Unit IV Climate PDF

d UNIT he IV is CLIMATE bl...

d UNIT he IV is CLIMATE bl pu This unit deals with Atmosphere — compositions and structure; elements of weather be T and climate re Insolation — angle of incidence and distribution; heat budget o R of the earth — heating and cooling of atmosphere (conduction, convection, terrestrial radiation, advection); temperature — factors tt E controlling temperature; distribution of temperature — horizontal and vertical; inversion of temperature C Pressure — pressure belts; winds-planetary seasonal and local, air masses and fronts; tropical and extra tropical cyclones no N Precipitation — evaporation; condensation — dew, frost, fog, mist and cloud; rainfall — types and world distributon World climates — classification (Koeppen), greenhouse effect, global warming and climatic changes ©  CHAPTER COMPOSITION AND STRUCTURE OF ATMOSPHERE d he C an a person live without air? We eat Table 8.1 : Permanent Gases of the Atmosphere food two - three times a day and drink Constituent Formula Percentage by Volume water more frequently but breathe is every few seconds. Air is essential to the Nitrogen N2 78.08 survival of all organisms. Some organisms like Oxygen O2 20.95 Argon Ar 0.93 humans may survive for some time without bl Carbon dioxide CO2 0.036 food and water but can’t survive even a few Neon Ne 0.002 minutes without breathing air. That shows the Helium He 0.0005 reason why we should understand the pu atmosphere in greater detail. Atmosphere is a mixture of different gases and it envelopes the Krypto Xenon Hydrogen Kr Xe H2 0.001 0.00009 0.00005 be T earth all round. It contains life-giving gases like oxygen for humans and animals and carbon Gases re dioxide for plants. The air is an integral part of o R Carbon dioxide is meteorologically a very the earth’s mass and 99 per cent of the total important gas as it is transparent to the mass of the atmosphere is confined to the incoming solar radiation but opaque to the height of 32 km from the earth’s surface. The tt E outgoing terrestrial radiation. It absorbs a part air is colourless and odourless and can be felt of terrestrial radiation and reflects back some only when it blows as wind. part of it towards the earth’s surface. It is C largely responsible for the green house effect. Can you imagine what will happen The volume of other gases is constant but the to us in the absence of ozone in the volume of carbon dioxide has been rising in no N atmosphere? the past few decades mainly because of the burning of fossil fuels. This has also increased the temperature of the air. Ozone is another COMPOSITION OF THE ATMOSPHERE important component of the atmosphere found © The atmosphere is composed of gases, water between 10 and 50 km above the earth’s vapour and dust particles. Table 8.1 shows surface and acts as a filter and absorbs the details of various gases in the air, particularly ultra-violet rays radiating from the sun and in the lower atmosphere. The proportion of prevents them from reaching the surface of the gases changes in the higher layers of the earth. atmosphere in such a way that oxygen will be almost in negligible quantity at the height of Water Vapour 120 km. Similarly, carbon dioxide and water Water vapour is also a variable gas in the vapour are found only up to 90 km from the atmosphere, which decreases with altitude. In surface of the earth. the warm and wet tropics, it may account for  COMPOSITION AND STRUCTURE OF ATMOSPHERE 77 four per cent of the air by volume, while in the The zone separating the tropsophere from dry and cold areas of desert and polar regions, stratosphere is known as the tropopause. The it may be less than one per cent of the air. Water air temperature at the tropopause is about vapour also decreases from the equator minus 800C over the equator and about minus towards the poles. It also absorbs parts of the 45oC over the poles. The temperature here is insolation from the sun and preserves the nearly constant, and hence, it is called the earth’s radiated heat. It thus, acts like a blanket tropopause. The stratosphere is found above allowing the earth neither to become too cold the tropopause and extends up to a height of nor too hot. Water vapour also contributes to 50 km. One important feature of the d the stability and instability in the air. stratosphere is that it contains the ozone layer. This layer absorbs ultra-violet radiation and he Dust Particles shields life on the earth from intense, harmful form of energy. Atmosphere has a sufficient capacity to keep The mesosphere lies above the stratosphere, small solid particles, which may originate from which extends up to a height of 80 km. In this different sources and include sea salts, fine soil, layer, once again, temperature starts is smoke-soot, ash, pollen, dust and disintegrated decreasing with the increase in altitude and particles of meteors. Dust particles are reaches up to minus 100°C at the height of 80 generally concentrated in the lower layers of km. The upper limit of mesosphere is known bl the atmosphere; yet, convectional air currents as the mesopause. The ionosphere is located may transport them to great heights. The between 80 and 400 km above the mesopause. higher concentration of dust particles is found pu It contains electrically charged particles known in subtropical and temperate regions due to as ions, and hence, it is known as ionosphere. dry winds in comparison to equatorial and Radio waves transmitted from the earth are polar regions. Dust and salt particles act as reflected back to the earth by this layer. be T hygroscopic nuclei around which water vapour Temperature here starts increasing with height. condenses to produce clouds. The uppermost layer of the atmosphere above re o R STRUCTURE OF THE ATMOSPHERE The atmosphere consists of different layers with tt E varying density and temperature. Density is highest near the surface of the earth and decreases with increasing altitude. The column C of atmosphere is divided into five different layers depending upon the temperature condition. They are: troposphere, stratosphere, no N mesosphere, thermosphere and exosphere. The troposphere is the lowermost layer of the atmosphere. Its average height is 13 km and extends roughly to a height of 8 km near © the poles and about 18 km at the equator. Thickness of the troposphere is greatest at the equator because heat is transported to great heights by strong convectional currents. This layer contains dust particles and water vapour. All changes in climate and weather take place in this layer. The temperature in this layer decreases at the rate of 1°C for every 165m of height. This is the most important layer for all biological activity. Figure 8.1 : Structure of atmosphere  78 FUNDAMENTALS OF PHYSICAL GEOGRAPHY the thermosphere is known as the exosphere. Elements of Weather and Climate This is the highest layer but very little is known about it. Whatever contents are there, these are The main elements of atmosphere which are extremely rarefied in this layer, and it gradually subject to change and which influence human merges with the outer space. Although all life on earth are temperature, pressure, winds, layers of the atmosphere must be exercising humidity, clouds and precipitation. These influence on us, geographers are concerned elements have been dealt in detail in Chapters with the first two layers of the atmosphere. 9, 10 and 11. d EXERCISES he 1. Multiple choice questions. (i) Which one of the following gases constitutes the major portion of the atmosphere? is (a) Oxygen (c) Argon (b) Nitrogen (d) Carbon dioxide bl (ii) Atmospheric layer important for human beings is: pu (a) Stratosphere (c) Troposphere (b) Mesosphere (d) Ionosphere (iii) Sea salt, pollen, ash, smoke soot, fine soil — these are associated with: be T (a) Gases (c) Water vapour re (b) Dust particles (d) Meteors o R (iv) Oxygen gas is in negligible quantity at the height of atmosphere: (a) 90 km (c) 100 km tt E (b) 120 km (d) 150 km (v) Which one of the following gases is transparent to incoming solar radiation C and opaque to outgoing terrestrial radiation? (a) Oxygen (c) Helium no N (b) Nitrogen (d) Carbon dioxide 2. Answer the following questions in about 30 words. (i) What do you understand by atmosphere? © (ii) What are the elements of weather and climate? (iii) Describe the composition of atmosphere. (iv) Why is troposphere the most important of all the layers of the atmosphere? 3. Answer the following questions in about 150 words. (i) Describe the composition of the atmosphere. (ii) Draw a suitable diagram for the structure of the atmosphere and label it and describe it.