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NCERT Class 9 Geography Chapter 4: Climate of India

NCERT Class 9 Geography

Chapter 4: Climate

Terminology

  • Climate – Sum total of weather for 30 years or more
  • Weather – Atmosphere at a given point of time
  • Includes temp. , ppt. , pr. , wind, humidity
  • Monsoon from Arab β€œmausim” – seasonal reversal in wind direction
  • India – Monsoon land
  • Temp. from Rajasthan (500C) to J&K (-450C)
  • Rainfall – 400 cm in Meghalaya to 10 cm in Ladakh & Raj.
  • Tamil Nadu – winter rains
  • Rain decrease from east to west in north plains
  • Coastal area has less extreme in temperature

Controls of Climate

  • Latitude – Temp. From equator to poles
  • Altitude - Temp. With ht. (higher areas – less dense air) – hills are cooler
  • Pressure & Wind – depend on latitude & altitude, influence temp & rain
  • Distance from Sea – Distance increase – extreme weather - continentally
  • Ocean Currents – Warm & cold current
  • Relief Features – Mts. act as barrier
  • Deserts on western margins of continents in subtropics: Prevailing winds are tropical easterly winds & go dry on reaching western margins.

India – Climatic Controls

  • Latitude – Tropic of Cancer divides in tropics & subtropics
  • Altitude – Himalayas prevent cold wind from C. Asia – mild winters
  • Pressure and surface winds – NE Winds
  • In South deflect right – Coriolis force
  • Ferrel Law – right in NH & left in SH
  • Summer – LP in interior of India
  • SW Monsoon from HP to LP
India - Climatic Controls
  • Upper air circulation – Jet Streams – Westerly Flow at 27Β°-30Β° north & so called Subtropical westerly - In India – South of Himalayas (except summer) – Year Round and cause western disturbances
  • In summer – move north of Himalayas
  • Tropical easterly jet stream: Over peninsular India at 14Β°N in summers
  • Western cyclonic disturbances – Occur in Winters
  • Tropical Cyclones – Occur in Monsoons & in Oct-Nov as easterly flow

Monsoons

  • In 200 N & S tropics
  • Differential heating of water and land
  • Shifting of ITCZ (NE & SE winds converge) – In summer at Ganga plain
  • High Pr. East of Madagascar – 200S
  • Heating of Tibetan Plateau
  • Movement of westerly jet in Himalayas & easterly in Peninsula

Southern Oscillations

Southern Oscillation
  • Pr. Diff. over Tahiti (Pacific Ocean, 18Β°S/149Β°W) & Darwin, N. Australia (Indian Ocean, 12Β°30՚S/131Β°E) – Intensity of Monsoon
  • Negative SOI: late monsoon or below average

El- Nino

  • β€˜El Nino’ Spanish implies β€˜child or baby Christ’ : Starts flowing during Christmas
  • Warm Peruvian Coast, instead of cold Peruvian current, every 2 to 5 years
  • Changes in pressure conditions are connected to El Nino
  • Called as ENSO (El Nino Southern Oscillations)
  • In sea-surface temp. & weakening trade winds
  • Cause poor monsoon in India

Monsoon Mechanism

  • Pulsating
  • 100 - 120 days – June to Sept
  • Initially – Burst of Monsoon (after pre-monsoon showers)
  • At southern tip in June
  • 2 branches – Bay of Bengal (Assam in 1st week of June- deflect to west by Himalayas) & Arabian Sea (reach Mumbai by 10th June)
  • Both branch merge at Ganga Plains by June end
  • Retreat or withdrawal is gradual – starts in Sept in NW India
  • Islands – Monsoon appear in April to May & retreat Dec to Jan

Seasons

  • Cold Weather – Winter – Nov to Feb – frost & snow in North – NE winds (dry) – Winter rain in Tamil Nadu, cyclonic disturbances form N & NW – β€œMahawat – winter rain” if small good for Rabi crop
  • Hot Weather – March to May, heat belt shift north, high temp, LP, loo – hot, dry gusty winds, localized storms – Kal Baisakhi in Bengal
  • Pre-Monsoon Showers: Kerala & Karnataka – Mango ripening – Mango showers
  • Advancing Monsoon – SW monsoon – windward side of Western Ghats receive rain, maximum in NE India – Mawsynram (stalagmite & stalactite caves) – has breaks – wet & dry spells - uncertainties
  • Retreating Monsoon – Transition – Clear Sky & temp. Rise – October Heat (high temp & humidity in day) – Cyclonic depression in Andaman sea- affect east coast of India.
Normal Dates of Withdrawal

Unifying Bond

  • Himalayas – Protect north winds
  • Peninsula – Moderating influence
  • Rhythmic cycle of seasons
  • Water to rivers
  • Agriculture

✍ Manishika