geography grade 10 essay heating of the atmosphere

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Gr. 10 GEOGRAPHY: The Heating of the Atmosphere T1 W3

Greenhouse effect, Global Warming and Impact of climate change on Africa discussed

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Essay on the atmosphere: top 6 essays on atmosphere | climatology |geography.

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Here is a compilation of essays on ‘Atmosphere’ for class 6, 7, 8, 9 and 10. Find paragraphs, long and short essays on ‘Atmosphere’ especially written for school students.

Essay on Atmosphere

Essay Contents:

• Essay on the Chemistry of Earth’s Atmosphere

Essay # 1. Introduction to Atmosphere:

The atmosphere is a turbulent gaseous blanket that surrounds the earth. The mass of this surrounding atmosphere is less than a millionth part of that of the whole earth, yet its activities and influences are far-reaching. On the average each person breaths 15 kg of air per day. The presence of the atmosphere is necessary to sustain all the types of life of the earth.

It is the atmosphere that plays its role tending to equalize the temperature of the earth’s surface. By its agency weather is produced which causes rock weathering. Weather is of vital importance in the execution of engineering projects. Many construction works have been delayed due to adverse weather conditions.

Many construction activities can be carried out only in certain seasons or in favourable weather. The atmosphere plays its role as a medium for transfer of water, since water continuously is evaporated into the atmosphere and later precipitated on to the earth in the form of rain or snow which is gathered into the streams and glaciers, and assists in wearing the rocks and transport the sediments to the sea. Engineering attention is well focused on winds on instances of damage or failure of bridges and buildings.

The atmosphere is an important geological agent. The atmosphere chemically reacts with the rocks oxidizing them to form new minerals. It generally breaks the rocks into smaller fragments leading to disintegration.

The atmosphere acts as a thermal blanket which not only distributes the heat received from the sun but also tends to prevent the escape of heat from the earth. Sunlight is subjected to diffusion by the gaseous molecules and the suspended dust particles.

Moreover the gaseous envelope surrounding the earth protects the earth from excessive ultra violet radiation and from violent bombardment by meteorites. It may be realized that millions of meteorites fall into the atmosphere of the earth every day but they all get disintegrated by severe heat caused by friction.

The disintegrated fragments settle on the earth’s surface as fine cosmic dust. In exceptional instances some large meteorites may pass through the atmosphere and drop on the earth and may penetrate into the ground for a few metres.

By the daily weather at a place we mean the temporary state of prevailing atmospheric conditions like temperature, air pressure, wind humidity, cloudiness and precipitation. Climate is the combined effect of weather over a long period of time. Soils and vegetation in a region are to a great extent determined by the climate of the region. The geological processes especially the weathering of rocks and minerals and land erosion are all influenced by climate.

Essay # 2. Meaning of Atmosphere:

The several hundred kilometres thick air which envelopes the earth all around is called atmosphere. It is composed of various gases. Most of the earth’s life exists at the lower part of atmosphere, the zone near the solid earth.

It acts like a greenhouse and keeps the average temperature of the earth around 35°C and also protects the earth from the harmful radiation of the sun. The atmosphere is a storehouse for water vapour and serves as the medium of faster air transport.

Essay # 3. Composition of the Atmosphere :

The atmosphere is a thick gaseous envelope which surrounds the earth from all sides and is attached to the earth’s surface by gravitational force. The at­mosphere is a significant component of the biospheric ecosystem because the life on the earth’s surface is because of this atmosphere otherwise the earth would have become barren like moon.

Besides providing all necessary gases for the sustenance of all life forms in the biosphere, it also filters the incoming solar radia­tion and thus prevents the ultraviolet solar radiation waves to reach the earth’s surface and thus protects the earth from becoming too hot.

The height of the atmos­phere is estimated between 16 to 29 thousand kilome­tres from the sea level. It is estimated that 97 per cent of the effective atmosphere is upto the height of 29 km. In fact, the air is mechanical mixture of several gases.

The atmosphere is composed of:

(ii) Vapour, and

(iii) Particulates.

