Geography

 

 

The ultimate source of atmospheric energy is in fact heat and light received through space from the Sun. This energy is known as solar insolation. The Earth receives only a tiny fraction of the total amount of Sun’s radiations. Only two billionths or two units of energy out of 1,00,00,00,000 units of energy radiated by the sun reaches the earth’s surface due to its small size and great distance from the Sun. The unit of measurements of this energy is Langley (Ly). On an average the earth receives 1.94 calories per sq. cm per minute (2 Langley) at the top of its atmosphere.

Incoming solar radiation through short waves is termed as insolation. The amount of insolation received on the earth’s surface is far less than that is radiated from the sun because of the small size of the earth and its distance from the sun. Moreover water vapour, dust particles, ozone and other gases present in the atmosphere absorb a small amount of insolation.

The amount of insolation received on the earth’s surface is not uniform everywhere. It varies from place to place and from time to time. The tropical zone receive the maximum annual insolation. It gradually decreases towards the poles. Insolation is more in summers and less in winters.
The following factors influence the amount of insolation received.
(i) The angle of incidence:-The angle formed by the sun’s ray with the tangent of the earth’s circle at a point is called
angle of incidence. It influences the insolation in two ways. First, when the sun is almost overhead, the rays of the sun are vertical. The angle of incidence is large hence, they are concentrated in a smaller area, giving more amount of insolation at that place. If the sun’s rays are oblique, angle of incidence is small and sun’s rays have to heat up a greater area, resulting in less amount of insolation received there. Secondly, the sun’s rays with small angle, traverse more of the atmosphere, than rays striking at a large angle. Longer the path of sun’s rays, greater is the amount of reflection and absorption of heat by atmosphere. As a result the intensity of insolation at a place is less.
(ii) Duration of the day. (daily sunlight period) :-The duration of day is controlled partly by latitude and partly by the season of the year. The amount of insolation has close relationship with the length of the day. It is because insolation is received only during the day. Other conditions remaining the same, the longer the days the greater is the amount of insolation. In summers, the days being longer the amount of insolation received is also more. As against this in winter the days are shorter the insolation received is also less. On account of the inclination of the earth on its axis at an angle of 23 ½ , rotation and revolution, the duration of the day is not same everywhere on the earth. At the equator there is 12 hours day and night each throughout the year. As one moves towards poles duration of the days keeps on increasing or decreasing. It is why the maximum insolation is received in equatorial areas.

(iii) Transparency of the atmosphere.Transparency of the atmosphere: Transparency of the atmosphere also determines the amount of insolation reaching the earth’s surface. The transparency depends upon cloud cover, its thickness, dust particles and water vapour, as they reflect, absorb or transmit insolation. Thick clouds hinder the insolation to reach the earth while clear sky helps it to reach the surface. Water vapour absorb insolation, resulting in less amount of insolation reaching the surface.

Heat Budget

Energy emitted by the Earth’s climate system tends to maintain a balance with solar energy coming into the system. This balance, known as the radiation budget, allows the Earth to maintain the moderate temperature range essential for life as we know it.
There is positive radiation balance between 35°S and 40°N, which drives the weather systems. Ocean currents even out the difference
When incoming short-wave solar radiation (Figure 3), known as insolation, enters the Earth’s climate system, a portion of it is absorbed at the Earth’s surface, causing the surface to heat up. Some of the absorbed energy is then radiated outward in the form of long-wave infrared radiation. Cloud layers trap some of the radiation from the Earth’s surface, and then emit long-wave radiation, both outward and back to the surface. The temperature of the Earth’s surface is about 33°C higher due to long-wave radiation contribution from the atmosphere .
The amount of radiation emitted by the Earth’s surface that makes it back to space is the result of many interrelated influences, such as the amount of cloud cover, cloud heights, characteristics of cloud droplets, amount and distribution of water vapor and other greenhouse gases, land features, surface temperature, and the transparency of the atmosphere. In the warm tropical areas, low values of outgoing longwave radiation (OLR) correspond to large amounts of high, cold clouds while high values of OLR correspond to relatively clear areas or cloudy areas with low, warm clouds. In the extra-tropics OLR values typically decrease with decreasing temperature.

