IX Geography Chapter 4 – Climate

 

IX Geography

Chapter 4 – Climate

 

v Climate refers to the sum total of weather conditions and variations over a large area for a long period  of time ( <30 Y).

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

v The elements of weather and climate are the same, i.e. temperature, atmospheric pressure, wind, humidity and precipitation.

v On the basis of the monthly atmospheric conditions, the year is divided into four seasons such as

·      Winter

·      Summer

·      Rainy Seasons

·      The retreating monsoon with some regional variations (Transition Season)

Coriolis Force

 *An apparent force caused by the earth’s rotation 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.

Eg. South-east winds become south-west winds.

Climatic Controls

The climate of any place depends on the following factors:

1) Latitude : The amount of solar energy received varies according to latitude due to the curvature of the earth.

That’s why air temperature generally decreases from the equator towards the poles.

2) Altitude: The atmosphere becomes less dense and temperature decreases when we go to the higher altitude from the earth surface.

This is the reason why hills are cooler during summers.

3) Pressure and wind system:

The pressure and wind system of any area depends on the latitude and altitude of the place. It

influences the temperature and rainfall pattern.

4) Distance from the sea

 

The sea exerts a moderating influence on the climate. As the distance from the sea increases, its

moderating influence decreases and people experience extreme weather conditions. This condition is

known as continentality i.e. very hot during summers and very cold during winters.

5) Ocean currents

Ocean currents along with onshore winds affect the climate of the coastal areas. For example, any coastal area with warm or cold currents flowing past it, will be warmed or cooled if the winds are onshore.

6) Relief features

 

Relief 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 rainbearing winds. Precipitation is any form of moisture which falls to the earth. It includes rain, snow, hail .

Factors Affecting India’s Climate

 

Latitude

The Tropic of Cancer passes through the middle of the country from the Rann of Kachchh in the west to  Mizoram in the east. India’s climate has characteristics of tropical as well as subtropical climates.

Altitude

India has mountains to the north and also has a vast coastal area where the maximum elevation is about 30 metres. Owing to the mountains, subcontinent experiences comparatively milder winters as compared to central Asia.

Pressure and Winds

The climate and weather conditions in India are governed by the following atmospheric conditions:

*  Pressure and surface winds

*  Upper air circulation

*  Western cyclonic disturbances and tropical cyclones

Air moves from the high-pressure area over the southern Indian Ocean, in a south-easterly 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 territories of India.

Jet streams** are fast flowing, narrow, meandering air currents in the atmosphere.

The Indian Monsoon

 

*The climate of India is strongly influenced by monsoon winds. The seasonal reversal of the

wind system is known as “monsoon”. The monsoons are experienced in the tropical area roughly

between 20° N and 20° S.

*The duration of the monsoon is between 100-120 days from early June to mid-September. Around the time of its arrival, the normal rainfall increases suddenly and continues constantly for several days, which is known as the “burst” of the monsoon.

Mechanism of the monsoons

 

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, is also known as the monsoon-trough during the monsoon season.

3.  The presence of the high-pressure area, east of Madagascar, approximately at 20°S over the

Indian Ocean 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 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 also impact the Indian Monsoon.

The changes in the pressure conditions over the southern oceans also affect the monsoons. The  irregularly periodic variation in winds and sea surface temperatures over the tropic al eastern Pacific Ocean that affects the climate of the tropics and subtropics is known as Southern Oscillation or SO.

The Onset of the Monsoon and Withdrawal

Inter-tropical Convergence Zone or ITCZ

 

*It s a broad trough of low pressure in equatorial latitudes.

*This is the area where northeast and southeast trade winds converge.

*This convergence zone lies more or less parallel to the equator but moves northwards or southwards with the movement of the sun.

 

 

Arrival of the Monsoon in different parts of India

 

The monsoon arrives at the southern tip of the Indian peninsula generally by the 1st week of June.

Subsequently, it proceeds into two – the Arabian Sea branch and the Bay of Bengal branch.

*The Arabian Sea branch reaches Mumbai on approximately the 10th of June.

*  The Bay of Bengal branch arrives in Assam in the 1st  week of June.

*  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 northwestern part of the Ganga plains.

*  Delhi receives the monsoon showers from the Bay of Bengal branch by the end of June.

*  By the first week of July, 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.

 

Rajasthan

Western Rajasthan obtain scanty rainfall because the Arabian sea branch of the monsoon winds move parallel to the Aravalli range without shedding any orographic rainfall. Moreover, the high temperature in Rajasthandoes  not allow the winds to condense to form clouds.

OROGRAPHIC RAINFALL

 Rainfall that occurs when moisture laden air is forced to rise over a mountain range. As the air rises, it cools. The amount of moisture that air can hold decreases with decreasing temperature.

So the water vapour in the rising airstream condenses, and rain falls on the windward side of the mountain.

The air descending on the leeward side contains less moisture, resulting in a rainshadow where there is little or no rain.

On the western coastal plains (western side of the western ghats) we experience orographic rainfall.

Mawsynram

The heaviest rainfall of the world occurs in Mawsynram because it is situated in funnel shaped Garo,Khasi and Jaintia hills.

