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What is Climate?, Climate is the characteristic condition of the, atmosphere near the earth's surface at a certain, place on earth., It refers to the sum total of weather conditions and, variation over a large area for a long period of time., It is the long-term weather of that area which, remains at least 30 years., , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 2
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What is Weather?, Weather refers to the state of, atmosphere over an area at, any point of time. The, elements of both weather, and climate are same. It is the, combination of temperature,, humidity, precipitation, wind,, cloudiness, and, other, atmospheric conditions at a, specific time., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 3
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Monsoon, The word monsoon is derived from the Arabic word ‘mausim’, which literally means season., ‘Monsoon’ refers to the seasonal reversal in the wind, direction during a year., The World is divided into a number of Climatic Regions. The, Climate of India is described as the ‘monsoon’ type. This type, of climate is found in South and Southeast Asia. But, there are, perceptible regional variations in climatic conditions within, the country., Two important elements viz., temperature and precipitation,, often vary from place to place and season to season., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 4
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Difference in Temperature, In summer, the temperature in parts of Rajasthan Desert, is 50°C, and it is around 20°C in Pahalgam in J & K. On, a winter night, temperature at Drass in J & K may less, than -45°C, and at Tiruvananthapuram it may be of, 22°C., In some places temperature between day and, night temperature differs. In the Thar Desert, it rise to, 50°C, in day and drop down to near 15°C in night. But, in the Andaman and Nicobar islands or in Kerala, there, is no much difference in day and night temperatures., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 5
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Precipitation, Precipitation varies in its form, types and amount and, seasonal distribution. It is in the form of snowfall in the, upper parts of Himalayas, it rains over the rest of the, country. The annual precipitation varies from 400 cm in, Meghalaya to less than 10 cm in Ladakh and western, Rajasthan. Most parts of the country receive rainfall from, June to September. But Tamil Nadu coast gets rain during, October and November., Rainfall generally decrease from east to west in the, Northern Plains. These variations have given rise to, variety in lives of people, their food, clothes and houses., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 6
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Vegetation, Vegetation can affect both temperature and, the precipitation patterns in an area., , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 7
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FACTORS AFFECTING CLIMATE, , RELATED TO AIR, PRESSURE & WIND, , RELATED TO LOCATION, , •Latitude, , Surface pressure & wind, , •Altitude, , Upper air circulation, , •Relief Features, , Western cyclones, , •Distance from Sea, •The Himalayan Mt., •Distribution of Land & water, 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 9
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Latitude, Latitude is the, distance a place, lies north or, south of the, equator and is, measured by an, imaginary, line, called lines of, latitude., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 10
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LATITUDE, , High range, of Temp, , High Temp, Low range, , EQUATORIAL REGION, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 11
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Latitude, As latitude increases, the intensity of solar energy, decreases. Due to curvature of the Earth, the, amount of solar energy varies according to latitude., In India, the Tropic of Cancer passes through the middle, of the country from the Rann of Kuchchh in the west to, Mizoram in the east., Almost half of the country, lying south of the Tropic of, Cancer, belongs to the tropical area. All the remaining, area, north of the Tropic, lies in the sub-tropics., Therefore, India’s climate has characteristics of tropical, as well as subtropical climates., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 12
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Tropical, Temperate and Polar Zones, • The tropical zone is between 23.5o north (the tropic of, Cancer) and 23.5o south (the tropic of Capricorn) of the, Equator. The Sun’s rays are most intense and the, temperatures are always warm., • The temperate zones are between 23.5o and 66.5o, north and between 23.5o and 66.5o south of the, Equator. The Sun’s rays strike Earth at a smaller angle, than near the Equator., • Polar zones are between 66.5o north and south, latitudes and the poles. The sun’s rays strike Earth at a, very small angle in the polar zones., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 13
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Highland Climates, In general, highland climates are cooler and wetter than, nearby areas at lower elevations., , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 14
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Earth’s Major Climate Zones, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 15
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North Frigid Zone, , Temperate Zone, , Torrid Zone, , Temperate Zone, , South Frigid Zone, 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 16
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ALTITUDE, Temperature decreased from low to high altitude, , HIGH ALTITUDE, , AGRA, 160C in Jan, , DARJILING, 40C in January, , LOW ALTITUDE, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 17
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Air Temperature decreases with altitude., , As elevation increases, the air gets cooler because of, the energy drawn from the surroundings., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 18