Let us suppose that the total heat (incoming solar radiation) received at the top of the atmosphere is 100 units (see fig. 10.2) Roughly 35 units of it are reflected back into space even before reaching the surface of the earth. Out of these 35 units, 6 units are reflected back to space from the top of the atmosphere, 27 units reflected by clouds and 2 units from the snow and ice covered surfaces.
Out of the remaining 65 units (100-35), only 51 units reach the earth’s surface and 14 units are absorbed by the various gases, dust particles and water vapour of the atmosphere.
The earth in turn radiates back 51 units in the form of terrestrial radiation. Out of these 51 units of terrestrial radiation, 34 units are absorbed by the atmosphere and the remaining 17 units directly go to space. The atmosphere also radiates 48 units (14 units of incoming radiation and 34 units of outgoing radiation absorbed by it) back to space. Thus 65 units of solar radiation entering the atmosphere are reflected back into the space. This account of incoming and outgoing radiation always maintains the balance of heat on the surface of the earth.

 

Landform

Each landform has its unique physical shape, size, materials and is a result of the action of certain geomorphic processes and agent(s). Every landform has a beginning. Landforms once formed may change in their shape, size and nature slowly or fast due to continued action of geomorphic processes and agents. Due to changes in climatic conditions and vertical or horizontal movements of landmasses, either the intensity of processes or the processes themselves might change leading to new modifications in the landforms.

Evolution

It implies stages of transformation of either a part of the earth’s surface from one landform into another or transformation of individual landforms after they are once formed. That means, each and every landform has a history of development and changes through time. A landmass passes through stages of development somewhat comparable to the stages of life — youth, mature and old age.

Geomorphic Agents

Changes on the surface of the earth owe mostly to erosion by various geomorphic agents. Running water, ground-water, glaciers, wind and waves are powerful    erosional and depositional agents shaping and changing the surface of the earth aided by weathering and mass wasting processes. These geomorphic agents acting over long periods of time produce systematic changes leading to sequential development of landforms.

Fluvial landforms

The landforms created as a result of degradational action (erosion) or aggradation work (deposition) of running water is called fluvial landforms.

These landforms result from the action of surface flow/run-off or stream flow (water flowing through a channel under the influence of gravity). The creative work of fluvial processes may be divided into three physical phases—erosion, transportation and deposition.

The landforms created by a stream can be studied under erosional and depositional categories.

Erosional category

Valleys, gorge and Canyon

The extended depression on ground through which a stream flows throughout its course is called a river valley. A gorge is a deep valley with very steep to straight sides. A canyon is characterized by steep step-like side slopes and may be as deep as a gorge.

At a young stage, The profile of valley  is typically ‘V’ shaped. As the cycle attains maturity, the lateral erosion becomes prominent and the valley floor flattens out. The valley profile now becomes typically ‘U’ shaped with a broad base and a concave slope.

Potholes, Plunge pools

Potholes are more or less circular depressions over the rocky beds of hills streams.Once a small and shallow depression forms, pebbles and boulders get collected in those depressions and get rotated by flowing water. Consequently, the depressions grow in dimensions to form potholes.Plunge pools are nothing but large, deep potholes commonly found at the foot of a waterfall. They are formed because of the sheer impact of water and rotation of boulders.

Incised or Entrenched Meanders

They are very deep wide meanders (loop-like channels) found cut in hard rocks.In the course of time, they deepen and widen to form gorges or canyons in hard rock.The difference between a normal meander and an incised/entrenched meander is that the latter found on hard rocks.

River Terraces

They are surfaces marking old valley floor or flood plains.They are basically the result of vertical erosion by the stream. When the terraces are of the same elevation on either side of the river, they are called as paired terraces.When the terraces are seen only on one side with none on the other or one at quite a different elevation on the other side, they are called as unpaired terraces.

Depositional Features

Alluvial Fans

They are found in the middle course of a river at the foot of slope/ mountains.When the stream moves from the higher level break into foot slope plain of low gradient, it loses its energy needed to transport much of its load.Thus, they get dumped and spread as a broad low to the high cone-shaped deposits called an alluvial fan.

Deltas

They are found in the mouth of the river, which is the final location of depositional activity of a river. \The coarser material settle out first and the finer materials like silt and clay are carried out into the sea.

 

 Flood Plains, Natural Levees

Natural levees are found along the banks of large rivers. They are low, linear and parallel ridges of coarse deposits along the banks of a river.The levee deposits are coarser than the deposits spread by flood water away from the river.

