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NCERT Class 9 Geography Chapter 4: Climate of India
NCERT Class 9 Geography
Chapter 4: Climate
Terminology
- Climate β Sum total of weather for 30 years or more
- Weather β Atmosphere at a given point of time
- Includes temp. , ppt. , pr. , wind, humidity
- Monsoon from Arab βmausimβ β seasonal reversal in wind direction
- India β Monsoon land
- Temp. from Rajasthan (500C) to J&K (-450C)
- Rainfall β 400 cm in Meghalaya to 10 cm in Ladakh & Raj.
- Tamil Nadu β winter rains
- Rain decrease from east to west in north plains
- Coastal area has less extreme in temperature
Controls of Climate
- Latitude β Temp. From equator to poles
- Altitude - Temp. With ht. (higher areas β less dense air) β hills are cooler
- Pressure & Wind β depend on latitude & altitude, influence temp & rain
- Distance from Sea β Distance increase β extreme weather - continentally
- Ocean Currents β Warm & cold current
- Relief Features β 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 β Climatic Controls
- Latitude β Tropic of Cancer divides in tropics & subtropics
- Altitude β Himalayas prevent cold wind from C. Asia β mild winters
- Pressure and surface winds β NE Winds
- In South deflect right β Coriolis force
- Ferrel Law β right in NH & left in SH
- Summer β LP in interior of India
- SW Monsoon from HP to LP
- Upper air circulation β Jet Streams β Westerly Flow at 27Β°-30Β° north & so called Subtropical westerly - In India β South of Himalayas (except summer) β Year Round and cause western disturbances
- In summer β move north of Himalayas
- Tropical easterly jet stream: Over peninsular India at 14Β°N in summers
- Western cyclonic disturbances β Occur in Winters
- Tropical Cyclones β 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) β In summer at Ganga plain
- High Pr. East of Madagascar β 200S
- Heating of Tibetan Plateau
- Movement of westerly jet in Himalayas & easterly in Peninsula
Southern Oscillations
- Pr. Diff. over Tahiti (Pacific Ocean, 18Β°S/149Β°W) & Darwin, N. Australia (Indian Ocean, 12Β°30ΥS/131Β°E) β Intensity of Monsoon
- Negative SOI: late monsoon or below average
El- Nino
- βEl Ninoβ Spanish implies βchild or baby Christβ : 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 β June to Sept
- Initially β Burst of Monsoon (after pre-monsoon showers)
- At southern tip in June
- 2 branches β 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 β starts in Sept in NW India
- Islands β Monsoon appear in April to May & retreat Dec to Jan
Seasons
- Cold Weather β Winter β Nov to Feb β frost & snow in North β NE winds (dry) β Winter rain in Tamil Nadu, cyclonic disturbances form N & NW β βMahawat β winter rainβ if small good for Rabi crop
- Hot Weather β March to May, heat belt shift north, high temp, LP, loo β hot, dry gusty winds, localized storms β Kal Baisakhi in Bengal
- Pre-Monsoon Showers: Kerala & Karnataka β Mango ripening β Mango showers
- Advancing Monsoon β SW monsoon β windward side of Western Ghats receive rain, maximum in NE India β Mawsynram (stalagmite & stalactite caves) β has breaks β wet & dry spells - uncertainties
- Retreating Monsoon β Transition β Clear Sky & temp. Rise β October Heat (high temp & humidity in day) β Cyclonic depression in Andaman sea- affect east coast of India.
Unifying Bond
- Himalayas β Protect north winds
- Peninsula β Moderating influence
- Rhythmic cycle of seasons
- Water to rivers
- Agriculture
β Manishika