Lecture Notes on Climatology

A D Tathe

May 2012

For Intermediate Met Training Course

India Meteorological Department

Contents

Page No.

01. Earth-Sun Relationship ...... 03 02. Solar Radiation ...... 08

03. Terrestrial Radiation ...... 10 04. Terrestrial heat balance ...... 11 05. Distribution of Solar Radiation . . . . . 14

06. Weather, Climate and Climatic Elements . . . . 17 07. Controls of Climate ...... 18

08. General Circulation of the atmosphere . . . . 21 09. Distribution of Wind and Pressure over the surface of the earth . 25 10. Distribution of Temperature over the surface of the earth . 29

11. Equatorial Trough and Inter Tropical Convergence Zone (ITCZ) . 35

12. Climatic Zones ...... 36

References ...... 44

Lecture Notes on Climatology By A.D.Tathe Page 2 of 45 respect to the sun explains whywe have seasons. around the sun. The study of the geometric relationship of the earth with earth are affected by latitude, the rotation of the earth and its revolution Sun. variationsThe in the Earth is affected by the geometric relationship of the Earth with respect to the surface of the Earth. The amount and intensity solar of radiation reaching the the most important sources, that drive environmental processes acting at the spring and autumn largely disappear. regions, the transition from summer to winter and vice versa is so sudden that terms of temperature the continental subtropical regions the natural seasons are usually defines in direction into ‘south- amount as ‘rainy season’ and ‘dry season’ or in terms of the associated wind in tropics, rather division into seasons is usually made in terms of rainfa ll ‘spring’ and‘summer’. The terms ‘summer’ and ‘winter’ are not so significant with latitude. In middle latitudes, the year is divided into ‘autumn’, ‘winter’, distance of 147.5 million km, and this position is called as perihelion. On 4 passing through the north and south poles. E I. Instead, seasons are caused by the tilt of earth's axis of rotation. radiation. The difference in distance is the earth- million km, and this position is called as aphelion. These annual variations in July the earth is kilometers. On 3 annually. The average distance of the earth from the sun is about 150 million focus. An elliptical orbit causes the earth's distance from the sun to va ry earth's orbit around the sun is not circular, but elliptical i the earth rotates at a uniform rate once every 24hours approximately,which s called a mean solar day. Lecture Notes on Climatology By A.D.Tathe Solar radiation is one of many sources of energy, andprobably one of Generally the manner of the division of the year into seasons varies The term earth rotation refers to the spinning the earth of onits axis The orbit of the earth around the sun is called earth revolution. The arth Rotation and Revolution and Rotation arth sun distance influence aslight change in the receipt of solar

rd farthest from the sun at an approximate distance of 152.5

January the earth is closest to the sun at an approximate west monsoon’ and ‘north - (hot or cold), or rainfall (rainy anddry), or both. In polar Earth Earth amount and intensity solar of radiation reaching the

Page – – Sun Relationship

t not

Turning in aneastward direction the cause of different seasons. east monsoon’ as in India. In

(Fig. 1) with sun at its

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Lecture Notes By A D Tathe - ver May 2012

parallelism of axes. parallel to its position at any other time as it orbits the sun, a property called it revolves around the Sun. As a result, the earth's axis of rotation remains shown in Fig axis 2. The rotation of remains pointing in the same direction as ecliptic. In other words it makes an angle of 23½º with the plane of elliptic as sun. II. Lecture Notes on Climatology By A.D.Tathe T The Earth's axis istilted Earth's The by 23½º from the perpendicular to the plane of the The ilt of the earth’s axis earth’s the of ilt plane of the ecliptic of the plane Fig. 1 Fig. Fig. 2 Fig.

: :

Page

is the plane of the Earth's orbit around the Earth’s ellipticalorbit Earth’s ellipticalorbit

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Lecture Notes By A D Tathe - ver May 2012 light. light. to the thickness of the atmosphere, increase in reflection and scattering of the beam of light is spread over alarger area anddecreases in intensity due angle. As the sun angle decreases, rays strike the earth at the highest radiation occurs where the sun's The most intense incoming solar (polar night) sunlight the year, called the " respect to a point on earth during angle that a solar rays makes with parallelism causes changes in the oriented itself so the North Pole is facing away from, and the South Pole into phenomenon keeps all places north of latitude of 66½ tangent rays in the northern hemisphere pass over the pole. Cancer (23½º N latitude). As the noon’s rays are vertical over 23½º N, the the sun (Fig. 3). The III. summer solstice overhead at noon, is located at 23½ north º latitude. This date is known as the hemisphere. Lecture Notes on Climatology By A.D.Tathe

The The and tilt constant The This is the longest day of the year placesfor located north of Tropic of On June 21 or 22, the axis of rotation of the earth is inclined towards Solstices (polar day) winter solsticewinter .

, while, locations below latitude of 66½ and marks the first day the of summer in the northern uslr point subsolar Fig. 3 Fig. sun angle sun

occurs onDecember 21when or 22 the earth has : Page ". ". Summer SolsticeSummer , the place where the sun lies directly

º N in 24 h 24 Nin º º Sº are in darkness

ours of 5

This This of of 45

Lecture Notes By A D Tathe - ver May 2012 called as Tropic of Capricorn. The places poleward of the Sun (Fig. 4). The Sun lays directly overhead at noon at 23½º S latitude, the beginning of autumn season in the northern hemisphere. March 21or 22 called equal over the entire earth (Fig. 5). period The between summer and winter is these times, the tangent rays strike the poles so that the days and nights are sidewayswith respect to the sun rather than towards or away the from sun. at directly on the equator. The axis rotation of is still inclined buttilted is it IV. hemisphere. darkness.winter The solstice refers to the first day of winter in the northern receives 24hours of daylight andthe places poleward 66½ of Lecture Notes on Climatology By A.D.Tathe

Midway between the solstices are two dates when the sun shines Equinoxes as autumn. The

Fig. 5 Fig.

: autumnal equinox autumnal Fig. 4 Fig. Autumnal and Spring Equinox and Autumnal : Page Winter Solstice

on September 22 or 23 indicates

66½

º Nare in theº º S latitude latitude S º

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Lecture Notes By A D Tathe - ver May 2012

Sun and winter when it is tipped away fr opposite seasons. Summer occurs when a hemisphere is tipped toward the sun angle is the reason the northern and southern hemispheres have from the Sun creating low sun angles. yielding high sun angles whereas during the winter, the earth is oriented away V. a transition between the two more extreme seasons, summer and winter. equinox spring is the first day of the spring season and as such this date is called as the angle and consequently the greater variation in surface heating. over these places. Poleward of this region there is greater variation in the sun overhead over the course of ayear and the sun angle does not vary much betw Cancer 23½º N and Tropic of Capricorn 23½º S latitudes only. Places perpendicular to the surface (directly overhead) at places between Tropic of VI. Lecture Notes on Climatology By A.D.Tathe

een the two tropics experience two times when the sun is directly The Seasons The During the summer months the earth is inclined toward the Sun As seen in Fig. 6, over the course of a year, the sun's rays of seasons Annual march . Equinoxes mark the seasons of autumn and spring andare Fig. 6 Fig.

