Chapter 4 Climate Notes Class 9th Social Science Geography

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Climate

It is a sum total of weather conditions and variations over a large are for a long period of time (more than 30 years)

Weather 

It is the state of the atmosphere over an area at any point in time.

Elements of Weather and Climate

The temperature, atmosphere, pressure, wind, humidity, and precipitation. (rainfall)

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India has monsoon type climate.

Q. Temperature and precipitation vary from place to place and season to season why?

  • In Summer, the temperature reaches 50°C in some parts of Rajasthan while it is 20°C in Jammu and Kashmir.
  • On a winter night, the temperature in Jammu and Kashmir is minus 45°C whereas it is 22°C in thiruwanthpuram.
  • The annual precipitation in Meghalaya is more than 400 cm while it is less than 10 cm in parts of Rajasthan and Jammu and Kashmir.
  • Most of the parts of the country receive rainfall from June to September whereas Tamilnadu receives rainfall during October and November.
  • Coastal areas do nor experience much variations in climate conditions.

Climate controls of any place

There are six major controls of the climate of any place.

They are latitude, altitude, pressure and wind system, distance from the sea, ocean currents be relief features.

  1. Latitude– Due to the curvature(curve) of the earth, solar energy received varies according to the latitude.
  2. Altitude– Temperature decreases with higher altitude (height)
  3. Wind System and Pressure- They affect the climate of any place.
  4. Distance from the sea – The places wear the sea have a moderate climate and the places away from the sea have extreme climate (continentality)
  5. Ocean Currents – The onshore winds affect the climate of coastal areas.
  6. Relief Features – High mountains act as barriers for cold or hot winds.

Factors affecting India’s Climate

  1. Latitude – The tropic of cancer passes through the middle of the country. So, in the south of tropic of cancer we have a tropical climate and in the north of Tropic of cancer have a sub-tropical climate.
  2. Altitude – The Himalayas prevent the cold winds from central Asia from entering India, So we have milder winter.

Pressure and Wind System

The weather and climate are influenced by the following at atmospheric conditions. They are

  1. Pressure and winds
  2. Upper air circulation
  3. Cyclons

The air always moves from high pressure are the too low-pressure area.

In winter, a high pressure is formed north of Himalayas and so, the cold and dry winds blow towards the south.

Jet System

  • These are the high altitude winds in the atmosphere. Their speed varies from 110 km/hr in summer and 184 km/hr in winter.
  • They have located over 27°-30° North Latitude (Westly) Jetstream
  • Easterly Jetstream blows over India over 14°N Latitude.

The Mechanism of Monsoon in India

  • The differential heating and coding of land and water. The seas experience high pressure and the land experiences low pressure.
  • In summer, equatorial through is positioned over Ganga a plain.
  • The presence of high pressure is last of Madagascar.
  • The Tibetan plateau gets intensely heated during summer which results in strong vertical air current movement of air.
  • The movement of the westerly jet streams and easterly jet streams.

Southern Oscillation (S.O.)

Normally the south Pacific Ocean experiences high pressure and the Indian Ocean experience low pressure. But in recent years, there is a reversal in the pressure conditions, i.c. the Indian ocean experience high pressure and pacific ocean experiences low pressure. This periodical change is known as So.

El Nino

A warm ocean current flows over the Peruvian coast instead of the cold current, every 2 to 5 years. It is could as EL Nino.

The Onset of the Monsoon

  • The monsoon in India is pulsating in nature.
  • The duration of the monsoon is between 100-120 days.
  • Monsoon Burst – Around the time of the arrival of monsoon, the normal rainfall increases suddenly and continues for several days.