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Factors That Affect Climate, Water Bodies, Large bodies of water such as lakes and oceans have an, important effect on the temperature of an area because, the temperature of the water body influences the, temperature of the air above it., , Atmospheric Circulation, Global winds are another factor that influences climate, because they distribute heat and moisture around Earth., , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 19
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Natural Processes That Change Climates, Solar Activity, When the Sun is most active, it contains dark blemishes, called sunspots. The formation of sunspots appears to, correspond with warm periods in Europe and North, America., , Earth Motions, Geographic changes in Earth’s land and water bodies, cause changes in climate. Changes in the shape of, Earth’s orbit and the tilt of Earth on its axis are other, Earth motions that affect global climates., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 20
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Human Impact on Climate Changes, The Greenhouse Effect, The greenhouse effect is a natural warming of both, Earth’s lower atmosphere and Earth’s surface from solar, radiation being absorbed and emitted by the, atmosphere., , Global Warming, As a result of increased levels of carbon dioxide and, other greenhouse gases, global temperatures have, increased. This increase is called global warming., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 21
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The Pressure and Surface Winds, The pressure and wind system of any area depend on the latitude, and altitude of the place. It influences the temperature and rainfall, pattern., The climate and weather conditions in India are governed by the, atmospheric conditions like:, • Pressure and surface winds;, • Upper air circulation; and, • Western cyclonic disturbances and tropical cyclones., India lies in the north easterly winds region. These winds originate, from the subtropical high-pressure belt of the northern, hemisphere. They blow south, get deflected to the right due to the, Coriolis force and move towards equatorial low-pressure area., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 22
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SURFACE WIND, , POLAR HIGH, , SUB TROPICAL LOW PRESSURE, , NORTH-EAST, TRADE WIND, , SUB TROPICAL HIGH PRESSURE, , INTER TROPICAL CONVERGENCE ZONE, , SUB TROPICAL HIGH PRESSURE, SOUTH-EAST, TRADE WIND, SUB TROPICAL LOW PRESSURE, POLAR HIGH, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 23
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AIR MASSES CIRCULATE GLOBALLY, • At the Equator, temperatures are relatively, high. Land and water masses heat up and as a, result these warm the air over them., • Air heated at the equatorial region rises to, the top of the atmosphere., • More air rising beneath it forces the air mass, to spread north and south toward the poles., , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 24
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Coriolis Effect, • The rotation of the Earth causes all moving, objects in the Northern Hemisphere,, including air mass, to deflect to the right and, those in the Southern Hemisphere to move to, the left., • This Coriolis effect is absent at the Equator., • Coriolis Force- prevents a direct simple flow, from the Equator to the Poles., • This is also known as ‘Ferrel’s Law’., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 25
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The Pressure and Surface Winds in India, The pressure and wind conditions in India is unique. During winter,, there is a high-pressure in the north of the Himalayas. Cold dry, winds blow from this region to the low-pressure areas over the, oceans to the south. In summer, a low-pressure area develops over, interior Asia and in north-western India. This causes a complete, reversal of the direction of winds during summer. Air moves from, the high-pressure area over the southern Indian Ocean, in a southeasterly direction, crosses the equator, and turns right towards the, low-pressure areas over the Indian subcontinent. These are known, as the Southwest Monsoon winds. These winds blow over the, warm oceans, gather moisture and bring widespread rainfall over, the mainland of India., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 27
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LOW AND HIGH PRESSURE, , HIGH PRESSURE, IN WINTER, , ARABIAN, SEA, , BAY OF, BENGAL, , INDIAN OCEAN, 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 28
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DISTANCE FROM SEA, , SIMLA, , DELHI, , KOLKOTA, MUMBAI, , CHENNAI, , Coastal areas have equable climate where, as Interior parts have extreme climate., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 29
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Relief, • Relief too plays a major role in determining, the climate of a place. High mountains act, as barriers for cold or hot winds; they may, also cause precipitation if they are high, enough and lie in the path of rain-bearing, winds. The leeward side of mountains, remains relatively dry., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 30
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RELIEF, , Receives high, rainfall, , Receives low, rainfall, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 31
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RELIEF, The Rain Shadow Effect, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 32
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Jet Stream, • The upper air circulation in India is dominated, by a westerly flow, known as the jet stream., • These are a narrow belt of high altitude (above, 12,000 m) westerly winds in the troposphere., Their speed varies from about 110 km/h in, summer to about 184 km/h in winter., • Many jet streams have been identified. The, most constant are the mid-latitude and the sub, tropical jet stream., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 34
