Climate Class - IX NCERT solution of chapter-4 1. Choose the correct answer from the four alternatives given below: (i) Which one of the f...
Climate
Class - IX
NCERT solution of chapter-4
1. Choose the correct answer from the four alternatives given below:
(i) Which one of the following places receives the highest rainfall in the world?
(a) Silchar
(b) Mawsynram
(c) Cherrapunji
(d) Guwahati
Answer: Mawsynram
(ii) The wind blowing in the northern plains in summers is known as:
(a) Kaal Baisakhi
(b) Loo
(c) Trade Winds
(d) None of the above
Answer:Loo
(iii) Which one of the following causes rainfall during winters in the north-western part of
India?
(a) Cyclonic depression
(b) Retreating monsoon
(c) Western disturbances
(d) Southwest monsoon
Answer:Western disturbances
(iv) Monsoon arrives in India approximately in:
(a) Early May
(b) Early July
(c) Early June
(d) Early August
Answer:Early June
(v) Which one of the following characterises the cold-weather season in India?
(a) Warm days and warm nights
(b) Warm days and cold nights
(c) Cool days and cold nights
(d) Cold days and warm nights
Answer: Warm days and cold nights
2. Answer the following questions briefly:
(i) What are the factors affecting the climate of India?
Answer: The controls affecting the climate of India are latitude, altitude, pressure and wind system, distance from the sea, ocean currents and relief features.
(ii) Why does India have a monsoon type of climate?
Answer: The word ‘monsoon’ usually refers to the seasonal reversal in the direction of wind during the year. The climate of India is strongly influenced by monsoon winds. Hence, it is said to have a monsoon type of climate.
(iii) Which part of India does experience the highest diurnal range of temperature and why?
Answer:The North-western part of India (The Thar desert) experiences the highest diurnal range of temperature as it receives the least amount of rainfall and also it is away from sea. So, the temperatures go to the extreme in this part of India.
(iv) Which winds account for rainfall along the Malabar Coast?
Answer: Southwest monsoon winds are responsible for rainfall along the Malabar Coast.
(v) What are Jet streams and how do they affect the climate of India?
Answer:Jet Streams 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. The sub-tropical westerly jet stream blowing south of the Himalayas are responsible for the western cyclonic disturbances experienced in the north and north-western parts of the country during the winter months. The sub-tropical easterly jet stream blowing over peninsular India is responsible for the tropical cyclones that affect the eastern coastal regions of India during the monsoon as well as during the October to November period.
(vi) Define monsoons. What do you understand by “break” in monsoon?
Answer: Monsoon refers to the complete reversal of winds over a large area leading to a change of seasons.
"Break" in monsoon refers to the wet and dry spells of the monsoon. The monsoon rains take place for a few days at a time and are interspersed with rainless intervals. Breaks are related to the movement of the monsoon trough.
(vii) Why is the monsoon considered a unifying bond?
Answer: The seasonal alteration of the wind systems and the associated weather conditions provide a rhythmic cycle of seasons. The Indian landscape, it’s animal and plants life, and the entire agricultural calendar and
the life of the people (including their festivities) revolve around this phenomenon. Year after year, people of India from north to south and from east to west, eagerly await the arrival of the monsoon.
These monsoon winds bind the whole country by providing water to set the agricultural activities in motion. The river valleys which carry this water also unite as a single river valley unit.Thus, monsoon is a unifying bond.
3. Why does the rainfall decrease from the east to the west in Northern India?
Answer: The rainfall in the eastern part of India occurs due to the Bay of Bengal branch of southwest monsoons. As the moisture bearing winds of the Bay of Bengal branch of the South-West monsoon move further and further inland, their moisture content decreases. As a result, there is a gradual decrease of rainfall from East to West direction.
4. Give reasons as to why
(i) Seasonal reversal of wind direction takes place over the Indian subcontinent?
Answer:Seasonal reversal of wind direction over the Indian subcontinent takes place due to pressure differential. A major part is played by the El Nino in the seasonal reversal of wind direction over the Indian subcontinent.
(ii) The bulk of rainfall in India is concentrated over a few months.
Answer: The rainfall received by India is largely due to the south-west monsoon winds. As these winds blow over warm oceans, they bring abundant moisture to the subcontinent. The duration of the monsoon is between 100 to 120 days. Hence, the bulk of rainfall received by the country is concentrated over a few months.
(iii) The Tamil Nadu coast receives winter rainfall.
Answer:The Tamil Nadu coast receives winter rainfall as the north-eastern winds, which are retreating monsoon winds take up moisture as they move over Bay of Bengal during winters and pour the rains due to obstruction from the Eastern Ghats.
(iv) The delta region of the eastern coast is frequently struck by cyclones.
Answer: This is because the cyclonic depressions that originate over the Andaman-sea/are brought in by the sub-tropical easterly jet stream blowing over peninsular India during the October to November period. The depression moves along East to West direction thus hitting the Eastern coasts.
