Climate and Weather Systems

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Atmospheric Science — Key Facts for BPSC Examination

Atmosphere Layers:

Layer	Altitude	Key Feature
Troposphere	0-12 km	Weather occurs here
Stratosphere	12-50 km	Ozone layer
Mesosphere	50-80 km	Meteors burn up
Thermosphere	80-700 km	Aurora, ISS orbits
Exosphere	700+ km	Fades into space

Greenhouse Effect:

• Natural process warming Earth ~33°C
• Gases: CO₂, CH₄, H₂O, N₂O
• Without: Earth avg temp = -18°C; With: +15°C

⚡ BPSC Tip: Distinguish between weather (short-term, hours-days) and climate (long-term, decades) — this distinction is frequently tested!

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Climate and Weather — BPSC Study Guide

Atmospheric Composition and Structure

Gases by Volume (Dry Air):

Gas	Percentage
Nitrogen (N₂)	78.09%
Oxygen (O₂)	20.95%
Argon (Ar)	0.93%
CO₂	0.04%
Trace gases	<0.01%

Water Vapor: 0-4% variable (most important greenhouse gas)

Importance of Ozone Layer:

• Located in stratosphere (15-35 km)
• Absorbs UV-B and UV-C radiation
• Depletion: CFCs, halons break down ozone
• Ozone hole: Antarctica (October), Arctic (smaller)

Solar Radiation and Energy Balance

Insolation (Incoming Solar Radiation):

• Uneven distribution due to Earth’s curvature
• Maximum at equator, minimum at poles
• Key controller of temperature and atmospheric circulation

Heat Budget:

Component	Approximate %
Reflected by clouds/atmosphere	30%
Absorbed by atmosphere	20%
Absorbed by Earth’s surface	50%

Temperature Distribution:

Factor	Effect
Latitude	Primary control (tropical → polar)
Altitude	Temperature decreases ~6.5°C/km
Ocean/Continental	Maritime = milder; Continental = extreme
Winds	Transport heat and moisture
Currents	Warm = warming; Cold = cooling

Isotherms: Lines connecting points of equal temperature

Atmospheric Pressure and Circulation

Pressure Belts (Atmospheric):

Belt	Latitude	Pressure Type
Equatorial low	0°-5°	Thermal low
Sub-tropical high	25°-35°	Hadley cell descent
Sub-polar low	60°-65°	Polar front
Polar high	90°	Cold, dense air

Global Wind Circulation:

Wind System	Latitude	Direction	Character
Trade winds	0°-30°	NE (N hemisphere), SE (S hemisphere)	Consistent
Westerlies	30°-60°	SW (N hemisphere), NW (S hemisphere)	Variable
Polar easterlies	60°-90°	NE (N hemisphere), SE (S hemisphere)	Cold, dry
Monsoons	South Asia	Seasonal reversal	Wet summers, dry winters

Coriolis Effect:

• Deflects moving objects to right (N hemisphere), left (S hemisphere)
• Formula: $F = 2m\omega \sin\phi \cdot v$
• m = mass, ω = Earth’s angular velocity, φ = latitude, v = velocity
• Zero at equator, maximum at poles

Jet Streams:

Type	Location	Speed	Significance
Polar jet	50°-70° N/S	400 km/h	Storm track
Subtropical jet	20°-30° N/S	200 km/h	Monsoon influence

Monsoon System

Mechanism:

Summer (June-August):
- Land heats faster than sea (ITCZ moves north)
- Low pressure over Asia, high over Indian Ocean
- Moisture-laden winds from SW Indian Ocean → India
- Orographic rainfall on Western Ghats, Himalayas

Winter (December-February):
- High pressure over Asia (Siberian), low over Indian Ocean
- Dry NE winds from land → ocean
- Clear skies, cool temperatures

Indian Monsoon Features:

Aspect	Details
Onset	Kerala receives SW monsoon ~June 1
Withdrawal	Withdraws from NW India ~September
Arabian Sea branch	Hits Western Ghats, goes to Himalayas
Bay of Bengal branch	Strikes Myanmar, goes to NE India
Break monsoon	Mid-season dry spell (July-August)
Monsoon breaks	Active/depressed phases

Monsoon Prediction Factors:

• ENSO (El Niño-Southern Oscillation)
• Indian Ocean Dipole (IOD)
• Snow cover over Himalayas
• MJO (Madden-Julian Oscillation)

⚡ BPSC PYQ: “Explain the mechanism of Indian monsoon with reference to differential heating of land and sea” Answer: During summer, intense heating of the Tibetan plateau creates low pressure while the Indian Ocean remains relatively cool with high pressure. This pressure differential draws moisture-laden southwest winds from the Indian Ocean toward the subcontinent, causing heavy rainfall. The reversal in winter produces the northeast monsoon.