 

 Meanders and oxbow lakes

• They are formed basically because of three reasons: (i) propensity of water flowing over very gentle gradient to work laterally on the banks; (ii) unconsolidated nature of alluvial deposits making up the bank with many irregularities; (iii) Coriolis force acting on fluid water deflecting it like deflecting the wind.
• The concave bank of a meander is known as cut-off bank and the convex bank is known as a slip-off
• As meanders grow into deep loops, the same may get cut-off due to erosion at the inflection point and are left as oxbow lakes.

Braided Channels

When selective deposition of coarser materials causes the formation of a central bar, it diverts the flow of river towards the banks, which increases lateral erosion. Similarly, when more and more such central bars are formed, braided channels are formed. Riverine Islands are the result of braided channels.

 

Karst Topography

Any limestone, dolomite or gypsum region showing typical landforms produced by the action of groundwater through the process of solution and deposition is called as Karst Topography (Karst region in the Balkans).

Sinkholes

A sinkhole is an opening more or less circular at the top and funnel-shaped towards the bottom.When as sinkhole is formed solely through the process of solution, it is called as a solution sink.When several sink holes join together to form valley of sinks, they are called as blind valleys.

 

Caves

In the areas where there are alternative beds of rocks (non-soluble) with limestone or dolomite in between or in areas where limestone are dense, massive and occurring as thick beds, cave formation is prominent. Caves normally have an opening through which cave streams are discharged Caves having an opening at both the ends are called tunnels.

Stalactites and stalagmites

They are formed when the calcium carbonates dissolved in groundwater get deposited once the water evaporates.These structures are commonly found in limestone caves.Stalactites are calcium carbonate deposits hanging as icicles while Stalagmites are calcium carbonate deposits which rise up from the floor.When a stalactite and stalagmite happened to join together, it gives rise to pillars or columns of different diameters.

GLACIERS

Masses of ice moving as sheets over the land (continental glacier or piedmont glacier if a vast sheet of ice is spread over the plains at the foot of mountains) or as linear flows down the slopes of mountains in broad trough-like valleys (mountain and valley glaciers) are called glaciers.

EROSIONAL LANDFORMS

Cirque

Cirques are the most common of landforms in glaciated mountains. They are deep, long and wide troughs or basins with very steep concave to vertically dropping high walls at its head as well as sides. A lake of water can be seen quite often within the cirques after the glacier disappears. Such lakes are called cirque or tarn lakes.

Horns and Serrated Ridges

Horns form through head ward erosion of the cirque walls. If three or more radiating glaciers cut headward until their cirques meet, high, sharp pointed and steep sided peaks called horns form.

 

Glacial Valleys/Troughs

Glaciated valleys are trough-like and U-shaped with broad floors and relatively smooth, and steep sides. There may be lakes gouged out of rocky floor or formed by debris within the valleys. There can be hanging valleys at an elevation on one or both sides of the main glacial valley. Very deep glacial troughs filled with sea water and making up shorelines (in high latitudes) are called fjords/fiords.

 

Depositional landforms

 

Moraines

They are long ridges of deposits of glacial till. Terminal moraines are long ridges of debris deposited at the end (toe) of the glaciers. Lateral moraines form along the sides parallel to the glacial valleys. The lateral moraines may join a terminal moraine forming a horse-shoe shaped ridge. deposits varying greatly in thickness and in surface topography are called ground moraines.

 

Eskers

When glaciers melt in summer, the water flows on the surface of the ice or seeps down along the margins or even moves through holes in the ice. These waters accumulate beneath the glacier and flow like streams in a channel beneath the ice. Such streams flow over the ground (not in a valley cut in the ground) with ice forming its banks. Very coarse materials like boulders and blocks along with some minor fractions of rock debris carried into this stream settle in the valley of ice beneath the glacier and after the ice melts can be found as a sinuous ridge called esker.

Outwash Plains

The plains at the foot of the glacial mountains or beyond the limits of continental ice sheets are covered with glacio-fluvial deposits in the form of broad flat alluvial fans which may join to form outwash plains of gravel, silt, sand and clay.

Drumlins

Drumlins are smooth oval shaped ridge-like features composed mainly of glacial till with some masses of gravel and sand. The long axes of drumlins are parallel to the direction of ice movement. They may measure up to 1 km in length and 30 m or so in height.