Nitrogen (78%) and oxygen (21%) are major gases which constitute 99% of the total gaseous composition of the atmosphere. The remaining one per cent is represented by argan (0.93%), carbon dioxide (0.03%), neon (0.0018%), helium (0.0005%), ozone (0.00006%), hydrogen (0.00005%), krypton (trace), xenon (trace), methane (trace) etc.

Oxygen is the most important gas from the stand point of living organisms because they inhale it for their survival. Oxygen is also essential for combustion of burning matter. Nitrogen acts as dilutent and is generally chemically inactive.

Carbon dioxide is used by green plants for photosyn­thesis. It absorbs most of radiant energy from the earth and reradiates it back to the earth. Thus, carbon diox­ide, a greenhouse gas, increases the temperature of the lower atmosphere and the earth’s surface.

The concen­tration of carbon dioxide in the atmosphere is gradu­ally increasing due to burning of fossil fuels (coal, petroleum and natural gas) and deforestation. Ozone gas absorbs most of the ultra-violet rays radiated from the sun and thus prevents the earth from becoming too hot.

ii. Water Vapour:

The vapour content in the at­mosphere ranges between zero and 5 per cent by volume. Climatically, water vapour is very important constituent of the atmosphere. The atmospheric va­pour is received through the evaporation of moisture and water from the water bodies (like seas and oceans, lakes, tanks and ponds, rivers etc.), vegetation and soil covers. Vapour depends on temperature and therefore it decreases from the equator pole-ward in response to decreasing temperature towards the poles.

The content of vapour in the surface air in the moist tropical areas, at 50° and 70° latitudes is 2.6%, 0.9% and 0.2% (by volume) respectively. The content of vapour decreases upward. More than 90 per cent of the total atmospheric vapour is found upto the height of 5 km. If there is condensation of all the atmospheric vapour at a time, there would result a one-inch thick layer of water around the earth.

Even this meagre amount of water vapour in the atmosphere is responsible for various types of weather phenomena. The moisture content in the atmosphere creates several forms of condensation and precipitation e.g., clouds, fogs, dew, rainfall, frost, hailstorm, ice, snowfall etc.

Vapour is almost transpar­ent for incoming shortwave solar radiation so that the electromagnetic radiation waves reach the earth’s sur­face without much obstacles but vapour is less trans­parent for outgoing shortwave terrestrial radiation and therefore it helps in heating the earth’s surface and lower portion of the atmosphere because it absorbs terrestrial radiation.

iii. Particulate Matter:

The solid particles present in the atmosphere include dust particles, salt particles, pollen, smoke and soot, volcanic ashes etc. Most of the solid particles are kept in suspension in the atmos­phere. These particulates help in the scattering of solar radiation which adds varied charming colour of red and orange at sunrise and sunset.

The sky appears blue in colour due to selective scattering of solar radiation by dust particles. Salt particles become hygroscopic nuclei and thus help in the formation of water drops, clouds and various forms of condensation and precipi­tation.

On the basis of chemical composition, the at­mosphere is divided into two broad zones viz.:

(1) Homosphere.

(2) Heterosphere.

(1) Homosphere represents the lower portion of the atmosphere and extends upto the height of 90 km from sea level. The main constituent gases are oxygen (20.946%) and nitrogen (78.084%). Other gases are argan, carbon dioxide, neon, helium, krypton, xenon, hydrogen etc.

This zone is called homosphere because of the homogeneity of the proportion of various gases. In other words, the proportions of different gases are uniform at different levels in this zone. It may be pointed out that man is increasingly disturbing the natural proportions of gases through his ever-increasing economic activities and modern technologies. For ex­ample, the proportion of carbon dioxide is rapidly increasing due to burning of fossil fuels (coal, petro­leum and natural gas) and deforestation.

The concen­tration of atmospheric carbon dioxide at the beginning of the industrial revolution (1860 A.D.) was fixed at 280 to 290 ppm (parts per million) by volume but now it has increased to 350-360 ppm (1988 A.D.) thus registering an overall increase by 25 per cent from the pre-industrial level.

On the other hand, the proportion of ozone gas is rapidly decreasing due to ever-increasing production and consumption of CFCs (chloro- fluorocarbons) and halogenated gases.

