A Wind Is Always Named for Where It Comes From, Never Where It Goes
Learn how uneven heating makes air rise and sink to produce wind, why land and sea breezes reverse between day and night, how the planetary winds relate to pressure belts, and what ocean currents do to coastal climates.
Does a sea breeze blow towards the sea or from it?
From the sea — and the rule that settles it applies to every wind on this page.
A wind is named for the direction it comes from, never the direction it goes. A sea breeze comes from the sea and blows onto the land. A land breeze comes from the land and blows out to sea. The westerlies blow from the west, which means they travel eastwards.
That naming convention catches students out constantly, and it costs marks in every question about winds. It is also completely consistent: once you know it, the name of a wind tells you its direction without any further thought.
What produces all of them is the same thing — the uneven heating established in the previous part of this chapter. Uneven heating creates differences in air pressure, and air flowing from high pressure to low pressure is what wind is.
This page covers the second part of the CBSE Class 9 Science chapter on the Earth as a system.
A wind is named for the direction it comes from, never the direction it goes. A sea breeze comes from the sea and blows onto the land. A land breeze comes from the land and blows out to sea. The westerlies blow from the west, which means they travel eastwards.
That naming convention catches students out constantly, and it costs marks in every question about winds. It is also completely consistent: once you know it, the name of a wind tells you its direction without any further thought.
What produces all of them is the same thing — the uneven heating established in the previous part of this chapter. Uneven heating creates differences in air pressure, and air flowing from high pressure to low pressure is what wind is.
This page covers the second part of the CBSE Class 9 Science chapter on the Earth as a system.
How does uneven heating produce wind?
By making air rise in one place and sink in another, which creates a pressure difference that air then flows along.
The chain has four links:
- Air that is heated expands, becomes less dense, and rises
- Where air rises, it leaves behind an area of low pressure at the surface
- Air that is cooler is denser and sinks, creating an area of high pressure
- Air then flows horizontally along the surface from the high pressure to the low pressure — and that horizontal flow is wind
So the sequence runs: uneven heating gives density differences, which give vertical movement, which gives pressure differences, which give horizontal flow.
Everyday evidence of the rising step. Smoke from an agarbatti or a cooking fire goes upwards, carried by the heated air around it. Hold a hand above a hot tawa and you feel the rising air against your palm before you feel any radiated heat. Warm air rising is the everyday half of the mechanism.
Wind is caused by a pressure difference, not directly by heat. Heat produces the pressure difference, and the pressure difference produces the wind. That is why a weather forecaster studies a map of pressure rather than a map of temperature when predicting wind — the pressure map is one step closer to the answer.
The steeper the pressure difference, the stronger the wind. A large difference over a short distance drives air fast; a gentle difference drives it slowly. That single relationship explains why a cyclone, with a very deep low pressure at its centre, produces violent winds, while a broad shallow pressure pattern gives only a light breeze.
The same chain works at every scale. It explains a breeze across a field, the land and sea breezes of the next section, the monsoon over a whole subcontinent, and the planetary winds that circle the globe. Only the size of the heated and cooled regions changes — the mechanism does not.
The chain has four links:
- Air that is heated expands, becomes less dense, and rises
- Where air rises, it leaves behind an area of low pressure at the surface
- Air that is cooler is denser and sinks, creating an area of high pressure
- Air then flows horizontally along the surface from the high pressure to the low pressure — and that horizontal flow is wind
So the sequence runs: uneven heating gives density differences, which give vertical movement, which gives pressure differences, which give horizontal flow.
Everyday evidence of the rising step. Smoke from an agarbatti or a cooking fire goes upwards, carried by the heated air around it. Hold a hand above a hot tawa and you feel the rising air against your palm before you feel any radiated heat. Warm air rising is the everyday half of the mechanism.
Wind is caused by a pressure difference, not directly by heat. Heat produces the pressure difference, and the pressure difference produces the wind. That is why a weather forecaster studies a map of pressure rather than a map of temperature when predicting wind — the pressure map is one step closer to the answer.