: Page Annual March of Seasons Annual March

om the Sun. the om thetiltThe its earthof and impact on

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Lecture Notes By A D Tathe - ver May 2012 energy per unit area incident on the earth is equal to output, our energy. earth The intercepts an infinitesimally small part of the sun’s and weather. and seasonal variations in length of the day, receipt, and escape of radiation revolution) explain the changing elevation of the sun as well as the latitudinal earth’s atmosphere and surface. The two movements (viz. rotation and = 1 cal cm = cal 1 and the earth. The energy per unit area is expressed in Langleys(ly) and1ly perpendicular to the sun’s direction at the mean distance between the sun boundary of the earth’s atmosphere that is received onasurface held earth from thesun} S is called as the Solar Constant. { The sun radiates approximately 56×10 and 0.7 μm). occursatrelatively short wavelengths theinvisible spectrum (between 0.4μm scattered by the atmosphere. The maximum emission of solar radiation surface as direct radiation, the remainder being reflected, absorbed, or Lecture Notes on Climatology By A.D.Tathe The sun at atemperature of about 6000 Kº is the source of nearly all of The weather results from the interaction of solar radiation on the The The S = × -2 105 Solar Constant Solar . the Thus solarconstant the for earthis2 Ly.

− 10 × 1056 %. Only aportion of the sun’s radiation reaches the earth’s 26 ××π cal

105.1(4 min cm − ) 1

213 isdefined as the fluxof solarradiation at theouter

Solar Radiation Solar Page ≈ 2 × 105.1 .0 cal cm 26 13

cm cal of energy per minute. The

is the mean distance of the -2

min -1

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Lecture Notes By A D Tathe - ver May 2012 a circular non- solar constant. received at the top of the atmosphere is 0.5 ly min- energy of amount average global the 7, Fig. in shown as πr2), versus (4πr2 does the spherically shaped rotating earth. sun facing side of the disc will intercept the same amount of solar radiation as Lecture Notes on Climatology By A.D.Tathe

Since the area of asphere is four times the area of one side of a disc If the surface, oriented perpendicular to the sun’s rays, is thought of as rotating disc with aradius r equal to the radius of the earth, the

Page Fig. 7 Fig.

1, or onequarter of the

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Lecture Notes By A D Tathe - ver May 2012 atmosphere and no cloud. moon. The major reason thisfor is the presence of clouds. The moon has no its surface. only about 0.07, indicating that it absorbs most of the solar radiation striking albedo of the earth- radiation. It is described in terms of percentage of reflected radiation. The Albedo of long waves, particularly between 5.5μ and 7μ and above 27μ. strongabsorberaatmosphere the isin vapour 10μ. maximumWater at a with temperature of 294 Kº, andgives out long radiation it receives from the sun. The earth approaches an average surface of the earth is long surface and its atmosphere. The radiation emitted from the land and water Lecture Notes on Climatology By A.D.Tathe Some typical albedo are : Thus, viewed from space, the earth shinesmore brilliantly than the It is defined as the ratio of the reflected radiation to the total intercepted The absorption of solar radiation raises the temperature of the earth’s

Forests Seas (high sun angle) Sand Old snow Cloud tops Fresh snow

atmosphere system is 0.30. The moon has an albedo of

Terrestrial R - wave radiation, in contrast to the short Page

0.03 0.05 0.15 0.50 0.60 0.75 adiation - wave radiation in the range 4μ – – – – – – – 0.10 0.10 0.35 0.70 0.90 0.90

- 10 wave wave -

80μ 80μ of of 45

Lecture Notes By A D Tathe - ver May 2012 hemisphereare presumed to benotlarge. northern hemisphere but the difference between the northern and southern about 0.5 ly min rapid fluctuationsout periods. Averaging over aperiod of number years of can smooth the more atmosphere. Thus along temperature of the earth or its atmosphere during the interglacial periods. general, there seems to be no over mean all the in significant trend so slowly, however, the that net energy change per year isvery small. In net gain or loss of energy during the period of averaging. The changes occur Lecture Notes on Climatology By A.D.Tathe The mean temperature of the earth undergoes fluctuations of varying The total amount of solar radiation received on a horizontal surface i Fig. 8 Fig. -

term mean heat balance exists at each point of the earth andits : -1 . In this. In explanation, the figuresrepresent estimatesthe for Mean heat balance in the northern hemisphere in balance northern the heat Mean . The remaining slowervariations provide evidence of a Terrestrial heat balance Page

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Lecture Notes By A D Tathe - ver May 2012 respectively. atmosphere separately. This transport of heat is estimated at 4% and23 % into consideration, aheat balance exists also for the earth’s surface andthe space. The other 50 % is radiated back to space by the atmosphere. 24 %, 16 % is reabsorbed in the atmosphere while 8% returns directly to the the ground and the radiation from the atmosphere to the ground. Out of this ground upwards is called the ‘effective radiation’. temperature of the earth as a whole remains the same. The radiation from the atmosphere. This 58 % must be radiated back to space since the yearly mean space and the remaining 58% is absorbed by the ground and the is denoted by negative. counted positive and the radiation emitted or reflected and scattered to space away the from sun than in the direction towards the sun. to the fact that the larger dust particles scatter more radiation in the direction considerably greater than that returned to space (9 %). This difference is due the remaining 9%. ground, which accounts for 33% and the diffuse reflection, which makes up atmosphere system. It is composed of the reflection onclouds and onthe reflected back into space, which represents the albedo of the earth- O The atmosphere including clouds absorbs 15 %. The remaining 42% is arrives as the diffuse sky radiation. So that 43 % reaches the ground together. Lecture Notes on Climatology By A.D.Tathe When When the heat transports by turbulence and by condensation are taken The 24% represents the difference between the actual radiation from The 42 % of the incoming solar radiation is returned directly back to the In the Fig. 8, the radiation received by the earth and the atmosphere is It is noticed that the diffuse radiation towards the ground ut of these 27 % penetrates directly to the earth’s surface and 16 %

Page

(16 %) is 12 of of 45

Lecture Notes By A D Tathe - ver May 2012 By direct radiation Receives surfaceThe the of earth The following is the summary of the separate heat balance of the earth: = Total By condensation radiation By absorption of ground radiation By absorption of solar Receives The atmosphere Total By turbulent transfer By diffuse radiation Lecture Notes on Climatology By A.D.Tathe =

