GeographyICSE Class 9 · Atmospheric Pressure and Winds

Pressure Belts, Planetary Winds and Local Winds (ICSE Class 9 Geography)

Updated 17 October 2026 · Draft, not yet fact-checked

Atmospheric pressure falls with altitude and temperature rise, and air moves from high to low pressure as wind, deflected by the Coriolis effect. There are seven pressure belts; planetary winds are the trade winds, westerlies and polar easterlies; periodic winds include land and sea breezes and monsoons; local winds include the loo, chinook, foehn and mistral.

Understand Pressure Belts, Planetary Winds and Local Winds

1. Pressure. Atmospheric pressure is the weight of the air column on a unit area, measured by a barometer in millibars (mean sea-level pressure about 1,013 mb). It falls with altitude (about 1 mb for every 10 m in the lower atmosphere), falls when air is warm and rises when air is cold; water vapour makes air lighter. Lines joining equal pressures are isobars.

2. Pressure belts. Equatorial low (doldrums), two sub-tropical highs (horse latitudes, about 30 degrees), two sub-polar lows (about 60 degrees) and two polar highs.

3. Factors affecting wind. The pressure gradient (greater difference gives stronger wind), the Coriolis effect (deflection right in the northern, left in the southern hemisphere), friction.

4. Planetary winds.

*Trade winds*: blow from sub-tropical highs to the equatorial low; north-east in the north, south-east in the south.
*Westerlies*: blow from sub-tropical highs to sub-polar lows; south-west in the north, north-west in the south.
*Polar easterlies*: blow from polar highs to sub-polar lows.

5. Periodic winds. *Sea breeze* (day: from sea to land) and *land breeze* (night: from land to sea); *monsoons* reverse direction with the season.

6. Local winds. *Loo*: hot, dry wind of the northern plains of India and Pakistan in summer. *Chinook*: warm, dry wind on the eastern slopes of the Rockies that melts snow. *Foehn*: warm, dry wind on the northern side of the Alps. *Mistral*: cold, dry wind from the Alps to the Mediterranean coast of France.

7. Variable winds. *Cyclones* are low-pressure systems with winds spiralling inwards; *anticyclones* are high-pressure systems with winds spiralling outwards; *jet streams* are fast narrow high-altitude winds.

Pressure Belts, Planetary Winds and Local Winds: key facts

Pressure: Sea level 1,013 mb
1 mb per 10 m of height
Barometer
Belts: Equatorial low
Sub-tropical high 30 degrees
Sub-polar low 60 degrees
Polar high
Planetary winds: Trade: NE and SE
Westerlies: SW and NW
Polar easterlies
Local winds: $L oo : I n d ia ∣ C hin oo k : R oc k i es ∣ F oe hn : A l p s ∣ M i s t r a l : F r an ce$

Pressure Belts, Planetary Winds and Local Winds in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Beach evening

Suppose a family on a beach finds the breeze cool in the afternoon and blowing from the sea, while at night it reverses and blows from the land.

Explain the pattern.

Try it first, then show the solutionSolution

By day land heats faster, giving low pressure over land; wind blows from the sea (sea breeze).
At night land cools faster, giving high pressure over land; wind blows to the sea (land breeze).

Answer: Sea breeze by day, land breeze by night.

Memory hook: Day sea-to-land, night land-to-sea.

Tricks to remember Pressure Belts, Planetary Winds and Local Winds

Short memory aids. Say each one aloud once, then use it on a question the same day.

Trade = go to equator
Trade winds blow toward the equator.
Use it when: Planetary winds.
Loo = Lahore-Lucknow
Loo is hot and dry over the plains of India.
Use it when: Local winds.

Pressure Belts, Planetary Winds and Local Winds: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Pressure change · 2 marks · Short answerBoard level

A place at sea level records 1,013 mb. Estimate the pressure at 300 m, using 1 mb per 10 m. [2]

Try it first, then show the solutionSolution

Fall = 300 / 10 = 30 mb.
1,013 - 30 = 983 mb.

Answer: About 983 mb.

Example 2: Planetary winds · 4 marks · Short answerHarder board level

Name the pressure belts between which (a) trade winds, (b) westerlies blow, and give their directions in the northern hemisphere. [4]

Try it first, then show the solutionSolution

(a) From sub-tropical high to equatorial low: north-east.
(b) From sub-tropical high to sub-polar low: south-west.

Answer: (a) Sub-tropical high to equatorial low; north-east (b) Sub-tropical high to sub-polar low; south-west.

Example 3: Land and sea breeze · 3 marks · Short answerHarder board level

Explain why a sea breeze blows by day and a land breeze at night. [3]

Try it first, then show the solutionSolution

Land heats and cools faster than sea.
By day land is warmer, low pressure rises over land, so air flows from sea.
At night the sea is warmer, so air flows from land to sea.

Answer: Differential heating reverses the pressure difference between land and sea.