A part of the bay of Bengal branch of the monsoon winds gets trapped into these hills and shed all its moisture here

 

Withdrawal of the Monsoon

 

The withdrawal of the monsoon begins in northwestern states of India by early September. By midOctober, it withdraws completely from the northern half of the peninsula.

*From north to the south,  withdrawal of monsoon takes place from the first week of December to the first week of January. By  early December, the monsoon has withdrawn from the rest of the country.

 

The Seasons

 

4 main seasons can be identified in India:

1.  The cold weather season (Winter)

2.  The hot weather season (Summer)

3.  The advancing monsoon (Rainy Season)

4.  The retreating monsoon with some regional variations (Transition Season)

The Cold Weather Season (Winter)

 

Winter 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 from south to the north.

*  Days are warm and nights are cold.

*  The weather is marked by clear sky, low temperatures and low humidity and feeble, variable  winds.

*  This season is extremely important for the cultivation of ‘rabi’ crops.

The Hot Weather Season (Summer)

 

*From March to May, hot weather season is observed in India. The summer months experience rising temperature and falling air pressure in the northern part of the country.

* A striking feature of the hot weather season is the ‘loo’. Loo is the strong, gusty, hot, dry winds blowing during the day over the north and northwestern India.

*Towards the close of the summer season, pre-monsoon showers come on the coastal regions of Kerela and Karnataka which help in the early ripening of mangoes, and are often referred to as ‘mango showers’.

Kalbaisakh: kalbaisakh are locally formed thunderstorms during the summer evenings in Assam and West  Bengal and cause heavy rainfall with violent winds in the adjoining areas.

Advancing Monsoon (The Rainy Season)

 

South-east trade winds originate over the warm subtropical areas of the southern oceans. They cross

the equator and blow in a southwesterly direction entering the Indian peninsula as the south-west monsoon.

*The monsoon winds cover the country in about a month. Mawsynram in the southern ranges of the Khasi Hills receives the highest average rainfall in the world.

*A phenomenon associated with the monsoon is its tendency to have ‘breaks’ in rainfall. These breaks in monsoon are related to the movement of the monsoon trough.

*The trough and its axis keep on moving northward or southward and determine the spatial distribution of rainfall.

*The frequency and intensity of tropical depressions also determine the amount and duration of monsoon  rains. The monsoon is known for its uncertainties. The alternation of dry and wet spells vary in intensity,  frequency and duration.

Retreating/Post Monsoons
(The Transition Season)

 

The months of October-November form a period of transition from hot rainy season to dry winter conditions. The retreat of the monsoon is marked by clear skies and rise in temperature. While day

temperatures are high, nights are cool and pleasant.

Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive during the day. This is commonly known as ‘October heat’. In the second half of October, the mercury begins to fall rapidly in northern India.

Distribution of Rainfall

1.  Parts of the western coast and northeastern India receive over about 400 cm of rainfall annually.

2.  Rainfall is less than 60 cm in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab.

3.  Rainfall is low in the interior of the Deccan plateau, and east of the Sahyadris.

4.  Snowfall is restricted to the Himalayan region.

5.  The annual rainfall is highly variable from year to year.

Monsoon as a Unifying Bond

The unifying influence of the monsoon on the Indian subcontinent is quite noticeable. The

seasonal alteration of the wind systems and the associated weather conditions provide a rhythmic cycle of seasons. The uncertainties of rain and uneven distribution are very much typical of the monsoons.

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 unify  the whole country by providing water to set the agricultural. Activities .

 

 

 

Worksheet

class IX (Climate)

Q. 1. Define Climate. Explain the term Weather and Climate.

Q. 2. What are the elements of weather and climate?

Q. 3.What is meant by seasons?

Q.4.Describe the climate of India.

Q.5.Describe the regional variations in temperature and precipitations in India.

Q. 6. Explain the climatic control of a place.

Q.7. Describe the factors affecting India’s climate.

Q.8. Why do we have (India) tropical and sub-tropical climate?

Q. 9. Why does India experience milder winter than central Asia?

Q. 10. What is meant by Coriolis force?

Q. 11. What are Jet Streams?

Q.  12.  Which  are  the  important  facts  to  keep  in  mind  to  understand  the  mechanism  of Mansoon?

Q. 13. What is meant by Southern Oscillation?

Q. 14. What is ‘the burst of the mansoon’?

Q. 15. What are the features of the Cold Weather Season(Winter)?

Q. 16. Why does Tamil Nadu receive winter rain fall?

Q. 17. What are the features of the Hot Weather Season(Summer)?

Q. 18. What are the four main seasons in India?

Q. 19. What is a loo?

Q. 20. What is meant by ‘Kaal Baisakhi’?

Q. 21 What are “ Mango Showers”?

Q. 22. Explain the features of Advancing Monsoon or the Rainy Season.

Q. 23. What are the vagaries of Indian Monsoon?

Q.24. What are the features of Retreating Monsoon?

Q. 25 Describe the distribution of rainfall in India.

Q. 26. What is meant by the October – heat?

Q. 27. Why the deltas of the Godawari and the Krishna and the Kaveri are frequently struck

by cyclones?

Q.28. How does Monsoon act as a Unifying Bond?

Q. 29. What is the impact of variation in the climatic conditions in India?

Q.30. Why do Peninsular plateau get moderate temperature but the northern plain not?

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