Page 27 % 54 % 23 % 16 % 15 % 16 % 47 % 4 %

By radiation Loses Total = Total By turbulent transfer By radiation Loses (evaporation) By condensation Total = Total

24 % 54 % 50 % 23 % 47 % 13 4 % of of

Lecture Notes By A D Tathe - ver May 2012 A) surfacethe of ear latitudes, seasons and time of the day i.e. the angle of sun’s rays with the cause of weather and climate. rateThe of receipt of solar energyvaries with curve is that it reaches zero during winterwhen there is no solar radiation. Antarctic circles, resembles that of middle latitudes. The only difference in this curves show alarge seasonal variation. maximum and asingle minimum, both of which coincide with the solstice. The between 23½º and 66½º in each hemisphere. It shows asingle strong shown Fig. 9. shows two maxima and two minima for the low latitudes. at all places situated between two tropics. As a result the solar radiation curve the year with little seasonal variation. The noon rays are vertical twiceyear a Lecture Notes on Climatology By A.D.Tathe Fig. 9 Fig.

Distribution of solar radiation without atmosphere The unequal distribution of solar radiation over the earth is the primary The annual march of the solar radiation at the top of the atmosphere is T Th In tropics, the intensity of solar radiation remains quite high throughout : he high latitude (80º), which represents belts poleward of Arctic and e mid latitude curve (40º) is broadly representative of the belts lying

Annual solar radiation at the outer limit atmosphere of the outer the at radiation Annual solar th.

Distribution of solar rad iation of solar Distribution Page

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Lecture Notes By A D Tathe - ver May 2012 shown in Fig. 10. B) compared to the winter hemisphere. southern hemisphere during the winter solstice. northern hemisphere. The same feature is observed in the middle latitudes of days combined together produce a broad maximum in middle latitudes of pole. is symmetrical about the equator with the amount decreasing to zero at each latitudes. passing through much greater thickness of the atmosphere than in the lower due to higher obliquity the of solar beam resulting in the path of the beam outer limits of the atmosphere. The depletion is maximum at high latitudes radiation reaching the surface of the earth is less than that received at the is depleted by scattering, reflection and absorption. Thus the amount of Lecture Notes on Climatology By A.D.Tathe Fig. 10 Fig.

Distribution of solar radiation with atmosphere (without clouds) The distribution of solar radiation with atmosphere but without clouds is Latitudinal variation of radiation is small in summer hemisphere During summer solstice the more nearly vertical solar beam and larger At the time of the equinoxes the latitudinal distribution of sola A :

r beam, while passing through the atmosphere (without clouds), surface (with atmosphere butclouds) (with atmosphere without surface

Latitudinal distribution of solar energy at the earth’s earth’s energy the ofat distribution solar Latitudinal Page

solar radiation

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Lecture Notes By A D Tathe - ver May 2012 hemisphere. due to greater cloudiness and more ocean surface in the southern and 20ºS. the lesser amount near the equator in the southern hemisphere is radiation (Fig. 11) is not found at the equator but rather at about latitude 20ºN amountofreachingit thesurface the of earth. The maximum total annual C) because of abundant cloudiness In the high latitudes, the lowest annual radiation values ar radiation is received in the sub- warm continents, where convective clouds are in abundant. Maximum solar Lecture Notes on Climatology By A.D.Tathe Fig. 11 Fig.

Distribution of solar radiation with atmosphere and clouds The clouds reflect a large amount of solar radiation reducing the In the equatorial belt, area of least solar radiation coincides with the :

Total annual solar radiation received at the earth’s surface by latitude belts Page tropics, which are relatively less cloudy region.

* *

e overoceans

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Lecture Notes By A D Tathe - ver May 2012 'climate' is defined as 'the synthesis of the day what you expect,weather is what youget” climate and thestatesof of the atmosphere as time passes. weather and climate. Primarily these elements are combinations of the same atmospheric variables, called the elements of II obtained and freaksor abnormal values donotexert toostrong long enough to ensure that representative values thefor month or season are month or season and are determined over aperiod of about 30years. This is with associated values of elements ranges within which phenomena occur, and the frequencies of weather types than simple averages as the climate also involves extreme values, andthe meteorological elements that affect to a more enduring regime of the atmosphere. speak of today’s weather, or of last week’s. given place for a brief period of time; it is an everyday experience. Thus we period to another location to another, and in agiven location climate can change from onetime variable that characterizes the local weather location and time period the climate is the p for agiven time period andagiven location. More technically, meteorological terms that subsidence, favorsskies. fair cloud and precipitation are likely, while downward air movement, or some slight upward or downward movement. the motionWhere is upward, While air movement is predominantlyhorizontal in a direction, there is also masses of contrasting temperature and moisture from one locality to another. direction andspeed of the wind, andit is the wind that in turn moves air It is atmospheric pressure that to an important degree determines the particular importance in determining the characteristics of the other variables. Precipitation, Humidity, andWind Cloudiness. The Lecture Notes on Climatology By A.D.Tathe Weather is the instantaneous state of the atmosphere, or the sequence Although weather and climate are not identical both are described by Elements of Climate and Weather Climatic data are usually expressed in terms of an individual calendar According to The Meteorological Glossary, published by the Climate is usually defined as weather is . . Weather, Weather isWeather the sum total of the atmospheric variables at a

usefully summarized by the popular phrase “Climate

are relatedare but not interchangeable Climate

Page

andClimatic Elements

its locality'. its the average weather plus the extremes

Climate, on the other hand, refers . robability distribution of each

. Synthesis here means more Climatechanges from one Weather andWeather climate are atmospheric pressure of is

The difference between Pressure - to - day values of the

, Temperature, an influence.

for agiven UKMO 17 of of 45 is is

Lecture Notes By A D Tathe - ver May 2012 A) more specific controls are derived from various geographic factors. represent the overall general background control of weather and climate. The heating and cooling differences, and the air movements (winds) they induce, land, and even between cities and their surrounding country sides. These decrease in the latter. side tend to make for increased precipitation in the former instance and a on a mountain’s windward side the transfer of warm or cold air masses. In addition, the upward thrust of air the path of prevailing winds, it acts to block the movement of air and hence Thus altitude is aclimatic control. a Where high mountain chain lies athwart temperatures(and often also moreprecipitation) than adjacentlowlands. increasing Altitude, places at higher elevations are likely to have lower B) than aland surface lacking snow. sunshine falls. Thus astrongly reflecting snow surface is heated much less of solar heating also varieswith the nature of the surface on which the southward during the year, thereby producing the seasons. The effectiveness climate is colder. The zone of maximum solar radiation shifts northward and latitudes the sun is lower in the sky, the solar radiation is weaker, and the solar radiation is intense, and the climate is warm and tropical; in high low la In control. climatic basic most between snow heating andcooling differences also exist between continents and oceans, important of which is the differential between high and low latitudes. But heating occurs onawide variety geographic of scales, the largest andmost

sun, some parts experience anet gain and others a net loss. While the earth as a whole loses as much heat to space as it gains from the unequal heating and cooling of the atmosphere in different parts of the earth. p Lecture Notes on Climatology By A.D.Tathe lace

