Detailed Chapter Notes (Part - 1) - Climate Notes | Study Social Studies (SST) Class 9 - Class 9

Class 9: Detailed Chapter Notes (Part - 1) - Climate Notes | Study Social Studies (SST) Class 9 - Class 9

The document Detailed Chapter Notes (Part - 1) - Climate Notes | Study Social Studies (SST) Class 9 - Class 9 is a part of the Class 9 Course Social Studies (SST) Class 9.
All you need of Class 9 at this link: Class 9

Introduction

Difference between Weather and Climate.Detailed Chapter Notes (Part - 1) - Climate Notes | Study Social Studies (SST) Class 9 - Class 9Detailed Chapter Notes (Part - 1) - Climate Notes | Study Social Studies (SST) Class 9 - Class 9India has Diverse Climatic Conditions

We can take two important elements: Temperature and Precipitation, and examine how they vary from place to place and season to season.

Different Climatic Zones in IndiaDifferent Climatic Zones in IndiaTemperature 

  • In summer, the mercury occasionally touches 500 C in some parts of the Rajasthan desert, whereas it may be around 200 C in Pahalgam in Jammu and Kashmir. On a winter night, the temperature at Drass in Jammu and Kashmir may be as low as minus 450 C. Thiruvananthapuram, on the other hand, may have a temperature of 200 C.
  • In certain places, there is a wide difference between day and night temperatures. In the Thar Desert, the day temperature may rise to 500 C, and drop down to near 150 C the same night. On the other hand, there is hardly any difference in day and night temperatures in the Andaman and Nicobar islands or in Kerala.

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 the 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 parts of the country receive rainfall from June to September. But some parts like the Tamil Nadu coast get most of its rain during October and November
  • Coastal areas experience less contrast in temperature conditions, seasonal contrast is more in the interior of the country.

Detailed Chapter Notes (Part - 1) - Climate Notes | Study Social Studies (SST) Class 9 - Class 9

Try yourself:Most parts of India receive rainfall during which of the following months?
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Climatic Controls

  • The climate of a place is determined by the interplay of various factors such as location, altitude, distance from the sea, pressure and winds and upper air circulation.
  • Due to the curvature of the earth, the amount of solar energy received varies according to latitude. As a result, temperature decreases from the equator towards the poles.
  • As one goes from the surface of the earth to higher altitudes, the atmosphere becomes less dense and temperature decreases. The hills are therefore cooler during summers.
  • The pressure and wind system in any area depend on the latitude and altitude of the place. Thus it influences the temperature and rainfall pattern.
  • The sea exerts moderating influences on climate: As the distance from the sea increases, its moderating influence decreases, and the people experience extreme weather conditions. This condition is known as continentality.
  • Ocean currents, along with onshore winds affect the climate of the coastal areas.
  • Relief too plays a major role in determining the climate of a place. High mountains act as barriers for cold or not winds; they may also cause precipitation if they are high enough and lie in the path of rain-bearing winds. The leeward side of the mountains remains dry.

Factors Affecting India’s Climate

Latitude

  • Indian is situated roughly between 80 N and  370 N latitudes
  • India is divided into almost two equal parts by the tropic of cancer
  • The southern half lies in the tropical zone and the western half in the subtropical zone. 
  • Therefore, India’s climate has characteristics of tropical as well as subtropical climates.

Altitude

  • India has mountains to the north, which have an average height of about 6000 meters.
  • The Himalayas prevent the cold winds from Central Asia from entering the subcontinent.
  • It is because of these mountains that this subcontinent experiences comparatively milder winters as compared to Central Asia.

Pressure and Winds

  • India lies in the subtropical high-pressure belt, thus, the winds originate from the land and move outwards towards the equatorial low-pressure belt. 
  • These winds are known as northeast trade winds and are devoid of any moisture. But due to unequal heating of land and water in the summer, low pressure develops over the interior of landmasses. 
  • This low pressure attracts the winds from the south of the equator. After crossing the equator the southeast trade winds get deflected and are known as southwest monsoons. The climate of India is also affected by jet streams. 
  • This is a fast-flowing wind blowing in a narrow zone in the upper atmosphere. The jet streams are responsible for the sudden outbreak of monsoons in Northern India. A subtropical westerly jet stream brings in the western disturbances in winter. These disturbances cause heavy snowfall on the mountains and light rains in the northwestern part of India.

Try yourself:Which one of the following causes rainfall during winters in north-western part of India?
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The Indian Monsoon

The climate of India is strongly influenced by monsoon winds. The Arabs, who had come to India as traders benefited from the reversal of the wind system as they came by sailing ships at the mercy of winds, they named this seasonal reversal of the wind system ‘monsoon’.