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Climate and Weather — Comprehensive BPSC Notes

Precipitation Processes

Types of Precipitation:

Type	Formation	Examples
Convective	Air heated, rises, cools	Thermal thunderstorms, equatorial rain
Orographic	Moist air forced up mountains	Western Ghats rain, Cherrapunji
Cyclonic/Frontal	Convergence of different air masses	Mid-latitude depressions
Convergence	Low pressure draws air together	ITCZ thunderstorms

Orographic Precipitation Formula: $$P = k \cdot H$$ Where P = precipitation, H = altitude, k = constant depending on moisture content

Cloud Types (for BPSC identification):

Cloud Family	Types	Altitude	Weather
High	Cirrus, Cirrostratus, Cirrocumulus	>20,000 ft	Fair to overcast
Middle	Altostratus, Altocumulus	6,500-20,000 ft	May indicate rain
Low	Stratus, Nimbostratus, Stratocumulus	<6,500 ft	Drizzle, rain
Vertical development	Cumulus, Cumulonimbus	All levels	Thunderstorms

Climate Classification (Köppen System)

Köppen Climate Groups:

Letter	Climate	Characteristics
A	Tropical	All months >18°C
B	Dry	Evaporation > precipitation
C	Mesothermal	Mild winters, warm summers
D	Microthermal	Severe winters, warm summers
E	Polar	Very cold, no summer

Indian Climate Types:

Type	Region	Features
Af (Tropical rainforest)	Andaman-Nicobar, Kerala coast	No dry month
Am (Tropical monsoon)	Western coast, NE India	Short dry season
Aw (Tropical savanna)	Most of Peninsula	Dry winter
Cwg (Subtropical humid)	Eastern Himalayas	Dry winter
BWhw (Hot desert)	Thar Desert, Rajasthan	Very dry, hot
Cfa/Cfb (Humid subtropical)	Indo-Gangetic plain	Hot summers

Tropical Monsoon Climate (Am/Aw):

• Distinct wet and dry seasons
• Annual rainfall: 1000-3000 mm
• Temperature: 20°C-35°C range
• Highest rainfall: Cherrapunji (11,777 mm/year)

Extreme Weather Events

Cyclones:

Aspect	Arabian Sea Cyclones	Bay of Bengal Cyclones
Frequency	Less common	More frequent
Peak season	May-June, Oct-Nov	Oct-Nov
Track	West/northwest	North/northeast
Notable	1999 Odisha cyclone	1970 Bhola cyclone

Cyclone Structure:

• Eye (calm, clear, 20-50 km diameter)
• Eye wall (strongest winds, heaviest rain)
• Spiral rain bands

Floods in Bihar:

River	Issue	Major Flood Events
Kosi	Shifting course, siltation	1954, 2008, 2019
Gandak	Silt accumulation	Multiple
Ganga	Monsoon overflow	Frequent

Heat Waves:

• India defines: Day temp ≥40°C (plains), ≥30°C (coastal)
• Heat wave conditions persist 4+ days above normal
• Deadly in North India, especially May-June

Climate Change

Evidence:

Indicator	Observation
Global temperature	+1.1°C since pre-industrial
Sea level	+20 cm in 20th century
Ice sheets	Greenland, Antarctic loss
CO₂ levels	420 ppm (pre-industrial: 280)
Extreme events	Increased frequency

IPCC Projections:

• 1.5°C rise by 2030-2052 (if warming continues)
• Sea level rise: 0.3-1.0 m by 2100
• More intense cyclones, altered monsoon

Impact on India:

• Glacial recession in Himalayas (flood risks)
• Monsoon variability increase
• Sea level threat to coastal cities
• Agricultural disruption
• Heat stress mortality increase

⚡ BPSC Strategy: Map-based questions are common. Be able to draw pressure belts, monsoon circulation, cyclone paths, and Köppen climate zones for India.

⚡ Common BPSC Questions:

1. “Explain the mechanism of Indian monsoon with the help of a diagram” (15 marks)
2. “Discuss the distribution of rainfall in India” (10 marks)
3. “Describe the formation and distribution of tropical cyclones” (10 marks)
4. “Explain the greenhouse effect and climate change concerns” (12 marks)

⚡ Bihar-specific Focus: Know the characteristics of Bihar’s climate — sub-tropical monsoonal with three distinct seasons: summer (March-May), rainy season (June-October), winter (November-February). Annual rainfall: ~1000 mm, highly variable.

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