See also:

• CLIMATE

In a strict sense, meteorology deals with the physics of the atmosphere. It considers the various atmospheric phenomena individually, and seeks to determine their physical causes and relations. Its view is largely theoretical. When meteorology (q.v.) is considered in its broadest meaning, climatology is a subdivision of it. Climatology is largely descriptive. It aims at giving a clear picture of the interaction of the various atmospheric phenomena at any place on the earth's: See also:

• SURFACE

Various forms of graphic presentation are employed to emphasize and simplify the numerical results. In Hann's Handbuch der Klimatologie, vol i., will be found a See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

The relative amounts of insolation received at different latitudes and at different times have been carefully determined. The values all refer to conditions at the upper limit of the earth's atmosphere, i.e. without the effect of absorption by the atmosphere. The accompanying figure (fig. 1), after See also:

• DAVIS (or DAVYS), JOHN (1550 ?-16o5)
• DAVIS, ANDREW JACKSON (1826—1910)
• DAVIS, CHARLES HOWARD (1857- )
• DAVIS, CUSHMAN KELLOGG (1838-1900)
• DAVIS, HENRY WILLIAM BANKS (1833- )
• DAVIS, HENRY WINTER (1817-1865)
• DAVIS, JEFFERSON (1808–1889)
• DAVIS, THOMAS OSBORNE (1814–1845)

At the pole there is one maximum at the summer See also:

• SOLSTICE (Lat. solstitium, from sal, sun, and sistere, to stand still)

The result is to From Davis's Elementary Meteorology. Fla. 1.-Distribution of Insolation over the Earth's Surface. give the pole a maximum. On the 21st of June there are there-fore two maxima of insolation, one at lat. 431 ° and one at the See also:

• NORTH
• NORTH, BARONS
• NORTH, MARIANNE (1830—1890)
• NORTH, ROGER (1653-1734)
• NORTH, SIR THOMAS (1535?-16o1?)

Therefore, the values of insolation diminish from a maximum at the equator to a minimum at both poles. The effect of the earth's atmosphere is to weaken the sun's rays. The more nearly vertical the sun, the less the thickness of atmosphere traversed by the rays. The values of insolation at the earth's surface, after passage through the atmosphere, have been calculated. They vary much with the condition of the air as to dust, clouds, See also:

• WATER

— Equator. 40°. N. Pole. Equator. 40°. N. Pole. See also:

• WINTER, JOHN STRANGE
• WINTER, PETER (c. 1755-1825)

Zenker, the relative thickness of the atmosphere at different altitudes of the sun, and also the amount of transmitted insolation:fact, in the higher latitudes, the former sometimes follow the meridians more closely than they do the See also:

• PARALLELS

The See also:

• UNIFORM

It has the maximum annual amount of insolation. Its annual range of temperature is very slight. It is the summer zone. Beyond the tropics the contrasts between the seasons rapidly become more marked. The polar zones have the greatest variation in insolation between summer and winter. They also have the minimum amount of insolation for the whole year. They may well be called the winter zones, for their summer is so See also:

• SHORT, FRANCIS JOB (1857– )

Furthermore, the unsymmetrical distribution of land in the low latitudes of the northern and southern hemispheres results in an unsymmetrical position of the hot belt with reference to the equator, the belt extending farther north than south of the equator. The polar limits of the temperate zones are fixed by the See also:

• ISOTHERM (Gr. ivos, equal, and %pan, heat)

Also See also:

• ATLAS

The polar zones in the wind classification, therefore, remain just as in the older scheme. Need of a Classification of Climates.—A broad See also:

• DIVISION (from Lat. dividere, to break up into parts, separate)

Continental Climate.—Continental climate is severe. The annual temperature ranges increase, as a whole, with increasing distance from the oceans. The coldest and warmest months are usually See also:

• JANUARY

Yet even in the arid continental interiors in summer the See also:

• ABSOLUTE (Lat. absolvere, to loose, set free)

Diurnal cumulus clouds, often absent because of the excessive dryness of the air, are replaced by clouds of blowing dust and See also:

