No.

No.

No.

No.

No.

• The Crust
• The Mantle
• The Core

• The crust is the outermost solid part of the earth.
• It is fragile in nature.
• The thickness of the crust varies under the oceanic and continental areas.
• Oceanic crust is thinner as compared to the continental crust.
• The continental crust is thicker in the areas of major mountain systems.
• The crust made up of heavier rocks having a density of 3 g/cm3.
• The kind of rock seen in the oceanic crust is basalt.
• The mean density of material in the oceanic crust is 2.7 g/cm3.

• The portion of the interior beyond the crust is called the mantle.
• It is in a solidstate.
• It has a density higher than the crust portion.
• The thickness ranges from 10-200 km.
• The mantle extends from Moho’s discontinuity to a depth of 2,900 km.
• The asthenosphere is the upper portion of Mantle.
• It is the chief source of magma that finds its way to the surface during volcanic eruptions.
• The crust and the uppermost part of the mantle are called lithosphere.

• The core-mantle boundary is positioned at the depth of 2,900 km.
• The inner core is in the solid state whereas the outer core is in the liquid state.
• The core is made up of very heavy material mostly constituted by nickel and iron. Hence it is also called the “nife” layer.

• There are various ways of heating and cooling of the atmosphere.
• The earth after being warmed by insolation transfers the heat to the atmospheric layers in long waveform.

• The air in interaction with the land gets heated gradually and the upper layers in touch with the lower layers also get heated. This process is called conduction.
• This process takes place when two bodies of uneven temperature are in contact with one another, there is a flow of energy from the warmer to the cooler body.
• The heat transfer continues until both the bodies reach the same temperature or the contact is interrupted.
• This process is significant in heating the lower layers of the atmosphere.

• The air in contact with the earth upsurges vertically on heating in the form of currents and transfers the heat of the atmosphere.
• This vertical heating of the atmosphere is known as convection.
• The convective transfer of energy is limited only to the troposphere.

• The transfer of heat through horizontal movement of air is called advection.
• The horizontal movement of the air is comparatively more significant than the vertical movement.
• Most of the diurnal variation in weather is caused by advection only in the middle latitudes.
• During summer in tropical regions predominantly in Northern India, local winds called ‘loo’ is the result of advection process.

• Factors for General Circulation of the Atmosphere

• The pattern of planetary winds largely depends on:
  • Latitudinal variation of atmospheric heating
  • The emergence of pressure belts
  • The migration of belts following the apparent path of the sun
  • The distribution of continents and oceans
  • The rotation of the earth
• The general circulation of the atmosphere also sets in motion the marine water circulation which affects the climate of the Earth.
• The air at the ITCZ (Inter Tropical Convergence Zone) upsurges because of convection caused by high insolation and low pressure is generated.
• The winds from the tropics join at this low-pressure zone.
• The joined air upsurges along with the convective cell.
• It reaches the top of the troposphere up to an altitude of 14 km.
• It further moves toward the poles. This causes accumulation of air at about 30o North and South.
• Another reason for sinking is the cooling of air when it reaches 30 degrees North and South latitudes.
• Downward near the land surface, the air flows towards the equator as the easterlies.
• The easterlies from either side of the equator converge in the Inter-Tropical Convergence Zone (ITCZ).
• Such circulations from the surface up and vice-versa are called cells.
• This type of a cell in the tropics is called HadleyCell.
• In the mid-latitudes, the circulation is that of dipping cold air that comes from the poles and the mounting warm air that blows from the subtropical high.
• At the surface, these winds are called westerlies and the cell is known as the Ferrel cell.
• At polar latitudes, the cold dense air subsides near the poles and blows towards middle latitudes as the polar easterlies. This cell is called the polarcell.
• These Ferrel cells, Hadley Cell, and polar cell set the configuration for the general circulation of the atmosphere.

