Atmosphere: Composition, Structure, Insolation, Temperature and Pressure, Winds, Humidity, Precipitation and World Climatic Types
Atmosphere: Composition, Structure, Insolation, Temperature and Pressure, Winds, Humidity, Precipitation and World Climatic Types
This domain tests the atmosphere's layers, the energy budget, pressure and wind belts, moisture processes and Köppen-style climate types. Numerical and cause–effect questions are common.
Core rules and concepts
- Dry air: nitrogen about 78%, oxygen about 21%, argon about 0.93%, carbon dioxide about 0.04%.
- Layers: troposphere (weather; lapse rate about 6.5°C per km), stratosphere (ozone layer), mesosphere (coldest), thermosphere and exosphere.
- Insolation is incoming solar radiation; about 30% is reflected (albedo). Temperature falls with altitude in the troposphere and can invert on clear calm nights.
- Pressure belts: equatorial low, subtropical high, subpolar low, polar high. Winds blow from high to low pressure and are deflected by the Coriolis force, zero at the equator.
- Planetary winds: trade winds, westerlies, polar easterlies. Humidity is absolute (mass per volume) or relative (percentage of saturation).
- Precipitation types: convectional, orographic and cyclonic/frontal. World climates follow Köppen groups such as A, B, C, D and E.
Worked example
Chennai receives most rain in October–December. Reasoning: the ITCZ shifts south, the northeast monsoon draws moist air from the Bay of Bengal, and the Tamil Nadu coast lies windward. The Western Ghats force the same winds to rise, but the rain shadow falls on the leeward side.
Traps
Ozone is in the stratosphere, not the troposphere. Relative humidity changes with temperature even if vapour content is unchanged. Orographic rain falls on the windward slope. Coriolis deflection is zero at the equator, not maximum.