The direction of Monsoon WindsThe direction of Monsoon Winds

The monsoons are experienced in the tropical area roughly between 200N - 200 S

To understand the mechanism of the monsoons, the following facts are important:

  • The differential heating and cooling of land and water create a low pressure on the landmass of India while the seas around experience comparatively high pressure.
  • 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 50 N of the equator – also known as the monsoon-trough during the monsoon season).
  • The presence of the high-pressure area, east of Madagascar, approximately at 200 S over the Indian Ocean. The intensity and position of this high-pressure area affect the Indian Monsoon.
  • The Tibetan plateau gets intensely heated during summer, which results in strong vertical air currents and the formation of high pressure over. The plateau at about 9 km above sea level.
  • 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.
  • Changes in the pressure conditions over the southern oceans also affect the monsoons. 
  • Normally when the tropical eastern South Pacific Ocean experiences high pressure, the tropical eastern Indian Ocean experiences low pressure. 
  • The difference in pressure over Tahiti (the Pacific Ocean, 180 S/149W) and Darwin in northern Australia (the Indian Ocean, 120 30’S/ 131E) are computed to predict the intensity of the monsoons. If the pressure differences are negative, it means below average and late monsoons.

The Onset of The Monsoon And Withdrawal

  • The Monsoon, unlike the trades, are not steady winds but are pulsating in nature, affected by different atmospheric conditions encountered by it, on its way over the warm tropical seas. 
  • The duration of the monsoon is between 100-120 days from early June to mid-September. The monsoon arrives at the southern tip of the Indian peninsula generally by the first week of June. 
  • Subsequently, it divides into two – the Arabian Sea branch and the Bay of Bengal branch. The Arabian Sea branch reaches Mumbai about ten days later on approximately the 10th of June. 
  • The Bay of Bengal branch arrives is Assam in the first week of June. The lofty mountains cause the monsoon winds to deflect towards the west over the Ganga Plains. By mid-June, the Arabian Sea branch of the monsoon arrives over Saurashtra-Kachchh and the central part of the country. 

Detailed Chapter Notes (Part - 1) - Climate Notes | Study Social Studies (SST) Class 9 - Class 9

  • The Arabian Sea and the Bay of Bengal branches of the monsoon merge over the northwestern part of the Ganga plains. Delhi generally 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. Withdrawal or the retreat of the monsoon is a more gradual process. 
  • The withdrawal of the monsoon begins in the 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 monsoon has withdrawn from the rest of the country.
    Detailed Chapter Notes (Part - 1) - Climate Notes | Study Social Studies (SST) Class 9 - Class 9

The Seasons

Four main seasons can be identified in India:

  • Cold weather season  --  December to February
  • Hot weather season  --  March to May
  •  Advancing monsoon season  --  June to September
  • Retreating monsoon season  -- October and November

The Cold Weather Season (Winter)

Detailed Chapter Notes (Part - 1) - Climate Notes | Study Social Studies (SST) Class 9 - Class 9

Atmospheric Conditions over the Indian Subcontinent in the Month of January
  • The cold weather season begins from mid-November in India and stays till February.
  • December and January are the coldest months in the northern part of India. The temperature decreases as one move from the south to the north.
  • Days are warm and the nights are cold. Frost is common in the north and the higher slopes of the Himalayas experience snowfall.
  • 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.
  • In the northern part of the country, a feeble high-pressure region develops, with light winds moving outwards from this area.
  • The weather is normally marked by a clear sky, low temperatures, and low humidity and feeble variable winds.
  • 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. Locally known as ‘mahawat’ are of immense importance for the cultivation of ‘rabi’ crops.
  • The northeast trade winds cause a fair amount of rainfall in Chennai or the Coromandel Coast in winter.

Hot weather season (Summer)

Atmospheric Conditions over the Indian Subcontinent in the Month of JuneAtmospheric Conditions over the Indian Subcontinent in the Month of June

  • Due to the apparent movement of the sun, the global heat belt shifts northward. As such, from March to May, it is not weather season in India.
  • Temperature increases from south to north. In peninsular India, temperatures remain lower.
  • High temperature between 38C and 480 in the plains.
  • Local dust storms accompanied by light rains.
  • Hot, dry winds, ‘loo’ is common in May and June.
  • Kerala and Karnataka coast receivers pre-monsoon showers (Mango showers)
  • West Bengal and Assam are affected by northwesterly winds (Kalbaisakhi).

Try yourself:What causes rainfall in West Bengal during the hot weather season?
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The document Detailed Chapter Notes (Part - 1) - Climate Notes | Study Social Studies (SST) Class 9 - Class 9 is a part of the Class 9 Course Social Studies (SST) Class 9.
All you need of Class 9 at this link: Class 9
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