• SAND
• SAND, GEORGE (1804-1876)

A. S. 0. N. D. J. C. 300 200 100 00 -100 -20° -30° J. F. Bd N N J. F M. A.

M. J. J. A. S. 0. N. D. J. M, Madeira. V, Valentia. Bd, Bagdad.

N, Nerchinsk. Desert See also:

• PLANTS

See also:

• MONSOON
• MONSOON (Arabic Mausim, season)

At an altitude of rd,000 ft., more or less, pressure is reduced to about one-half of its sea-level value. The highest human habitations are found under these conditions. On high mountains and plateaus the pressure is lower in winter than in summer, owing to the fact that the atmosphere is compressed to lower levels in the winter and is See also:

• EXPANDED

Altitude tempers the heat of the low latitudes. High mountain peaks, even on the equator, can remain snow-covered all the year See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

Mountains often provoke rainfall, and local " islands," or better, " lakes," of heavier precipitation result. Mountains resemble marine climates in having higher wind velocities than continental lowlands. Mountain summits have a nocturnal maximum of wind velocity, while plateaus usually have a aiurnal maximum. Mountains both modify the general, and give rise to local winds. Among the latter the well-known mountain and valley winds are often of considerable hygienic importance in their control of the diurnal period of humidity, cloudiness and rainfall, the ascending wind of daytime tending to give clouds and rain aloft, while the opposite conditions prevail at night. Supan's Climatic Provinces.—The broad classification of climates into the three general groups of marine, continental and mountain, with the subordinate divisions of desert, littoral and monsoon, is convenient for purposes of summarizing the interaction of the climatic elements under the controls of land, water and altitude. But in any detailed study some scheme of classification is needed in which similar climates in different parts of the world are grouped together, and in which their geographic distribution receives particular See also:

• CONSIDERATION (from Lat. considerare, to look at closely, examine, generally taken to be from con-, and the base seen in sidus, sideris, a star, the word being supposed to be originally an astrological or astronomical term)

Obviously, no classification of climates which is at all complete can approach the simplicity of the See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

These cyclones, although comparatively in-frequent, are notable features of the climate of the areas in which they occur, generally bringing very heavy rains. The devastation produced by one of these storms often affects the economic condition of the See also:

• PEOPLE

It has been well said that "night is the winter of the tropics." Over an See also:

• AREA

Towards the margins of the zone, with increasing annual ranges of temperature, seasons in the extra-tropical sense gradually appear. Physiological Effects of Heat and Humidity.—Tropical heat is associated with high relative humidity except over deserts and in dry seasons. The air is therefore muggy and oppressive. The high temperatures are disagreeable and hard to bear. The " hot-See also:

• HOUSE
• HOUSE (O. Eng. hiss, a word common to Teutonic languages, cf. Dut. huis, Ger. Haus; in Gothic it is only found in gudhiss, a temple; it may be ultimately connected with the root of " hide," conceal)

Pressure.—The uniform temperature distribution in the tropics involves uniform pressure distribution. Pressure gradients are weak: The annual fluctuations are slight, even on the continents. The diurnal variation of the See also:

• BAROMETER (from Gr. (3apoc, pressure, and µETpov, measure)

The trades, except where they blow on to. windward coasts or over mountains, are drying winds. They cause the deserts of northern Africa and of the adjacent portions of Asia; of Australia, South Africa and southern South America. The monsoons on the southern and eastern coasts of Asia are the best known winds of their class. In the northern summer the south-west monsoon, warm and sultry, blows over the latitudes from about zo° N. to and beyond the northern tropic, between Africa and the Philippines, giving rains over India, the See also:

• EAST
• EAST, ALFRED (1849- )

Land and Sea Breezes The sea See also:

• BREEZE

M. A, M. J. J. A. S. 0. N. D. J. annual mean. The lOOOr1IS mean annual rainfalL 250 of weak pressure gradients and high temperature, and are commonly associated with the rainy season, being most common at the beginning and end of the regular rains: In many places, thunderstorms occur daily throughout their season, with extra-ordinary regularity and great intensity.