On the basis of thermal conditions the homosphere has been divided into three layers viz.:

(i) Troposphere,

(ii) Stratosphere, and

(iii) Mesosphere.

(2) Heterosphere extends from 90 km to 10,000 km. Different layers of this sphere vary in their chemi­cal and physical properties.

There are four distinct layers of gases in this sphere:

(i) Molecular nitrogen 4ayer is dominated by molecular nitrogen and extends upward upto the height of 200 km (90 to 200 km),

(ii) Atomic oxygen layer extends from 200 to 1100 km.

(iii) Further upward there is helium layer which extends upto the height of 3500km.

(iv) Atomic hydrogen layer is the topmost layer of the atmosphere and extends upto the outermost limit of the atmosphere.

Essay # 4. Structure of the Atmosphere :

The modern knowledge about the atmosphere is based on the information received through rockets, radar and satellites. The effective height of the atmos­phere is estimated between 16 and 29 thousand kilo­metres from the sea level but the height of the atmos­phere upto 800 km is most important. About 50 per cent of the atmosphere lies below the altitude of 5.6 km and 97 per cent of the atmosphere is confined to the height of only 29 km.

The upper limit of the atmos­phere, though unknown, is considered to be 10,000 km from sea level. The earth’s atmosphere consists of a few zones or layers like spherical shells.

On the basis of the characteristics of temperature and air pressure there are four layers from the earth’s surface upward e.g.:

(1) Troposphere,

(2) Stratosphere,

(3) Mesosphere, and

(4) Thermosphere (fig. 32.1).

(1) Troposphere :

The lowermost layer of the atmosphere is known as troposphere and is the most important layer because almost all of the weather phenomena (e.g., fog, cloud, dew, frost, rainfall, hailstorm, storms, cloud-thunder, lightning etc.) occur in this layer. Thus, the tropo­sphere is of utmost significance for all the life forms including man in the biospheric ecosystem because these are concentrated in the lowest part of the atmos­phere.

Temperature decreases with increasing height at the rate of 6.5°C per 1000m. This rate of decrease of temperature is called normal lapse rate. There is sea­sonal variation in the height of troposphere. In other words, the height of troposphere changes from equator towards the poles (decreases) and from one season of a year to other season (increases during summer while it decreases during winter).

The average height of the troposphere is about 16 km over the equator and 6 km over the poles. The upper limit of the troposphere is called tropopause which is about 1.5 km thick. The height of tropopause is 17 km over the equator and 9 to 10 km over the poles. There is also seasonal variation in the height of tropopause.

Its height is 17 km during January and July over the equator and the temperature at this height is -70°C. The height of tropopause during July and January over 45°N latitude is 15 km (tempera­ture -60°C) and 12.5 km (temperature -58°C) respec­tively. The height decreases further poleward as it is 10 km during July (temperature -45°C) and 9 km during January (temperature -58°) over the North Pole.

It is apparent that temperature at the top of tropopause is lowest over the equator (-70°C) and is relatively high over the poles. Since temperature decreases upward at the rate of 6.5°C per 1000m and hence it is natural that temperature at the height of 17 km over the equator becomes much lower than at the height of 9-10 km over the poles. The word troposphere literally means ‘zone or region of mixing’ whereas the word tropopause means ‘where the mixing stops’.

(2) Stratosphere :

The layer just above the troposphere is called stratosphere but there is contrasting opinion about the height and thickness of this layer. The average height over the middle latitudes has been determined to be 25-30 km, whereas it is estimated to be 80 km by others. On an average the upper limit of the strato­sphere is taken to be 50 km.

There is also contrasting opinion about the change or no change of temperature with increasing height in this sphere. A few scientists believe that the stratosphere is isothermal i.e., there is no change in temperature with increasing height while others hold that temperature gradually rises upward as it becomes O 0 C or 32°F at the height of 50 km, the upper limit of the stratosphere which is known as stratopause.

Though the stratosphere is more or less devoid of major weather phenomena but there is circulation of feable winds and cirrus cloud in the lower stratosphere. The lower part of this layer is very important for life-forms in the biospheric ecosystem height of 15-30 km though ozone has been discovered because there is concentration of ozone between the upto the height of 80 km.