Since within the troposphere temperature normally decreases with Altitudes Latitudinal differences in the amounts of solar energy received are the Radiation Solar in Variations Latitudinal Climatic Controls are the f The

most fundamentalcon trol of both weather andclimate is the -cov

ered andsnow

Controls of Climate Controls Page and the downward movement of air onits lee - free areas,free between forested and cultivated actors affecting the titudes the sun is high in the sky, the

climateparticular of

The unequal

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Lecture Notes By A D Tathe - ver May 2012 paths a common scale of atmospheric motion. The frequency of occurrence and the weather changes and are conspicuous features ondaily weather maps are of C) doing give some coastal important in transportingwarmth andchill in anorth- major wind systems, are also an important climatic control. They are highly E) in position, and they too are of great climatic importance. especially the highs over the subtropical oceans, tend to besemi permanent important factors in determining climate. Some pressure and wind systems, tornado. easterlies that encircle the low latitudes, to the small but extremelyviolent such as the belts of westerlywinds in middle latitudes and the belts of and atmospheric motion. They range from those of hemispheric magnitude, surfaces, so there is a great variety scales of relating to atmospheric pressure variety geographic of scales of differential heating and cooling of terrestrial regions of net heat gain to regions of net loss. And just as there is agreat climate, (winds). Air in motion,which in itself is animportant element of weather and differences in atmospheric pressure which in turn induce air movements surfaces lead not only to regional temperature contrasts but also to between land and water areas, and between snow D) winter cold than do oceanic and coastal areas. n Lecture Notes on Climatology By A.D.Tathe on coastal continental areas experience more intense summer heat and

followed by these transient mobile pressure and winds systems are Ocean currents, both warm andcold, which are largely induced by the Ocean Currents The mobile low Differences in heating and cooling between high and low latitudes, Pressure and Wind Systems Continents heat and cool more rapidly than do oceans. Consequently Oceans and of Continents Distribution also operates as acontrol, itfor serves as a transporter of heat from

and high-

regions distinctive climates. (Fig. 12 Page pressure systemswhich bring day

south direction, andin so - covered and bare land

- to 19 -

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Lecture Notes By A D Tathe - ver May 2012

country sides. than the adjacent slopes; and cities are usuallywarmer than the adjacent wi low heat conductivity, are inclined to experience more frosts than doareas cold northerly winds. Areas with sandy, loosely packed soil, because of their exposure, which not only away face the from sun, but are also more open to more direct sunlight and have a warmer climate than those with anorthern vegetation and soil. In the Northern Hemisphere south- such as its exposure, the slope of the land, and the characteristics of F) Lecture Notes on Climatology By A.D.Tathe Fig. 12 Fig. th hard packed soils; valleys normally have more frequent and severe frosts

Finally, the climat the Finally, Features Local :

dark arrows andCold Currents by open arrows) Major Ocean Currents. (Warm Currents are shown by

e of a place is affected by a variety of local features, Page * * facing slopes receive

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Lecture Notes By A D Tathe - ver May 2012 the straightforward consequence of the geometry the earth of . T greater at averaged incoming solar radiation per unit area of the earth’s surface therefore because of the fact that the polar regions are covered in ice and snow and that the tropical regions actually receive more energy from the sun emit back to space, while the converse is true in high latitudes. Lecture Notes on Climatology By A.D.Tathe Fig. 1 Fig. Fig. 1 Fig.

tropics are much warmer than the poles. As discussed : 4 The simplest observed global characteristic the of atmosphere is that

: 3 reflect much of the incoming radiation back to space. A

the equator than at the poles1 (Fig. General Circulation of Circulation atmosphere the General Latitudinal transport of heat and angular angular and momentum transport of heat Latitudinal Latitudinal variation in annual average of radiation average annual in variation Latitudinal Page

3) . The

difference

earlier

nother he annually

, this is is a this , than they is much is

arises arises fact 21 of of

45 is is

Lecture Notes By A D Tathe - ver May 2012 Single currents. earth. This transport is accomplished by atmospheric winds and ocean and oceanic transport processes distribute the energy equally around the surplus and deficit of radiation in different regions of the globe, atmospheric high latitudes, as depicted schematically in (Fig. 14 acting to transport excess energy the from tropics to make upthe deficit in overyear a (incoming equals outgoing). Hence, there must be a process a non- toward the poles, descends and flows back toward equator at the surface . where the surface air converges andrises at the equator, spreads laterally currents caused by temperature and density differences. contained fluid and movements within this fluid would bethe convective atmospheric circulation Lecture Notes on Climatology By A.D.Tathe rotating Earth Over the globe, the energy balance is nearly balanced when averaged This creates the single cell circulation 1 model (Fig. The latitudinal transfer cell, heat of would circulation single resu a in lt If the Earth’s surface were smooth, uniform, stationary, and - Fig. 1 Fig. Cell Model of the General Circulation

: 5 and sun being directly over the equator. would bevery simple. The atmosphere would act as a Single Page - Cell Model of General Circulation

). compensate To thefor

5 )

possible on only

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Lecture Notes By A D Tathe - ver May 2012 northward. and is formed as warm air rises above the Equator and starts to flow cell in 1735. The Hadley cell is the strongest of the three cells of circulation Hadley Cell cells these of each spanning 30degrees of latitude. The latitudes that mark the boundaries and Southern Hemisphere are each divided into three cells of circulation, coriolis force due to the Earth’s rotation. In this circulation model, the Northern used to describe the atmospheric transport of energy. It considers effects of Three for the increases speed. The increased speed and the Coriolis force are responsible Because of conservation of angular momentum, the poleward moving air has become awesterlywind (it is moving to the east) dueto the Coriolis force. moves poleward. By the Because the stratosphere is stable, risingair that reaches the tropopause, found. The ITCZ moves north and south following the sun during the year. Zone (ITCZ) andcorresponds regions overwhich the tropical rain forests are and heavy precipitation. This area is called the Inter 1 (Fig. Lecture Notes on Climatology By A.D.Tathe - 6 subtropical jet George Hadley, anEnglish meteorologist, theorized this first circulation This model represents the average circulation of the atmosphere and is The rising air cools condenses and forms aregion intense of clouds Cell Model of the General Circulation ). Fig. 1 Fig.