The onset of the monsoon in India

  • The monsoon arrives in the southern tip of Indian Peninsular by the first week of June.
  • Then it is branched off. One branch goes to the Bay of Bengal and other branch proceeds to Arabian sea.
  • The Arabian sea branch reaches Mumbai by 10th June and Bay of Bengal branch reaches Assam by this time.
  • The lofty mountain deflects the monsoon towards the west and the Arabian branch also reaches central India.
  • Both branches merge in the north-west and U.P., M.P., and Delhi etc. receive rainfall by June 29th.
  • By mid-July, Himachal Pradesh and the rest of the states receive rainfall.

The Seasons

There are 4 seasons identified in India. They are

  1. Cold Weather seasons (Winter)
  2. Hot Weather Seasons (Summer)
  3. Advancing Monsoon (Rainy)
  4. Retreating Monsoon (Transition)

Cold Weather Seasons (Winter)

  • The cold weather seasons begins from mid-November and stays until February.
  • December and January are the coldest moths.
  • The temperature decreases from south to north.
  • The days are warm and nights are cold. Frost is common in the north.
  • The wind blows from land to see. So far most parts it is the dry season.
  • It is a season of cyclonic disturbances which causes winter rainfall.
  • The winter rainfall locally known as ‘Mahawat’ has great importance for the cultivation of rabi crops.
  • Peninsular India does not have much winter season.

The Hot Weather Season (Summer)

  • March to May are the not-weather season in India.
  • In March the highest temperature 38°C is recorded in the Deccan plateau.
  • In April the highest temperature 45°C in North-West.
  • In peninsular India, the temperature remains lower due to the influence of Ocean.
  • It experiences rising temperature and falling air pressure.
  • Loo these are the strong, gust hot and dry winds blow during the day in the north.
  • Dust storms are common in north India.
  • It is a season of thunder storms, Violent Winds, and heavy rainfall.
  • In West Bengal, these storms are called ‘Kaal Baisakhi’.
  • Towards the end of the summer, Pre-monsoon showers are common is Kerala and Karnataka known as ‘Mango showers’ which help in the early repinning of Mangoes.

Advancing Monsoon (The Rainy Season)

  • By early June, the low pressure intensifies in the northern plains which attacks the South-West monsoon winds.
  • The coming of South-West monsoon which brings rainfall in India.
  • Early in the season, Western Ghats receive more than 250 cm rainfall.
  • Mawsynram (Meghalaya) receives the highest rainfall in the world.
  • Rajasthan and parts of Gujarat receive scanty (less) rainfall.
  • An important feature of this season is ‘Monsoon break’.
  • Monsoon Break – Monsoon rains take place only for a few days at a time when there are rainless intervals known as ‘Monsson Break’.
  • Monsoon through determines the distribution of rainfall i.e., the places near the axis of through receives rainfall.
  • The monsoon is known for its uncertainties. It causes a flood in one part and causes drought in the other.
  • Since it is irregular, it disturbs the farming schedule of millions of farmer.

Retreating Monsoon (Transition)

  • During October-November, South-West monsoon winds become weaker.
  • It is a period of transition from hot rainy season to dry winter.
  • Day temperature is high and nights are cool.
  • The weather becomes oppressive during the day due to high temperature and humidity are known as ‘October heat’.
  • It is the period of cyclones which are very destructive and causes great damage to life and property.

Distribution of Rainfall

  • Parts of western coast and north-east receives more than 400 cm rainfall annually.
  • Parts of Gujarat, Rajasthan, Haryana, and Punjab receives less than 60 cm rainfall.
  • Leh in Jammu and Kashmir receives the lowest rainfall.
  • Monsoon is variable from year to year. So the areas of heavy rainfall are affected by floods and the areas of low rainfall are affected by droughts.

Why is monsoon considered a unifying bond?

  • The seasonal alteration of the Wind Systems provides a rhythmic cycle of the season.
  • The Indian landscape, its animal and pant life, its agricultural calendar and the life of the people including their festivities revolve around monsoon.
  • Year after year, people throughout India eagerly await the arrival of the monsoon.
  • The monsoon wind binds the whole country by providing water to set agricultural activities.
  • The river valleys which carry this water unit the country as a single valley unit.
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