The lower portion of the stratosphere having maximum concentration of ozone is called ozonosphere, which is confined between the height of 15 km to 35 km from sea level though the upper limit has been fixed at 55 km. Ozone (O 3 ) defined as ‘a three-atom isotope of oxygen or merely a triatomic form of oxygen (O 3 )’ is a faintly blue irritating gas with a characteristic pungent odour. The ozone gas is unstable because the creation and destruction of this gas is a gradual and continuous natural process.

It acts as a protective cover for the biological communities in the biosphere be­cause it absorbs almost all of the ultra-violet rays of solar radiation and thus protects the earth’s surface from becoming too hot. Recently, the researchers have shown that there is gradual depletion of ozone gas in the atmosphere due to human activities. It may be pointed out that combining of atmospheric oxygen (O 2 ) with individual oxygen molecules results in the creation of ozone (O 2 + O → O 3 ) whereas the breaking of ozone (O 3 ) into O 2 and O results in the depletion or destruction of ozone.

The main culprits of ozone de­struction are halogenated gases called chlorofluorocarbons, halons and nitrogen oxides. The chlorofluorocarbons, popularly known as CFCs, be­long to the category of synthetic chemicals and are relatively simple compounds of the elements chlorine, fluorine and carbon and are initially stable compounds which do not have any toxic effect on life processes in the biosphere at ground level.

These synthetic chemi­cals are widely used as propellants in spray can dis­pensers, as fluids in air conditioners and refrigerators etc. Chlorofluorocarbons, when used as propellants, are released into the air and are transported in the stratosphere by vertical atmospheric circulation. Chlo­rine when separated from chlorofluorocarbons reacts with water and thus depletes ozone rather breaks ozone into O 2 and O.

Besides, nitrogen oxides released by supersonic jets which fly at the height of 18-22 km also depletes ozone. Depletion of ozone would result in the rise of temperature of the ground surface and lower atmosphere. This would cause global warming, acid rain, melting of continental glaciers and rise in sea level, skin cancer to white-skinned people, poisonous smogs, decrease in photosynthesis, ecological disaster and ecosystem instability.

(3) Mesosphere :

Mesosphere extends between 50 km and 80 km. Temperature again decreases with increasing height.

In fact, the rise of temperature with increasing height in the stratosphere stops at stratopause. At the uppermost limit of mesosphere (80 km) temperature becomes -80°C. This limit is called mesopause above which temperature increases with increasing height.

(4) Thermosphere :

The part of the atmosphere beyond mesopause is known as thermosphere wherein temperature in­creases rapidly with increasing height. It is estimated that the temperature at its upper limit (height unde­cided) becomes 1700°C.

It may be pointed out that this temperature cannot be measured by ordinary ther­mometer because the gases become very light due to extremely low density. That is why one does not feel warm when one stretches one’s arm in the air.

Thermosphere is divided into two layers viz.:

(1) Lono­sphere, and

(2) Exosphere.

(1) Ionosphere extends from 80 km to 640 km. There are a number of ionic layers (with increasing heights) in this sphere e.g., D layer, E layer, F layer, and G layer. D layer (between the height of 60 km – 99 km) reflects the signals of low frequency radio waves but absorbs the signals of medium and high frequency waves.

This layer disappears with the sunset because it is associated with solar radiation. E layer, also known as Kennelly – Heaviside layer, is confined in the height between 99 km – 130 km. This layer reflects the medium and high frequency radio waves back to the earth. This layer is produced due to interaction of solar ultra-violet photons with nitrogen and nitrogen mol­ecules and thus it also disappears with the sunset. Sporadic E layer is associated with high velocity winds and is created under special circumstances.

This layer reflects very high frequency radio waves. E 2 layer is generally found at the height of 150 km and is produced due to reaction of ultra-violet solar photons with oxygen molecules and thus this layer also disappears during nights. F layer consists of two sub-layers e.g. F 1 , and F 2 layers (150 km – 380 km) and are collectively called ‘Appleton layer’. These layers reflect medium and high frequency radio waves back to the earth. G layer (400 km and above) most probably persists day and night but is not detectable.