: 6 are the Equator, 30° North and South, and 60° North and South . time the air moving northward reached about 30° N it Three Page - Cell Model of General Circulation

- Tropical Conv ergence

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Lecture Notes By A D Tathe - ver May 2012 cell is called the Ferrel cell. CellFerrel near 60°N. spreading air at 30°N. This colliding air rises, creating abelt of low pressure surface collides with the weak, northwesterly surface flow that resulted from from the southwest. Near 60ºN, the southeasterly moving air moving the along the surface polar easterlies, although the upper winds are still predominantly southward moving airdeflects sharply to the right. This wind regime is called spreading southward. Since the coriolis force is strongest at the poles, the causing an area of subsidence and high pressure. As the air sinks, it begins between 60°N and the North Pole. At the pole, cold, dense air descends, Polar Cell in the northern hemisphere and southeast in the southern hemisphere. surfaceThis air forms the turning west (in the northern hemisphere) as it goes due to the Coriolis force. exchange of polar air moving southward and tropical air moving northward. circulation of the Ferrel cell. This net circulation pattern is greatly upset by the surface convergence andnet upward vertical motion at 60°N induces the downwardvertical motion and surface convergence at 30°N coupled with phenomena, induced by interaction between the other two cells. The stronger the Ferrel cell at the surface and aloft. It is believed the cell is aforced upper andlow explained as the Hadley and Polar cells. Unlike the other two cells, where the high pressure belt at the surface that results from the sinking air at 30° Lecture Notes on Climatology By A.D.Tathe The mid The This is the northernmost cell circulation of and its mean position is Once the sinking air reaches the ground, some flows to the equator, This poleward moving air leads to the formation semi of

- - level flows are reversed, agenerallywesterly flowdominates latitude circulation cell between the Polar cell andthe Hadley trade winds

Page The FerrelThe cell circulation is not as easily * *

which

blow steadily from the northeast - permanent . .

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Lecture Notes By A D Tathe - ver May 2012 are not symmetrical to the poles. with respect to the poles, the zones of the easterlywinds in the polar regions in the surface layers. Since Greenland and Antarctica are not symmetrical pressure distribution is anticyclonic, because of the low temperature of the air pressure decreases here toward the pole. rather irregular because of the migrating pressure centers. On the whole, the frequent calms. hotter than the oceans. The central regions of the high- around the earth but are interrupted over the continents since the land is In summer hemisphere, these high- hemispheres by zone of high pressure called ‘subtropical’ high- general pressure distribution shown in Figures 17 and 18. easterly windswith acomponent towards the equator prevail. the regions of the migrating cyclones and anticyclones. hemisphere than in the northern hemisphere. These zones of westerlies are ‘prevailingwesterlies’. These westerlies are better developed in the southern deflected into southwest winds under the influence of the coriolis force. the southeast trade winds may reach into the northern hemisphere andget doldrums is displaced north far from its symmetrical position at the equator, the earth it even extends into southern hemisphere. Where the zone of develop. The zone of doldrums is largely north of equator. Oversome parts of meet directly at asurface of discontinuity onwhich strong rainsqualls may other of the equatorial zone. Then the northeast trades and southeast trades ‘doldrums’. However, the doldrums are frequently absent in one part or the separated near the equator by azone of prevailing calms known as winds prevail in the northern and southern hemisphere respectively. They are Lecture Notes on Climatology By A.D.Tathe Wind and and of Wind Distribution In the surface layers the of arctic and of the Antarctic zone, the In the region of the westerlies even the mean pressure distribution is Near the equator, a zone of low pressure is found. It is followed in both The wind distribution as described is closely connect Poleward from the region westerlies, of beyond 65to 75 latitude Beyond the trade wind regions each of hemisphere are the zones of In subtropical region, the northeast trade winds and southeast trade

Page Pressure Pressure

pressure belts do not extend continually

over

the surface o

pressure beltshave

f the e f the pressure belts. ed with the the with ed arth

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Lecture Notes By A D Tathe - ver May 2012 pressure over the more northward over the continents. westerlies surround the northern hemisphere completely, but are displaced side of the continental anticyclone, the winds are westerly. the Thus belts of the winter so that the cyclonic activity is now at amaximum. On the north centers of low pressure over the oceans are considerably intensified during south side of the continental anticyclone, the winds are northeasterly. The colder than the adjoining oceans where astrong high is developed. On the pronounced over India and the Indian Ocean. deflection of the southeast trades into the southwest monsoon is especially hemisphere, which are deflected to southwest as they cross the equator. The observed are continuation of the southeast trade winds of the southern northeast trade winds are absent. Instead, the southwest winds that are because of the smaller land area in the southern hemisphere. than the water. But the disturbance of the pressure distribution is much less The southern hemisphere has winter in July so that here the land is colder lowis in direct connection with the equatorial low over the continents, which interrupt the high- much warmer than the surrounding oceans. Hence alow pressure is found noticeable during the extreme months of January andJuly. modifications of the pressure and wind distribution. These deviations are more pressure belt by the continents during Januar over the continent. But the interruption of the southern subtropical high- a result, the zone of doldrums with its low pressure shows asouthward bulge Lecture Notes on Climatology By A.D.Tathe Effect of land and sea on the on the wind and pressure distribution onthe and onthe pressure wind sea of land and Effect The southern hemisphere has its summer during January. Thus the During January the northern in hemisphere, the continent is much Over the continents, in the northern hemisphere during July, the During July, the large continental mass of the northern hemisphere is The unequal heating of water andland produces considerable

continents is now lower than over the adjoining oceans. As Page

* *

y slight. only is

pressure belt. The continental

- pre ssure zone of doldrums.

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Lecture Notes By A D Tathe - ver May 2012 between water and land, by the altitude, and by the prevailing winds. af soalr radiation. Hence its distribution depends largely onthe latitude. Also, it is small in tropical and sub - in the southern hemisphere. The temperature decrease with latitude is very latitude of the northern hemisphere is temperature than the southern hemisphere. Also onthe yearly average, each N. 20º of Januar equator but at 10º N. Equator is the hottest circle latitude of only during latitudinal control of temperature is found moredominant. Lecture Notes on Climatology By A.D.Tathe fected by the nature of the surface of the earth especially bydifferences the Latitude Equator 10º N 10º N 20º N 30º N 40º N 50º N 60º N 70º N 80º N 90º 20º S 20º S 10º 90º S 90º S 80º S 70º 6 S 50º S 40º S 30º 0º S 0º y. In the month of July, the warmest parallel latitude is somewhat north The atmospheric temperature is controlled principally by the incoming The northernhemisphere whole as a hasa higher annual mean The yearly averages show that the warmest latitude is not at the Considering the mean temperature of each latitude (Table 1), the Table 1. Table Distribution of Temperature over the surface of the earth

: - - Year 25.9 42.4 53.4 61.9 73.2 77.5 79.2 80.1 77.5 68.7 57.4 42.5 30.0 12.7 - - 27.6 16.6 7.5 1.0 8.9

tropical latitudes.