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JET STREAM IN WINTER, , TIBET, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 35
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Jet Stream, Jet streams are located at 27°-30° north latitude, are, known as subtropical westerly jet streams. Over India,, these jet streams blow south of the Himalayas, all, through the year except in summer. The western cyclonic, disturbances experienced in the north and north-western, parts of the country are brought in by this westerly flow., In summer, the subtropical westerly jet stream moves, north of the Himalayas with the apparent movement of, the Sun. An easterly jet stream, called the tropical, easterly jet stream blows over peninsular India,, approximately over 14°N during the summer., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 36
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JET STREAM IN SUMMER, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 37
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Western Disturbances, • The western cyclonic disturbances are weather, phenomena of the winter months brought in by the, westerly flow from the Mediterranean region. They, usually influence the weather of the north and northwestern regions of India. Tropical cyclones occur during, the monsoon as well as in October - November, and are, part of the easterly flow. These disturbances affect the, coastal regions of the country., • Thus very often the coast of Orissa and Andhra Pradesh, are affected by those disasters., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 38
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WESTERN DISTURBANCE, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 39
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OCEAN CURRENTS, Solar energy, wind, and Earth’s rotation creates Ocean currents, Current- the systematic patters of water movement., Gyres- two great circular water motion., Northern Hemisphere- the ocean current moves clockwise., Southern Hemisphere- the ocean current move anti-clockwise., , Trade winds push warm surface waters westward at the equator., As the waters encounter the continents, they split into northand south-flowing currents along the eastern coast, forming, north and south gyres., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 40
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Surface Water blown by the winds at point A will weirs to the, right of its initial path and continue eastward. Water at point, B weirs to the right and continues westward., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 41
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Winds driven by uneven solar heating and Earth’s spin, drive the, movement of the ocean’s surface currents. The prime movers are the, powerful westerlies and the persistent trade winds (easterlies), 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 44
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The Köppen Climate Classification System, The Köppen climate classification system uses, mean monthly and annual values of temperature and, precipitation to classify climates., According to the Köppen classification, the earth can be, divided into several major climatic zones and bands:, Tropical climate, Temperate climate, Subtropical climate, Oceanic climate, Arid climate, Continental climate, Equatorial climate, Subarctic climate, Semiarid climate, Polar climate, Mediterranean climate, Climate of Antarctica, 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 45
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Tropical Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 46
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Subtropical Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 47
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Arid Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 48
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Equatorial Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 49
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Semiarid Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 50
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Mediterranean Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 51
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Temperate Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 52
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Oceanic Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 53
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Continental Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 54
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Subarctic Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 55
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Polar Climate, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 56
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Polar climates are those in which the mean temperature, o, of the warmest month is below 10 C., , Polar Climate, 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 57
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Climate of Antarctica, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 58
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The Indian Monsoon, The climate of India is strongly influenced by, monsoon winds. The sailors who came to India in, historic times were one of the first to have noticed, the phenomenon of the monsoon. They benefited, from the reversal of the wind system as they came, by sailing ships at the mercy of winds. The Arabs,, who had also come to India as traders named this, seasonal reversal of the wind system ‘monsoon’., , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 59
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Atmospheric Conditions over the Indian Subcontinent, in the Month of January, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 60
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Atmospheric Conditions over the Indian Subcontinent, in the Month of June, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 61