(2) Exosphere represents the uppermost layer of the atmosphere. In fact, we know very little about the atmosphere extending beyond 640 km height from the sea level. The density becomes extremely low and the atmosphere resembles a nebula because it is highly rarefied. The temperature becomes 5568°C at its outer limit but this temperature is entirely different from the air temperature of the earth’s surface as it is never felt.

Essay # 5. Heating of the Atmosphere:

The sun is the main source of energy and heat. It provides solar energy (insolation) or fuel for the process of weather and climate. The energy emitted by the sun is known as solar radiation. The incoming solar radiation to the earth is known as insolation.

It is estimated, that the earth is receiving nearly two calories of heat per square centimetre per minute. This fixed amount of heat is known as solar constant. Of the incoming solar radiation nearly 50 per cent is able to reach the earth surface and the rest 50 per cent is reflected back into the space from the atmosphere and from ground.

The amount of insolation differs from place to place and depends on:

(a) Distance from the sun and its elevation,

(b) The amount of atmosphere to be crossed,

(c) Duration of sunlight, and 

(d) The output of energy by the sun.

The perpendicular rays have to pass through a smaller portion of atmosphere and spread over a small extent of surface. That is why regions receiving direct and perpendicular rays are warmer than others. Similarly, insolation has a direct relationship with the duration of sunlight.

As the duration of sunlight varies with latitude and seasons, so is the case with insolation. Besides, the output of energy from the sun varies to the extent of 5-10 per cent with the increase or decrease of the sunspots. This results in the variation of solar constant by nearly 2 per cent.

The atmosphere is heated in four ways:

(1) Convection,

(2) Conduction,

(3) Radiation, and 

(4) Compression.

(1) Convection:

Transfer of heat of atmosphere from one place to another is known as convection. When the surface of the earth is heated more as compared to the upper layers of atmosphere, the air near the earths’ surface also gets heated and rises above due to decrease in density.

By the continuous upward movement of hot air, a vacuum is produced and cooler air from the surrounding areas comes in. In this way, convectional current takes place and the heat is transferred to upper layers of atmosphere. Convection is the main process in the heating of the atmosphere.

(2) Conduction:

Conduction is a process of transfer of heat by molecular activity. When two bodies with unequal temperature come into contact, there is a flow of energy from the warmer body to the cooler one. The lower layer of atmosphere especially that comes into direct contact with the surface of the earth gets heated through the process of conduction.

(3) Radiation:

Radiation is the direct heating by the transmission of heat waves. The upper layer of atmosphere absorbs some amount of heat of the rays of the sun as they pass through the atmosphere. Radiation from the earth is called terrestrial radiation. Due to certain chemical and physical properties of the elements of atmosphere, they absorb more heat from the terrestrial radiation rather than the radiation from the sun.

(4) Compression:

Another method of heating is compression. When cold air descends, its weight compresses the air below and the air of the lower layer is heated up due to pressure from above and temperature rises.

Heat Balance:

It is found that there is a balance of incoming solar radiation and the amount of terrestrial radiation returned to space. The balance of incoming and outgoing radiation is termed as heat balance.

Global Warming:

Global warming means the increase of temperature of the earth. The various gases present in atmosphere absorb and radiate the sunlight by greenhouse process. This process increases the temperature of the earth. There are various factors responsible for heating of the earth.

1. Actions of human being:

The human activities add methane and carbon dioxide to the atmosphere mainly through burning of fossil fuels and various agricultural activities. The carbon dioxide allows incoming solar radiation to enter into the earth surface but it absorbs the terrestrial radiation and sends back to the earth. The process helps increase surface temperature of the earth.

2. Industrialization:

Rapid industrialization, technological change, revolution in agricultural development and transport have resulted in large supply of carbon dioxide, methane and chlorofluorocarbon gases to the atmosphere. Some of these gases are consumed by vegetation and some portion dissolved in ocean water.

Nearly 50 per cent remains in the atmosphere. These gases absorb the terrestrial radiation and send back to the earth. The process helps increase surface temperature of the earth.

Scientists have predicted that by 2020, temperature over the earth would be higher than that of the same during the last 1000 years. Therefore, it is very essential to reduce greenhouse effect and lower the amount of carbon dioxide which is mainly responsible for global warming.