Cloudiness.—Taken as a whole, the tropics are not favoured with such clear skies as is often supposed. Cloudiness varies about as does the rainfall. The maximum is in the equatorial belt of calms and rains, where the sky is always more or less cloudy. The minimum is in the trade latitudes, where See also:

• FAIR

Following this scheme there are: (1) the equatorial belt; (2)` the trade-wind belts; (3) the monsoon belts. In each of these sub-divisions there are modifications due to marine and continental influences. In general, both seasonal and diurnal phenomena are more marked in continental interiors than on the oceans, islands and windward coasts. Further, the effect of altitude is so important that another group should be added to include (4) mountain climates. 1. The Equatorial Belt.—Within a few degrees of the equator, and when not interfered with by other controls, the annual See also:

• CURVE (Lat. curvus, bent)

Thesedouble rainy and dry seasons are easily modified by other conditions, as by the monsoons of the Indo-Australian area, so that there is no rigid belt of equatorial rains extending around the world. In South America, east of the See also:

• ANDES

A. M. J. J. A._ 5. 0. N. 0. mean annual rainfall at 9 Sao' Paulo is 54.13 in. 1 and at Mexico 22* W in. 6 ' The districts of tropical 5 rains of this type lie 3 along the equatorial z margins of the torrid a zone, outside ' of the lati- tudes of the equatorial FIG. 6.-Annual march of cloudiness type of rainfall.

The in the tropics. E, Equatorial type; rainy season becomes M, Monsoon type. shorter with increasing distance from the equator. The weather of the opposite seasons is strongly contrasted. The single dry season lasts longer than either dry season in the equatorial belt, reaching eight months in typical cases, with the wet season lasting four months. The lowlands often become dry and parched during the long dry trade-wind season (winter) J. E E M 0 J. F. M. A. M. J.

J. A. S. 0. N. D. J. 911 800 700 200 150 100 50 0 150 100 50 0 200 150 100 50 0 200 150 100 50 0 200 150 100 50 0 200 150 100 50 0 J. F. M. A. M.

J. J. A. S. 0. N. D. J. tropics. S.A, South Africa. M, Mexico. Q, Quito.

H, Hilo. S.P, Sao Paulo. P.D, See also:

• PORT

M. A. M. J. J. A. S. 0. N. D. J. the year. The See also:

• NILE
• NILE, BATTLE OF THE
• NILE, SOBAT

The so-called 90° tropical type of temperature See also:

• VARIA (mod. Vicovaro)

S. O. N. D. J. See also:

• ABSENCE (Lat. absentia)

The eastern coasts of Guiana, Central America, south-eastern Brazil, south-eastern Africa, and eastern Australia are well watered, while the interiors are dry. The eastern highland of Australia constitutes a more effective barrier than that in South Africa; hence the Australian interior has a more extended desert. South America in the south-east trade belt is not. well enclosed on the east, and the most arid portion is an interior district close to the eastern See also:

• BASE

5). The trade type of rainfall is often much complicated by the combination with it of the tropical type and of the monsoon type. In the See also:

• MALAY

A typical temperature curve for a monsoon ranges of See also:

• TEMPERA (the Italian term), or DISTEMPER

On the coast of the Gulf of Guinea, for example, there is a small rainy monsoon area during the summer; heavy rains fall on the seaward slopes of the Cameroon Mountains. See also:

• GORGE

The rainfall on tropical mountains and highlands often differs considerably in amount from that on the lowlands, and other features common to mountain climates the world over are also noted. The Characteristics of the Temperate Zones. General.—As a whole, the " temperate zones " are temperate only in that their mean temperatures and their physiological effects are intermediate between those of the tropics and those of the polar zones. A marked changeableness of the weather is a striking characteristic of these zones. Apparently irregular and haphazard, these continual weather changes, although they are essentially non-periodic, nevertheless run through a fairly systematic series. Climate and weather are by no means synonymous over most of the extra-tropical latitudes. Temperature.—The mean annual temperatures at the margins of the north temperate zone differ by more than 700. The ranges between the mean temperatures of hottest and coldest months reach 1200 at their maximum in north-eastern Siberia, and 8o° in North America. A January mean of -6o° and a July mean of 95°, and maxima of over 120° and minima of -9o°, occur in the same zone. Such great ranges characterize the extreme land climates. Under the influence of the oceans, the windward coasts have much smaller ranges. The annual ranges in middle and higher latitudes exceed the diurnal, the conditions of much of the torrid zone thus being exactly reversed.

