It roughly extends to a height of 8 km near the poles and about 18 km. at the equator.
- Thickness of troposphere at the equator is the greatest because heat is transported to great heights by strong convection currents.
- Temperature decreases with height in this layer, roughly at the rate of 1°C for 165 meters of ascent. This is known as normal lapse rate.
- This layer contains dust particles and over 90% of the earth’s water vapour.
- All vital atmospheric processes leading to various climatic and weather conditions take place in this layer.
- Aviators of jet aeroplanes often avoid this layer due to presence of bumpy air pockets and fly through tropopause which separates troposphere from stratosphere.
- Here air is at rest and movement is almost horizontal. It is an isothermal region and is free of clouds, dust and water vapour.
- Its upper strata is rich in ozone which prevents ultra-violet radiation by absorbing them.
- Upto a height of 20 km. temperature remains constant and afterwards it gradually increases upto a height of 50 kms.
- It extends up to a height of 80 km. from the earth’s surface.
- Temperature decreases with height again and reaches up to 100°C at the height of 80 km.
- It extends upto a height of 150 km. It is a region of electrically charged or ionized air lying next to mesophere.
- It protects us from falling meteorites.
- If reflects Radio waves.
- It is due to this sphere that the radio waves travel in curved path and that radio-transmission is received by us.
- Aurora comprises an electric discharge and is usually accompanied by a magnetic storm.
- Because of this electric discharge the air particles at higher attitude begin to shine.
- This light in the Northern Hemisphere is called Aurora Borealis and in southern hemisphere as Aurora Australis.
- Insolation is the incoming solar radiation. It is received in the form of short waves.
- The earth’s surface receives this radiant energy at the rate of two calories per square centimeter per minute.
- Of the total radiant solar energy that strikes the outer surface of the atmosphere, about 51% is able to reach the earth’s surface directly or indirectly (scattered) and is absorbed.
- The rest in lost through scattering (by gas molecules), reflection (by clouds) and absorption (largely by water vapour) passing through the atmosphere.
- The amount of insolation reaching the earth’s surface and its effectiveness per unit are depend upon.
- The angle of incidence or the inclination of sun’s rays;
- The duration of sun-shine or the length of the day, and
- Transparency of the atmosphere.
Factors controlling temperature
Latitude, Differential Heating of land and water, Winds , Ocean currents , Attitude , Aspect , Cloud cover etc.
- The difference between the mean temperature of any place and the mean temperature of its parallel is called the temperature anomaly or thermal anomaly. It thus expresses, deviation from the normal.
- The largest anomalies occur in the Northern Hemisphere and smallest in the southern Hemisphere.
- The anomaly is said to be negative when the temperature at a place is less than the expected temperature of the latitude and positive when the temperature is more than the expected temperature of the latitude.
- For the year as a whole the anomalies are negative over the continents from about 40° latitude towards the poles and positive towards the equator.
- On the Oceans, the anomalies are positive poleward from about 40° latitude and negative towards the equator.
Atmospheric pressure depends primarily on three factors: Altitude, Temperature, Earth Rotation
Combined Influence of Rotation and Temperature on Pressure
- Low temperatures at the poles result in the contraction of air and hence the development of high pressure.
- High temperatures along the equator results in the expansion of air and hence the development of low pressure. This is called the Doldrums Low Pressure.
- Air blowing away from the poles crosses parallels which are getting longer.
- It, therefore, spreads out to occupy greater space, that is, it expands and its pressure falls.
- These low pressure belts become noticeable along parallels 60° N and 60° S.
- As air moves away from the poles, more air moves in from higher levels to take its place. Some of this comes from the rising low pressure air in latitudes 60° N and 60° S.
- Air rising at the equator spreads out and moves towards the poles.
- As it does so it crosses parallels which are getting shorter and it has to occupy less space. It contracts and its pressure rises.
- This happens near to latitudes 30° N and 30° S and in these latitudes the air begins to sink, thus, building up the high pressure belts of these latitudes.
- These are called the Horse Latitude High Pressures.
- They blow from the Polar High Pressures to the Temperate Low Pressures.
- They are better developed in the Southern Hemisphere than in the Northern Hemisphere.
- They are irregular in the Northern Hemisphere.
- They blow from the Horse Latitudes to the Temperate Low Pressures.
- They are deflected to the right to become the S. Westerlies in the Northern Hemisphere and to the left to become the N. Westerlies in the Southern Hemisphere.
- They are variable in both direction and strength. They contain depressions.
- The word ‘trade’ comes from the Saxon word tredan which means to tread or follow a regular path.
- They blow from the Horse Latitudes to the Doldrums.
- They are deflected to the right to become the N.E. Trades in the Northern Hemisphere and to the left to become the S.E. Trades in the Southern Hemisphere.
- They are very constant in strength and direction.
- They sometimes contain intense depressions.
- The word Himalaya means the abode of snow, as most of its higher peaks are covered with perpetual snow.
- They are the youngest and the highest folded mountains on the earth, rising to over 8,000 m above the sea level, which run in an east-west direction along the northern boundary of India for 2,400 km and are 240-500 km broad.
