NDA Geography · Climatology, Atmosphere and Weather
Cyclones, Fronts and Local Winds
Cyclones 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.
Why this matters
16 PYQs — the largest subtopic in the chapter, and rich in HARD multi-statement traps. Three blocks of marks: tropical vs temperate (extratropical) cyclones and their rotation/formation conditions; fronts and air masses; and the named local winds (Mistral, Sirocco, Chinook, Santa Ana, Loo, Bora, Purga...). The local-wind names are pure recall — drill them to reflex.
Concept 1 of 4
Tropical vs temperate cyclones
Intuition
A cyclone is a low-pressure storm whose winds spiral INWARD — anticlockwise in the Northern Hemisphere, clockwise in the Southern (because Coriolis deflects to the left there). TROPICAL cyclones are compact, born over warm seas, and feed on ocean heat. TEMPERATE (extratropical) cyclones are larger, born in the mid/high latitudes along FRONTS where warm and cold air masses meet (the Polar Front Theory). Cyclones bring cloudy, rainy weather; anticyclones bring fair weather.
Definition
- Cyclone rotation: winds spiral inward, anticlockwise in the Northern Hemisphere, CLOCKWISE in the Southern (Coriolis deflects left in the SH). Anticyclones rotate the opposite way.
- Tropical cyclones — form over warm tropical seas (need warm water, Coriolis, upper-air divergence, LOW vertical wind shear). Called hurricanes (N Atlantic / E N Pacific), typhoons (NW Pacific / China), cyclones (Indian & S Pacific Oceans), Willy Willy (Australia), Baguio (Philippines).
- Temperate / extratropical cyclones — form in mid and high latitudes along the Polar Front; they cover a much larger area than tropical cyclones and generally move WEST to EAST (NOT east to west).
- Cyclones → cloudy/rainy weather; anticyclones → fair weather.
Worked example
Three claims: (1) in the Northern Hemisphere cyclones rotate anticlockwise and anticyclones clockwise; (2) cyclones bring rainy weather, anticyclones fair weather; (3) in the Southern Hemisphere the cyclonic spiral is clockwise because Coriolis acts to the left. How many are correct?
Practice this conceptself-check · 4 quick reps
From the bank · past-year question
Which of the following statements regarding cyclones and anti-cyclones is/are correct ?
1. In the Northern Hemisphere, cyclones rotate counter clockwise and anticyclones rotate clockwise.
2. Cyclones are often associated with cloudy or rainy weather, whereas anticyclones are often associated with fair weather.
3. In the Southern Hemisphere, the cyclonic spiral will be clockwise because the Coriolis force acts to the left.
Select the answer using the code given below :
[Q112 · Apr · 2024]
Temperate cyclones move WEST to EAST
An extratropical-cyclone trap claims 'they move from east to west'. Mid-latitude (temperate) cyclones are steered by the westerlies and move west to east. They DO develop in mid/high latitudes and DO affect a larger area — those two claims are true.
Hurricane vs typhoon by ocean
Tropical cyclones of the North Atlantic / eastern North Pacific are hurricanes; those of the NW Pacific are typhoons. A trap swaps these names. The Indian and South Pacific Oceans just call them 'cyclones'.
Concept 2 of 4
Fronts and air masses
Intuition
An AIR MASS is a huge body of air with uniform temperature and humidity, formed over a large source region (tropical or polar, land or sea) — it forms under SETTLED conditions, not cyclonic ones. Where two air masses meet, the boundary is a FRONT. At a WARM front, advancing warm air rides gently up over cold air; at a COLD front, advancing cold air shoves under warm air, forcing it up steeply — which is why cold fronts spawn thunderstorms.
Definition
- An air mass forms in a tropical OR polar source region, over continents OR oceans, and changes the weather of areas it moves into. It forms under stable/settled conditions — it does NOT 'develop in a cyclonic condition' (that claim is false).
- A front is the boundary between two air masses.
- Warm front — advancing warm air rides up OVER a retreating colder air mass (gentle slope, steady rain). This is the correct definition.
- Cold front — advancing cold air undercuts warm air, lifting it steeply — associated with thunderstorms.