Latitudinal distribution of temperature (ºF) of distribution temperature Latitudinal Page January - - - 12.6 25.7 35.8 46.6 60.1 71.4 77.7 79.3 79.5 78.4 71.2 58.1 4 19.2 15.3 26.0 42.0 7.7 3.0

1.0 warmer than the corresponding latitude

- - July 45.1 35.6 30.0 15.6 38.1 48.2 58.5 68.0 75.0 78.1 80.4 82.4 81.1 75.2 64.6 57.4 - 54.0 39.1 9.4

Range

60.4 61.6 72.0 62.0 51.7 35.1 20.2 11.9 12.9 11.2 23.0 34.2 45.4 54.4

8.5 9.7 4.3 1.8 2.5

of of

Lecture Notes By A D Tathe - ver May 2012 fact that the temperature does not depend on the radiative balance alone. while the temperature maxima is found at the equator. This is because of the The greatest surplus of radiation during January occurs at about 30º south, greater in winter than in summer (due to the seasonal variation of radiation). temperature decrease from the equator toward either pole is considerably warmer in the northern than in the southern hemisphere. This is due to factorresponsible its forhigher mean temperature. The oceansare also surfaces. summer and cooled to much lower temperatures in winter than the water northern hemisphere. Landsurfaces are heated much more strongly in higher annual range is due to the much larger continental areas in the temperature and large annual range than the southern hemisphere. The intense during the winter season than during the summer season. of the general circulation; hence the general circulation is considerably more earth. during the wholeyear each for hemisphere separately andfor the whole latitude. This drop is dueto the sharp decrease of continental area beyond 30º S annual temperature range decreases to asecondary minimum at 50º south. radiation is larger at poles than at the equator. South of 30º S latitude the increases towards both poles since the yearlyvariation of incoming solar January. these latitudes the monthly maxima and minima are not reached in July andin the mean temperatures July of andJanuary because of the reason that at equator and at 10º N latitude the range is not equal to the difference between temperature of the warmest and of the coldest month. It is notices that at the Lecture Notes on Climatology By A.D.Tathe earth Whole hemisphere hemisphere Part of he he of Part Southern Northern globe

During January the northern hemisphere has its winter.The The greater land covers in the northern hemisphere is not the only It is seen that northern hemisphere has higher annual mean The meridional temperature gradient acts as a regulator of the intensity Table 2. Table Table 2 shows the mean temperature during January andjuly and The annual temperature range is very small in tropical latitudes and The annual range of temperature is the difference between the mean

: Year 57.7 56.0 59.3

Mean temperatures (ºF) Page January 54.6 62.7 46.5

July 60.8 49.5 72.3

Annual Ra 13.2 25.8 6.2

nge 30

of of

Lecture Notes By A D Tathe - ver May 2012 hemisphere owing to the smaller continental areas. again have a much more regular shape than the found. In the southern hemisphere, which now has itswinter, the isotherms and southwestern Asia, regions surrounded by closed 90º F isotherms is warmer than the adjoining oceans. Over north Africa, the Arabian peninsula earth’s surface is more uniform. parallels of latitude more closely than in the northern hemisphere since the continents are warmer than the oceans. drift and the prevailingwesterly winds. Atlantic is seen. This is due to the combination of the effects of north Atlantic Siberia. that the continents are colder than the oceans. The coldest region is found in isotherms are deflected toward lower latitudes over the continents, indicating are not parallel to the latitude circles. In the northern hemisphere, the than during the summer. warmer than the east coasts. Consequently, during winter the the west coasts of the temperate zones are months of January and July. seen in Fig. distribution temperature and onthe sea of land Effect

Lecture Notes on Climatology By A.D.Tathe During July (Fig. 20 ), the July continentsDuring of the northern hemisphere are On the whole the isotherms in the southern hemisphere follows the In the southern hemisphere, January isthe summer month when the During January asweepof isotherms over eastern part of the north The meridional temperature gradient is much greater during winter As seen 19 in Fig. The effect of land and water onthe temperature distribution can be b) a)

The prevailingwinds

equ between the Antarctic Ocean and the southern oceans in more from the Arctic ice by land barriers, there being nosuch barrier the partial protection of its oceans from the cold polar waters and which cross the equator and hemisphere into the northern hemisphere by the southeast trades, the transport of warm equatorial waters from the southern 19 atorial latitudes. and Fig. 20, which show the sea-

, over large part of the globe the January isotherms

everywhere in temperate latitudes are westerly.

Page

isotherms over the northern

level isotherm during the

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Lecture Notes By A D Tathe - ver May 2012 Lecture Notes on Climatology By A.D.Tathe Page * *

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Lecture Notes By A D Tathe - ver May 2012 convergence zone (ITCZ). regions of doldrums; portions of it could be described as intertropical the summer hemisphere. The equatorial trough would besaid to contain oceans andin southern Asia andthe Indian Ocean. It moves into or toward and Pacific, but it varies greatlywith season in the western portions of those the equatorial trough is fairly constant in the eastern portions of the Atlantic cause stability major in variations variations slight in weather. The position of most ideally barotropic region of the atmosphere. Yet humidity is so high that Hemispheres. This entire region is very oneof homogeneous air, probably the the subtropical high pressure belts of the Northern and Southern Equatorial Trough is the quasi winds near meet the equator, surface convergence anduplift take place. Trade winds approaching the equator from north andsouth. As the trade circulation pattern called the Hadley Cell. The rising air isreplaced by the centered onthe equator. This rising aircomprises one segment of a warmed at the surface and rises. This creates a band of low air pressure, influence of land masses, among other factors. are not perfectly symmetrical above and below the equator, because of the equator, but migrates north and south with the seasons. These movements answer to this puzzle lies in the fact that the ITCZ is not stationary onthe cyclones, when the Coriolis force is at its weakest near the equator. The intensify to hurricanes. It may seem puzzling that the ITCZ can produce activity. Under certain circumstances, tropical depressions on the ITCZ the doldrums, creates azone of Cumulus clouds and attendant shower Lecture Notes on Climatology By A.D.Tathe Equatorial Trough and Inter Tropical Convergence Zone (ITCZ) Zone Convergence Tropical and Trough Inter Equatorial On or near the equator, where average solar radiation is greatest, air is The convergence of the Southeast andNortheast Trade Winds, within

- Page continuous belt of low pressure lying betw

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Lecture Notes By A D Tathe - ver May 2012

