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CHAPTER — 4, CLIMATE, , , , , , POINTS TO REMEMBER:, , The atmospheric conditions, landforms and drainage are the three basic, elements of the any natural environment., , Weather refers to the state of the atmosphere over an area at any point of, time., , Climate refers to the sum total of weather conditions and variations over a, large area for a long period of time (more than thirty years)., , The elements of weather and climate are the same, i.e. temperature,, atmospheric pressure, wind, humidity and precipitation., , The weather conditions fluctuate very often even within a day. But there is, some common pattern over a few weeks or months, i.e. days are cool or hot,, windy or calm, cloudy or bright, and wetordry., , On the basis of the generalized monthly atmospheric conditions, the year is, divided into seasons such as winter, summer or rainy seasons., , , , Factors affecting Climate of India, , , , , , , , , , ! | { { | |, , , , , , Latitude Altitude Distance Ocean Relief Pressure, from sea current features or and Wind, landscape system, or surface, of earth., , , , , , , , , , , , , , , , , , , , , , , , , , , , 97 Class IX - Social Science

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SI Factors How do they affect Reason, , no | affecting climate, climate of, India, , lL. | Latitude The more we move Due to curvature of, away from equator, earth the amount of solar, colder will be the energy decreases as we, climate, move from equator fo, , poles, , 2. | Altitude As we move up in height | As atmosphere become, colder will be the less dence and, climate temperattite decrases, , with increasing height, , 3. | Distance from | The more a place is at The moderating, , sca distance from sea the influcnce of sca (sca, more extreme climatic breeze) deereases with, condition it will have. distance., , 4. | Ocean current | The climatic condition As cold or warm current, of a coastal place is, accordingly modify the, affected by the warm nature of onshore winds, and cold current flowing | and affects the climate., past by, , 5. | Relief features | Landscape like high Due to their size and, , or landscape or | mountain aets as barrier | height they can restrict, surface of for cold or hot winds, the flow of winds and, earth, they alsoieause alter the climate of a, precipitation or rain place., shadow on leeward., 6. | Pressure and They are dependent on, , , , Wind system, , , , the latitude and altitude, of a place hence has, effect on climate, accordingly., , , , , , , , The Tropic of Cancer passes through the middle of the country from the, Rann of Kuchchh (Gujarat) inthe west to Mizoram in the east., , Thus India’s climate has characteristics of both tropical as well as, subtropical climates., , The Himalayas prevent the cold winds from Central Asia from entering the, subcontinent. Therefore, we experience comparatively milder winters as, compared to central Asia., , , , 98 Class IX - Social Science

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Tropical Condition 5, cyclones associate! wit, Climate and, , , , , , , , , , , , Pressure, and Surface, winds, , , , Atmospheric, , , , , , , , , , , Weather, , Western, cyclonie, Disturbance, , India lies in the region of north easterly.winds. These winds originate from, the subtropical high-pressure belt of the northern hemisphere., , Due to the rotation of earth winds deflects towards the right in the northern, hemisphere and towards thesleft in the southern hemisphere by a force, called Coriolis force. This is also known as Ferrell’s law., , Jet streamsiare a narrow belt of high altitude (above 12,000 m) westerly, winds inthe troposphere., , Vi., , Their speed varies from about 110 km/h in summer to about 184, km/hin winter., , These jet streams are located approximately over 27°-30" north, latitude,, , They are also known as subtropical westerly jet streams., , Over India, jet streams blow south of the Himalayas, all through the, year except in summer., , In summer, the subtropical westerly jet stream moves north of the, Himalayas with the apparent movement ofthe sun., , An easterly jet stream, called the sub- tropical easterly jet stream, blows over peninsular India, approximately over 14°N during the, summer months., , , , 99 Class IX - Social Science

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The western cyclonic disturbances experienced in the north and north-western, parts of the country are brought in by this westerly flow., , 1. The western cyclonic disturbances are weather phenomena of the, winter months brought in by the westerly flow from the, Mediterranean region., , I. They usually influence the weather of the north and north-western,, regions of India., , Al 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, , 1. Itis a Spanish word meaning “The child” and refers to baby Christ, a5, this starts flowing during Christmas., , I. The presence of Al Nino leads to an increase.in sea Surface, temperature and weakning of the trade winds inthe region., , There are following important facts to understand the» Mechanism of the, monsoons:, , 1, The differential heating and cooling of land andwater, , i. The shift of the position of Inter Tropical Convergence Zone (ITCZ) in, summer, , i. The presence of the high-pressure area, in east of Madagascar due, tolow temperature:, , Vv. The Tibetan plateau getsintensely heated during summer,, , Vv. The movement of the westerly jet stream to the north of the, Himalayas, , Vi. The presence of the tropical easterly jet stream over the Indian, peninsula in summer., , Vil. Changesin the pressure conditions over the southern oceans., , The climate of India is strongly influenced by monsoon winds., 1 The word monsoon is derived from the Arabic word ‘mausim’ which, literally means season., is ‘Monsoon’ refers to the seasonal reversal in the wind direction, during a year., Ml. The sailors who came to India in historic times were one of the first, to have noticed the phenomenon of the monsoon., , IV. The Arabs, who had also come to India as traders named this, seasonal reversal of the wind system ‘monsoon’., , Vv. The monsoons are experienced in the tropical area roughly between, 20° Nand 20°S., , , , 100 Class IX - Social Science

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Around the time of 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 splits into two branches— the Arabian Sea, branch and the Bay of Bengal branch., , 1. The Arabian Sea branch reaches Mumbai about ten days later on, approximately the 10th of June. This is a fairly rapid advance. By, mid-June the Arabian Sea branch of the monsoom arrives over, Saurashtra-Kuchchh and the central part of the country., , i The Bay of Bengal branch also advances rapidlyand arrivesin Assam, in the first week of June. The lofty mountains cause the monsoon, winds to deflect towards the west over.the Gangayplains. The, Arabian Sea and the Bay of Bengal branches ofthe monsoon merge, over the northwestern part of the Ganga plains., , Delhi generally receives the monsoon showers fromthe Bay of Bengal branch by the, end of June (tentative date is 29th of June). By the first week of July, western Uttar, Pradesh, Punjab, Haryana and eastern Rajasthan experience the monsoon. By midJuly, the monsoon reaches Himachal Pradesh and the rest of the country., , Withdrawal or the retreat of the monsoon fs a more gradual process. The, withdrawal of the monsoon begins’ in northwestern states of India by early, September. By mid-October, it withdraws completely from the northern half of the, peninsula. The withdrawal from the southern half of the peninsula is fairly rapid. By, early December, the monsoonis withdrawn from the rest of the country., , . The islands reteive the very first monsoon showers, progressively from, south to north, from the last week of April to the first week of May. The, withdrawal, takes place progressively from north to south from the first, week of December to the first week of January. By this time the rest of the, country isalready under the influence of the winter monsoon., , , , Four Main Seasons, , , , , , , , , , $ } } ), , The retreating, monsoon (with some, regional variations), , , , The cold The hot The advancing, weather season weather season monsoon, , , , , , , , , , , , , , , , , , , , , , 101 Class IX - Social Science