๐ฆ️ Class 11 Geography – Chapter 4
Climate (เคเคฒเคตाเคฏु)
๐ค️ Weather vs. Climate
- Weather (เคฎौเคธเคฎ) → Transient (เค्เคทเคฃिเค) เคธ्เคฅिเคคि of atmosphere (1 day – 1 week).
- Climate (เคเคฒเคตाเคฏु) → Average of weather conditions for a long time (50+ years).
๐ Factors Affecting Indian Weather
- Surface distribution of air pressure & heat
- Upper air circulation & inflow of air masses
- Rain-bringing systems:
- ๐จ️ Western Disturbances
- ๐ Tropical Cyclones
๐ง️ Main Features of Indian Monsoon
- Seasonal change in wind direction.
- Monsoon winds → Uncertain & Irregular (เค เคจिเคถ्เคिเคค เคต เค เคธंเคเคค).
- Brings climatic uniformity despite regional variations.
๐ Factors Affecting Climate of India
- Latitude → South = Tropical ☀️ | North = Temperate ๐ฟ
- Himalayas → Block ❄️ cold polar winds + cause monsoon rainfall.
- Water & Land Distribution → Peninsular India = moderate ๐ | Interior North = extremes ๐ก️
- Other factors → Distance from coast, Altitude, Relief.
๐ Traditional Seasons of India (6 เคเคคुเคँ)
- ๐ธ Basant (Spring) – March-April
- ๐ฅ Grishma (Summer) – May-June
- ๐ง️ Varsha (Rainy) – July-August
- ๐ Sharad (Autumn) – Sept-Oct
- ❄️ Hemant (Pre-Winter) – Nov-Dec
- ๐ง Shishir (Winter) – Jan-Feb
๐บ️ Koppen’s Climatic Regions of India
- ๐ด Amw → Monsoon with short dry season (West Coast)
- ๐️ As → Dry monsoon in summer (Coromandel Coast)
- ๐พ Aw → Tropical Savanna (Peninsular India)
- ๐ต BShw → Semi-Arid Steppe (Rajasthan, Gujarat, Haryana, Punjab)
- ๐️ BWhw → Hot Desert (West Rajasthan)
- ๐ฝ Cwg → Dry Winter (Northern Plains)
- ๐จ️ Dfc → Cold Wet Winter (Eastern region)
- ๐ง E → Polar Climate (Kashmir mountains)
๐ ITCZ (Inter-Tropical Convergence Zone)
- Low pressure zone at equator.
- July → ITCZ shifts to 20°–25°N (Gangetic plain) = Monsoon Trough.
- South-East trade winds cross equator → turn into South-West Monsoon due to Coriolis effect.
- Winter → ITCZ shifts south → North-East Monsoon.
๐ El Niรฑo (เคเคฒ เคจीเคจो)
- Spanish word = "Child Christ".
- Occurs near Peru coast (Dec, Christmas).
- Warms Humboldt Current → Global effect (Droughts ๐ต & Floods ๐).
- Weakens Indian Monsoon ๐ง️.
๐ฆ️ Monsoon (เคฎॉเคจเคธूเคจ)
- Word from Arabic = "Seasonal reversal of winds".
๐ฉ️ Monsoon Blast
- Heavy rainfall due to moisture-laden winds = sudden torrential rain ⛈️.
⛅ Monsoon Break
- Dry spell of 2+ weeks due to ITCZ shift or weak cyclones.
๐ฌ️ Monsoon Withdrawal
- Starts Sept (NW India) → Mid-Oct (rest of India, except South).
- Causes North-East Monsoon rainfall in Tamil Nadu.
๐ Understanding Monsoon
- Based on meteorological data (Land + Ocean + Atmosphere).
- Measured using Tahiti – Port Darwin pressure difference.
- IMD uses 16 parameters for long-term prediction.
๐ก️ Seasons (IMD Classification)
- ❄️ Winter (Jan–Feb)
- ๐ฅ Summer (Mar–May)
- ๐ง️ South-West Monsoon (Jun–Sept)
- ⛅ Retreating Monsoon (Oct–Dec)
๐ฆ️ Mechanism of Weather in India
(เคญाเคฐเคค เคฎें เคฎौเคธเคฎ เคी เคช्เคฐเค्เคฐिเคฏा)
☀️ Mechanism of Weather in Summer (เค्เคฐीเคท्เคฎ เคเคคु เคฎें เคฎौเคธเคฎ เคी เคช्เคฐเค्เคฐिเคฏा)
๐ Surface Air Pressure & Winds
- Early Summer (Uttarayan) → Sun shifts northwards → Air circulation reverses in lower & upper atmosphere.
- By mid-July → ITCZ (Inter-Tropical Convergence Zone) shifts north, parallel to Himalayas (20°–25° N).
- This causes low-pressure belt near the surface → attracts monsoon winds.
๐ Jet Stream Flow
- At 12 km altitude, strong horizontal air currents = Jet Streams.
- Western Jet Stream → Brings Western Disturbances ❄️ in winter.
- Eastern Jet Stream → Pulls Tropical Cyclones ๐ช️ towards India in summer.
❄️ Mechanism of Weather in Winter (เคถीเคค เคเคคु เคฎें เคฎौเคธเคฎ เคी เคช्เคฐเค्เคฐिเคฏा)
๐ Surface Air Pressure & Winds
- Central & West Asia → Develops high-pressure system over Tibet (north of Himalayas).
- Winds blow outward from high pressure to low pressure → reach India as dry continental winds.
- These dry winds mix with Trade Winds in NW India, but this contact zone keeps shifting.
๐ฌ️ Impact
- Winters remain dry & cool in most of India.
- Occasionally, Western Disturbances bring rain & snow in North India.
๐ง️ Withdrawal of Monsoon (เคฎॉเคจเคธूเคจ เคी เคตाเคชเคธी)
- Begins 2nd week of September → From North India.
- Completes withdrawal from South India by Oct–Dec.
- Unlike sudden arrival, withdrawal is slow & gradual.
๐ค️ Weather Changes
- Clear sky ☀️
- Day → Hotter | Night → Cool & Pleasant
- High diurnal temperature range (เคฆिเคจ เคเคฐ เคฐाเคค เคा เค ंเคคเคฐ).
๐ช️ Cyclonic Activity
- Bay of Bengal Cyclones move SE → NW, bringing heavy rain ๐ to coastal & central India.