The steeper the pressure difference, the stronger the wind. A large difference over a short distance drives air fast; a gentle difference drives it slowly. That single relationship explains why a cyclone, with a very deep low pressure at its centre, produces violent winds, while a broad shallow pressure pattern gives only a light breeze.
The same chain works at every scale. It explains a breeze across a field, the land and sea breezes of the next section, the monsoon over a whole subcontinent, and the planetary winds that circle the globe. Only the size of the heated and cooled regions changes — the mechanism does not.
Why do land and sea breezes reverse between day and night?
Because land heats and cools faster than water, so which of the two is warmer reverses between day and night.
Water has a much greater capacity to absorb heat for a given rise in temperature than land has. So through a sunny day the land becomes much hotter than the sea beside it, and through the night the land loses its heat quickly while the sea stays comparatively warm.
Sea breeze — daytime.
- The land becomes hotter than the sea
- Air over the land warms, expands and rises, leaving low pressure over the land
- The cooler, denser air over the sea is at higher pressure
- Air therefore flows from the sea to the land — a sea breeze
Land breeze — night-time.
- The land cools faster and becomes cooler than the sea
- Now the air over the sea is warmer and rises, leaving low pressure over the sea
- The cooler air over the land is at higher pressure
- Air flows from the land to the sea — a land breeze
So the breeze reverses because the relative temperatures reverse, and not because anything about the mechanism changes. The same four steps run in both cases, with the warm and cool regions swapped.
Everyday evidence. On the coast at Mumbai or Chennai, the afternoon brings a cool breeze in off the water, and by the small hours it has turned around and blows offshore. Fishermen have always used both — going out on the land breeze before dawn and returning on the sea breeze in the afternoon, with the wind behind them each way.
A breeze is named for where it comes from. A sea breeze blows from the sea onto the land; a land breeze blows from the land out to sea. Reversing that naming is the commonest error in the whole topic, and it is worth saying the direction out loud — from the sea, onto the land — rather than relying on the name alone.
The monsoon is the same mechanism at a continental scale. In summer the landmass of India heats far more than the surrounding ocean, so air rises over the land and moist air is drawn in from the sea — bringing the rains. In winter the land cools more than the ocean and the flow reverses, blowing dry air out to sea. The monsoon is a sea breeze and a land breeze that take six months instead of twelve hours, and knowing that makes both easier to remember.
Water has a much greater capacity to absorb heat for a given rise in temperature than land has. So through a sunny day the land becomes much hotter than the sea beside it, and through the night the land loses its heat quickly while the sea stays comparatively warm.
Sea breeze — daytime.
- The land becomes hotter than the sea
- Air over the land warms, expands and rises, leaving low pressure over the land
- The cooler, denser air over the sea is at higher pressure
- Air therefore flows from the sea to the land — a sea breeze
Land breeze — night-time.
- The land cools faster and becomes cooler than the sea
- Now the air over the sea is warmer and rises, leaving low pressure over the sea
- The cooler air over the land is at higher pressure
- Air flows from the land to the sea — a land breeze
So the breeze reverses because the relative temperatures reverse, and not because anything about the mechanism changes. The same four steps run in both cases, with the warm and cool regions swapped.
Everyday evidence. On the coast at Mumbai or Chennai, the afternoon brings a cool breeze in off the water, and by the small hours it has turned around and blows offshore. Fishermen have always used both — going out on the land breeze before dawn and returning on the sea breeze in the afternoon, with the wind behind them each way.
A breeze is named for where it comes from. A sea breeze blows from the sea onto the land; a land breeze blows from the land out to sea. Reversing that naming is the commonest error in the whole topic, and it is worth saying the direction out loud — from the sea, onto the land — rather than relying on the name alone.