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Facts of Mechanism of the Monsoons, In India, the monsoons are experienced in the tropical area, roughly between 20°N and 20°S. The Following facts are the, Mechanism of the Monsoons., (a) The differential heating and cooling of land and water, creates low pressure on the landmass of India while the, seas around experience comparatively high pressure., (b) The shift of the position of Inter Tropical Convergence Zone, (ITCZ) in summer, over the Ganga plain (this is the equatorial, trough normally positioned about 5°N of the equator. It is also, known as the monsoon-trough during the monsoon season)., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 62
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Inter Tropical Convergence Zone (ITCZ), The Inter Tropical Convergence Zone, (ITCZ) is a broad trough of low pressure, in equatorial latitudes. This is where the, northeast and the southeast trade winds, converge. This convergence zone lies, more or less parallel to the equator but, moves north or south with the apparent, movement of the sun., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 63
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Facts of Mechanism of the Monsoons, (c) The presence of the high-pressure area, east of, Madagascar, nearly at 20°S over the Indian Ocean. The, intensity of this high-pressure area affects the Indian, Monsoon., (d) The Tibetan plateau gets intensely heated during, summer, results in strong vertical air currents and the, formation of low pressure over the plateau at about 9 km, above sea level., (e) The movement of the westerly jet stream to the, north of the Himalayas and the presence of the tropical, easterly jet stream over the Indian peninsula during, summer., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 64
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Southern Oscillation, The changes in the pressure conditions over the southern, oceans also affect the monsoons. When the tropical eastern south, Pacific Ocean experiences high pressure, the tropical eastern Indian, Ocean experiences low pressure. But sometimes, there is a reversal in, the pressure conditions and the eastern Pacific has lower pressure in, comparison to the eastern Indian Ocean. This periodic change in, pressure conditions is known as the Southern Oscillation or SO., The difference in pressure over Tahiti in Pacific Ocean and Darwin in, northern Australia of Indian Ocean is predicted the intensity of the monsoons., If the pressure differences were negative, it would mean below average and, late monsoons. A feature connected with the SO is the El Nino, a warm ocean, current that flows past the Peruvian Coast, in place of the cold Peruvian, current, every 2 to 5 years. The changes in pressure conditions are connected, to the El Nino. Hence, the phenomenon is referred to as ENSO (El Nino, Southern Oscillations)., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 65
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SOUTHERN OSCILLATION, , Darwin, , Tahiti, , 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 66
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Effect of El Niño, El Nino is a name given to the, periodic development of a warm, ocean current along the coast of, Peru as a temporary replacement of, the cold Peruvian current. ‘El Nino’, is a Spanish word meaning ‘the, child’, and refers to the baby Christ,, as this current starts flowing during, Christmas. The presence of the El, Nino leads to an increase in seasurface, temperatures, and, weakening of the trade winds in the, region., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 67
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Beginning of the Monsoon, The duration of the monsoon is between 100-120 days from, early June to mid-September., During its arrival, the normal rainfall increases suddenly and, continues constantly for several days. This is known as the, ‘burst’ of the monsoon, and can be distinguished from the, pre-monsoon showers., The monsoon arrives at the southern tip of the Indian, peninsula generally by the first week of June., Subsequently, it proceeds into two –, (i) the Arabian Sea branch and, (ii) the Bay of Bengal branch., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 69
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Beginning of the Monsoon, The Arabian Sea branch reaches Mumbai about ten days later on, approximately the 10th of June. This is a fairly rapid advance., The Bay of Bengal branch also advances rapidly and arrives in Assam, in the first week of June. The lofty mountains causes the monsoon, winds to deflect towards the west over the Ganga plains., By mid-June the Arabian Sea branch of the monsoon arrives over, Saurashtra-Kuchchh and the central part of the country. The Arabian, Sea and the Bay of Bengal branches of the monsoon merge over the, north-western part of the Ganga plains., Delhi generally receives the monsoon showers from the Bay of Bengal, branch by the end of June (tentative date is 29th of June). By the July, first week, western Uttar Pradesh, Punjab, Haryana and eastern, Rajasthan experience the monsoon. By mid-July, the monsoon reaches, Himachal Pradesh and the rest of the country., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 70
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End of the Monsoon, Withdrawal or the retreat of the monsoon is a more gradual, process. The withdrawal of the monsoon begins in north-western, states of India by early September. By mid-October, it withdraws, completely from the northern half of the peninsula. Then it, quickly withdraw from the southern half of the peninsula. By, early December, the monsoon has totally withdrawn from the, country., , The islands receive the very first monsoon showers, from south to, north, between the last week of April and the first week of May., Then it withdraw from north to south during the first week of, December to the first week of January. By this time, the other, parts of the country is already influencing the winter monsoon., 02-03-2015, , R. Ezhilraman, PGT-Social Science, , 72
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RHYTHM OF SEASONS, , HOT WEATHER, , COLD WEATHER, , RETREATING MONSOON, , SOUTH WEST MONSOON, , Let us discuss each of them individually, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 75
