The temperature is the measurement in degrees of how hot (or cold) a thing (or a place) is.
The temperature of the atmosphere is not same across the Earth. It varies in spatial and temporal dimensions. The temperature of a place depends largely on the insolation received by that place. The interaction of insolation with the atmosphere and the earth’s surface creates heat which is measured in terms of temperature. It is important to know about the temperature distribution over the surface of the earth to understand the weather, climate, vegetation zones, animal and human life etc. following factors determine the temperature of air at any place.

1. The latitude of the place – Intensity of insolation depends on the latitude. The amount of insolation depends on the inclination of sun rays, which is further depends upon the latitude of the place. At the equator sun’s rays fall directly overhead throughout the year. Away from the equator towards poles, the inclination of the Sun’s rays increases. In conclusion, if other things remain the same, the temperature of air goes on decreasing from the equator towards poles.
2. The altitude of the place – the atmosphere is largely heated indirectly by re-radiated terrestrial radiation from the earth’s surface. Therefore, the lower layers of the atmosphere are comparatively warmer than the upper layers, even in the same latitudes. For example, Ambala (30 21’ N) and Shimla (31 6’) are almost at the same latitude. But the average temperature of shimla is much lower than the Ambala. It is because Ambala is located in plain at an altitude of 272 m above sea level whereas Shimla is located at an altitude of 2202 m above sea level. In other words, the temperature generally decreases with increasing height (figure 6(a)). The rate of decrease of temperature with height is termed as the normal lapse rate. It is 6.5°C per 1,000 m. That’s why, the mountains, even in the equatorial region, have snow covered peaks, like Mt. Kilimanjaro, Africa.
3. Distance from the Sea – the land surface is heated at a faster rate than the water N surface. Thus the temperature of the air over land and water surfaces is not the same Student Notes: at a given time. In summers, the sea water is cooler than the land and in winters, land is much colder than the sea water. The coastal areas experience the sea breezes during the daytime and the land breezes during the night time. This has a moderating influence on the temperature of the coastal areas. Against this the places in the interior, far away from the sea, have extreme climate. The daily range of temperature is less near the coastal area and it increases with increase in distance from the sea coast (figure 6(b)). The low daily range of temperature is the characteristic of marine climate. That’s why, the people of Mumbai have hardly any idea of extremes of temperature.

(a) Horizontal Distribution of Temperature
Distribution of temperature across the latitudes over the surface of the earth is called its horizontal distribution. On maps, the horizontal distribution of temperature is commonly shown by “Isotherms”, lines connecting points that have equal temperatures. An isotherm is made of two words ‘iso’ and ‘therm’, ‘Iso’ means equal and ‘therm’ means” temperature. If you study an isotherm map you will find that the distribution of temperature is uneven. The factors responsible for the uneven distribution of temperature are as follows:
(i) Latitude
(ii) Land and Sea Contrast
(iii) Relief and Altitude
(iv) Ocean Currents
(v) Winds
(vi) Vegetation Cover
(vii) Nature of the soil
(viii) Slope and Aspect

(b) Vertical Distribution of Temperature
The permanent snow on high mountains, even in the tropics, indicate the decrease of temperature with altitute. Observations reveals that there is a fairly regular decrease in temperature with an increase in altitude. The average rate of temperature decrease upward in the troposphere is about 6 C per km, extending to the tropopause. This vertical gradient of temperature is commonly referred to as the standard atmosphere or normal lapse rate, but is varies with height, season, latitude and other factors. Indeed the actual lapse rate of temperature does not always show a decrease with altitude.