The monsoon is the same mechanism at a continental scale. In summer the landmass of India heats far more than the surrounding ocean, so air rises over the land and moist air is drawn in from the sea — bringing the rains. In winter the land cools more than the ocean and the flow reverses, blowing dry air out to sea. The monsoon is a sea breeze and a land breeze that take six months instead of twelve hours, and knowing that makes both easier to remember.
What are the planetary winds and how do they relate to the pressure belts?
They blow from the high-pressure belts towards the low-pressure belts, deflected sideways by the Earth's rotation.
The global pressure belts, working outwards from the equator:
- Equatorial low pressure belt — intense heating makes air rise, so surface pressure is low and surface winds are light. This belt is called the doldrums
- Subtropical high pressure belts — around north and south, where the air that rose at the equator has cooled and sinks back down
- Subpolar low pressure belts — around north and south
- Polar high pressure areas — very cold, dense air sinking at each pole
The planetary or permanent winds, each blowing from a high belt to a low one:
- Trade winds — from the subtropical highs towards the equatorial low. They blow from the north-east in the northern hemisphere and from the south-east in the southern
- Westerlies — from the subtropical highs towards the subpolar lows. From the south-west in the northern hemisphere and the north-west in the southern
- Polar easterlies — from the polar highs towards the subpolar lows
Why they are not straight north-south winds. Air flowing from towards the equator would blow due south in the northern hemisphere if the Earth stood still. The Earth's rotation deflects moving air — to the right in the northern hemisphere and to the left in the southern — so a southward flow becomes a north-easterly one.
Read the names with the convention. The north-east trades blow from the north-east, and therefore travel towards the south-west, towards the equator. The westerlies blow from the west and therefore travel eastwards. The naming rule from the opening section decodes every one of them.
Everyday trace of the trade winds. Sailing ships crossing the oceans used the trade winds going one way and the westerlies coming back, and the reliability of those winds for commerce is what the word trade records in their name.
The pressure belts are the cause and the winds are the consequence. That order matters. A question asking why the trade winds exist wants the subtropical high and the equatorial low named, and the flow between them described — not simply a statement of which direction they blow. The belts come from the uneven heating of the previous part of this chapter, and the winds come from the belts, so the whole chapter is one chain.
The global pressure belts, working outwards from the equator:
- Equatorial low pressure belt — intense heating makes air rise, so surface pressure is low and surface winds are light. This belt is called the doldrums
- Subtropical high pressure belts — around north and south, where the air that rose at the equator has cooled and sinks back down
- Subpolar low pressure belts — around north and south
- Polar high pressure areas — very cold, dense air sinking at each pole
The planetary or permanent winds, each blowing from a high belt to a low one:
- Trade winds — from the subtropical highs towards the equatorial low. They blow from the north-east in the northern hemisphere and from the south-east in the southern
- Westerlies — from the subtropical highs towards the subpolar lows. From the south-west in the northern hemisphere and the north-west in the southern
- Polar easterlies — from the polar highs towards the subpolar lows
Why they are not straight north-south winds. Air flowing from towards the equator would blow due south in the northern hemisphere if the Earth stood still. The Earth's rotation deflects moving air — to the right in the northern hemisphere and to the left in the southern — so a southward flow becomes a north-easterly one.
Read the names with the convention. The north-east trades blow from the north-east, and therefore travel towards the south-west, towards the equator. The westerlies blow from the west and therefore travel eastwards. The naming rule from the opening section decodes every one of them.
Everyday trace of the trade winds. Sailing ships crossing the oceans used the trade winds going one way and the westerlies coming back, and the reliability of those winds for commerce is what the word trade records in their name.
The pressure belts are the cause and the winds are the consequence. That order matters. A question asking why the trade winds exist wants the subtropical high and the equatorial low named, and the flow between them described — not simply a statement of which direction they blow. The belts come from the uneven heating of the previous part of this chapter, and the winds come from the belts, so the whole chapter is one chain.
How do ocean currents form and what do they do to a coast?
Winds drag the surface water along, and the currents then carry heat from where it arrived to where it did not.