- A front's passage usually brings a fairly rapid (not slow) change of weather — so 'a front causes a SLOW change in weather' is the false statement.
Worked example
Three claims about fronts: (1) a front's movement causes a SLOW change in weather; (2) cold fronts are associated with thunderstorms; (3) a warm front is where advancing warm air overrides and rises above colder air. Which are correct?
Practice this conceptself-check · 3 quick reps
From the bank · past-year question
Consider the following statements regarding 'fronts' :
1. The movement of a front causes a slow change in weather in the area over which it moves.
2. Cold fronts are associated with thunderstorms.
3. Warm front is the boundary between an advancing mass of warm air where it is overriding and rising above a mass of colder air.
Which of the statements given above is/are correct ?
[Q74 · Apr · 2024]
A front's passage is a RAPID change, not slow
The statement 'the movement of a front causes a SLOW change in weather' is false — a passing front brings a comparatively abrupt shift (temperature, wind, cloud and rain all change quickly).
Air masses form in SETTLED conditions
An air mass needs a large, calm source region to take on uniform properties — it does NOT 'develop in a cyclonic condition'. That is the odd-one-out in 'which is NOT true' questions.
Concept 3 of 4
Named local winds
Intuition
Local winds are short-range winds with regional names, and the NDA tests the name-to-place pairing relentlessly. Group them by region — Mediterranean (Sirocco, Mistral, Khamsin), North America (Chinook, Santa Ana), the Middle East / Mesopotamia (Shamal), Siberia (Purga). The classic odd-one-out: the Harmattan blows in West Africa, NOT the Mediterranean.
Definition
Memorise the wind-to-place pairs:
- Mediterranean winds — Sirocco (hot, from the Sahara), Mistral (cold, down the Rhone), Khamsin (hot, Egypt). The Harmattan is NOT Mediterranean — it blows over West Africa.
- North America — Chinook (warm, dry; 'snow-eater', raises winter temperatures fast), Santa Ana (hot, dry; fuels Southern California wildfires).
- Mesopotamia / Middle East — Shamal (warm, dry).
- Siberia — Purga (cold blizzard wind blowing out of Siberia).
- The doldrums (equatorial low) is a belt of calm winds, NOT a local wind.
| 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. |
Practice this conceptself-check · 5 quick reps
From the bank · past-year question
Which one among the following local winds is NOT related to Mediterranean Sea ?
[Q80 · Sep · 2024]
Harmattan is West African, not Mediterranean
Grouped with Khamsin, Sirocco and Mistral (all Mediterranean), the Harmattan is the outsider — a dry, dusty West African wind.
Chinook is HOT-DRY, the doldrums is CALM
The Chinook is a warm, dry descending wind that raises temperatures quickly in winter (true). The doldrums is a belt of calm equatorial winds — a pressure belt, not a local wind.
Concept 4 of 4
Conditions for a tropical cyclone to form
Intuition
A tropical cyclone is born only when several ingredients line up in the FORMATIVE stage: a very warm sea (above 26 degrees C) to feed it energy, plenty of moisture high in the atmosphere, and an unstable atmosphere that lets air keep rising. These belong to the initial formation stage, not maturity or decay.
Definition
Ingredients required in the formation / initial stage of a tropical cyclone:
- A warm sea-surface temperature above ~26 degrees C (the energy source).
- High relative humidity in the atmosphere up to a good height (above ~700 m / mid-troposphere).
- Atmospheric instability so warm moist air keeps rising and condensing.
These conditions define the BIRTH of the storm — the formative stage, not full maturity or decay.
Worked example
A warm sea (above 26 degrees C), high humidity aloft and an unstable atmosphere are associated with which stage of a tropical cyclone's life?
Practice this concept2 quick reps
From the bank · past-year question
Consider the following characteristics of a tropical cyclone:
1. A warm sea temperature of > 26°C
2. High relative humidity of atmosphere at a height of > 700 m
3. Atmospheric instability
The above mentioned characteristics are associated with which one of the following cycles of its development?
[Q149 · Sep · 2017]
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
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
Drill every past-year question on this subtopic
16 questions from the bank — paginated, with cart and Word-export support.