NDA Geography · Teaching notes
Climatology, Atmosphere and Weather — NDA Geography
This is one of the heavyweight chapters in NDA Geography — 57 PYQs across 2017–2026, and the densest-HARD recall strand, because the paper blends two demands: it asks you to TRACE A PROCESS (why does the Coriolis force vanish at the equator? how does a cold front spawn thunderstorms? why is the outer atmosphere hottest yet feels cold?) and to RECALL A NAMED FACT (which local wind is the Mistral? what does Koppen's 'Cfa' mean?). So the chapter teaches in one long arc, from the air column outward and from cause to consequence: (1) Atmospheric layers, composition and aurora — the five shells of the atmosphere, what each is made of, and the solar-wind light show; (2) Insolation, temperature and solar geometry — how the Sun heats the Earth, the lapse rate, and temperature inversion; (3) Atmospheric pressure and winds — pressure belts, the Coriolis force, geostrophic and planetary winds; (4) Humidity, condensation, clouds and precipitation — water in the air, the cloud families, and how rain/snow/sleet/hail form; (5) Cyclones, fronts and local winds — tropical vs temperate cyclones, warm/cold fronts, and the named local winds; (6) Climate classification and zones — Koppen's letter codes and the world's climatic regions. Around 25 concepts, every PYQ tagged. The mechanism concepts (Coriolis, fronts, lapse rate, cyclogenesis) carry most of the HARD marks; the named-fact tables (layers, local winds, Koppen codes, cloud types) are pure recall you must drill to reflex.
Subtopic notes
Atmospheric Layers, Composition and Aurora
12 PYQsThe atmosphere is built in five shells — troposphere, stratosphere, mesosphere, thermosphere, exosphere — each with its own temperature behaviour, gases and phenomena, from all our weather down low to the ozone shield and the aurora high up.
Open note
Insolation, Temperature and Solar Geometry
5 PYQsInsolation is the incoming solar energy; how much a place receives depends on the angle of the Sun's rays, the day length and the surface beneath — and crucially the air is warmed from BELOW, by the Earth re-radiating heat, not directly by sunlight.
Open note
Atmospheric Pressure and Winds
6 PYQsDifferences in air pressure set air in motion, and the Earth's rotation (the Coriolis force) bends that motion — together they create the planetary wind belts, the geostrophic winds aloft, and the high-pressure anticyclones.
Open note
Humidity, Condensation, Clouds and Precipitation
10 PYQsWater vapour in the air (humidity) condenses when air is cooled past saturation, forming dew, fog, frost and clouds; when the droplets grow heavy enough they fall as precipitation — rain, snow, sleet or hail.
Open note
Cyclones, Fronts and Local Winds
16 PYQsCyclones are low-pressure storms with inward-spiralling winds — tropical ones born over warm seas, temperate ones born along fronts where air masses meet — and around them swirl the named local winds the NDA loves to test.
Open note
Climate Classification and Zones
8 PYQsKoppen's scheme sorts the world's climates by temperature and rainfall into letter-coded types (A tropical, B dry, C warm-temperate, D cold, E polar), and the NDA tests both the letter codes and the example regions of each climatic zone.
Open note
PYQ weightage by concept
24 concepts · 57 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
24 concepts · 57 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| The five layers of the atmosphere | 4 | 7% |
| The normal lapse rate and the tropopause | 2 | 4% |
| Composition of the atmosphere | 2 | 4% |
| Aurora and the origin of the Coriolis effect | 2 | 4% |
| Regional climate-vegetation and a cold local wind | 2 | 4% |
| Conditions for a tropical cyclone to formfoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| How the atmosphere is heated | 2 | 4% |
| Measuring air temperature and the lapse rate | 1 | 2% |
| Temperature inversion | 1 | 2% |
| The angle of the Sun's rays and the solstice | 1 | 2% |
| Concept | PYQs | Share |
|---|---|---|
| Pressure belts and planetary winds | 2 | 4% |
| The Coriolis force | 2 | 4% |
| The geostrophic wind | 1 | 2% |
| Anticyclones | 1 | 2% |
| Concept | PYQs | Share |
|---|---|---|
| Cloud families and rain-bearing clouds | 3 | 5% |
| Sleet, cloudburst and inversion of rainfall | 3 | 5% |
| Humidity and relative humidity | 2 | 4% |
| Condensation forms vs precipitation forms | 2 | 4% |
| Concept | PYQs | Share |
|---|---|---|
| Named local winds | 7 | 12% |
| Tropical vs temperate cyclones | 6 | 11% |
| Fronts and air masses | 2 | 4% |
| Concept | PYQs | Share |
|---|---|---|
| Climate regions and the odd-one-out | 4 | 7% |
| Koppen's climate classification codes | 3 | 5% |
| The ITCZ and the tropical climates | 1 | 2% |
