. Summer. Autumn. Dec., Jan., Feb. See also:Mar., See also:Apt., May. See also:June, July, Aug. Sept., Oct., Nov. Km. °C. °C. °C. °C. Ground + 1.9 + 5.1 +13'0 + 7'5 0.5 + 1.4 + 4' 7 +13'6 + 7' 7 I•o - 0.2 + 2.4 +I1.8 + 6•I I .5 - 0.2 + 0.1 9.7 + 4.0 2 .0 - 1.4 - 2.1 7.3 + 2.2 2'5 - 3.7 - 4.3 5.0 + 0'4 3.0 - 6•o - 6.4 2•I - P7 3'5 -8.7 -9.3 -1-0.2 -4.2 4'0 - 10.9 - 12.2 - 2'7 - 6.5 4'5 - 14.2 - 15.2 - 5.3 - 9'3 5.0 -17.0 -18.5 - 8.3 -12.4 6•o -23.7 -25.2 -14'8 -18'7 7.0 -31.5 -32.0 -21.7 -25.8 8.0 -39'0 -39'0 -29'3 _33'5 9.0 -46.9 -46.7 -38.0 -41.4 Io•o -54'6 -52'7 45'3 -48'3 I I.0 -57.9 -53'6 50.3 -54'4 12.0 -57.9 -53.1 52.7 -57.1 13.0 -56.9 -52°2 51'5 -57.1 14.0 -55.5 -52.5 -51'3 -57'1 It is evident that the annual average vertical gradient of temperature over Paris is between 40 and 6° C. per moo metres of ascent in the free air, agreeing closely with the value 5° per I000 metres, which has come into extensive use since the year 189o, on the recommendation and authority of Hann, for the reduction of land observations to sea-level. The winter gradients are less than those for summer, possibly owing to the influence of the condensation into cloud and rain during the winter season in France; the same value may not result from observations in the United States, where the clouds and precipitation of winter do not so greatly exceed those of summer. The work at Trappes is therefore not necessarily representative of the general average of the northern hemisphere, but belongs to a coastal region in which during the summer time, at great heights, the air is cooler than in the winter time, since during the latter season there is an extensive flow of warm south winds from the ocean over the cold See also:east winds from the land. Sounding balloons have also been used elsewhere with great success. The greatest heights attained by them have been 25,989 metres at Uccle, See also:Belgium, on the 5th of See also:September 1907, and 25,800 metres at Strassburg, August 1905. The most extensive meteorological explorations of the free atmosphere have been those accomplished in See also:Germany by See also:Richard Assmann and See also:Arthur Berson, beginning (1887) in co-operation with the German Verein for the Promotion of See also:Aeronautics and the Aeronautic Section of the German Army, afterwards under the auspices of the Prussian Meteorological Office,. but later as a wholly independent institution at Lindenberg. ll the details of the work during 1887-1889 and the scientific results of seventy balloon voyages were published in three large volumes, Wissenschaftliche Luftschiffahrten (Berlin, 1900). The work done at Tegel at the Aeronautical Observatory of the Berlin Meteorological Office, the 1st of October 1899 to See also:April 1905, was published in three volumes of Ergebnisse. But the location at Tegel had to be given up and a new independent establishment, the " Royal Prussian Aeronai iic Observatory," was founded at Lindenberg, under the direction of Dr Assmann, who has published the results of his work in annual volumes of the Ergebnisse of that institution, considering it as a continuation of the work done at Berlin and Tegel. In addition to these elaborate official publications various summaries have been published, the most instructive of which is the chart embodying daily observations .with corresponding isotherms at all attainable altitudes, published monthly since January 1903 in Das Wetter. The growth of this aerial work and the reliability of the results may be inferred from a statement of the number of ascensions made each year: 1899, 6; 1900' 39; 190I, 169; 1902, 261; 1903, 481; 1905, 513. This large number, combined with 581 voyages of Teisserenc de Bort at Trappes and many others made in England, Annual Temperatures and Wind. Tegel, 1903. Tegel, 1904. Lindenberg, 1905. Lindenberg, 1905. Altitude. Days. °C. Days. °C. Days. Sc. Days. Metres per sec.