The solar energy received by the earth’s surface including both ground surface and water surface (of the seas and the oceans) is converted into heat energy ill the form of sensible heat (heat that can be measured by thermometer) and is temporarily stored. This stored energy is radiated from the ground and water surface in the form of long-waves into the atmosphere.

The proc­ess of radiation of heat energy from the earth’s surface is called ground radiation (including radiation from both, ground surface and water surface). The part of this ground radiation after being absorbed by the at­mosphere is again radiated back to the earth’s surface. This process of radiation of terrestrial heat energy from the atmosphere back to the earth’s surface is called counter-radiation. The counter-radiation is effected mainly by water vapour and atmospheric carbon diox­ide.

Heating of the Atmosphere by Direct Insolation :

The heat energy is radiated from the outer sur­face of the sun (photosphere) in the form of long-waves. The atmosphere absorbs 14 per cent of incoming short wave solar radiation through ozone, water vapour etc. present therein. Seven per cent of this energy is spread in the lower atmosphere up to the height of 2km. It is apparent that this amount is too low to heat the atmos­phere significantly.

Conduction :

The transfer of heat through the molecules of matter in any body is called conduction.

The transfer of heat under the process of conduction may be accom­plished in two ways viz.:

(i) From one part of a body to the other part of the same body, and

(ii) From one body to the other touching body.

Conduction may be effec­tive only when there is difference in temperatures in different parts of a single body or in two bodies and the process continues till the temperatures of all parts of a body or of two touching bodies become same.

It is obvious that heat moves from warmer body to the cooler body through molecular movement. The rate of transfer of heat through molecular movement depends on the heat conductivity of the substance. The sub­stance or a body which allows transfer of heat through conduction at a very fast rate is called good conductor of heat while the substance or a body which retards conduction of heat is called bad or poor conductor of heat. Metal is a good conductor of heat while air is very poor conductor of heat.

The earth’s surface is heated during day-time after receiving solar radiation. The air coming in contact with the warmer ground surface is also heated because of transfer of heat (conduction of heat) from the ground surface through the molecules to the air. Since air is very poor conductor of heat and hence the transfer of heat from the ground surface through conduction is effective only up to a few metres in the lower atmosphere.

The ground surface becomes colder than the air above during winter nights and thus heat is transferred from the lower portion of the atmos­phere to the ground surface and thus the atmosphere is cooled.

Terrestrial Radiation :

The process of transfer of heat from one body to the other body without the aid of a material medium (e.g., solid, liquid or gas) is called radiation.

There are two basic laws which govern the nature of flow of heat energy through radiation:

(a) Wien’s displacement law ‘states that the wave­length of the radiation is inversely proportional to the absolute temperature of the emitting body’.

(b) Stefan-Boltzmann law ‘states that flow, or flux of radiation is proportional to the fourth power of the absolute temperature of the radiating body’.

The earth’s surface after receiving insolation from the sun through shortwave electromagnetic ra­diation gets heated and radiates heat to the atmosphere in the form of long-wave or infrared radiation through­out 24 hours. It may be remembered that the atmos­phere is more or less transparent for incoming shortwave solar radiation but it absorbs more than 90 per cent of outgoing long-wave terrestrial radiation through water vapour, carbon dioxide, ozone etc.

Thus, the terrestrial radiation is the most important source of heating of the atmosphere. The process of radiation of heat from the earth’s surface is called ground radiation. The part of this ground radiation after being absorbed by the at­mosphere is radiated back to the earth’s surface. This process of radiation of terrestrial heat energy from the atmosphere back to the earth’s surface is called coun­ter-radiation which is effected mainly by water vapour and atmospheric carbon dioxide.

This mechanism known as greenhouse effect keeps the lower atmosphere and the ground surface relatively warmer. Thus, the atmos­phere acts as window glass-pane which allows the shortwave solar radiation to come in and prevent the long-wave terrestrial radiation to escape into space.

It is obvious that the increase in the concentra­tion of carbon dioxide in the atmosphere will increase the greenhouse effect and thus the temperature of the earth’s surface would increase. It may be pointed out that carbon dioxide also absorbs long-wave terrestrial radiation and helps in keeping the lower atmosphere and the ground surface warmer. Water vapour absorbs both the incoming shortwave solar radiation and out­going long-wave terrestrial radiation.