- Their real stretch is between the Indus and the Brahmaputra, thus forming India’s northern frontier from Jammu and Kashmir to Arunachal Pradesh.
- The Himalayas comprise three almost parallel fold ranges inerpersed with deep valleys and extensive plateaus.
The Himadri or the Greater Himalayas: This is the innermost (northernmost), loftiest and most continuous of the Himalayan ranges with an average height of 6,000 m and always covered with snow.
- The alpine zone (4,800m and above) vegetation comprises rhododendrons, trees with crooked and twisted stems, thick shrubs with a variety of beautiful flowers and grass.
- Some of the world’s loftiest peaks are found in greater Himalayas such as.
- Mt. Everest (8,848m, located in Nepal, highest peak in the world).
- Mt. Godwin Austin or K2 (8,611m, located in India but under Pakistan occupational
- Kanchanjunga (8,596 m, in India).
- Dhaulagiri (8,166 m, in Nepal).
- Nanga Parbat (8,126m, in India).
- Nanda Devi (7,817 m, in India) etc.
- Few passes, though at a very high elevation (over 4,500 m) and snowbound for most of the year, occur in these ranges such as Bara Lapcha La and shipli La (Himachal Pradesh), Thaga la, Niti and Lipu Lekh; (UP), Nathula and Jelep La (Sikkim), and Brazil and Jogila (Kashmir)etc.
The Himachal or the Lesser or Middle Himalayas: Lying to the north of Siwaliks, they have an averages elevation of about 3,500-5000m with an average width throughout the year.
- The southern slopes are rugged and bare while northern slopes are gentler and have thick to 2,400 m elevation, coniferous forests are found at 2,400 to 3,000 m elevation and in lower slopes are found chir, deodar, blue pines, oak and magnolia.
- Some of the important ranges of Lesser Himalayas are Pir Panjal, Nag Tiba, Mahabharat and Mussoorie range. These are snowcapped but less inaccessible.
- Some of the important hill stations of Himachal range are Chakrata, Mussoorie, Shimla, Ranikhet, Nainital, Almora and Darjeeling, all situated at height between 1,500 m and 2,000 m above sea level.
The Siwaliks or Outer Himalayas: They are the outermost range of Himalayas made up mostly of tertiary sediments brought by rivers from the main Himalayan ranges.
- They consists of foot-hills running to the south of Himachal from Jammu and Kashmir to Arunachal Pradesh.
- They are 1,000 to 1,500 m high with a width ranging from 15 to 50 km. The region is mostly illdrained (like that of Terai) but cooled and finely wooded. Valleys, termed duns, separate the Siwalik range from the Himachal.
- Some of the duns in these ranges are: Udhampur and Kotli valleys in Jammu and Dehradun, Kota, Patli and Chaukhamba valleys in UP.
The Trans Himalayas or Tibetan Himalayas
- It comprises the Karakoram and the Kailash range.
- The trans-Himalaya consists of lofty peaks and glaciers. Some important peaks are K2, the highest peak (8,611m), Hidden Peak (8,068m), Broad Peak (8,047 m), Gasherbrum II (8,035 m), Rakaposhi (7,788 m) and Haramosh (7,397 m).
- The largest glaciers are Hispar and Batura (over 57km long) of Hunza valley and Biafo and Baltaro (60 km long) of shigar Valley.
- The Siachen of Nubra Valley is the longest with a length of over 72 km.
|Facts to be Remembered|
Community Development programme launched (October).
Three-tier structure of local self-governing bodies (Panchayati Raj) launched (October).
Rural Electrification Corporation set up.
Drought Prone Areas Programme started (December).
A Joint Consultative Council on Community Development and Panchayati Raj constituted (December).
Crash Scheme for Rural Employment introduced.
Pilot Intensive Rural Employment Project (PIREP) lanuched.
Accelerated Rural Water Supply Programme started.
Food for Work Programme started (April).
Desert Development Programme started (April).
Integrated Rural Development Programme launched.
NREP and RLEGP merged into one single rural employment programme to be known as Jawahar Rozgar Yojana (JRY) (April)
Indira Awaas Yojana started.
Million Wells Scheme started.
The Parliament passed the Constitutional 73rd Amendment Act to grant constitutional status to the Panchayati Raj institutions (December).
Employment Assurance Scheme implemented (October).
National Social Assistance Programme (NSAP) launched (August).
Jawahar Gram Samridhi Yojana launched (1 April).
Swarnjayanti Gram Swarozgar Yojana launched (1 April).
Innovative Stream for Rural Housing and Habitat Development Scheme launched (1 April).
Adivasi Mahila Sashastikaran Yosana has been in troduced.
National Commission for Religious and Linguistic Minorities started functioning since March 21, 2005.
Significance of Himalayas
- The Himalayas are of great significance for the land and people of the subcontinent.
- Physical Barrier: The Himalayas act as physical barrier between the subcontinent.
- Birthplace of Rivers: The massive snowfields and glaciers of the Himalayas are sources of many perennial rivers upon whose water depends much of irrigation and hydroelectric power of the Indo-Gangetic plain. The silt brought by these rivers have made the Indo-Gangetic plain very fertile, making it one of the most densely populated regions in the world.
