66) What are the six major controls of the climate of the world?
Answer: (i) Latitude: Due to the round shape of the Earth, the amount of solar energy received varies according to latitude. As a result, air temperature decreases from the equator towards the poles.
(ii) Altitude: As one moves up to the higher altitudes, the atmosphere becomes less dense and temperature decreases. Therefore, hills are the cooler during summers.
(iii) Pressure and winds: Pressure and wind system of an area depend on the latitude and altitude of the place. Thus, it influences the temperature and rainfall pattern.
(iv) Distance from the sea: If the region is close to the sea, it makes the temperature moderate but if it is away from the sea, it experiences extreme weather conditions.
(v) Ocean currents: Ocean currents along with the onshore winds affect the climate of a coastal area. Any coastal area with warm or cold currents flowing past it, will become warm or cold if the winds are onshore.
(vi) Relief: High mountains act as barriers for cold and hot winds. They may also cause precipitation if they lie in the path of rain-bearing winds. The leeward side of mountains remains dry, whereas the windward side is able to receive rain.
67) State how the pressure and wind conditions over India are unique.
Answer:(i) During winter, a high pressure area develops north of the Himalayas.
(ii)Cold dry winds blow from this region to the low pressure areas over the oceans to the south.
(iii) In summer, a low pressure area develops over interior Asia as well as over northwestern India.
(iv) This causes a complete reversal of the direction of winds during summer.
(v) Air moves from the high pressure area over the southern Indian ocean in a south-westerly direction, crosses the equator and turns right towards the low pressure area over the Indian sub-continent.
(vi) These winds are known as south-west monsoon winds.
(vii) These winds blow over the warm oceans, gather moisture and bring widespread rainfall over the mainland of India.
68) What are jet streams? How do they affect the climate?
Answer : Jet streams are fast blowing winds moving in the upper air of the atmosphere. Sub-tropical Westerly Jet Streams: These jet streams are located approximately over 27o-30o north latitude; therefore, they are known as sub-tropical westerly jet streams. Over India, these jet streams blow south of the Himalayas all through the year except in summer. During winters, the cyclonic disturbances are brought into India by these jet streams. (ii) Tropical-easterly Jet Streams: These easterly jet streams blow over peninsular India, approximately over 14oN, during the summer months. It is believed to be responsible for the sudden outbreak of the south-west monsoon in India.
69) State the factors which help us understand the mechanism of monsoon. Or Discuss the mechanism of monsoons.
Answer: (i) 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. (ii) The shift in the position of Inter Tropical Convergence Zone (ITCZ) in summer over the Ganga plain is a trough of low pressure in the equatorial latitude. This is where the northeast and the Southeast trade winds converge.
(iii) The presence of the high pressure area, east of Madagascar also affects the Indian monsoons.
(iv) The Tibetan plateau gets intensely heated during summer, which results in the formation of low pressure area over the plateau.
(v) The movement of the westerly jet streams to the north of the Himalayas and the presence of tropical easterly jet streams over the Indian Peninsula during summers, also affects the mechanism of monsoon.
70) What do you understand by the phenomenon of ENSO?
Answer: (i) Normally, when the tropical eastern south pacific ocean experiences high pressure, the tropical eastern Indian Ocean experiences low pressure.
(ii) But in certain years, there is a reversal in the pressure conditions and the eastern pacific has low pressure in comparison to the Indian Ocean.
(iii) This periodic change in pressure conditions is known as Southern Oscillation (SO). (iv) The difference in pressure over Tahiti, in the Pacific Ocean and Darwin in northern Australia is computed to predict the intensity of the monsoon.
(v) 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.
(vi) The changes in pressure conditions are connected to the El Nino. Hence, the phenomena is referred to as ENSO (El Nino Southern Oscillations).
71) What do you know about the onset of monsoon in India?
Answer: (i) Around the time of arrival of the monsoon, the normal rainfall increases suddenly and continues constantly for several days.