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The monsoon type of climate is characterised by a distinct, seasonal pattern. The weather conditions greatly change from one, season to the other. These changes are particularly noticeable in, the interior parts of the country. But, the coastal areas do not, experience much variation in temperature though there is variation, in rainfall pattern., , In India, Four main seasons can be identified:, (i) the cold weather season,, (ii) the hot weather season,, (iii)the advancing monsoon and, (iv) the retreating monsoon with some regional variations., R. Ezhilraman, PGT-Social Science, 02-03-2015, , 76
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COLD WEATHER SEASON, ► It, extends, from, December to February., ► Vertical sun rays shift, towards, southern, hemisphere., ► North India experiences, intense cold where as, this season is not well, defined in south India., ► Light wind blow makes, this season pleasant in, south India., ► Occasional, tropical, cyclone visit eastern, coast in this season., , Tropical Cyclone, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 77
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The cold weather season begins from mid- November in northern India and, stays till February. December and January are the coldest months. The, temperature decreases from south to the north. The average temperature of, Chennai, on the eastern coast is between 24°-25° Celsius, while in the northern, plains, it ranges between 10°-15° Celsius. Days are warm and nights are cold., Frost is common in the north and the higher slopes of the Himalayas experience, snowfall., During winter, the northeast trade winds blow from land to sea. So, most part of, the country faces a dry season. Some amount of rainfall occurs on the Tamil, Nadu coast from these winds as, trade winds blow from sea to land., , In the northern part of the country, a feeble high-pressure region develops, with, light winds moving outwards from this area. Influenced by the relief, these, winds blow through the Ganga valley from the west and the northwest. The, weather is normally marked by clear sky, low temperatures and low humidity, and feeble, variable winds., R. Ezhilraman, PGT-Social Science, 02-03-2015, , 78
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TEMPERATURE- JANUARY, , 150, C, , 250, C, , 100, C`, 200, C, , 200, C, 200, C, , 200, C, 250, C, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 79
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PRESSURE- JANUARY, , HIGH, PRESSURE, , 101, 4, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 80
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In the northern plains, there is the inflow of cyclonic, disturbances from the west and the northwest. These lowpressure systems, from the Mediterranean Sea and western, Asia and move into India, along with the westerly flow. They, cause the winter rains (locally known as ‘mahawat’) over the, plains and snowfall in the mountains. Although the amount of, rainfall is small, it is more importance for cultivating the ‘rabi’, crops., But, the peninsular region does not have a well-defined cold, season. There is rare seasonal change in temperature, pattern during winters due to the moderating influence of the, sea., R. Ezhilraman, PGT-Social Science, 02-03-2015, , 81
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WIND DIRECTION- WINTER, , Bay of Bengal, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 82
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WINTER RAINFALL, RAINFALL DUE, TO WESTERN, DISTURBANCES, , RAINFALL DUE, TO NORTH EAST, WIND, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 83
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, , , , , , Winter is cold., Children dress warmly to, play in the snow., , Animals head to their winter, homes., , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 84
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HOT WEATHER SEASON, ► It extends from March to, May., ► Vertical sun rays shift, towards, Northern, hemisphere., ► Temperature, rises, gradually from south to, north., ► Highest, Temperature, experiences in Karnataka, in, March,, Madhya, Pradesh in April and, Rajasthan in May., , May 480C, , April 380C, , March 300C, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 85
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Due to the apparent northward movement of the Sun, the global, heat belt shifts northward. So, from March to May, it is hot weather, season in India. In March, the highest temperature is about 38°C, in, Deccan plateau. In April, temperatures in Gujarat and Madhya, Pradesh are around 42°C. In May, 45°C temperature is common in, the north-western parts of the country. In peninsular India,, temperatures remain lower due to the moderating influence of the, oceans., The summer months experience rising temperature and falling air, pressure in the northern part of the country. By the end of May, an, elongated low-pressure area develops in the region extending from, the Thar Desert in the northwest to Patna and Chotanagpur plateau, in the east and southeast. Circulation of air begins to set in around, this trough., R. Ezhilraman, PGT-Social Science, 02-03-2015, , 86
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TEMPERATURE- JULY, , 250, C, 300, C, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 87
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PRESSURE- JULY, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 88
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An important feature of the summer season is the ‘loo’. These are, strong, gusty, hot, dry winds blowing during the day, sometimes till, late evening over the north and North-western India. Direct, exposure to these winds may be harmful. Dust storms are very, common during May in northern India. These storms bring, temporary relief as they lower the temperature and may bring light, rain and cool breeze. This is also the season for localised, thunderstorms, associated with violent winds. In West Bengal,, these storms are known as the ‘Kaal Baisakhi’., By close of the summer season, pre-monsoon showers are common, especially, in Kerala and Karnataka. They help in the early ripening, of mangoes, and are often referred to as ‘mango showers’., R. Ezhilraman, PGT-Social Science, 02-03-2015, , 90