• The general circulation of the atmosphere also influences the oceans.
• Warming and cooling of the Pacific Ocean is most significant in terms of general atmospheric circulation.
• The warm water of the central Pacific Ocean gradually drifts towards the South American coast and substitutes the cool Peruvian current.
• Such presence of warm water off the coast of Peru is known as the El Nino.
• The El Nino is associated with the pressure variations in Australia and Central Pacific.
• This variation in pressure condition over the Pacific is known as the southern oscillation.

• The combined phenomenon of ElNino and southern oscillation is known as ENSO.

• 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.
• During its revolution around the sun, the earth is farthest from the sun (152 million km) on 4th July. This position of the earth is called aphelion.
• On 3rd 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 3rd January is slightly more than the amount received on 4th July.
• Variation in the solar output does not have great effect on daily weather changes on 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.(important )
• The fact that the earth’s axis makes an angle of 66 with the plane of its orbit round the sun has a greater influence on the amount of insolation received at different latitudes. Note the variations in the duration of the day 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 320 Watt/m2 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.
• The Equator receives comparatively less insolation than the tropics. Generally, at the same latitude, the insolation is moreover the continent than over the oceans. 
• In winter, the middle and higher latitudes receive less radiation than in summer.

• 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 the 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 waveform.
• This energy heats up the atmosphere from below. This process is known as terrestrial radiation.
• The longwave radiation is absorbed by 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.

• • 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.
  • why the earth neither warms up nor cools down despite the huge transfer of heat that takes place??
• Consider that the insolation received at the top of the atmosphere is 100 per cent.

• Roughly 35 units are reflected back to space even before reaching the earth’s surface. (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
• 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

Variation in the Net Heat Budget at the Earth’s Surface

• 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.
• 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.

• The interaction of insolation with the atmosphere and the earth’s surface creates heat which is measured in terms of temperature.
• While heat represents the molecular movement of particles comprising a substance, the temperature is the measurement in degrees of how hot (or cold) a thing (or a place) is.

• The temperature of air at any place is influenced by 

1. the latitude of the place; 
2. the altitude of the place; 
3. distance from the sea, the air- mass circulation; 
4. the presence of warm and cold ocean currents; 
5. local aspects.

1. 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.
2. The altitude: The atmosphere is indirectly heated by terrestrial radiation from below. Therefore, the places near the sea-level record higher temperatures 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.
3.  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.
4. 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 temperatures and the places that come under the influence of cold air- masses experience low temperatures. Similarly, the places located on the coast where the warm ocean currents flow record higher temperatures than the places located on the coast where the cold currents flow.

• The global distribution of temperature can well be understood by studying the temperature distribution in January and July.
• The Isotherms are lines joining places having equal temperature.
• The northern hemisphere the land surface area is much larger than in the southern hemisphere. Hence, the effects of land mass and the ocean currents are well pronounced.
• In January the isotherms deviate to the north over the ocean and to the south over the continent. This can be seen on the North Atlantic Ocean. The presence of warm ocean currents, Gulf Stream and North Atlantic drift, make the Northern Atlantic Ocean warmer and the isotherms bend towards the north. Over the land the temperature decreases sharply and the isotherms bend towards south in Europe.
• It is much pronounced in the Siberian plain. The mean January temperature along 60° E longitude is minus 20° C both at 80° N and 50° N latitudes.
• The mean monthly temperature for January is over 27° C, in equatorial ocean over 24° C in the tropics and 2° C – 0° C in the middle latitudes and –18° C to – 48° C in the Eurasian continental interior.
• The effect of the ocean is well pronounced in the southern hemisphere. Here the isotherms are more or less parallel to the latitudes and the variation in temperature is more gradual than in the northern hemisphere. The isotherm of 20° C, 10° C, and 0° C runs parallel to 35° S, 45°S and 60°S latitudes respectively.
• In July the isotherms generally run parallel to the latitude. The equatorial oceans record warmer temperature, more than 27°C. Over the land more than 30°C is noticed in the subtropical continental region of Asia, along the 30° N latitude. Along the 40° N runs the isotherm of 10° C and along the 40° S the temperature is 10° C.