(ii) This is known as 'burst' of the monsoon and can be distinguished from the pre-monsoon showers.
(iii) The monsoon arrives at the southern tip of the Indian Peninsula generally by the first week of June.
(iv) Then it gets divided into two?the Arabian Sea branch and the Bay of Bengal branch. (v) The Arabian Sea branch reaches Mumbai about ten days later.
(vi) The Bay of Bengal branch also advances rapidly and arrives in Assam in the first week of June.
72) How does the process of withdrawal of monsoon take place in India?
Answer: (i) Withdrawal or the retreat of monsoon is a more gradual process.
(ii) The withdrawal of the monsoon begins in the northwestern states of India, by early September.
(iii) By mid-October, it withdraws completely from the northern half of the peninsula.
(iv) The withdrawal from the southern half of the peninsula is fairly rapid.
(v) By early December, the monsoon withdraws from the rest of the country.
73) State the chief characteristics of the cold weather season in India.
Answer: (i) Cold weather season takes place from December to February.
(ii) The temperature decreases from south to north.
(iii) The average temperature of the Northern Plains ranges between 10o to 50oC whereas the average temperature of Chennai is between 24oC to 25oC.
(iv) Days are warm and nights are cold. (v) During this season, northeast trade winds prevail over the country; they blow from the land to the sea and are dry.
(vi) Tamil Nadu coast receives rainfall, as these winds blow from the sea to the land.
(vii) The weather is marked by clear skies, low temperatures, low humidity and feeble variable winds.
74) What is the role of western disturbances' in the Indian climate?
Answer: (i) A characteristic feature of the cold weather season over the northern plains is the inflow of cyclonic disturbances from the west and the northwest.
(ii) These low pressure systems originate over the Mediterranean sea and Western Asia and move into India, along with easterly flow.
(iii) They cause the much needed winter rains over the plains and snowfall in the mountains.
(iv) Although the total amount of winter rainfall, locally known as 'Mahawat' is small, it is very useful for rabi crops. These winds are called western disturbances since they came from the western part of India.
75) State the chief characteristics of the hot weather season in India.
Answer:(i) India experiences the hot weather season from the month of March to May. (ii) The temperature in the northern plains of India is between 42 to 45oC and in the Deccan plateau, between 35 to 38oC.
(iii) Towards the end of May, an elongated low pressure area develops in the region extending from the Thar Desert to Patna and Chotanagpur plateau.
(iv) During the hot weather season, strong, gusty, hot, dry winds known as the 'Loo' blows. Direct exposure to these winds may even prove to be fatal.
(v) Dust storms are very common during the month of May in northern India. These storms bring temporary relief as they lower the temperatures.
(vi) This is also the season of localised thunderstorms associated with violent winds and torrential rains known as Kaal Baisakhi in West Bengal.
76) Give a brief account of how monsoons advance into India.
Answer: (i) In early June, the low pressure conditions over the northern plains intensify. (ii) These south-east trade winds cross the equator and blow in south- westerly direction, entering the Indian peninsula as the south-west monsoons.
(iii) As these winds blow over warm oceans, they bring abundant moisture to the sub-continent. (iv) These winds are strong and blow at an average velocity of 30 km per hour. (v) Early in the season, the windward side of the Western Cxhats receh es very heavy rainfall, more than 250 cm.
(vi) The maximum rainfall of this season is received in the northeastern part of the country. Mawsynram in Khasi Hills receives the highest average rainfall in the world.
(vii) Rainfall in the Gangs valley decreases from east to the west Rajasthan and parts of Gujarat get scanty rainfall.
77) What do you understand by the phenomenon of 'breaks in the rainfall'?
Answer: (i) The Indian monsoon have wet and dry spells. The monsoon rains take place only for a few days, at a time. They are interspersed with rainless intervals.
(ii) These breaks in monsoon are related to the movement of the monsoon trough.