Lecture Notes on Climatology By A.D.Tathe • • • • • • • • • • • climatic groups may bedescribed as tropical rainy, intended to correspond with five principal vegetation groups. These five recognizes Köppen implied bythe outputnumerical of a climate model. Alternatively, it also may beused to develop a future climatology that is The classification may beapplied to present ingenious symbolic nomenclature in designating the climatic types. A unique anddistinctive feature of the system is the employment of an of Geography. classification system is the most widely used for teaching andstudying Among the various types of classification of climate, Köppen's in mind. limits vegetation of climate, climate zone boundaries having beenselected with It Wladimir Köppen of the University Graz of in Austria. Köppen's scheme to classify world climates was devised in 1918 by classifying the world’s climates. The Köppen Climate Classification System is the most widely for used average precipitation and temperature: The classification is based on the 26 values of monthly andannual is easy to use and data requirements are minimal. Th precipitation. differences in the seasonal distribution of temperature and Each of these climates is further divided into sub- combination of letters, and each of which has a precise meaning. Each type of climate is described by a formula consisting of a temperate rainy, cold snow is based on the concept that native vegetation is the best expressi is is the is is most widely used systems for classifying climate because it

five principal groups of world climates that are Page Climatic Zones Climatic

- forest, and polar.

- day climatic conditions.

divisions based upo

dry, warm warm dry,

of of on on 45 n

Lecture Notes By A D Tathe - ver May 2012 GroupTypes Climate and Köppen’s

Lecture Notes on Climatology By A.D.Tathe • E : : E : D : C : B : A designated by capital letters as : K The ö (annual mean) Precipitation (mm) (annual mean) (ºC) Temperature ppenclassification includes five major categories which are

Page : : : : Polar Climates Polar Cold snow Warm temperate rainy Climates Climates Dry Tropical rainy Climates

Jan to Dec (12 monthlyvalues), r Jan to Dec (12 monthlyvalues), t - forest Climates

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Lecture Notes By A D Tathe - ver May 2012 Definition and description of climate types of description climate and Definition : A Af Within the A group of climates three main types are recognised. nee do not thrive with monthly temperatures lower than 18 ºC. The megatherms : : Brazil,Sudan,South Africa, northern Australia,India, Burmaand Indo- is high. This type of climate is found in some parts of Colombia, Venezuela, reached by migrating equatorial rain belt only during the season when the sun a distinct dry season in winter. These are developed over the regions that are : Aw monsoon wind blows against a mountain range during part of the year. support rainforest. These are found mainly in the coastal regionswhere a rainfall so great that ground remains sufficiently wet throughout the year to Am Cong whose climate of this type are the Amazon Valley in South America, the These are mainly located within the equatorial rain belt. Among the regions temperature and precipitation, both remaining high throughout the year. Lecture Notes on Climatology By A.D.Tathe : : : d continuously high temperatures andrelatively abundant precipitation. o Basin, the Guinea coast in Africa, and the East Indies. : This savanna type of climate differs from the tropical type in that it has This climate is characterized by the short dry season, but with total : Within this climate there is minimum of seasonal variation in higher. The average temperature of the coldest month is 18 ºC or than (10 when precipitation in driest month is less than 6cm and more Tropical rainy climate In tropical rainy climates certain plants, known as megatherms, when precipitation in driest month is 6cm or more Tropical rain forest climate when precipitation in driest month is less than (10 – Tropical savannaclimate climate monsoon Tropical

– – r/25)

Page

in Köppen’s scheme Köppen’s in

r/25) r/25)

china.

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Lecture Notes By A D Tathe - ver May 2012 the large continental masses of the northern hemisphere. oceans has already become rather dry. These are found mainly in the heart of interior of the continents at higher latitudes, where any air arriving the from to20º 25º north and south latitudes. The k mo deserts andsteppes. represents the transition from dessert climates to more humid climates. distinguished,thearid dessert type and semiarid steppe type; the steppe type resulting type of vegetation, the two main subdivisions of B climates are moderating maritime influences. According to the degree of dryness andthe the boundary of B climates. The B climates predominantly occur in the interior of a combination of temperature and precipitation data is used to determine the smallness of precipitation but also on the magnitude of potential evaporation, moisture in the ground for plants. Since the aridity the on dependonly s not precipitation. The amount of precipitation that falls is not sufficient in providing where t is the average annual temperature in ºC. : B tropical Formulaidentifying for and BSBW margins Lecture Notes on Climatology By A.D.Tathe in winter Precipitation maximum in summer Precipitation maximum distributed Precipitation evenly tion in the subtropical anticyclones. As such theses are found at around continents, often on the lee side of mountain ranges, which prevent any BS BW A further subdivision (by adding letter ‘h’ or ‘k’) separates the hot The The : - subtropical deserts and steppes from the cold temperate-

: :

: : k h In dry climates there is anexcess of evaporation over The annual precipitation () r in cm should beless than (2t14) + Dry climate type of B climates owe their existence mainly othe subsiding : : Semiarid or Steppe type dry climate Arid or Dessert typedry climate

r = 2t +28 =2t r =2t r +14 =2t r and humidclimates Boundary between when when Page

t < 18 ºC ºC 18 < t ºC >=18 t

type of B climates are typical of the

BS BS

r = ½ ( 2t ) 2t =½( r r = ½ ( 2t + 28 ) +28 2t =½( r ) +14 2t =½( r and BS Boundarybetween BW

boreal 39 of of 45

Lecture Notes By A D Tathe - ver May 2012 : C C frequent in winter. maritime air is more frequent in summer and dry continental air is more summers reflect the shift of the zone of doldrums. At higher latitudes the moist than of the latitude. In tropical highland regions, the dry winters and warm and the coldest month temperature below 18ºC is aneffect of altitude rather subtropical Africa. Many these of regions are considerably above sea level; Brazil, Mexico, east coast of Australia and on the plateaus of tropical and C to the temperature and the length of the summer season. divided according to the seasonal variation of the precipitation and according whereas over southern side they are veryrare. The climates of C type are boundaries of the regions of C climate, the snow and frost are quite common receive more precipitation than that withB climates. Over the northern 18ºC and nomonth has amean temperature below – a cool season during which at least 1month has amean temperature below C systems are more frequent so that considerable precipitation occurs. subtropical anticyclone and the frontal activity isweak. But in winter frontal of the middle latitudes. In summer these regions are in the zone of the Lecture Notes on Climatology By A.D.Tathe f s w : : : The Cclim The : The summer dry type C climate occurs on the : C : w

climates are located in northern India, southern china, southern but more than or equal to – The average temperature of the coldest month is less than 18ºC times the precipitation in the driest summer month when precipitation in wettest month of winter is at least three times the precipitation in driest winter month when Warm temperateWarm rainy climate Warm temperate rainy climate without dryseason Warm temperate rainy climate with dry summer Warm ates are distinguished from the A types by the existence of precipitation in wettest month in summer is at least ten temperate rainy climate with dry winter Page 3ºC.