An ocean current is a large-scale movement of surface water in a definite direction, continuing over great distances.
How currents form:
- Prevailing winds dragging the surface water along — the main cause, which is why the current pattern follows the wind pattern
- Differences in water temperature and salinity, which change the water's density and set it moving
- The Earth's rotation, deflecting the flow as it deflects the winds
- The shape of the coastlines and ocean basins, which guide and channel the flow
Warm and cold currents. A current flowing from lower latitudes towards higher ones is a warm current; one flowing from higher latitudes towards lower ones is a cold current.
What a current does to the climate of a coast:
- A warm current keeps a coast warmer than its latitude alone would suggest, and can keep ports free of ice in winter when nearby coasts are frozen
- A cold current makes a coast cooler and often drier. Cool air holds less moisture, and air lying over cold water is stable and gives little rain — which is why several of the world's coastal deserts lie beside cold currents
- Where a warm and a cold current meet, fog is common, and such places are often rich fishing grounds, because the mixing brings nutrients up to the surface
Everyday relevance. A coastal town has a smaller range of temperature between day and night, and between summer and winter, than an inland town at the same latitude. Part of that is the sea's slow response to heating, as the breeze section explained, and part is the current running past the coast.
Currents are how the ocean redistributes heat, and that closes the chain this chapter began.
- Uneven heating by angle delivers more energy to the tropics than to the poles
- Those differences create pressure belts
- The belts drive the planetary winds
- The winds drag the ocean currents
- The currents carry warm water polewards and cold water back towards the equator
Without that redistribution the equator would grow ever hotter and the poles ever colder. The atmosphere and the ocean together move the surplus heat away from where it arrives, and that is why the actual range of temperature across the Earth is far smaller than the range of radiation received. The winds and currents are not a separate topic from uneven heating; they are its consequence and its remedy.
An ocean current is a large-scale movement of surface water in a definite direction, continuing over great distances.
How currents form:
- Prevailing winds dragging the surface water along — the main cause, which is why the current pattern follows the wind pattern
- Differences in water temperature and salinity, which change the water's density and set it moving
- The Earth's rotation, deflecting the flow as it deflects the winds
- The shape of the coastlines and ocean basins, which guide and channel the flow
Warm and cold currents. A current flowing from lower latitudes towards higher ones is a warm current; one flowing from higher latitudes towards lower ones is a cold current.
What a current does to the climate of a coast:
- A warm current keeps a coast warmer than its latitude alone would suggest, and can keep ports free of ice in winter when nearby coasts are frozen
- A cold current makes a coast cooler and often drier. Cool air holds less moisture, and air lying over cold water is stable and gives little rain — which is why several of the world's coastal deserts lie beside cold currents
- Where a warm and a cold current meet, fog is common, and such places are often rich fishing grounds, because the mixing brings nutrients up to the surface
Everyday relevance. A coastal town has a smaller range of temperature between day and night, and between summer and winter, than an inland town at the same latitude. Part of that is the sea's slow response to heating, as the breeze section explained, and part is the current running past the coast.
Currents are how the ocean redistributes heat, and that closes the chain this chapter began.
- Uneven heating by angle delivers more energy to the tropics than to the poles
- Those differences create pressure belts
- The belts drive the planetary winds
- The winds drag the ocean currents
- The currents carry warm water polewards and cold water back towards the equator
Without that redistribution the equator would grow ever hotter and the poles ever colder. The atmosphere and the ocean together move the surplus heat away from where it arrives, and that is why the actual range of temperature across the Earth is far smaller than the range of radiation received. The winds and currents are not a separate topic from uneven heating; they are its consequence and its remedy.
Exam tip
Exam tip: name the wind by where it comes from, and the pressure belts by name
A wind is named for where it comes from. A sea breeze blows from the sea; the westerlies blow from the west and therefore eastwards. Say the direction in words rather than trusting the name.