(iii) The trough and its axis keeps on moving northward or southward which determines the distribution of rainfall.
(iv) When the axis of the monsoon trough lies over the plains, rainfall is good in these parts.
(v) On the other hand, whenever the axis shifts closer to the Himalayas, there are longer dry spells in the plains and widespread rains in the mountains catchment areas of the Himalayan rivers.
(vi) These heavy rains bring devastating floods that cause damage to life and property in the plains.
78) Give a brief account of the condition and characteristics of the retreating monsoons.
Answer: (i) This is the transition period during the months of October and November.
(ii) With the apparent movement of the Sun towards the south, the low pressure trough over the northern plains becomes weaker. This is gradually replaced by a high pressure system.
(iii) The south-west monsoon winds weaken and start withdrawing gradually.
(iv) By the beginning of October, the monsoon withdraws from the northern plains.
(v) The months of October and November form a period of transition from hot rainy season to dry winter conditions.
(vi) When monsoons retreat, skies get clear and the temperature rises.
(vii) While day temperatures are high, nights are cool and pleasant. The land is still moist.
(viii) Owing to the conditions of high temperature and humidity, the weather becomes oppressive during the day. This is commonly known as October Heat.
(ix) The low pressure conditions get transferred to the Bay of Bengal by early November. (x) The cyclonic depressions originate from the Andaman Sea and cause heavy and widespread rains on the eastern coast.
(xi) These tropical cyclones are often very destructive and affect the coast of Oclisha, West Bengal anci Bangladesh.
79) What is the distribution of rainfall in India?
Answer:(i) 1 lie western coast and northeastern India receive rainfall of over about 400cm.
(ii) It is less than 60 cm in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab.
(iii) Rainfall is equally low in tile interiors of the Dec can plateau and east of the Sahyadris. (iv) A third area of low precipitation is around Leh in jammu and Kashmir.
(v) The rest oi the country receives model ate rainfall.
(vi) Snowfall is restricted to the Himalayan region.
80) Why do the north-east trade winds change their direction while blowing through the Ganga valley?
Answer: (i) A feeble higli pressure area develops over (lie north-western part of India in the cold weather season. Light winds begin to blow outwards.
(ii) These dry north-westerlies winds come; in contact With the Indian trades (north-easterlies) over (lie Ganga valley.
(iii) The direction of north-easterlies changes as result of (his contact as well as under the influence of topography.
(iv) Their direction is north-westerlies down the Ganga, alley and northerlies over the Ganga-Brahmaputra Delta.
(v) Over the Bay of Bengal, the trade winds retain their original north- easterlies direction, as they are free from the influence of any topography over the sea.
81) Why is monsoon considered a unifying bond?
Answer: (i) The Himalayas protect the subcontinent from extremely cold winds from Central Asia. This enables northern India to have uniformly higher temperature when compared to oilier areas on the same latitude.
(ii) The Peninsular plateau under the influence of the sea from three sides has moderate temperatures.
(iii) The seasonal alternation of wind systems and the associated weather conditions provides a rhythmic cycle of seasons.
(iv) Even the uncertainties of rain and uneven distribution are very typical of the monsoon.
(v) The Indian landscape, its animals and plant life, its entire agricultural calendar and the life of the people including their festivities revolve around this phenomenon.
(vi) These monsoon winds bind the whole country by providing water to get the agricultural activities in motion. The river valleys which carry this water also unite as a single river valley unit.
82) Differentiate between South West (S.W.) monsoons and North East (N.E.) monsoons.
They blow from south-west to north- east from June to September.
They blow from north-east to south-west from the month of Dec, Jan and Feb.
These are onshore humid winds because they blow from sea to land.
These are offshore dry winds because they blow from land to sea.
These are warm winds as they come from lower latitudes near equator.
They are rather cool winds because they blow.
These warm and humid winds cause widespread rainfall.
These cold and dry offshore winds give no rains to India except Coromandel coast.
