UPSC Geography Atmosphere / वायुमंडल NCERT Extracts - Atmosphere

Composition and Structure of Atmosphere

• The air is an integral part of the earth's mass and 99 per cent of the total mass of the atmosphere is confined to the height of 32 km from the earth's surface.
• The atmosphere is composed of gases, water vapour and dust particles.
• The proportion of gases changes in the higher layers of the atmosphere in such a way that oxygen will be almost in negligible quantity at the height of 120 km.
• Similarly, carbon dioxide and water vapour are found only up to 90 km from the surface of the earth.
• Carbon dioxide is meteorologically a very important gas as it is transparent to the incoming solar radiation but opaque to the outgoing terrestrial radiation.
• It absorbs a part of terrestrial radiation and reflects back some part of it towards the earth's surface.
• It is largely responsible for the greenhouse effect.
• The volume of other gases is constant but the volume of carbon dioxide has been rising in the past few decades mainly because of the burning of fossil fuels.
• This has also increased the temperature of the air.
• Ozone is another important component of the atmosphere found between 10 and 50 km above the earth's surface and acts as a filter and absorbs the ultra-violet rays radiating from the sun and prevents them from reaching the surface of the earth.

• Water vapour is also a variable gas in the atmosphere, which decreases with altitude.
• In the warm and wet tropics, it may account for four per cent of the air by volume, while in the dry and cold areas of desert and Polar Regions, it may be less than one per cent of the air.
• Water vapour also decreases from the equator towards the poles.
• It also absorbs parts of the insolation from the sun and preserves the earth's radiated heat.
• It thus, acts like a blanket allowing the earth neither to become too cold nor too hot.
• Water vapour also contributes to the stability and instability in the air.
• Atmosphere has a sufficient capacity to keep small solid particles, which may originate from different sources and include sea salts, fine soil, smoke-soot, ash, pollen, dust and disintegrated particles of meteors.
• Dust particles are generally concentrated in the lower layers of the atmosphere; yet, convectional air currents may transport them to great heights.
• The higher concentration of dust particles is found in subtropical and temperate regions due to dry winds in comparison to equatorial and Polar Regions.
• Dust and salt particles act as hygroscopic nuclei around which water vapour condenses to produce clouds.

Layers

Layers of the Atmosphere

• The column of atmosphere is divided into five different layers depending upon the temperature condition.
• They are: troposphere, stratosphere, mesosphere, thermosphere and exosphere.

The Troposphere

• 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 165 m of height.
• This is the most important layer for all biological activity.
• The zone separating the tropsophere from stratosphere is known as the tropopause.
• The air temperature at the tropopause is about minus 80°C over the equator and about minus 45°C over the poles.
• The temperature here is nearly constant, and hence, it is called the tropopause.

The Stratosphere

• The stratosphere is found above the tropopause and extends up to a height of 50 km.
• One important feature of the stratosphere is that it contains the ozone layer.
• This layer absorbs ultra-violet radiation and shields life on the earth from intense, harmful form of energy.

The Mesosphere

• The mesosphere lies above the stratosphere, which extends up to a height of 80 km.
• In this layer, once again, temperature starts decreasing with the increase in altitude and reaches up to minus 100°C at the height of 80 km.
• The upper limit of mesosphere is known as the mesopause.

The Ionosphere

• The ionosphere is located between 80 and 400 km above the mesopause.
• It contains electrically charged particles known as ions, and hence, it is known as ionosphere.
• Radio waves transmitted from the earth are reflected back to the earth by this layer.
• Temperature here starts increasing with height.

The Exosphere

• The uppermost layer of the atmosphere above the thermosphere is known as the exosphere.
• This is the highest layer but very little is known about it.
• Whatever contents are there, these are extremely rarefied in this layer, and it gradually merges, with the outer space.
• Although all layers of the atmosphere must be exercising influence on us, geographers are concerned with the first two layers of the atmosphere.
• The main elements of atmosphere which are subject to change and which influence human life on earth are temperature, pressure, winds, humidity, clouds and precipitation.

