Climatology — Quick Revision

A last-week revision sheet for climatology. Learn the tables; Prelims statements are usually built from one row.

The Atmosphere

Layer	Height (approx.)	Temperature with height	Remember
Troposphere	8 km (poles) – 18 km (Equator)	Falls (~6.5 °C/km)	Weather, clouds, water vapour
Stratosphere	to ~50 km	Rises	Ozone layer; calm — jet aircraft
Mesosphere	~50–80 km	Falls	Coldest; meteors burn
Thermosphere (ionosphere)	~80–400 km	Rises	Reflects radio waves; auroras
Exosphere	Above	—	Merges with space

Composition (dry air): nitrogen ~78%, oxygen ~21%, argon 0.93%, carbon dioxide ~0.04%.

High-yield facts

The atmosphere is heated mainly from below by long-wave terrestrial radiation.
Of 100 units of insolation: 35 reflected, 14 absorbed by the atmosphere, 51 by the surface (NCERT).
Maximum surface insolation: subtropical deserts (clear skies), not the Equator.
Energy surplus between ~40° N and 40° S; deficit poleward — transferred by winds and currents.
Temperature inversion: long, clear, calm winter nights → fog, smog, frost; cold air collects in valleys.
Montreal Protocol 1987; Kigali Amendment 2016 (HFCs).

Belt	Latitude	Origin	Associated wind / feature
Equatorial low	0°–5°/10°	Thermal	Doldrums; ITCZ
Subtropical high	~30°	Dynamic	Horse latitudes; hot deserts
Subpolar low	~60°	Dynamic	Polar front; temperate cyclones
Polar high	90°	Thermal	Polar easterlies originate

Wind	From → to	NH / SH direction
Trade winds	Subtropical high → equatorial low	NE / SE
Westerlies	Subtropical high → subpolar low	SW / NW; Roaring Forties, Furious Fifties, Shrieking Sixties in SH
Polar easterlies	Polar high → subpolar low	NE / SE

Coriolis force: right in NH, left in SH; zero at the Equator, maximum at the poles.
Cyclone (low): anticlockwise in NH; anticyclone (high): clockwise in NH.
Cells: Hadley (0–30°), Ferrel (30–60°), Polar (60–90°).

Jet	Where	Role
Subtropical westerly jet	~30° latitude, upper troposphere	South of the Himalaya in winter — western disturbances; north of Tibet in summer
Polar front jet	~50°–60°	Steers temperate cyclones
Tropical easterly jet	Over peninsular India in summer	Associated with the south-west monsoon

Term	Meaning
Absolute humidity	Actual amount of water vapour per unit volume of air
Relative humidity	Water vapour present as a percentage of what the air could hold at that temperature
Dew point	Temperature at which air becomes saturated
Fog	Cloud at ground level; visibility below 1 km

Rainfall type	Cause	Example
Convectional	Strong surface heating; rising air	Afternoon showers in equatorial regions
Orographic (relief)	Moist air forced over mountains	Heavy rain on the windward Western Ghats; rain shadow on the Deccan side
Cyclonic / frontal	Air rising in cyclones or along fronts	Temperate cyclone rain; western disturbances

Feature	Tropical cyclone	Temperate cyclone
Origin	Warm oceans, ~5°–30° latitude	Along the polar front, ~35°–65°
Energy	Latent heat of condensation	Contrast between warm and cold air masses
Fronts	None	Warm, cold and occluded fronts
Eye	Present	Absent
Movement	East to west with the trades, then may recurve	West to east with the westerlies
Over land	Weakens after landfall	Can persist over land and sea
Size	Smaller, more intense	Larger, less intense

Group	Type	Rule of thumb
A	Tropical humid	Coolest month above 18 °C
B	Dry	Evaporation exceeds precipitation
C	Warm temperate	Mild winters
D	Cold snow-forest	Severe winters
E	Polar	Warmest month below 10 °C
H	Highland	Altitude-controlled

Mediterranean climate (Cs) — dry summers, winter rain from westerlies; west sides of continents around 30°–40° latitude.

Traps to avoid

Winds are named after the direction they come from.
The Coriolis force is zero at the Equator.
Subtropical highs and subpolar lows are dynamic, not thermal.
Temperature rises with height in the stratosphere and thermosphere.
Clouds and wind prevent temperature inversion.
Temperate cyclones have fronts and no eye; tropical cyclones have an eye and no fronts.