- Influence on Climate: The Himalayas protect the Indo-Gangetic plain from the bitterly cold winds which blow from Central Asia and Tibet during winter. It compels the rain-bearing winds blowing from the sea in the south to shed all their load of rain on the Northern Plain.
- Flora and Fauna: The slopes of these mountains are forested and have in them valuable resources of timber and other useful products. These forests also provide shelter to a wide variety of wild life which is rarely seen anywhere else.
- Mineral Resources: The Himalayas have commercially valuable minerals such as copper, lead, zinc, bishmuth, antimony, nickel, cobalt and tungsten. They are also the storehouse of precious and semi-precious stones. Coal and petroleum are the other mineral fuels found in this region.
- Other Economic Resources: Green pasture of lower Himalayas have enabled sheep and goat rearing an important occupation. Sericulture is also carried on here.
- Tourist Abode: When the neighbouring lands are suffering from scorching heat in summer, the lower and upper range of Himalayas, because of their height, enjoy a cool and pleasant climate thus attracting a large number of tourists during spring and summer seasons.
The Great Northern Plains
- The great Northern Plain or the Indo-Gangetic Plain lies between the great Himalayas in the north and the plateau of peninsular India in the south.
- It forms a great curve from the Arabian Sea to the Bay of Bengal, nearly 2,400 km long and around 250-320 km broad, the most extensive plain indeed.
- It is said that this region was once a vast depression, which was filled with the silt brought down by the three great Himalayan rivers, namely the Indus, the Ganga and the Brahmaputra and their numerous tributaries.
- At some places, the thickness of the alluvium is as much as 2,000 m and it contains some of the richest soils.
- In these remarkably homogenous alluvial expanses are found little differences of slopes and aspect, such as, the Bhangar and that Khadar.
- The Bhangar refers to the upland formed by deposition of older alluvium in the river beds and the khadar are lowlands formed by deposition of detritus of new alluvium in the river beds.
- These two are separated by river terraces.
Bhabar and Terai: Bhabar or Ghar, which forms the northern boundary of the great plains, includes those regions where the Himalayas and other hilly regions join the plains.
- In this region coarse sand and pebbles are deposited which are brought down from the hills by the mountain streams.
- Bhabar lands are narrower in the east and extensive in the western and north-western hilly region. In this region only larger rivers flow on the surface while dry river courses are also marked in which water of smaller streams sinks underground and later reappears on the surface where the plains begin.
- This water converts large areas along the rivers into swamps known as terai, which is mostly ill-drained and densely forested.
The Western or Rajasthan Plains : These plains include the arid plain of Rajasthan, known as Marusthali of Thar, and the adjoining Bagar areas to the west of Aravalli, covering an area of 1.75 lakh km2.
- The presence of dry river beds (Saraswati, Drisdavati) proves that the region was once fertile.
- Luni, whose water is sweet in the upper reaches and saltish by the time it reaches the sea, is the only flowing river at present.
- There are several salt lakes in the region such as the Sambhar, Degana, Kuchaman and Didwana; from which table salt is obtained. In most of the region shifting and dunes occur.
The Punjab-Haryana Plains: These plains extending for 640 km from north-east to south-west and 300 km from west to east, covering an area of 1.75 lakh km2, are remarkably flat with average elevation being 200 to 204 m.
- These plains owe their formation to the Sutlej, the Beas and the Ravi rivers. Many low laying flood plains (called bet) are found here.
- The Bari Dab between Ravi and Beas rivers, the Bist Doab between the Beas and Sutlej and the Malwa plain are relatively more fertile plains which are irrigated by many canals.
The Ganga Plains: The Ganga plains, spread over Uttar Pradesh, Bihar and West Bengal, occupy an area of 3.57 lakh km2.
- The Yamuna that flows near the western boundary of the plain for about 800 km joins the Ganga at Prayag.
- The Ganga-Yamuna Doab comprising the Rohilkhand and the Avadh plain is the fertile area that is drained by the tributaries of Ganga.
The North Bengal Plains: The plains extending from the foot of Eastern Himalayas to the northern limb of Bengal basin cover an area of 23,000 km2.
- These plains are drained by the rivers joining the Brahmaputra and tributaries of Ganga in the western and eastern part respectively.
- The Bengal basin mainly comprises the Ganga delta that is low and flat and would be completely submerged if the sea level rises by 6m.
Brahmaputra Plains: This is a low level plain, rarely more than 80 km broad, surrounded by high mountains on all sides except on the west.
- These slope from east to west and are liable to frequent floods.
- These plains are the aggradational work of the Brahmaputra, Sesiri, Dihang and the Lohit. Geologically these are the least interesting part of India.
Significance of the Great Plans
- The northern plain is riverine region, being beautifully endowed with fertile soil, favourable climate, flat surface rendering possible the construction of roads and railways, and slow moving rivers.
- All these factors have made this plain very important.
- An extensive system of irrigation,, developed on the tributaries of the Sutlej, the Ganga, the Yamuna and others, has turned the once dreary and desolate tracts of the Punjab, Haryana, northern Rajasthan and UP., into populous spots.