These winds are known for their vagaries or uncertainties.
They do not suffer from the vagaries.
83) Why are the deltas of the Krishna, Kaveri and Godavari frequently struck by cyclones?
Answer: (i) The low pressure conditions over north-western India, get transferred to the Bay of Bengal by early November.
(ii) This shift is associated with the occurrence of cyclonic depressions which originate over the Andaman Sea.
(iii) These cyclones generally cross the eastern coasts of India and cause heavy and widespread rains.
(iv) These tropical cyclones are often very destructive.
(v) The thickly populated deltas of the Godavari, the Krishna and the Kaveri are frequently struck by cyclones, which cause great damage to life and property.
(vi) Sometimes, these cyclones arrive at the coasts of Odisha, W. Bengal and Bangladesh. The bulk of rainfall of the Coromandel coast is derived from depression and cyclones.
84) Which part of India experiences the highest diurnal range of temperature and why?
Answer: (i) Diurnal range of temperature is the difference between maximum and minimum temperature of a day.
(ii) Diurnal range of temperature is high in desert regions like Rajasthan, Thar Desert and interior parts of Rann of Kutch.
(iii) In these sandy areas, the day temperature may rise to 50o and drop down to near freezing point the same night.
(iv) It is so because the sand absorbs heat very fast during day and loses heat very fast at night.
85) Why does the rainfall decrease from east to the west in northern India?
Answer: (i) The northern plains receive rains from the Bay of Bengal branch of the S.W. monsoons.
(ii) It strikes the Myanmar's Arkan mountains and gets deflected westward along the Himalayas.
(iii) Maximum precipitation is recorded in the north-eastern part of India and West Bengal.
(iv) As the monsoon moves westwards, they gradually lose moisture and rainfall decreases from east to west over the northern plains.
(v) The clouds are almost exhausted by the time they reach western Rajasthan.
86) Give reasons why parts of Rajasthan, Gujarat and the leeward side of the Western Ghats are drought prone.
Answer:(i) Western Rajasthan and part of Gujarat are desert type regions with extreme climate. Intense thermal heating makes the desert land very dry.
(ii) The Arabian Sea branch runs parallel to Aravallis, providing no barriers to the clouds, leaving it again a dry region.
(iii) The Bay of Bengal branch is unable to reach up to western part and in winters even western disturbances also hardly give any rains to this region.
(iv) The leeward side of the Western Ghats also lies in the rain shadow of S.W. monsoon. (v) With the result, regions lying at the same latitude are unable to receive rains, if they are on the leeward side of the Western Ghats.
87) Have you heard of onset of monsoons? How does it take place in India?
Answer: (i) With the arrival of monsoon, the normal rainfall increases suddenly and carries on for several days.
(ii) This is also known as 'burst of monsoon' and can be distinguished from the pre-monsoon showers.
(iii) The monsoon arises at Southern tip of Indian peninsula generally by the first week of June approximately.
(iv) Then it gets divided into two?The Arabian Sea branch and Bay of Bengal branch.
(v) Then it starts moving upwards, the Arabian Sea branch reaches Madhya Pradesh, U.P. in about ten days.
(vi) The Bay of Bengal branch also advances rapidly and arrives in Assam in the first week of June.
88) If you are living in North India, how would you experience cold weather season over there?
Answer: (i) Cold weather season normally takes place from December to February.
(ii) Temperature keeps on decreasing.
(iii) Average temperature is between 10o to 20o C.
(iv) Days are warm and nights are cold.
(v) North East trade winds blow from land to sea, which are incidentally cold and dry.
(vi) We prefer to wear woollen clothes and like to sit under the Sun.
89) The word 'monsoon' is derived from the Arabic word (a) Mausam (b) Mausim (c) Monsoon (d) Mausin
90) The 'coriolis force' is caused by (a) the earth's rotation (b) wind movements (c) jet streams (d) cyclonic disturbances