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, , , , , , Long, hot days., Summer fruit and, vegetables are ready to be, picked., You see many bees and, butterflies fly flower to, flower., , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 91
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Advancing Monsoon (The Rainy Season), SOUTH WEST MONSOON SEASON, , ► It extends from June to, September., ► Intense heating in north, west India creates low, pressure region., ► Low pressure attract the, wind from the surrounding, region., ► After having rains for a, few, days, sometime, monsoon fails to occur for, one or more weeks is, known as break in the, monsoon., , HIGH, LOW, TEMPERATURE, PRESSURE, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 92
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MONSOON WIND, , Arabian sea, Branch, , Bay of Bengal, Branch, , INTER TROPICAL, EQUATOR, CONVERGENCE ZONE, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 93
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ONSET OF SW MONSOON, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 94
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By early June, the low-pressure condition over the northern plains, attracts the trade winds of the southern hemisphere. These southeast trade winds originate over the warm subtropical areas of the, southern oceans. These winds are strong and blow at an average, velocity of 30 kmph. With the exception of the extreme north-west,, the monsoon winds cover the country in about a month., The south-west monsoon entirely changes the weather in India. The, Western Ghats receives heavy rainfall, more than 250 cm. The rain, shadow areas like Deccan Plateau and parts of Madhya Pradesh, also receives rain. The north-eastern part of the country receives, the maximum rainfall. Mawsynram in the southern ranges of the, Khasi Hills receives the highest average rainfall in the world., Rainfall in the Ganga valley decreases from the east to the west., Rajasthan and parts of Gujarat get scanty rainfall., R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 95
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The monsoon rains take place only for a few days at a time. They, are interspersed with rainless intervals. These breaks in monsoon, are related to the movement of the monsoon trough. The trough and, its axis keep on moving northward or southward, which determines, the spatial distribution of rainfall. Whenever the axis shifts closer, to the Himalayas, widespread rain occur in the mountainous, catchment areas of the Himalayan rivers, which also cause floods., The frequency and intensity of tropical depressions determine the, amount and duration of monsoon rains. These depressions form at, the Bay of Bengal and cross over to the mainland. The depressions, follow the axis of the “monsoon trough of low pressure”. It causes, heavy floods in one part, and droughts in the other. Sometimes it, disturbs the farming schedule of millions of farmers all over the, country., R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 96
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RETREATING MONSOON SEASON, ► It extends from October, to November, ► Vertical sun rays start, shifting towards Northern, hemisphere., ► Low pressure region shift, from northern parts of, India towards south., ► Owing to the conditions, of high temperature and, humidity, the weather, becomes, rather, oppressive., This, is, commonly known as the, ‘October heat’, , LOW PRESSURE, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 97
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WITHDRAWAL OF MONSOON, , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 98
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Parts of western coast and north-eastern India receive over about, 400 cm of rainfall annually. But, in western Rajasthan and, adjoining parts of Gujarat, Haryana and Punjab it is less than 60, cm. Rainfall is equally low in the interior of the Deccan plateau,, and east of the Sahyadris. Because of low precipitation found, around Leh in Jammu and Kashmir. The rest of the country, receives moderate rainfall. Snowfall is restricted to the Himalayan, region., Based on the nature of monsoons, the annual rainfall is highly, variable from year to year. Variability is high in the regions of low, rainfall such as parts of Rajasthan, Gujarat and the leeward side of, the Western Ghats. Similarly, the areas of high rainfall are often, affected by floods, areas of low rainfall are drought-prone., R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 99
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, , , , , , , , The sun shines more and, the days begin to get, warmer., Spring is a time when baby, animals are born., Spring is a time when plants, and trees wake up after a, long winters nap., , Spring showers help to, warm the earth, moisten, the soil, helping new plants, to grow., R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 101
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, , , , , , Leaves change to yellow,, orange, and red., , Picking fruit and, vegetables., Animals get ready for, winter., , R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 102
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The Himalayas protect the subcontinent from extremely cold winds, from central Asia. This enables northern India to have uniformly, higher temperatures when compared to other areas on the same, latitudes., Similarly, the peninsular plateau, under the influence of the sea, from three sides, has moderate temperatures., The unifying influence of the monsoon on the Indian subcontinent, is quite perceptible. The seasonal alteration of the wind systems, and the associated weather conditions provide a rhythmic cycle of, seasons., The Indian landscape, its animal and plant life, its entire, agricultural calendar and the life of the people, including their, festivities, revolve around this phenomenon., R. Ezhilraman, PGT-Social Science, , 02-03-2015, , 103
