NCERT Class 9 Geography Chapter 4 - Climate

Chapter 4 - Climate

Question and Answer
Question 1: Differentiate between climate and weather.




Climate refers to the sum total of weather conditions and variations over a large area for a long period of time.

Weather refers to the state of the atmosphere over an area at any point of time.


It doesn't change frequently.

It changes frequently.


Climate stays for a longer period of time.

Weather stays for a short period of time.

Question 2: What are the different climatic controls? Write briefly about them.
There are six major controls of the climate of any place. They are:
1. Latitude
Due to the curvature of the Earth, the amount of solar energy received varies according to latitude. As a result, a temperature generally decreases from equator towards the poles.

2. Altitude
As one goes from the surface of the earth to higher altitudes, the atmosphere becomes less dense and temperature decreases.

3. Pressure and wind system
The pressure and wind system of any area influences the temperature and rainfall pattern.

4. Distance from sea (continentality)
As the distance from the sea increases, its moderating influence decreases and the people experience extreme weather conditions. This condition is known as continentality.

5. Ocean currents
Ocean currents along with onshore winds affect the climate of coastal areas.

6. Relief
Relief plays a major role in determining the climate of a place. High mountains act as barriers for cold and hot winds.

Question 3: What are the controls affecting the climate of India?
The controls affecting the climate of India are
1. Latitude
2. Altitude
3.Pressure and wind
→ Latitude
1. The Tropic of Cancer passes through middle of the country from the Rann of Kuchchh in the west to Mizoram in the east.
2. Almost half of the country, lying south of the Tropic of Cancer, belongs to the tropical area.
3. All the remaining area, north of the Tropic, lies in the subtropics

→ Altitude
1. India has mountains like Himalayas that prevent the cold winds from the Central Asia from entering the subcontinent. That is why, India or the subcontinent experiences comparatively milder winters as compared to Central Asia.

→ Pressure and wind
1. The climate and associated weather conditions in India are governed by the following atmospheric conditions:
• Pressure and surface winds
• Upper air circulation
• Western cyclonic disturbances and tropical cyclones

Question 4: Write a short note on:
a) Coriolis force: An apparent force caused by the Earth’s rotation. The Coriolis force is responsible for deflecting winds towards the right in the Northern hemisphere and towards the left in the southern hemisphere. This is also known as ‘Ferrel's Law’.

b) 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. A number of separate jet streams have been identified. The most constant are the mid-latitude and sub-tropical jet stream.

c) Westerly Cyclonic Disturbances: The Western cyclonic disturbances are weather phenomena of the winter months brought in by the westerly flow from the Mediterranean region.

d) Tropical cyclones: 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.

Question 5: Write briefly about the mechanism of Indian monsoon.

1. 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.
2. 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  role during the monsoon season.
3. The presence of the high-pressure area, east of Madagascar, approximately at 20°S over the Indian Ocean. The intensity and position of this high-pressure area affects the Indian monsoon.
4. The Tibetan Plateau gets intensely heated during summer, which results in strong vertical air currents and the formation of low pressure over the plateau at about 9 km above the sea level.
5. 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.

Question 6: Describe the regional variations in the climatic conditions of India with the help of suitable examples.
Despite an overall unity in the general pattern, there are perceptible regional variations in climatic condition within the country.
→ 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 Kashmir may be as low as -45°C. Thiruvananthapuram, on the other hand, may have a temperature of 22°C.

→ Precipitation
The annual precipitation varies from over 400cm in Meghalaya to less than 10cm in Ladakh and western Rajasthan. Most parts of the country receive rainfall from June to September. But some parts like the Tamil Nadu coast get a large portion of its rain during October and November.

Question 7: What are the elements of weather and climate?
The elements of weather and climate are the same, i.e., temperature, atmospheric pressure, wind, humidity and precipitation.

Question 8: Define monsoon. What do you understand by ‘break’ and ‘burst’ in 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 monsoons are not steady winds but are pulsating in nature. 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.

One important phenomenon associated with the monsoon is its tendency to have ‘breaks’ in rainfall. In other words, 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 through.