Over much of the oceans of the temperate zones the annual range is less than ro°. In the south temperate zone there are no extreme ranges, the maxima, slightly over 3o°, being near the margin of the zone in the interior of South America, South Africa and Australia. In these same localities the diurnal ranges See also:

• RIVAL

Pressure and Winds.—The prevailing winds are the " wester lies," which are much less regular than the trades. They vary greatly in velocity in different regions and in different seasons, and are stronger in winter than in summer. They are much interfered with, especially in the higher northern latitudes, by seasonal changes of temperature and pressure over the continents, whereby the latter establish, more or less successfully, a See also:

• SYSTEM

Voyages to the west around Cape See also:

• HORN
• HORN (a common Teutonic word, cognate with Lat. cornu; cf. Gr. Kipas)
• HORN (Lat. cornu; corresponding terms being Fr. cor, trompe; Ger. Horn; Ital. corno)
• HORN, ARVID BERNHARD, COUNT (1664-1742)
• HORN, PHILIP DE MONTMORENCY, COUNT

At this season, however, the low temperatures, high pressures, and tendency to outflowing winds over the continents are unfavourable to rainfall, and the interior land areas as a rule then have their minimum. The warmer months bring the maximum rainfall over the continents. Conditions are then favourable for inflowing damp winds from the adjacent oceans; there is the best opportunity for convection; See also:

• THUNDER

The belts of minimum cloudiness are at about lat. 3o° N. and S. Over the continental interiors the cloudiest season is summer, but the amount is never very large. Otherwise, winter is generally the cloudiest season and with a fairly high mean annual amount. The absolute humidity as a whole decreases as the temperature falls. The relative humidity averages 9o%, more or less, over the oceans, and is high under the clouds and rain of cyclonic storms, but depends, on land, upon the wind direction, winds from an ocean or from a lower latitude being damper, and those from a See also:

• CONTINENT (from Lat. continere, "to hold together "; hence " connected," " continuous ")

Their tendency is to operate against man's highest development. The seasonal changes of the temperate zones stimulate man to activity. They develop him, physically and mentally. They encourage higher civilization. A cold, stormy winter necessitates forethought in the preparation during the summer of clothing, See also:

• FOOD
• FOOD (like the verb " to feed," from a Teutonic root, whence O. Eng. foda; cf. " fodder "; connected with Gr. lrareicOae, to feed)

The nature of these changes depends on the degree of development, the velocity of progression, the track, and other conditions of the disturbance which produces them. The particular weather types resulting from this control give the climates their distinctive character. The types vary with the season and with the geographical position. They result from a combination, more or less irregular,of periodic diurnal elements, under the regular control of the sun, and of non-periodic cyclonic and anticyclonic elements. In summer, on land, when the cyclonic element is weakest and the solar control is the strongest, the dominant types are associated with the regular changes from day to night. Daytime cumulus clouds; diurnal variation in wind velocity; afternoon thunder-storms, with considerable regularity, characterize the warmest months over the continents and present an See also:

• ANALOGY (Gr. avaXo-yLa, proportion)

The diurnal control is never very strong. Stormy weather prevails throughout the year although the weather changes are more frequent and stronger in the colder months. Climatic Subdivisions: There are fundamental differences between the north and south temperate zones. The latter zone is sufficiently individual to be given a place by itself. The marginal sub-tropical belts must also be considered as a separate group by themselves. The north temperate zone as a whole includes large areas of land, stretching over many degrees of latitude, as well as of water. Hence it embraces so remarkable a diversity of climates that no single district can be taken as typical of the whole. The simplest and most rational scheme for a classification of these climates is based on the fundamental differences which depend upon land and. water, upon the prevailing winds, and upon altitude. Thus there are the ocean areas and the land areas. The latter are then subdivided into western (windward) and eastern (leeward) coasts, and interiors. Mountain climates remain as a separate group. South Temperate Zone.–.-Because of the large ocean surface, the whole meteorological regime in the south temperate zone is more uniform than in the northern.