Since most of water vapour is concentrated in the lower atmosphere (90 per cent of the total atmospheric water vapour is found upto the height of 5km in the lower atmosphere) and hence both the incoming solar radiation and outgo­ing terrestrial radiation increase with increasing height. This is the reason that high mountains are called radiation windows.

Convection :

The transfer of heat energy through the move­ment of a mass of substance from one place to another place is called convection. The process of convection becomes effective only in fluids or gases because their internal mass motion activates convection of heat energy. The earth’s surface gets heated after receiving heat energy (insolation) from the sun.

Consequently, the air coming in contact with the warmer earth’s surface also gets heated and expands in volume. Thus, warmer air becomes lighter and rises upward and a vertical circulation of air is set in. Conversely, the relatively colder air aloft becomes heavier because of contraction in volume and thus descends to reach the earth’s surface. The descending air is warmed because of dry adiabatic rate and warm ground surface.

This warm air again ascends because of increase in volume and decrease in density. The whole mechanism of ascent of warmer air and descent of colder air generates convection currents in the lower atmosphere. This convective mechanism transports heat from the ground surface to the atmosphere and thus helps in the heating of the lower atmosphere. Similarly, horizontal convection currents are also generated on the ground surface.

Besides, atmosphere is also heated through la­tent heat of condensation, and expansion and compres­sion of air.

Essay # 6. Chemistry of Earth’s Atmosphere:

The Earth’s atmosphere is 99.9% nitrogen, oxygen and argon, of the remaining 0.1%, roughly half (0.04%) is accounted for by the three transition gases CO 2 , Ne and He.

The remaining minute fraction of the atmosphere (0.66%) is composed of a complex mixture of hundreds of trace gases, the most abundant being methane at 1.7 ppm. Many gases at the parts per trillion levels (10- 12 v/v), are entirely man-made but may still have significant effect on the environment.

Some trace gases control or affect the Earth’s climate and stability. Long lived gases that are increasing at substantial rates because of human activities are of particular current interest since they lead eventually to stratospheric ozone depletion, global warming, and disturbances in atmosphere chemistry that many believe will be harmful to human life.

As per the present estimate the composition of the atmospheric gases are presented in Table 10.1. Substantial effects of human activities on the global cycles of trace gases have arisen only during the last century.

Since 1800 the human population has increased from 1 to 7 billion, bringing with it fast changes in the surface of the earth and disturbing the global balance of the trace gases, changing in atmospheric composition that have occurred are unprecedented during the last several thousand years.

The rate of change is much faster now than can occur from natural climatic cycles, although it is hard to prove that there were no times when trace gas concentrations did not rise rapidly and later fall. The changes that are occurring now have their origin in the Industrial Revolution (since 1760) and the expansion of technology.

These changes are directly related to human events and activities. There is a prevalent belief that the changes man is causing to the atmospheric environment are unnatural and unhealthy.

There were various types of natural processes like volcanic, earthquake, decomposition and climatic transformations that led to the changes in global atmospheric composition in addition to man-made activities like industrialisation, urbanisation and modernisation of agricultural activities.

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3. Moisture in the atmosphere

1. water in the atmosphere in different forms, such as water vapour and liquid. 2. processes associated with evaporation, condensation and precipitation..

The atmosphere isn’t just made up of air but also contains water vapour.  This water vapour, which makes up  less than 0.001% of all the water on the Earth, is invisible. This tiny amount of water in the air is really important to our climate. When water vapour condenses onto tiny particles in the atmosphere, clouds form.

3. The concepts of dew point, condensation level, humidity, relative humidity – factors affecting relative humidity.

Dew point temperature is the temperature at which condensation takes place Clouds usually have a flat base because as air rises it cools, and dew point temperature is reached at that height.

Condensation level is the point at which rising air will cool to dew point, condense, and form clouds.