Solar Radiation

• The earth's surface receives most of its energy in short wavelengths.
• The energy received by the earth is known as incoming solar radiation which in short is termed as insolation.
• As the earth is a geoid resembling a sphere, the sun's rays fall obliquely at the top of the atmosphere and the earth intercepts a very small portion of the sun's energy.
• On an average the earth receives 1.94 calories per sq.cm per minute at the top of its atmosphere.
• The solar output received at the top of the atmosphere varies slightly in a year due to the variations in the distance between the earth and the sun.
• During its revolution around the sun, the earth is farthest from the sun (152 million km) on 4 July.
• This position of the earth is called aphelion. On 3 January, the earth is the nearest to the sun (147 million km).
• This position is called perihelion.
• Therefore, the annual insolation received by the earth on 3 January is slightly more than the amount received on 4 July.
• However, the effect of this variation in the solar output is masked by other factors like the distribution of land and sea and the atmospheric circulation.
• Hence, this variation in the solar output does not have great effect on daily weather changes on the surface of the earth.

Variability of Insolation at the Surface of the Earth

• The amount and the intensity of insolation vary during a day, in a season and in a year. The factors that cause these variations in insolation are :
• the rotation of earth on its axis;
• the angle of inclination of the sun's rays;
• the length of the day;
• the transparency of the atmosphere;
• the configuration of land in terms of its aspect. The last two however, have less influence.
• The fact that the earth's axis makes an angle of with the plane of its orbit round the sun has a greater influence on the amount of insolation received at different latitudes.
• The second factor that determines the amount of insolation received is the angle of inclination of the rays. This depends on the latitude of a place.
• The higher the latitude the less is the angle they make with the surface of the earth resulting in slant sun rays.
• The area covered by vertical rays is always less than the slant rays.
• If more area is covered, the energy gets distributed and the net energy received per unit area decreases.
• Moreover, the slant rays are required to pass through greater depth of the atmosphere resulting in more absorption, scattering and diffusion.
• The atmosphere is largely transparent to short wave solar radiation. The incoming solar radiation passes through the atmosphere before striking the earth's surface.
• Within the troposphere water vapour, ozone and other gases absorb much of the near infrared radiation.                                
• Very small-suspended particles in the troposphere scatter visible spectrum both to the space and towards the earth surface.
• This process adds colour to the sky.
• The red colour of the rising and the setting sun and the blue colour of the sky are the result of scattering of light within the atmosphere.
• The insolation received at the surface varies from about in the tropics to about 70 Watt/m2 in the poles.                               
• Maximum insolation is received over the subtropical deserts, where the cloudiness is the least. Equator receives comparatively less insolation than the tropics.
• Generally, at the same latitude the insolation is more over the continent than over the, oceans.                               
• In winter, the middle and higher latitudes receive less radiation than in summer.

Heating and Cooling of Atmosphere

• There are different ways of heating and cooling of the atmosphere.
• The earth after being heated by insolation transmits the heat to the atmospheric layers- near to the earth in long wave form.
• The air in contact with the land gets heated slowly and the upper layers in contact with the lower layers also get heated.                                
• This process is called conduction.
• Conduction takes place when two bodies of unequal temperature are in contact with one, another, there is a flow of energy from the warmer to cooler body.
• The transfer of heat continues until both the bodies attain the same temperature or the; contact is broken.                               
• Conduction is important in heating the lower layers of the atmosphere.
• The air in contact with the earth rises vertically on heating in the form of currents and further transmits the heat of the atmosphere.
• This process of vertical heating of the atmosphere is known as convection.
• The convective transfer of energy is confined only to the troposphere.
• The transfer of heat through horizontal movement of air is called advection.
• Horizontal movement of the air is relatively more important than the vertical movement.
• In middle latitudes, most of dirunal (day and night) variation in daily weather are caused by advection alone.
• In tropical regions particularly in northern India during summer season local winds called 'loo' is the outcome of advection process.                                
• The insolation received by the earth is in short waves forms and heats up its surface.
• The earth after being heated itself becomes a radiating body and it radiates energy to the atmosphere in long wave form.
• This energy heats up the atmosphere from below.
• This process is known as terrestrial radiation.                               
• The long wave radiation is absorbed by the atmospheric gases particularly by carbon dioxide and the other greenhouse gases.
• Thus, the atmosphere is indirectly heated by the earth's radiation.
• The atmosphere in turn radiates and transmits heat to the space.
• Finally the amount of heat received from the sun is returned to space, thereby maintaining constant temperature at the earth's surface and in the atmosphere.