Formula & revision sheet
0 formulas · 5 reference tables · 25 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
0 formulas · 5 reference tables · 25 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (2)
Composition of the atmosphere3 rows
| Where / which | Dominant gas(es) | Note |
|---|---|---|
| Lower atmosphere | Nitrogen ~78%, Oxygen ~21% | Argon + CO2 + trace gases make up the rest |
| Most abundant greenhouse gas | Carbon dioxide | Above methane, nitrous oxide, CFCs NDA 2018 — CO2 is the greenhouse gas in largest concentration. |
| Exosphere (outermost) | Helium and Hydrogen | The lightest gases float to the top NDA 2021 — exosphere = helium + hydrogen. |
Regional climate-vegetation and a cold local wind3 rows
| Fact | Answer | Note |
|---|---|---|
| Campos / Llanos grasslands | South America | Tropical savanna by local name |
| Natural vegetation of SE China | Subtropical broadleaf evergreen forest | Warm, humid south-east |
| A COLD local wind | Mistral | Santa Ana / Chinook / Loo are WARM NDA 2020 — Mistral is the cold one among warm-wind distractors. |
Watch out for (6)
- Ozone is in the STRATOSPHERE, weather in the TROPOSPHERE→ The five layers of the atmosphere
- Sequence trap→ The five layers of the atmosphere
- Direction matters→ The normal lapse rate and the tropopause
- Exosphere is light gases, not oxygen-rich→ Composition of the atmosphere
- Coriolis = rotation, not tilt or revolution→ Aurora and the origin of the Coriolis effect
- Mistral is cold; its lookalikes are warm→ Regional climate-vegetation and a cold local wind
Watch out for (2)
- Air is warmed from BELOW→ How the atmosphere is heated
- CLOUDY nights do NOT favour inversion→ Temperature inversion
Watch out for (3)
- Westerlies blow WEST-to-EAST→ Pressure belts and planetary winds
- Largest at the poles, zero at the equator→ The Coriolis force
- Anticyclone winds DIVERGE→ Anticyclones
Reference tables (1)
Cloud families and rain-bearing clouds5 rows
| Cloud | Family / altitude | Weather it brings |
|---|---|---|
| Cirrus | High, wispy ice clouds | Fair, no rain |
| Cumulus | Heaped fair-weather cloud | Usually fair; can build up |
| Nimbus (Nimbostratus) | Low, layered rain cloud | Steady CONTINUOUS rain NDA 2018 — Nimbostratus = continuous precipitation; NDA 2021 — nimbus = the rain-bearing cloud. |
| Cumulonimbus | Towering storm cloud | Heavy showers, thunderstorms |
| Stratus / Stratocumulus | LOW clouds (NOT high) | Overcast, drizzle NDA 2024 — Stratus/Nimbostratus/Stratocumulus are LOW clouds, not high. |
Watch out for (5)
- High humidity SLOWS evaporation→ Humidity and relative humidity
- Sleet FALLS — so it is precipitation→ Condensation forms vs precipitation forms
- Sleet definition — sub-freezing layer OVER a warm layer→ Condensation forms vs precipitation forms
- Stratus family are LOW clouds→ Cloud families and rain-bearing clouds
- Inversion of rainfall = TEMPERATE cyclone→ Sleet, cloudburst and inversion of rainfall
Reference tables (1)
Named local winds8 rows
| Local wind | Region | Character |
|---|---|---|
| Harmattan | West Africa | NOT Mediterranean (the odd one out) NDA 2024 — Harmattan is the one NOT related to the Mediterranean. |
| Sirocco | Mediterranean (from Sahara) | Hot, dusty |
| Mistral | Mediterranean (Rhone valley) | COLD, dry |
| Khamsin | Egypt / Mediterranean | Hot |
| Chinook | North America (Rockies) | Warm, dry 'snow-eater' |
| Santa Ana | Southern California | Hot, dry; causes wildfires NDA 2026 — Santa Ana wind drives Southern California wildfires. |
| Shamal | Mesopotamia / Middle East | Warm, dry NDA 2019 — Shamal is found in Mesopotamia. |
| Purga | Siberia | Cold blizzard wind NDA 2018 — Purga blows out from Siberia. |
Watch out for (6)
- Temperate cyclones move WEST to EAST→ Tropical vs temperate cyclones
- Hurricane vs typhoon by ocean→ Tropical vs temperate cyclones
- A front's passage is a RAPID change, not slow→ Fronts and air masses
- Air masses form in SETTLED conditions→ Fronts and air masses
- Harmattan is West African, not Mediterranean→ Named local winds
- Chinook is HOT-DRY, the doldrums is CALM→ Named local winds
Reference tables (1)
Koppen's climate classification codes6 rows
| Code | Climate type |
|---|---|
| Af | Tropical wet (rainforest) NDA 2018 — Af = tropical wet. |
| BWk | Mid-latitude (cold) desert |
| Cs | Mediterranean (dry summer) |
| Cfa | Humid subtropical NDA 2019 — Cfa = humid subtropical. |
| Cwg | Great Northern Plains of India (monsoon-influenced warm) NDA 2023 — Great Northern Plains = Cwg. |
| Df | Humid continental |
Watch out for (3)
- Second letter is the rainfall season→ Koppen's climate classification codes
- Perth is Mediterranean, not steppe→ Climate regions and the odd-one-out
- Monsoon = seasonal wind reversal→ Climate regions and the odd-one-out