subtropical boundaries

3ºC. These regions

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Lecture Notes By A D Tathe - ver May 2012 Islands. southern parts of Iceland, parts of Alaskan coast and over the Aleutian the west coast owing to the moderating effect of water. The climate of type C summers are short due to high latitude, but hewinters are relatively mild regions under maritime influence, however,the type C monthly variation of the precipitation. Outside the tropics C the locations the type C southwest coast of Australia, Tasmania and New Zealand. In continental Germany, northerly islands of Japan, northwestern parts of North America, maritimeinfluence and C The typical oceanic climate covering almost 30 per cent of the whole ocean area. cooler than those of the type C Japan, on the east coast of Australia. The summers of C States, onthe east coast of South America, over the southern islands of subdivided into hot summer ( precipitation is mainly caused by frontal lifting. tropics if their elevation is high enough. C The of southern California andfor small area along the west coast of Australia. c b a as follows. with hot andwarm summers. The stations with C occu dominated by subtropical high- temperature is moderated by the sea. Since the C Lecture Notes on Climatology By A.D.Tathe : : : when warmest month temperature is 22 ºC or above

ºC when warmest month temperature is less than 22 ºC of at least four warmest months remains greater than 10 ºC f when the temperature of less than four months remainsthan10 more

In some tropical stations belongs to this group, which show very small : The type C The type C A asfar temperature is concerned the C sb

climates are found mainly in the regions of westerlies where the

type occurs in more oceanic locations where the summer required s for when difference between driest and wettest months is less then of summer is more than 3cm. Depending on the temperature, the C climates are further

of Norway, over the Faeroes andthe Orkney Islands, over the fa sa

(hot summers) is found in the eastern and central Unite fa is characteristic for the Mediterranean coast, the interior

or C or represents the climate of British Isles, France and

and and fb a

), warm summer (b summer warm ), pressure belt in summer, the type C Page fa changesinto D w . This type is mainly found in locations under and the precipitation in then driest month

fa w

) andcool short summer ( wb climate resembles C or D or s

climate are found in the type is found in regions fb fc fb fb

towar

is found. Here the type of climate are

and temper d the pole. In fc f

sc is found on type is the the is type does not s 41 types types ature ature of of c) 45 d

Lecture Notes By A D Tathe - ver May 2012 locations with cold winters. A D with nodry season. The rule of summer dry climate does not extend to these great. As such D wettest summer month andduring the driest winter month is not sufficiently w subdivisions of D climate is recognised; D continental areas from 40º to 50º latitude to the polar circle. Two principal southern hemisphere andin the northern hemisphere they coverlargely the except in narrow coastal belt, where the winter dryness is less pronounced. Russia. The region north of Vladivostok has the winter dry climate D D the D and in northern China and Manchuria (Dw regions in the interior the isotherm of 10 ºC of the warmest month. D The climates are typical for type by the isotherm of – relatively long in the southern regions. The D types are separated from the C summers, which is long and short along the poleward boundaries and more occasional snow cover. These are also characterised by the hot type occurs only overeastern Asia. cold winters. summers, respectively, there occurs in Siberia a fourth subdivision dwith very climate. In addition to the the subdivisions a, b, c withwarm hot, andcool : D and D Lecture Notes on Climatology By A.D.Tathe ith D types of climate, the difference between the precipitation during the fb

climate occurs mainly in Poland, the Baltic States, and southwestern fa fa wd The climate type D The D The The D climates have more severe winter than the C climates, with : In the northernmost part of Asia the winter isso cold that the types D In North America the D The D regionswith hot summers are found only north in America (D : d Other small letters used with D climate are

climate or, in the western part of the country. In Europe and Asia the

are represented.

wc above 10 ºC. and the average temperature of warmest month temperature is The average temperature of the coldest month is less than – Cold snowCold

f and D

type covers much larger area than D is– when the average temperature of the coldest

fc of theof large continental masses. They are absent in 38 ºC or less. 3 ºC of the coldest month and from the E climates by -

forest climate forest represent the transition to the polar climates. D w

is observed only in eastern Asia. In many regions fb Page s

climate is found to the north of the region with climate exists only in the interior of Oregon.

a w ). ). , with d , with

ry season in winter andD same as that used with C w

type.

month 42 3 ºC ºC 3 of of wb

wc fa

fd 45 f ) , ,

Lecture Notes By A D Tathe - ver May 2012 in mountainin areas. transition from one climatic type to another occur very rapidlywith the ascent changes much more rapidlyvertical in the than in the horizontal direction, latitude provided that the altitude is high enough. Since the temperature EH Pole. Greenland and over the perpetually frozen ocean in the vicinity the of North found over the permanently continental ice plateau of Antarct even of the warmest month remains below freezing, are scanty. This type is small northern belt of Antarctic continent. found in the north coasts of Canada, Alaska, Iceland and Eurasia climates, even some dwarf forms of trees are found. The ET climates are lichens and grasses, some flowering plants andnear the border of the tree EF ET clima polar of northerly and southerlyzones of the earth. The following climatic subdivisions climate. Apart from the mountain regions the polar climates occupy the most Hence the warm Rather, it is the intensity andduration of a season of warmth, which critical. is and the ground frozen it makes little difference to plant life how cold it gets. below 10ºC Lecture Notes on Climatology By A.D.Tathe : : :

Polar climates owingto the elevation of the land may occur at any The data from the frost climates (EF), where the mean temperature The tundra climates (ET), the vegetation consists largely of mosses, : : In the higher latitudes, once the temperatures are well below freezing : : E

te are recognised. below 0ºC when the average temperature of the warmest month remains below 10ºC but above 0ºC. when the average temperature of the warmest month remains Polar climate due to due climate altitude high Polar PolarFrost climate climate Tundra Polar The average temperature of the warm - month isotherm is employed as the poleward boundary of E Polar Climate

Page

* *

s mnh remains month est and over ica and ica 43 of of 45

Lecture Notes By A D Tathe - ver May 2012

References

1. An introduction to climate, Glenn T. Threwartha and Lyle H. Horn, 5th Ed., McGraw-Hill, 1980. 2. General climatology, Howard J. Critchfield, 4th Ed., Prentice-Hall of India, 1983. 3. Climatology, Bernhard Haurwitz and James M. Austin, McGraw-Hill, 1944. 4. Climate and circulation of the tropics, Stefan Hastenrath, D.Reidel publishing Company, 1985. 5. Climate and Weather in the tropics, Herbert Riehl, Academic Press, 1979. 6. Physics of Climate, José P. Peixoto and Abraham H.Oort, American Institute of Physics, 1992. 7. The Atmosphere, Lutgens and Tarbuck.

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