Heat Budget of the Planet Earth

• The earth as a whole does not accumulate or loose heat. It maintains its temperature.
• This can happen only if the amount of heat received in the form of insolation equals the amount lost by the earth through terrestrial radiation.
• Consider that the insolation received at the top of the atmosphere is 100 per cent.
• While passing through the atmosphere some amount of energy is reflected, scattered and absorbed. Only the remaining part reaches the earth surface.
• Roughly 35 units are reflected back to space even before reaching the earth's surface.
• Of these, 27 units are reflected back from the top of the clouds and 2 units from the snow and ice-covered areas of the earth.
• The reflected amount of radiation is called the albedo of the earth.
• The remaining 65 units are absorbed, 14 units within the atmosphere and 51 units by the earth's surface.
• The earth radiates back 51 units in the form of terrestrial radiation.
• Of these, 17 units are radiated to space directly and the remaining 34 units are absorbed by the atmosphere (6 units absorbed directly by the atmosphere, 9 units through convection and turbulence and 19 units through latent heat of condensation).
• 48 units absorbed by the atmosphere (14 units from insolation + 34 units from terrestrial radiation) are also radiated back into space.
• Thus, the total radiation returning from the earth and the atmosphere respectively is 17+48=65 units which balance the total of 65 units received from the sun.
• This is termed the heat budget or heat balance of the earth.
• This explains, why the earth neither warms up nor cools down despite the huge transfer of heat that takes place.
• There are variations in the amount of radiation received at the earth's surface.
• Some part of the earth has surplus radiation balance while the other part has deficit.
• There is a surplus of net radiation balance between 40 degrees north and south and the regions near the poles have a deficit.
• The surplus heat energy from the tropics is redistributed pole wards and as a result the tropics do not get progressively heated up due to the accumulation of excess heat or the high latitudes get permanently frozen due to excess deficit.

Factors Controlling Temprature Distribution

• The temperature of air at any place is influenced by the latitude of the place; the altitude of the place; distance from the sea, the airmass circulation; the presence of warm and cold ocean currents; local aspects.

The latitude

• The temperature of a place depends on the insolation received.
• It has been explained earlier that the insolation varies according to the latitude hence the temperature also varies accordingly.

The altitude

• The atmosphere is indirectly heated by terrestrial radiation from below.
• Therefore, the places near the sea-level record higher temperature than the places situated at higher elevations.
• In other words, the temperature generally decreases with increasing height.
• The rate of decrease of temperature with height is termed as the normal lapse rate. It is 6.5°C per 1,000 m.                                                       

Distance from the sea

• Another factor that influences the temperature is the location of a place with respect to the sea.                               
• Compared to land, the sea gets heated slowly and loses heat slowly.
• Land heats up and cools down quickly.
• Therefore, the variation in temperature over the sea is less compared to land.
• The places situated near the sea come under the moderating influence of the sea and land breezes which moderate the temperature.

Air-mass and Ocean currents

• Like the land and sea breezes, the passage of air masses also affects the temperature.
• The places, which come under the influence of warm air-masses experience higher temperature and the places that come under the influence of cold airmasses experience low temperature.
• Similarly, the places located on the coast where the warm ocean currents flow record higher temperature than the places located on the coast where the cold currents flow.

Distribution of Temperature

• The temperature distribution is generally shown on the map with the help of isotherms.
• The Isotherms are lines joining places having equal temperature.
• In general the effect of the latitude on temperature is well pronounced on the map, as the isotherms are generally parallel to the latitude.

Inversion of Temperature

• Normally, temperature decreases with increase in elevation. It is called normal lapse rate.
• At times, the situations is reversed and the normal lapse rate is inverted. It is called Inversion of temperature.
• Inversion is usually of short duration but quite common nonetheless.
• A long winter night with clear skies and still air is ideal situation for inversion.
• The heat of the day is radiated off during the night, and by early morning hours, the earth' is cooler than the air above.
• Over polar areas, temperature inversion is normal throughout the year.
• Surface inversion promotes stability in the lower layers of the atmosphere.
• Smoke and dust particles get collected beneath the inversion layer and spread horizontally to fill the lower strata of the atmosphere.
• Dense fogs in mornings are common occurrences especially during winter season.
• This inversion commonly lasts for few hours until the sun comes up and beings to warm the earth.
• The inversion takes place in hills and mountains due to air drainage.
• Cold air at the hills and mountains, produced during night, flows under the influence of gravity.
• Being heavy and dense, the cold air acts almost like water and moves down the slope to pile up deeply in pockets and valley bottoms with warm air above. This is called air drainage. It protects plants from frost damages.