Temperature Inversion

Temperature decreases with increase in altitude. In normal conditions, as we go up, temperature decreases with normal lapse rate. It is 6.5°C per 1,000 m. Against this normal rule sometimes, instead of decreasing, temperature may rise with the height gained. The cooler air is nearer the earth and the warmer air is aloft. This rise of temperature with height is known as Temperature inversion. Temperature inversion takes place under certain specific conditions. These are discussed below:

•  Long winter nights – if in winters the sky is clear during long nights, the terrestrial radiation is accelerated. The reason is that the land surface gets cooled fairly quickly. The bottom layer of atmosphere in contact with the ground is also cooled and the upper layer remains relatively warm.
• Cloudless clear sky – The clouds obstruct the terrestrial radiation. But this radiation does not face any obstacles for being reflected into space when the sky is clear. Therefore the ground is cooled quickly and so is the air in contact with it cooled.
• Dry air – humid air absorbs the terrestrial radiation but dry air is no obstruction to terrestrial radiation and allows the radiation to escape into space.
• Calm atmosphere – the blowing of winds bring warm and cold air into contact. Under conditions of calm atmosphere the cold air stays put near the ground.
• Ice covered surface – in ice covered areas due to high albedo less insolation is received. During night due to terrestrial radiation most of the heat is lost to atmosphere and the surface is cooled. The air in contact with it is also cooled but the upper layer remains warm.

 

 

Most of the knowledge we have about Earth’s deep interior comes from the fact that seismic waves penetrate the Earth and are recorded on the other side.  Earthquake ray paths and arrival times are more complex than illustrated in the animations, because velocity in the Earth does not simply increase with depth. Velocities generally increase downward, according to Snell’s Law, bending rays away from the vertical between layers on their downward journey; velocity generally decreases upward in layers, so that rays bend toward the vertical as they travel out of the Earth . Snell’s Law also dictates that rays bend abruptly inward at the mantle/outercore boundary (sharp velocity decrease in the liquid) and outward at the outer core/inner core boundary (sharp velocity increase).

Major Points to remember about P S and Love waves

• P wave or primary wave. This is the fastest kind of seismic wave, and, consequently, the first to ‘arrive’ at a seismic station.
• The P wave can move through solid rock and fluids, like water or the liquid layers of the earth.
• P waves are also known as compressional waves.
• S waveor secondary wave, which is the second wave you feel in an earthquake. An S wave is slower than a P wave and can only move through solid rock, not through any liquid medium.
• Travelling only through the crust, surface wavesare of a lower frequency than body waves, and are easily distinguished on a seismogram as a result.

 

Earth’s Layers – Earth’s Composition

The Crust of Earth

It is the outermost and the thinnest layer of the earth’s surface, about 8 to 40 km thick. The crust varies greatly in thickness and composition – as small as 5 km thick in some places beneath the oceans, while under some mountain ranges it extends up to 70 km in depth.

The crust is made up of two layers­ an upper lighter layer called the Sial (Silicate + Aluminium) and a lower density layer called Sima (Silicate + Magnesium).The average density of this layer is 3 gm/cc.

The Mantle of Earth

This layer extends up to a depth of 2900 km.

Mantle is made up of 2 parts: Upper Mantle or Asthenosphere (up to about 500 km) and Lower Mantle. Asthenosphere is in a semi­molten plastic state, and it is thought that this enables the lithosphere to move about it. Within the asthenosphere, the velocity of seismic waves is considerably reduced (Called ‘Low Velocity

The line of separation between the mantle and the crust is known as Mohoviricic Discontinuity.

 

The Core of Earth

Beyond a depth of 2900 km lies the core of the earth.The outer core is 2100 km thick and is in molten form due to excessive heat out there. Inner core is 1370 km thick and is in plasticform due to the combined factors of excessive heat and pressure. It is made up of iron and nickel (Nife) and is responsible for earth’s magnetism. This layer has the maximum specific gravity.The temperatures in the earth’s core lie between 2200°c and 2750°c. The line of separation between the mantle and the core is called Gutenberg­Wiechert Discontinuity.

 

 

 

 

 

• An increase in the average temperature of Earth’s near surface air and oceans since the mid-20^th century
• 4^th assessment report of IPCC: global temperature increased 74+0.18 degree C during the 20^th century.
• Caused by greenhouse gases
  • Water vapour, Co2, Methane, Nitrous Oxide, Ozone, CFCs (in order of abundance)
• Since the industrial revolution, the burning of fossil fuels has increased the levels of Co2 in the atmosphere from 280 ppm to 390 ppm.

 

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.

 

 

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