Ground 365 9.2 366 9.1 365 8.5 365 4.65
500 M. 363 6.7 364 6.5 365 6.2 362 8.65
1,000 ,, 344 4'3 361 4'2 352 4.0 356 8.85
1,500 ,, 252 2.0 279 2.2 294 2.6 306 8'55
2,000 ,, 170 0.0 186 -0.2 242 0.5 257 9.5
2,500 „ 98 - I.8 132 - 1.7 179 - I•I 195 10.0
3,000 ,, 55 -3'9 79 -3'6 119 -2.8 127 Io•7
See also: Trappes. I, 2, 3 km. May, June May 15 3, 4 5 March Feb. 15 5, 6, 7 April Jan. 27 7, 8, 9 July July 28 9, 10, II - Sept. 14 The values above given as deduced from ial.high ascensions at Trappes show that between 11 and 14 km. there was no appreciable diminution of temperature, in other words, the air is warmer than could be expected and therefore has a higher potential temperature. This fact was first confirmed by the Berlin ascensions, and is now recognized as wellnigh universal. The altitude of the See also:base of this warm stratum is about 12 km. in areas of high pressure and Io km. in areas of low pressure. It is higher as we approach the tropics and above ordinary balloon work near the See also:equator if indeed it exists there. At first this unexpected warmth was considered the highest cirrus, from which Cleveland Abbe inferred that it had something to do with the absorption of the solar and terrestrial heat by dissolving cirri. But the most plausible explanation is that published simultaneously in September 1908 by W. J. See also:Humphreys of Washington, and Ernest See also:Gold of London. The daily diagrams in Das Wetter show that both the irregular and the periodic and the geographic variations of temperature in the upper strata are unexpectedly large, almost as large as at the earth's surface, so that the uniform temperature of space that was formerly supposed to prevail in the upper air must be looked for, if at all, far above the level to which sounding balloons have as yet attained. It is evident that both horizontal and vertical convection currents of great importance really occur at these great altitudes. These upper currents cannot be due to any very . local influence at the earth's surface, but only to the interchange of the air over the oceans and continents or between the polar and See also:equatorial regions. They constitute the important feature of the so-called general circulation of the atmosphere, which we have hitherto mistakenly thought of as confined to lower levels; their general direction is from See also:west to east over all parts of the globe as far as yet known, showing that they are See also:con-trolled by the rotation of the earth. It is likely that masses of air having special temperature conditions or clouds of vapour dust such as came from See also:Krakatoa, may be carried in these high currents around the globe perhaps several times before being dissipated. The average eastward See also:movement or the west wind at 3 km. above Germany is 10.7 M. per sec. or 1° of See also:longitude (at 45° latitude) in 42'4 minutes, or such as to describe the whole circumference of this small circle in Io•5 days. At the equator above the See also:calm See also:belt the velocity westward or the east wind as given by Krakatoa volcanic-dust phenomena was 34'5 m per sec., on 30 of a great circle daily, or around the equator in 12.5 days, while its poleward movement was only I ° per day or 1.3 metre per second. The average motion of the storm centres moving westward in northern tropical and equatorial regions but eastward in the north temperate zone is at the rate of one circumference or a small circle at latitude 45° in 19 days. Observations of the cloud movements gave Professor Bigelow the following results for the United States: Altitude. Moving Moving eastward. westward. 1o•o km. 36 m. p.s. 2.0 M. p.s. 7.5 35 2.0 5.0 26 1.5 3•o 20 1 •o 1.0 8 - 0.5 0 4 Temperature in Free Air over Europe 1899-1904. Annual Averages. International. All Altitude. Inter- Manned countries Berlin. national. balloons. Trappes. Feb. Aug. combined. 15 Ascents. 130 Ascents. 36 Ascents. 581 Ascents. Km. ° C. 'c . ° C. ° C. ° C. ° C. ° C. o - 8 3 - - + o•3 +18.2 + 5.4 6'o + 5'5 + 5'3 - 1'4 + 15'1 5.0 2 + 0.5 1.7 + 0.3 + 0.7 - 3.6 +10.2 0.5 3 - 5.o - 3'3 - 4.4 -- 4.0 - 8.7 + 4.8 - 4.0 4 -10.3 - 9.0 -10.3 - 9.4 -14'7 - 1'0 - 9'2 5 -16.6 -15.3 -16.5 -15'4 -21.9 - 7.1 -15.4 6 -24.2 -22.1 -23•o -21.9 -28.9 -13.3 -22.0 7 -30.2 -29.1 -30.2 -29.0 -36.1 -19.5 -29.0 8 -37'4 -36.2 -37.0 -36.2 _43.7 -27.1 -36.2 9 -46'4 -43.2 - -43'5 -50.1 -33'8 -43.2 I0 - -49'0 - -49'3 -55'4 -39'5 -49'2 Evidently, therefore, the great west wind (that James H. See also:Coffin deduced from' his work on the winds of the northern hemisphere and that William Ferrel deduced from his theoretical studies) repre- sents with its See also:gentle movement poleward a See also:factor of fundamental as possibly a matter of See also:error in the meteorographs, but this idea is importance. We must consider all our meteorological phenomena now abandoned. Assmann suggested that the altitude is that of except at the equator as existing beneath and controlled, if not Average temperature gradient Altitude Total Fall of Temperature from Ground upward. per loo metres. Month. Altitudes. (metres). October to March. April to September. From o to From moo to Cloudiness Cloudiness Cloudiness Cloudiness moo metres. 2000 metres. 0-7. 8-1o. o-7. 8-ro. ° C. ° C. ° C. ° C. ° C. ° C. January o•11 o•58 2000 8.24 7.63 15.33 14'18 _ February 0'39 0.30 1800 7.22 6.6o 14.20 12.97 March 0.33 0 40 1600 6 28 6.04 13.01 I I.75 April 0 73 0 48 1400 5'35 5' 15 11.66 Io•59 May 0.90 o'66 1200 4'48 4'35 10.32 9'32 June 0.99 0.72 1000 3.62 3.52 9.13 7.96 July 0.96 o•67 800 2'20 2.82 7'55 6.65 August . Additional information and CommentsThere are no comments yet for this article.
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