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Predicted Questions with Model Answers
Q1 (5 marks — 50 words): Explain the three-cell model of atmospheric circulation.
Model Answer:
The three-cell model comprises: (1) Hadley Cell (0°–30°): Hot equatorial air rises, moves poleward, descends at 30°, creating subtropical highs and trade winds. (2) Ferrel Cell (30°–60°): Mechanically driven; surface westerlies blow poleward. (3) Polar Cell (60°–90°): Cold polar air descends, polar easterlies blow equatorward. These cells drive trade winds, westerlies, and polar easterlies respectively.
Q2 (5 marks — 50 words): What is orographic rainfall? State any two examples of areas receiving such rainfall.
Model Answer:
Orographic rainfall occurs when moist air is forced upward by a mountain barrier — it cools adiabatically, reaches dew point, and produces heavy precipitation on the windward slope. The leeward side remains dry (rain shadow). Example 1: Cherrapunji/Mawsynram, Meghalaya (11,430–11,871 mm/year) — windward of Khasi Hills facing Bay of Bengal monsoon. Example 2: Western Ghats (Kozhikode, Kerala — 3,000+ mm/year) — windward of the Arabian Sea monsoon.
Q3 (5 marks — 50 words): Distinguish between relative humidity and absolute humidity. State the conditions under which dew is formed.
Model Answer:
Absolute humidity is mass of water vapour per unit volume (g/m³) — changes with temperature/pressure. Relative humidity (RH) is actual vapour as percentage of saturation capacity at that temperature — more useful for weather forecasting. Dew forms when: (a) surfaces cool by radiation on clear, calm nights to below dew point temperature; (b) RH reaches 100% at the surface; (c) no wind to mix and warm the air.
Q4 (10 marks — 150 words): Describe the factors controlling the distribution of insolation over the Earth's surface and explain how they create climatic differences between latitudinal zones.
Model Answer:
Insolation (incoming solar radiation, solar constant ~1,370 W/m²) varies across Earth's surface due to four key factors, creating distinct latitudinal climatic zones:
1. Angle of Incidence: At the equator, sun rays strike nearly perpendicular — high intensity concentrated over small area. At poles, oblique rays spread over larger area with the same energy → equatorial surfaces receive ~2× the insolation of polar regions. This is the primary driver of the equatorial–polar temperature gradient.
2. Day Length: At equator, day length is ~12 hours year-round. Polar regions experience 0 hours (polar night) to 24 hours (midnight sun) — extreme seasonal variation. Despite 24-hour summer daylight, low sun angle limits polar insolation. Temperate regions have significant seasonal variation (8–16 hours).
3. Atmospheric Path Length: At low sun angles (high latitudes), solar radiation travels through more atmosphere — greater scattering and absorption by aerosols, water vapour, and dust. Equatorial noon sun passes through minimum atmosphere. Result: less solar energy reaches polar surfaces.
4. Albedo: Ice/snow surfaces (polar) reflect 80–90% of incoming radiation; tropical oceans absorb 94%. This amplifies the equatorial–polar temperature difference and creates the ice-albedo feedback — as ice melts, albedo drops, more heat absorbed, more melting (dangerous positive feedback in climate change).
Resulting Climatic Zones:
- Tropical (0°–23.5°): High year-round insolation → hot, moist; heavy convectional rainfall; equatorial forests and savannas
- Subtropical (23.5°–35°): Hadley Cell descent; high insolation but reduced precipitation → world's deserts
- Temperate (35°–65°): Moderate insolation; seasonal variation; frontal rain; fertile farmlands
- Polar (>65°): Low insolation; extreme cold; ice deserts; permafrost; tundra
Understanding insolation variation is foundational to climate science, providing the energy driver behind all circulation, precipitation, and vegetation patterns studied in geography.
Q5 (10 marks — 150 words): Explain El Niño and its impact on India's monsoon and global weather patterns.
Model Answer:
El Niño (Spanish: "The Christ Child") is an irregular (every 2–7 years) anomalous warming of central and eastern Pacific Ocean surface waters by 2–5°C above normal, disrupting global atmospheric circulation.
Normal (Non-El Niño) Pacific Conditions:
Strong trade winds blow westward → warm water piles in western Pacific (Indonesia, Australia) → heavy rainfall there; cold upwelling off Peru coast sustains rich fishery; Walker Circulation cell active.
During El Niño:
Trade winds weaken or reverse → warm water moves eastward → Walker Circulation disrupted → warm water off South America coast, cold water in western Pacific.
Impact on India:
El Niño weakens the Indian Summer Monsoon. Warm eastern Pacific suppresses the east-west atmospheric pressure gradient needed to drive the monsoon. Historical examples: 1987, 2002, 2004, 2009 El Niño years all coincided with Indian monsoon deficiency (10–26% below normal), triggering droughts in Rajasthan, Gujarat, Maharashtra, and Karnataka. 2023–24 El Niño caused below-normal monsoon in August 2023.
Global Impacts:
- Australia/SE Asia/India: Drought
- Peru/Ecuador: Flooding
- East Africa: Above-normal rainfall
- Global temperature spikes — El Niño years (1997–98, 2015–16, 2023–24) are typically the warmest on record
La Niña (opposite): Strengthens Indian Monsoon (2010, 2020–22 La Niña — above-normal monsoon and flooding in India).
Monitoring: Southern Oscillation Index (SOI) — pressure difference between Tahiti and Darwin; negative SOI = El Niño. INCOIS (Hyderabad) monitors ENSO and issues Indian Ocean climate outlooks.