Human Development

• Both growth and development refer to changes over a period of time.
• The difference is that growth is quantitative and value neutral.
• It may have a positive or a negative sign.
• This means that the change may be either positive (showing an increase) or negative (indicating a decrease).
• Development means a qualitative change which is always value positive.
• This means that development cannot take place unless there is an increment or addition to the existing conditions.
• Development occurs when positive growth takes place. Yet, positive growth does not always lead to development. Development occurs when there is a positive change in quality.
• The concept of human development was introduced by Dr. Mahbub-ul-Haq.
• Dr Haq has described human development as development that enlarges people's choices and improves their lives. People are central to all development under this concept.
• These choices are not fixed but keep on changing. The basic goal of development is to create conditions where people can live meaningful lives.
• Nobel Laureate Prof. Amartya Sen saw an increase in freedom (or decrease in unfreedom) as the main objective of development.
• The four pillars of human development are Equity, Sustainability, Productivity and Empowerment.
• The human development index (HDI) ranks the countries based on their performance in the key areas of health, education and access to resources.
• These rankings are based on a score between 0 to1 that a country earns from its record in the key areas of human development.
• The indicator chosen to assess health is the life expectancy at birth.
• A higher life expectancy means that people have a greater chance of living longer and healthier lives.
• The adult literacy rate and the gross enrolment ratio represent access to knowledge.
• The number of adults who are able to read and write and the number of children enrolled in schools show how easy or difficult it is to access knowledge in a particular country.
• Access to resources is measured in terms of purchasing power (in U.S. dollars).
• Each of these dimensions is given a weightage of 1/3. The human development index is a sum total of me weights assigned to all these dimensions.
• The closer a score is to one, the greater is the level of human development.
• Therefore, a score of 0.983 would be considered very high while 0.268 would mean a very low level of human development.
• The human development index measures attainments in human development.
• It reflects what has been achieved in the; key areas of human development.
• Yet it is not the most reliable measure. This is because it does not say anything about the distribution.
• The human poverty index is related to the human development index.
• This index measures the shortfall in human development.
• Since 1990, the United Nations Development Programme (UNDP) has been publishing the Human Development Report every year.
• This report provides a rank-wise list of all member countries according to the level of human development.
• The Human Development index and the Human Poverty index are two important indices to measure human development used by the UNDP.
• It is a non-income measure.
• The probability of not surviving till the age of 40, the adult illiteracy rate, the number of people who do not have access to clean water, and the number of small children who are underweight are all taken into account to show the shortfall in human development in any region.
• Often the human poverty index is more revealing than the human development index.
• Bhutan is the only country in the world to officially proclaim the Gross National Happiness (GNH) as the measure of the country's progress.
• Material progress and technological developments are approached more cautiously taking into consideration the possible harm they might bring to the environment or the other aspects of cultural and spiritual life ^of the Bhutanese.
• This simply means material progress cannot come at the cost of happiness.
• GNH encourages us to think of the spiritual, non-material and qualitative aspects of development.

Some Important Facts

• Plank's law states that hotter a body, the more energy it will radiate and shorter the wavelength of that radiation.
• Specific heat is the energy needed to raise the temperature of one gram of substance by one Celsius.
• All living beings on this earth depend on the atmosphere for their survival. It provides us the air we breathe and protects us from the harmful effects of the sun's rays.
• Without this blanket of protection, we would be baked alive by the heat of the sun during day and get frozen during night. So it is this mass of air that has made the temperature on the earth liveable.
• Carbon dioxide released in the atmosphere creates a green house effect by trapping the heat radiated from the earth. It is therefore called a greenhouse gas and without it the earth would have been too cold to live in.
• However, when its level in the atmosphere increases due to factory smoke or car fumes, the heat retained increases the temperature of the earth. This is called global warming.
• This rise in temperature causes the snow in coldest parts of the world to melt. As a result the sea level rises, causing floods in the coastal areas.
• There may be drastic changes in the climate of a place leading to extinction of some plants and animals in the long run.
• An important factor that influences the distribution of temperature is insolation. Insolation is the incoming solar energy intercepted by the earth.
• The amount of insolation decreases from the equator towards the poles.
• Also, the crowded high rise buildings of the cities trap the warm air and thus raise the temperature of the cities.
• Air above us presses us with a great force on our bodies. However, we don't even feel it. This is because the air presses us from all directions and our body exerts a counter pressure.
• The standard unit of measuring temperature is degree Celsius. It was invented by Anders Celsius. On the Celsius scale the water freezes at 0°C and boils at 100°C.
• On the moon there is no air and hence no air pressure. Astronauts have to wear special protective space suits filled with air when they go to the moon.
• If they did not wear these space suits, the counter pressure exerted by the body of the astronauts would make the blood vessels burst. The astronauts would bleed.
• A wind is named after the direction from which it blows, e.g. the wind blowing from the west is called westerly.