The south temperate zone may properly be called "temperate." Its temperature changes are small; its prevailing winds are stronger and steadier than in the northern hemisphere; its seasons are more uniform; its weather is prevailingly stormier, more changeable, and more under cyclonic control. The uniformity of the climatic conditions over the far southern oceans is monotonously unattractive. The continental ateas are small, and develop to a limited degree only the more marked seasonal and diurnal changes which are characteristic of lands in general. The summers are less stormy than the winters, but even the summer temperatures are not high. Such an area as-that of New See also:

• ZEALAND (also SEALAND Or SEELAND; Danish Sjaelland)

70° N. 59 500 1 40° 48 49 6o° 61 IO° 2o° 3o° 42 40 5o Eq. ' 58 IO° 3o° 20° 40° 500 •6o° S. 57 66 56 46 48 75 These winter.rains are not steady and continuous, but are separated by spells of fine sunny weather. The amounts vary greatly.' In summer, when the trades are extended polewards by the out-flowing equatorward winds on the eastern side of the ocean anticyclones, mild, dry and nearly continuous fair weather prevails, with general northerly winds. The sub-tropical belts of winter rains and dry summers- are not very clearly defined. They are mainly limited to the western coasts of the continents, and to the islands off these coasts in latitudes between about 28° and 40°. The sub-tropical belt is exceptionally wide in the old world, and reaches far inland there, embracing the countries bordering on the Mediterranean in southern Europe and northern Africa, and then extending eastward across the Dalmatian coast and the southera part of the See also:

• BALKAN

Southern Australia is climatic-ally similar to South Africa. In summer the trades give rainfall on the eastern coast, decreasing inland. In winter the westerlies give moderate rains, chiefly on the south-western coast. The sub-tropical climates follow the tropical high pressure belts across the oceans, but they do not retain their distinctive character far inland from the west coasts of the continents (except in the Mediterranean case), nor on the east coasts. On the latter, summer monsoons and the occurrence of general summer rains interfere, as in eastern Asia and in See also:

• FLORIDA

J: J. A. S. O. N. D. J. the higher latitudes, 200 150 100 50'~,~ the summer becomes 150 the season of maxi- 100 _l~I~ t1~~_ mummonth'1ainfadistritbutiTheon SO 0 ~,~ of h panyis rainfag nin ownll i thecurvescomn two sufob r-200 t~ tropical regions is - ' p ,,`~..~~ See also:

• MALTA
• MALTA (or MEDITERRANEAN) FEVER

J. A. S. 0. N. D J. .. See also:

• ALEXANDRIA
• ALEXANDRIA (Arab. Iskenderia)

Large variations in the annual rainfall may be expected towards the equatorial margins of the sub-tropical belts. The main features of the sub-tropical rains east of the Atlantic are repeated on the Pacific coasts of the two Americas. In North America the rainfall decreases from See also:

• ALASKA

A. M. J. J. A. S. 0. N. D. J. storms which corre- i 1000 spond with the sub- tropical winterrains. From the position of the sub-tropical 90° belts to leeward of the oceans, and at the equatorial margins of the temperate zones, it follows that their temperatures are not 700 extreme.

Further, the .See also:

• PROTECTION

J. ranges of tempera- ture depend upon position with refer- ence to continental or marine influences. This is seen in the accompanying data and curves for Bagdad, See also:

• CORDOBA
• CORDOBA, GONZALO FERNANDEZ DE (1453–15.15)

The accompanying curve, giving an average for ten stations. shows the small annual amount of cloud, the winter maximum and the marked summer minimum, in a typical sub-tropical C. A Ba Bd C.