Give the wind mechanism as a four-step chain: heating, air rises, low pressure forms, air flows in from high pressure.
Wind is caused by a pressure difference, not directly by heat — and the steeper the difference, the stronger the wind.
For the breezes, say that land heats and cools faster than water, and then give both cases with the pressure named: day, land hot, low pressure over land, sea breeze; night, land cool, low pressure over sea, land breeze.
Add that the monsoon is the same mechanism at a continental and seasonal scale.
Name all four pressure belts: equatorial low (the doldrums), subtropical highs near , subpolar lows near , polar highs.
Name all three planetary winds with their directions: north-east trades towards the equator, south-west westerlies towards the subpolar lows, polar easterlies.
Say that the Earth's rotation deflects winds to the right in the northern hemisphere and the left in the southern.
For currents, give all four causes, and say that warm currents warm a coast while cold currents cool and dry it, with fog and good fishing where the two meet.
And finish the chain when asked: heating gives belts, belts give winds, winds give currents, currents redistribute heat.
Give the wind mechanism as a four-step chain: heating, air rises, low pressure forms, air flows in from high pressure.
Wind is caused by a pressure difference, not directly by heat — and the steeper the difference, the stronger the wind.
For the breezes, say that land heats and cools faster than water, and then give both cases with the pressure named: day, land hot, low pressure over land, sea breeze; night, land cool, low pressure over sea, land breeze.
Add that the monsoon is the same mechanism at a continental and seasonal scale.
Name all four pressure belts: equatorial low (the doldrums), subtropical highs near , subpolar lows near , polar highs.
Name all three planetary winds with their directions: north-east trades towards the equator, south-west westerlies towards the subpolar lows, polar easterlies.
Say that the Earth's rotation deflects winds to the right in the northern hemisphere and the left in the southern.
For currents, give all four causes, and say that warm currents warm a coast while cold currents cool and dry it, with fog and good fishing where the two meet.
And finish the chain when asked: heating gives belts, belts give winds, winds give currents, currents redistribute heat.
Did you know
Why the sea is the reason a coastal night is mild
Spend a summer night on the coast and then a summer night a few hundred kilometres inland at the same latitude, and the difference is unmistakable. The coast stays mild; the inland place cools sharply after dark and heats fiercely by afternoon.
The cause is a single property of water: it takes a great deal of heat to raise its temperature, and it gives out a great deal as it cools. Land does neither. The same sunshine that lifts a stretch of dry soil by many degrees lifts the sea beside it by very little.
So the sea acts as a moderator. By day it absorbs heat without warming much, keeping the air above it cooler than the air over the land. By night it releases heat slowly, keeping the air above it warmer than the land. The coast, breathing air off the water for part of every day, inherits that steadiness.
That is the same property the land and sea breeze depends on, seen from a different angle. The breeze exists because land and sea respond differently; the mild coastal climate exists because of the same difference, averaged over time instead of used to drive a wind.
It also explains a detail of the monsoon. The reason the rains come from the sea and not from the land is that the sea is the reservoir — it holds both the water and the stored heat, and the land can only heat up and draw them in.
And it is why a bucket of water left in a room on a cold night can keep a small space from freezing, and why a coastal city rarely records the extremes that an inland one does. One property of one substance, showing up at four different scales.
The cause is a single property of water: it takes a great deal of heat to raise its temperature, and it gives out a great deal as it cools. Land does neither. The same sunshine that lifts a stretch of dry soil by many degrees lifts the sea beside it by very little.
So the sea acts as a moderator. By day it absorbs heat without warming much, keeping the air above it cooler than the air over the land. By night it releases heat slowly, keeping the air above it warmer than the land. The coast, breathing air off the water for part of every day, inherits that steadiness.
That is the same property the land and sea breeze depends on, seen from a different angle. The breeze exists because land and sea respond differently; the mild coastal climate exists because of the same difference, averaged over time instead of used to drive a wind.
