🌦️ Class 11 Geography – Chapter 4
Climate (जलवायु)
🌤️ Weather vs. Climate
- Weather (मौसम) → Transient (क्षणिक) स्थिति of atmosphere (1 day – 1 week).
- Climate (जलवायु) → Average of weather conditions for a long time (50+ years).
🌍 Factors Affecting Indian Weather
- Surface distribution of air pressure & heat
- Upper air circulation & inflow of air masses
- Rain-bringing systems:
- 🌨️ Western Disturbances
- 🌀 Tropical Cyclones
🌧️ Main Features of Indian Monsoon
- Seasonal change in wind direction.
- Monsoon winds → Uncertain & Irregular (अनिश्चित व असंगत).
- Brings climatic uniformity despite regional variations.
🌏 Factors Affecting Climate of India
- Latitude → South = Tropical ☀️ | North = Temperate 🌿
- Himalayas → Block ❄️ cold polar winds + cause monsoon rainfall.
- Water & Land Distribution → Peninsular India = moderate 🌊 | Interior North = extremes 🌡️
- Other factors → Distance from coast, Altitude, Relief.
📅 Traditional Seasons of India (6 ऋतुएँ)
- 🌸 Basant (Spring) – March-April
- 🔥 Grishma (Summer) – May-June
- 🌧️ Varsha (Rainy) – July-August
- 🍂 Sharad (Autumn) – Sept-Oct
- ❄️ Hemant (Pre-Winter) – Nov-Dec
- 🧊 Shishir (Winter) – Jan-Feb
🗺️ Koppen’s Climatic Regions of India
- 🌴 Amw → Monsoon with short dry season (West Coast)
- 🏖️ As → Dry monsoon in summer (Coromandel Coast)
- 🌾 Aw → Tropical Savanna (Peninsular India)
- 🌵 BShw → Semi-Arid Steppe (Rajasthan, Gujarat, Haryana, Punjab)
- 🏜️ BWhw → Hot Desert (West Rajasthan)
- 🌽 Cwg → Dry Winter (Northern Plains)
- 🌨️ Dfc → Cold Wet Winter (Eastern region)
- 🧊 E → Polar Climate (Kashmir mountains)
🌀 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.
🌊 El Niño (एल नीनो)
- Spanish word = "Child Christ".
- Occurs near Peru coast (Dec, Christmas).
- Warms Humboldt Current → Global effect (Droughts 🌵 & Floods 🌊).
- Weakens Indian Monsoon 🌧️.
🌦️ Monsoon (मॉनसून)
- Word from Arabic = "Seasonal reversal of winds".
🌩️ 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.
🌬️ Monsoon Withdrawal
- Starts Sept (NW India) → Mid-Oct (rest of India, except South).
- Causes North-East Monsoon rainfall in Tamil Nadu.
📊 Understanding Monsoon
- Based on meteorological data (Land + Ocean + Atmosphere).
- Measured using Tahiti – Port Darwin pressure difference.
- IMD uses 16 parameters for long-term prediction.
🌡️ Seasons (IMD Classification)
- ❄️ Winter (Jan–Feb)
- 🔥 Summer (Mar–May)
- 🌧️ South-West Monsoon (Jun–Sept)
- ⛅ Retreating Monsoon (Oct–Dec)
🌦️ Mechanism of Weather in India
(भारत में मौसम की प्रक्रिया)
☀️ Mechanism of Weather in Summer (ग्रीष्म ऋतु में मौसम की प्रक्रिया)
🌍 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.
🌀 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 🌪️ towards India in summer.
❄️ Mechanism of Weather in Winter (शीत ऋतु में मौसम की प्रक्रिया)
🌍 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.
🌬️ Impact
- Winters remain dry & cool in most of India.
- Occasionally, Western Disturbances bring rain & snow in North India.
🌧️ Withdrawal of Monsoon (मॉनसून की वापसी)
- Begins 2nd week of September → From North India.
- Completes withdrawal from South India by Oct–Dec.
- Unlike sudden arrival, withdrawal is slow & gradual.
🌤️ Weather Changes
- Clear sky ☀️
- Day → Hotter | Night → Cool & Pleasant
- High diurnal temperature range (दिन और रात का अंतर).
🌪️ Cyclonic Activity
- Bay of Bengal Cyclones move SE → NW, bringing heavy rain 🌊 to coastal & central India.