 

Arid Landforms

Wind is one of the  dominant agents in hot deserts. The wind action creates a number of interesting erosional and depositional features in the deserts.

 

EROSIONAL LANDFORMS

Pediments and Pediplains

. Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris, are called pediments. through parallel retreat of slopes, the pediments extend backwards at the expense of mountain front, and gradually, the mountain gets reduced leaving an inselberg which is a remnant of the mountain. That’s how the high relief in desert areas is reduced to low featureless plains called pediplains.

Playas

Plains are by far the most prominent landforms in the deserts. In times of sufficient water, this plain is covered up by a shallow water body. Such types of shallow lakes are called as playas where water is retained only for short duration due to evaporation and quite often the playas contain good deposition of salts.

. Deflation Hollows and Caves

Weathered mantle from over the rocks or bare soil, gets blown out by persistent movement of wind currents in one direction. This process may create shallow depressions called deflation hollows. Deflation also creates numerous small pits or cavities over rock surfaces. The rock faces suffer impact and abrasion of wind-borne sand and first shallow depressions called blow outs are created, and some of the blow outs become deeper and wider fit to be called caves.

Mushroom, Table and Pedestal Rocks

Many rock-outcrops in the deserts easily susceptible to wind deflation and abrasion are worn out quickly leaving some remnants of resistant rocks polished beautifully in the shape of mushroom with a slender stalk and a broad and rounded pear shaped cap above. Sometimes, the top surface is broad like a table top and quite often, the remnants stand out like pedestals.

Depositional Landforms

When the wind slows or begins to die down, depending upon sizes of grains and their critical velocities, the grains will begin to settle.

Sand Dunes

Dry hot deserts are good places for sand dune formation. Obstacles to initiate dune formation are equally important. There can be a great variety of dune forms Crescent shaped dunes called barchans with the points or wings directed away from wind .Parabolic dunes form when sandy surfaces are partially covered with vegetation. That means parabolic dunes are reversed barchans with wind direction being the same.

Seif is similar to barchan with a small difference. Seif has only one wing or point. Longitudinal dunes form when supply of sand is poor and wind direction is constant. They appear as long ridges of considerable length but low in height. Transverse dunes are aligned perpendicular to wind direction. These dunes form when the wind direction is constant and the source of sand is an elongated feature at right angles to the wind direction.

 

 

An atmosphere is a layer of gases surrounding a planet or other material body, that is held in place by the gravity of that body. Many of the planets in this solar system have atmospheres, but none that we know of have an atmosphere quite like ours – one that can support life.

The air is a mixture of several gases. The air encompasses the earth from all sides. The air surrounding the Earth is called the atmosphere. The atmosphere is an integral part of our Earth. It is connected with the earth due to the gravitational force of the earth. It helps in stopping the ultra violet rays harmful for the life and maintain the suitable temperature necessary for life. The air is essential for the survival of all forms of life on the earth.

Composition of the atmosphere

 

The atmosphere is made up of different types of gases, water vapors and dust particles. The composition of the atmosphere is not static. It changes according to the time and place.

• Nitrogen N2  78%
• Oxygen O2 20.9%
• Argon Ar 9.34%
• Carbon dioxide CO2 3.84 %
• Neon
• Helium
• Methane
• Krypton
• Hydrogen
• Nitrous oxide
• Xenon
• Ozone

Water vapor is unique in that its concentration varies from 0-4% of the atmosphere depending on where you are and what time of the day it is.  In the cold, dry artic regions water vapor usually accounts for less than 1% of the atmosphere, while in humid, tropical regions water vapor can account for almost 4% of the atmosphere.  Water vapor content is very important in predicting weather.

Greenhouse gases whose percentages vary daily, seasonally, and annually have physical and chemical properties which make them interact with solar radiation and infrared light (heat) given off from the earth to affect the energy balance of the globe.

The atmosphere also change composition with height and can be divided into two layers. The lower layer is called the homosphere and has the composition we talked about earlier. It’s top is approximately the mesopause.

Above the homosphere lies the heterosphere, a layer in which the gases are stratified into four shells. The lowermost shell is dominated by molecular nitrogen (N2); next, a layer of atomic oxygen (O) is encountered, followed by a layer dominated by helium atoms (He), and finally, a layer consisting of hydrogen atoms (H).