Relative humidity is the amount of water vapour in the air relative to how much water vapour the air can hold. Relative humidity is expressed as a percentage. If air has an RH of 80%, it is more saturated (wet) than air of an RH of 30%

4. How and why clouds form.

5. Cloud names and associated weather conditions.

6. Different forms of precipitation – hail, snow, rain, dew and frost.

7. Mechanisms that produce different kinds of rainfall – relief, convectional and frontal and reading and interpreting Synoptic Weather Maps.

7.1 relief rainfall.

7.2 Convection rainfall

7.3 Frontal rainfall

7.4 Synoptic Weather Maps

Today’s Synoptic Chart

8. Weather elements: temperature, dew-point temperature, cloud cover, wind direction,wind speed and atmospheric pressure.

9. Weather conditions: rain, drizzle, thunderstorms, hail and snow, as illustrated on station models.

Most reporting in the 21st century are electronic. Below is the weather for Sutherland in the Northern Cape; the coldest place in South Africa.

<a href=”http://www.yr.no/place/South_Africa/Northern_Cape/Sutherland/”>yr.no: Forecast for Sutherland</a>  

10. Reading and interpreting a selection of synoptic weather maps.

• The atmosphere
• Grade 10 – Nautical Science
• 3 Meteorology (weather at sea)

Weather signs at sea – humidity

Meteorological instruments.

The atmosphere is divided up into a number of layers as follows:

• The Troposphere. This layer stretches from the surface of the earth up to 18 kilometers above the earth. Most of the weather changes occur in this layer.
• Stratosphere. This layer stretches from 18 to 32 kilometers above the earth. Very little water vapour is found in this layer.
• Ozonosphere. This layer lies between 32 and 80 kilometers above the earth. A high concentration of ozone is found in this layer which absorbs ultra violet radiation from the sun. Ozone is an unstable form of oxygen formed by electrical discharges.
• Ionosphere. This layer lies between 80 and 300 kilometers above the earth. It contains gas particles which have been ionised by the sun’s radiation. This layer is responsible for the reflection/refraction of radio waves. Ionised particles are particles that have either had an electron removed or added to its mass.

Heating of the atmosphere.

Since most of the weather changes occur in the troposphere, temperature changes in this layer are most important. The sun is the principle source of light and heat for the earth. Heat travels in the form of short wave radiation (ultra violet) which passes through the atmosphere without noticeably warming it. When it reaches the earth’s surface some of the heat is absorbed by the surface. The heat received by the earth from the sun is known as “insolation”. The amount of “insolation” per unit area varies with the latitude. The higher the latitude, the less this amount. The increase in temperature is dependent on the amount of “insolation” and the specific heat of the earth.

The specific heat of a substance is defined as the amount of heat required to raise the temperature of a specified quantity of the substance by 1° (C). If we assume a constant “insolation”, a surface with a high specific heat warms and cools less quickly than a surface with a low specific heat. The sea temperature in non-tidal waters changes very little over a period of 24 hours. As a general rule, sea temperatures are less than the temperatures of adjacent land by day and greater at night. In addition to receiving heat, the earth, being a warm body, also radiates heat and when the amount of radiation exceeds the ”insolation”, it cools, ie at night. The heat transferred to the atmosphere has a very profound effect on the weather.

How is it transferred?

• By radiation. Whilst the earth’s surface is heated by the short wave (UV) radiation of the sun, it in turn, radiates heat in long wave form (infra red). This warms the lower layers of the air. On a cloudless night, most of the heat is radiated into outer space. When there is cloud cover, most of the heat will be reflected back to earth. The clouds act as a sort of blanket.
• Conduction. Air in contact with the earth is warmed during the day and cooled at night.
• Convection. Air which is warmed expands and its density decreases. Since this makes it lighter than the cooler air around it, the warm air rises. Convection takes large amounts of warm air and water vapour from the surface to the upper levels. When the water vapour condenses into water droplets and precipitation occurs, the latent heat remains. Most of the atmospheric heating takes place this way.
• T urbulence. Air which flows over a rough surface tends to be reflected upwards, ie the mountains and hills will deflect the heat upwards. The rising air will be replaced by air from levels up to 600 metres. The rising air carries it’s warmth with it and the falling air brings its coolness.

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Grade 10: Social Sciences: Geography - Term 1 - Grade 10 Social Sciences Geography - Term 1 - The atmosphere

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