It also explains a detail of the monsoon. The reason the rains come from the sea and not from the land is that the sea is the reservoir — it holds both the water and the stored heat, and the land can only heat up and draw them in.
And it is why a bucket of water left in a room on a cold night can keep a small space from freezing, and why a coastal city rarely records the extremes that an inland one does. One property of one substance, showing up at four different scales.
Exam relevance
How do winds and currents feed into later physics and biology?
This page is where convection is first met as a mechanism for something on a global scale, and two later chapters build on it directly.
The physics of it is the foundation for Class 11 Physics Thermal Properties of Matter, examined in JEE Main and in NEET Physics. The rising of heated air is convection, and that chapter formalises it as one of the three modes of heat transfer, alongside conduction and radiation. The Class 9 chain — heating, expansion, reduced density, rising, pressure difference, flow — is the mechanism of convection stated in full, and it is reused for every convection situation from a boiling pan to a chimney.
The pressure reasoning feeds into Class 11 Physics Mechanical Properties of Fluids, where atmospheric pressure, its variation with height, and flow driven by pressure difference are treated quantitatively. The statement that a steeper pressure difference gives a faster flow becomes the basis of Bernoulli's principle and of flow through pipes.
The specific heat argument in the previous section becomes specific heat capacity in Class 11 Thermal Properties, examined in both JEE Main and NEET, with the numerical work the earlier chapter of this course introduced through . Water's unusually high specific heat capacity is exactly why land and sea behave differently, and it is a standard assertion-reason pairing.
The biology and ecology route leads to Class 12 Ecosystem and Biodiversity and Conservation, examined in NEET, where climate as a determinant of biomes is covered. Ocean currents supporting rich fishing grounds connects to productivity and nutrient cycling there.
What the questions look like. For NEET and for board work, assertion-reason items are the commonest, and the standard pairings are that a sea breeze blows from the sea, and that coastal climates are moderate because of water's high specific heat capacity. Diagram-based questions ask you to label the pressure belts or mark the direction of a breeze on a coastline sketch. For JEE Main, the convection and pressure content appears in Class 11 as numericals rather than as descriptions.
How board and competitive emphasis differ. A board paper asks you to explain with a diagram why a sea breeze blows by day, name the pressure belts, and describe the effect of currents on coastal climate. A competitive paper asks which mode of heat transfer is responsible, or sets a specific-heat numerical — so the mechanism and the property of water matter more than the terminology of belts and breezes.
The single trap that costs the most marks. Naming a wind by the direction it goes. A sea breeze comes from the sea and blows onto the land; the westerlies come from the west and travel eastwards. Every wind on this page follows that rule, and questions are written to catch a reversal — so state the direction in words, not by relying on the name.
A second trap worth naming. Saying that wind is caused by heat. Heat produces a pressure difference, and the pressure difference produces the wind. A question asking for the cause of wind wants pressure difference named, and an answer stopping at the Sun heats the air unevenly has given the first step of four.
The physics of it is the foundation for Class 11 Physics Thermal Properties of Matter, examined in JEE Main and in NEET Physics. The rising of heated air is convection, and that chapter formalises it as one of the three modes of heat transfer, alongside conduction and radiation. The Class 9 chain — heating, expansion, reduced density, rising, pressure difference, flow — is the mechanism of convection stated in full, and it is reused for every convection situation from a boiling pan to a chimney.
The pressure reasoning feeds into Class 11 Physics Mechanical Properties of Fluids, where atmospheric pressure, its variation with height, and flow driven by pressure difference are treated quantitatively. The statement that a steeper pressure difference gives a faster flow becomes the basis of Bernoulli's principle and of flow through pipes.
The specific heat argument in the previous section becomes specific heat capacity in Class 11 Thermal Properties, examined in both JEE Main and NEET, with the numerical work the earlier chapter of this course introduced through . Water's unusually high specific heat capacity is exactly why land and sea behave differently, and it is a standard assertion-reason pairing.
