Climatology explains why weather and climate vary from place to place. It starts with the Sun’s energy and how unevenly it heats the Earth; that uneven heating creates pressure differences, pressure differences drive winds, and winds carry moisture that becomes rain. The same chain explains the Indian monsoon, so this chapter is the foundation for Indian Climate and the Monsoon.

What UPSC asks

Prelims: layers of the atmosphere, temperature inversion, the Coriolis force, pressure belts and planetary winds, jet streams, local winds matched to regions, cloud types and climate regions.
Mains GS I: explaining a process — how jet streams influence the monsoon, why the west coasts of continents in mid-latitudes get winter rain, how temperate and tropical cyclones differ.

Key sub-topics

Theme	Topics
The atmosphere	Composition, layers, ozone
Heat	Insolation, heat budget, albedo, temperature inversion
Pressure and winds	Pressure belts, Coriolis force, three-cell circulation, planetary, seasonal and local winds, jet streams
Moisture	Humidity, condensation, clouds, types of rainfall
Weather systems and climate	Air masses, fronts, temperate cyclones, Köppen’s climate types

Start with Pressure Belts, Winds and Jet Streams, then The Atmosphere and the Heat Budget.