Question 9: Why is monsoon considered as a unifying bond?
The unifying influence of the monsoon on the Indian subcontinent is quite perceptible.
1. Himalayas protect the subcontinent from extremely cold winds from Central Asia.
2. Similarly, the Peninsular plateau, under the influence of the sea from 3 sides, has moderate temperatures.
3. The seasonal alteration of the wind system and the associated weather conditions provide a rhythmic cycle of seasons
4. The Indian landscapes, its animal and plant life, its entire agricultural calendar and the life of people, including their festivities, revolve around this phenomenon.
5. 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.

Question 10: Give an account of all seasons prevailing in India.
The monsoon type of climate is characterized by a distinct seasonal pattern. Four main seasons can be identified in India.

→ The cold weather season (Winter)
1. The cold weather season begins from the mid-November in Northern India and stays till February.
2. Days are warm and nights are cold. Frost is common in north and higher slopes of the Himalayas experience snowfall.
3. The weather is normally marked by clear sky, low temperature and humidity and feeble, variable winds.
4. A characteristic feature of the cold weather season over the northern plains is the inflow of cyclonic disturbances that cause the much-needed winter rains over the plains and snowfall in the mountains.
5. 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 hot weather season (Summer)
1. The summer season is from March to May. During this period, the global heat belt shifts towards north because of the apparent northward movement of the sun.
2. During summer, the temperatures rise and air pressure falls in the northern part of the country. Towards the end of May, an elongated low-pressure area develops in the region which extends from the Thar Desert in the northwest to Patna and Chhotanagpur in the east and southeast.
3. A characteristic feature of the hot weather season is the ‘loo’. These are strong, gusty, hot and dry winds which blow during the day over the north and northwestern India.
4. Dust storms are very common in northern India during the month of May. This is also the season of localized thunderstorms; accompanied by violent winds, torrential downpours, and hail.
5. Pre-monsoon showers are common towards the end of the summer season; especially in Kerala and Karnataka. They are often called ‘mango showers’ as they help in the early ripening of mangoes.

→ Advancing monsoon (Rainy)
1. The rainy season begins from early June.
2. The low-pressure condition over the northern plains intensifies at this time. It attracts the trade winds from the southern hemisphere. These south-east trade winds cross the equator and blow in a south-westerly direction to enter the Indian peninsula as the south-west monsoon. These winds bring abundant moisture to the subcontinent.
3. These winds blow at an average velocity of 30 km/h. The monsoon winds cover the country in about a month; barring the extreme north-west.
4. The windward side of the Western Ghats receives very heavy rainfall, early in the rainy season. The Deccan Plateau and parts of Madhya Pradesh also receive some rain, in spite of lying in the rain shadow area.
5. The north-eastern part of the country receives the maximum rainfall of this season. Mawsynram (Meghalaya) receives the highest average rainfall in the world.
6. Rainfall in the Ganga valley decreases from east to west. Rajasthan and parts of Gujarat get scanty rainfall.
Monsoon tends to have ‘breaks’ in rainfall; which means that there are wet and dry spells in between. The monsoon rains take place only for a few days at a time and then come the rainless intervals.
7. These breaks in the monsoon are because of the movement of the monsoon trough. The trough and its axis keep on moving northwards or southward due to various reasons. The movement of the monsoon trough determines the spatial distribution of rainfall.

→ Retreating Monsoon (The Transition Season)
1. During October-November, the sun apparently moves towards the south. During this period, the monsoon trough over the northern plains becomes weaker. The south-west monsoon winds weaken and start withdrawing gradually. The monsoon withdraws from the northern plains by the beginning of October.
2. The retreat of the monsoon is marked by clear skies and rise in temperature. While day temperatures are high, nights are cool and pleasant. Humidity is still present. High temperature and humidity, makes the weather quite uncomfortable during the day. This is commonly known as “October Heat”.
3. The temperature begins to fall rapidly in northern India by the second half of October. The low-pressure conditions over northwestern India move to the Bay of Bengal by early November. This shift leads to cyclonic depressions over the Andaman Sea. These cyclones usually cross the eastern coasts of India and cause heavy and widespread rain. These cyclones may also arrive at the Coasts of Orissa, West Bengal and Bangladesh. These cyclones contribute to the bulk of the rainfall of the Coromandel Coast.

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