Example 4: Chinook · 3 marks · Short answerHarder board level

Why is the chinook called a snow eater, and why is it warm and dry? [3]

Try it first, then show the solutionSolution

The wind descends the leeward slope of the Rockies.
Descending air is compressed and warms; it has lost moisture on the windward side.
Warm dry air melts snow quickly.

Answer: It is warm and dry because it descends the leeward slope, and it melts snow.

Example 5: Case: the calm belt · 6 marks · Case-basedHOTS / competency

Case. Sailing ships once stalled for days in a belt near the equator, and in another belt near 30 degrees N. (i) Name the belts. [2] (ii) Give a reason for the calm in the first. [1] (iii) Why were ships in the second in difficulty? [2] (iv) Name the winds that helped sailors cross the Atlantic in between. [1]

Try it first, then show the solutionSolution

(i) Doldrums and horse latitudes.
(ii) Rising hot air gives weak surface winds.
(iii) Descending air gives high pressure, calm and dry weather.
(iv) Trade winds.

Answer: (i) Doldrums and horse latitudes (ii) Rising air (iii) Descending air gives calms (iv) Trade winds.

Where students lose marks in Pressure Belts, Planetary Winds and Local Winds

The slips examiners see most often, and what to write instead.

Mistake: Writing that wind blows from low to high pressure
Direction reversed.
Do this: Wind blows from high to low.
Usually costs: 1 mark.
Mistake: Calling trade winds south-west in the north
Directions mixed.
Do this: North-east in the northern hemisphere.
Usually costs: 1 mark.
Mistake: Omitting the reason
Only the name of wind.
Do this: Add cause: pressure difference.
Usually costs: 1 mark.

Exam tips

Draw pressure belts with winds as arrows on a globe.
Give direction in both hemispheres.
Link every local wind to place and nature.
Show calculation for pressure with altitude.

Practice questions on Pressure Belts, Planetary Winds and Local Winds

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Winds blowing from sub-polar low to polar high are:
(a) none; winds blow from high to low
(b) polar easterlies
(c) trade winds
(d) westerlies
Hint
Think direction.
Answer
(a) none; winds blow from high to low.
Q2 · 1 mark · Very short answerBoard level
Which instrument measures air pressure? [1]
Hint
Mercury.
Answer
A barometer.
Q3 · 1 mark · Very short answerBoard level
Name the unit used for atmospheric pressure. [1]
Hint
mb.
Answer
The millibar (or hectopascal).
Q4 · 1 mark · Assertion-reasonHarder board level
Assertion (A): The Coriolis effect deflects winds to the right in the northern hemisphere.
Reason (R): It is caused by the rotation of the earth.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Rotation.
Answer
(a).
Q5 · 3 marks · Short answerHarder board level
State three differences between a cyclone and an anticyclone. [3]
Hint
Pressure.
Answer
Cyclone: low pressure centre, winds spiral inwards, stormy; anticyclone: high pressure centre, winds spiral outwards, clear weather.
Q6 · 3 marks · Short answerHarder board level
What are jet streams and why are they important to aircraft? [3]
Hint
Fast.
Answer
Jet streams are narrow fast winds high in the atmosphere; aircraft can save time and fuel flying with them.
Q7 · 2 marks · Very short answerBoard level
Why is pressure lower on a mountain top than at sea level? [2]
Hint
Less air.
Answer
There is less air above, so the weight of the column is smaller.
Q8 · 3 marks · Short answerHarder board level
Why are the doldrums rarely windy while the westerlies are strong in the southern hemisphere (roaring forties)? [3]
Hint
Land/ocean.
Answer
Doldrums have rising air and weak horizontal gradients; the southern ocean has few land obstacles and a strong pressure gradient between 30 and 60 degrees S.
Q9 · 4 marks · Case-basedHOTS / competency
Case. In summer afternoons, a village in north India experiences a hot dry wind. (i) Name it. [1] (ii) Suggest two precautions. [2] (iii) Why is it dry? [1]
Hint
Loo.
Answer
(i) Loo. (ii) Drink water and stay indoors in the afternoon. (iii) It blows from dry land.
Q10 · 3 marks · Long answerHOTS / competency
Case. A weather chart shows closely spaced isobars. Predict wind speed and justify. [3]
Hint
Gradient.
Answer
Winds will be strong because closely spaced isobars show a steep pressure gradient.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Pressure unit?Show answer
Millibar.
2.Sea level pressure?Show answer
1,013 mb.
3.Winds from sub-tropical high to equator?Show answer
Trade winds.
4.Hot dry wind of India?Show answer
Loo.
5.Cold wind of France?Show answer
Mistral.

Pressure Belts, Planetary Winds and Local Winds: frequently asked questions

What are isobars?

Lines of equal pressure.

Why is the Coriolis effect zero at the equator?

The deflection depends on latitude and is zero there.

What is a monsoon?

A seasonal reversal of wind.