(v) Parts of Rajasthan, Gujarat and the leeward side of the Western Ghats are drought-prone.
Answer: The parts of Rajasthan, Gujarat and the leeward side of the Western Ghats are drought prone as the Arabian Sea branch does not give enough rainfall in that region as it falls on the leeward side. The Aravalli mountains lie parallel to the direction of the winds so they do not force the winds to cause rains. Also, the Bay of Bengal branch becomes dry till it reaches Rajasthan.
5. Describe the regional variations in the climatic conditions of India with the help of suitable examples.
Answer:The regional variation in climatic conditions of India is mainly due to two factors- temperature and precipitation. These to elements vary from place to place and season to season.
1. Temperature: In summer, the mercury occasionally touches 50°C in some parts of the Rajasthan desert, whereas it may be around 20°C in Pahalgam in Jammu and Kashmir. On a winter night, temperature at Drass in Jammu and Kashmir may be as low as minus 45°C. Tiruvananthapuram, on the other hand, may have a temperature of 20°C.
2. Precipitation: There are variations not only in the form and types of precipitation but also in its amount and the seasonal distribution. While precipitation is mostly in the form of snowfall in the upper parts of Himalayas, it rains over the rest of the country. The annual precipitation varies from over 400 cm in Meghalaya to less than 10 cm in Ladakh and western Rajasthan.
Most part of the country receives rainfall from June to September whereas the Tamil Nadu coast receives rainfall during October and November. There is gradual decrease of rainfall generally from East to West.
6. Discuss the mechanisms of the monsoon.
Answer: The monsoon are experienced in the tropical regions roughly between 20°N to 20°S. There are various phenomena to explain the mechanism of monsoon in India.
1. Differential heating and cooling of land and water - At the end of May, due to high temperature, low-pressure area is found on the landmass and sea/ocean experience comparatively high pressure.
2. Shift in the position of Inter Tropical Convergence Zone (ITCZ) - In summer, ITCZ or the low pressure trough is shifted on the Ganga plain. It is also known as 'monsoon trough' during monsoon season.
3. Presence of high pressure area at 20°S over the Indian ocean (East of Madagascar) - The intensity and position of this high pressure area affects the Indian monsoon.
4. Intensely heating of Tibetan plateau - In summer, the intense heating of Tibetan plateau results in strong vertical air currents and formation of high pressure over the plateau at about 9 km above sea level.
5. Westerly jet stream and tropical easterly jet streams - The movement of westerly jet streams to the North of the Himalayas and the presence of the tropical easterly jet streams over the Indian peninsula during summer.
6. The periodic change in pressure conditions is known as Southern Oscillation (SO) - This change in the pressure conditions over the Southern ocean also affects the monsoon.
7. Give an account of weather conditions and characteristics of the cold season.
Answer: The cold weather season begins from mid-November in northern India and stays till February. December and January are the coldest months in the northern part of India. The temperature decreases as we go from the south to the north. The average temperature in Chennai, on the eastern coast, is between 24° – 25° Celsius. Whereas in the northern plains, it ranges between 10°C and 15° Celsius. Here, the days are warm, and the nights are cold. Frost is common in the north, and the higher slopes of the Himalayas experience snowfall. During this season, the northeast trade winds prevail over the country. They blow from land to sea, and hence, for the most part of the country, it is a dry season. Some amount of rainfall occurs on the Tamil Nadu coast from these winds as here they 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. A characteristic feature of the cold weather season over the northern plains is the inflow of cyclonic disturbances from the west and the northwest. These low-pressure systems originate over the Mediterranean Sea
and western Asia and move into India, along with the westerly flow. They cause the much-needed winter rains over the plains and snowfall in the mountains. Although the total amount of winter rainfall (locally known as ‘Mahawat’) is small, they are of immense importance for the cultivation of ‘rabi’ crops. The peninsular region does not have a well-defined cold season. There is hardly any
noticeable seasonal change in temperature pattern during winters due to the moderating influence of the sea.
8. Give the characteristics and effects of the monsoon rainfall in India.
Answer:Characteristics of Monsoon Rainfall are:
1.Its duration varies from 100-120 days (early June to mid September).
2. Around the time of its arrival, there is sudden increase and continuous rainfall for several days, called as 'Burst of monsoon'.
3. The retreat or withdrawal of the monsoon is a gradual process.
4. The monsoon takes place in wet and dry spells. The intervening rainless intervals are known as 'Breaks' in monsoon.
Effects of Monsoon Rainfall are:
1. The monsoon are known for their uncertainties and vagaries.
2. The alteration of dry and wet spells vary in intensity, frequency and duration.
3. On one part, it causes heavy flood; on the other part, it may be responsible for drought.
4. It is often irregular in its arrival an its retreat. Hence, it sometimes disturbs the farming schedule in the country.
5. At the same time it is considered as the unifying bond also.
I hope this will help you.
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