Importance of various components of atmosphere are:-

(i) Oxygen is very important for the living beings.
(ii) Carbon dioxide is very useful for the plants.
(iii) Dust particles present in the atmosphere create suitable conditions for the precipitation.
(iv) The amount of water vapour in the atmosphere goes on changing and directly affects the plants and living beings.
(v) Ozone protects all kinds of life on the earth from the harmful ultra violet rays of the sun.

 

Structure  and stratification of the atmosphere

Variations of temperature, pressure and density are much larger in vertical directions than in horizontal. This strong vertical variations result in the atmosphere being stratified in layers that have small horizontal variability compare to the variations in the vertical.

The atmosphere can be divided into five layers according to the diversity of temperature and density.
(a) Troposphere :-It is the lowest layer of the atmosphere. The height of this layer is about 18 kms on the equator and 8 kms on the poles. The main reason of higher height at the equator is due to presence of hot convection currents that push the gases upward.
This is the most important layer of the atmosphere because all kinds of weather changes take place only in this layer. Due to these changes development of living world take place on the earth. The air never remains static in this layer. Therefore this layer is called changing sphere or troposphere.
The environmental temperature decreases with increasing height of atmosphere. It decreases at the rate of 1 C at the height of 165 metre. This is called Normal lapse rate.
The upper limit of the troposphere is called tropopause. This is a transitional zone. In this zone characteristics of both the troposphere and ionosphere are found.

(b) Stratosphere :-This layer lies above the troposphere and spread upto the height of 50 kms from the Earth’s surface. Its average extent 40 kms.
The temperature remains almost the same in the lower part of this layer upto the height of 20 kms. After this the temperature increases slowly with the increase in the height. The temperature increases due to the presence of ozone gas in the upper part of this layer.
Weather related incidents do not take place in this layer. The air blows horizontally here. Therefore this layer is considered ideal for flying of aircrafts.

(c) Mesosphere :-It spreads above the stratosphere upto the height of 80 kms. from the surface of the earth. It’s extent is 30 kms. Temperature goes on decreasing and drops upto – 100 C.

(d) Ionosphere :-The ionosphere lies from about 80-400 km in height and is electrically charged as short wave solar radiation ionizes the gas molecules. The electrical structure of the atmosphere is not uniform and is arranged into three layers, D, E, and F. Since the production of charged particles requires solar radiation, the thickness of each layer, particularly the D and E layers, changes from night to day. The layers weaken and disappear at night and reappear during the day. The F layer is present during both day and night. This change in height of the various electrically charged layers doesn’t effect the weather, but does effect radio signals.

The auroras also take place in the ionosphere since this is the electrically charged layer. The aurora borealis (northern lights) and aurora australis (southern lights) is closely correlated to solar flare activity.

(e) Exosphere:-This is the last layer of the atmosphere located above ionosphere and extends to beyond 400 km above the earth.  Gases are very sparse in this sphere due to the lack of gravitational force. Therefore, the density of air is very less here.

 

The greenhouse effect is a natural process that warms the Earth’s surface. When the Sun’s energy reaches the Earth’s atmosphere, some of it is reflected back to space and the rest is absorbed and re-radiated by greenhouse gases. It is the process by which radiation from a planet’s atmosphere warms the planet’s surface to a temperature above what it would be without its atmosphere. If a planet’s atmosphere contains radioactively active gases (i.e., greenhouse gases) the atmosphere will radiate energy in all directions.

The greenhouse effect comes from molecules that are more complex and much less common. Water vapour is the most important greenhouse gas, and carbon dioxide (CO2) is the second-most important one. Methane, nitrous oxide, ozone and several other gases present in the atmosphere in small amounts also contribute to the greenhouse effect. In the humid equatorial regions, where there is so much water vapour in the air that the greenhouse effect is very large, adding a small additional amount of CO2 or water vapour has only a small direct impact on downward infrared radiation. However, in the cold, dry polar regions, the effect of a small increase in CO2 or water vapour is much greater. The same is true for the cold, dry upper atmosphere where a small increase in water vapour has a greater influence on the greenhouse effect than the same change in water vapour would have near the surface.

Green house effects changes are due to:-

• Energy;
•  Industry;
•  Agriculture;
•  Waste; and
• Land Use Land Use Change