Climatology and atmosphere
Climatology and atmosphere
The exam tests the atmosphere's energy and moisture budget and then applies it to Indian weather: insolation and albedo, temperature gradients, pressure belts and winds, condensation forms, tropical cyclones, and the monsoon mechanism.
Core rules
- Insolation is short-wave; terrestrial reradiation is long-wave. Albedo varies: fresh snow about 80–90%, dense forest about 10–15%.
- Normal lapse rate in the troposphere ≈ 6.5 °C per 1000 m. Adiabatic rates (dry ≈ 10 °C/km, saturated ≈ 5–6 °C/km) are cooling by expansion, not by mixing - keep the two distinct.
- Coriolis force increases from zero at the equator to maximum at the poles and deflects winds right in the northern hemisphere, left in the southern.
- Tropical cyclone needs sea-surface temperature ≥ 26.5 °C to about 50 m depth, a pre-existing low-level disturbance, weak vertical wind shear and latitude beyond about 5° so Coriolis can spin it.
- Monsoon: northward migration of the ITCZ, differential heating of the Tibetan Plateau, the subtropical jet's withdrawal, and moist cross-equatorial flow from the Indian Ocean.
Worked example
A hill station at 2400 m records 14 °C while the plain station at 200 m records 28 °C on the same day. Find the lapse rate. Reasoning: height difference = 2200 m = 2.2 km; temperature difference = 14 °C. Lapse rate = 14 ÷ 2.2 ≈ 6.4 °C per km, close to the normal environmental lapse rate of 6.5 °C/km. Because it is near normal, the hill station's coolness is explained by altitude alone, not by a cold-air incursion.
Traps that cost marks
Using adiabatic rates to explain a mountain's temperature; stating that cyclones form at the equator; saying land breeze blows from sea to land; confusing "monsoon burst" (sudden onset of rain) with the retreating monsoon; writing that the greenhouse effect and ozone depletion are the same phenomenon.