The biology and ecology route leads to Class 12 Ecosystem and Biodiversity and Conservation, examined in NEET, where climate as a determinant of biomes is covered. Ocean currents supporting rich fishing grounds connects to productivity and nutrient cycling there.
What the questions look like. For NEET and for board work, assertion-reason items are the commonest, and the standard pairings are that a sea breeze blows from the sea, and that coastal climates are moderate because of water's high specific heat capacity. Diagram-based questions ask you to label the pressure belts or mark the direction of a breeze on a coastline sketch. For JEE Main, the convection and pressure content appears in Class 11 as numericals rather than as descriptions.
How board and competitive emphasis differ. A board paper asks you to explain with a diagram why a sea breeze blows by day, name the pressure belts, and describe the effect of currents on coastal climate. A competitive paper asks which mode of heat transfer is responsible, or sets a specific-heat numerical — so the mechanism and the property of water matter more than the terminology of belts and breezes.
The single trap that costs the most marks. Naming a wind by the direction it goes. A sea breeze comes from the sea and blows onto the land; the westerlies come from the west and travel eastwards. Every wind on this page follows that rule, and questions are written to catch a reversal — so state the direction in words, not by relying on the name.
A second trap worth naming. Saying that wind is caused by heat. Heat produces a pressure difference, and the pressure difference produces the wind. A question asking for the cause of wind wants pressure difference named, and an answer stopping at the Sun heats the air unevenly has given the first step of four.
Key takeaways
Wind, breezes, planetary winds and currents: quick revision
- A wind is named for where it comes from, never where it goes. A sea breeze blows from the sea; the westerlies blow from the west and travel eastwards.
- Wind mechanism in four steps: heated air expands, becomes less dense and rises; low pressure forms below; cooler denser air sinks giving high pressure; air flows horizontally from high to low.
- Wind is caused by a pressure difference, not directly by heat — which is why forecasters read pressure maps. The steeper the difference, the stronger the wind.
- Land heats and cools faster than water, because water absorbs much more heat for a given rise in temperature.
- Sea breeze (day): land hotter, air rises over land, low pressure over land, air flows from sea to land.
- Land breeze (night): land cooler, air rises over sea, low pressure over sea, air flows from land to sea.
- The breeze reverses because the relative temperatures reverse. Fishermen go out on the land breeze and return on the sea breeze.
- The monsoon is the same mechanism at continental scale — summer heating of the land draws moist air in from the sea.
- Pressure belts: equatorial low (the doldrums), subtropical highs near , subpolar lows near , polar highs.
- Planetary winds: trade winds from the subtropical highs to the equatorial low, from the north-east in the north and south-east in the south; westerlies from the subtropical highs to the subpolar lows, from the south-west in the north; polar easterlies from the polar highs.
- The Earth's rotation deflects winds to the right in the northern hemisphere and the left in the southern, which is why they are not straight north-south.
- Ocean currents are formed by prevailing winds (the main cause), differences in temperature and salinity, the Earth's rotation, and the shape of coastlines and basins.
- A current from low to high latitudes is warm; from high to low it is cold.
- Warm currents warm a coast and can keep ports ice-free. Cold currents cool and dry a coast, and several coastal deserts lie beside them. Where warm and cold meet, there is fog and good fishing.
- Coastal places have a smaller temperature range than inland places at the same latitude.
- The whole chain: uneven heating gives pressure belts, belts give winds, winds drive currents, and currents redistribute heat from the tropics polewards — which is why the Earth's temperature range is far smaller than its radiation range.
Sketch a coastline and draw the breeze at two in the afternoon and at two in the morning, marking the high and low pressure each time — if the arrows reverse and the pressures reverse with them, the mechanism is yours.
- Wind mechanism in four steps: heated air expands, becomes less dense and rises; low pressure forms below; cooler denser air sinks giving high pressure; air flows horizontally from high to low.
- Wind is caused by a pressure difference, not directly by heat — which is why forecasters read pressure maps. The steeper the difference, the stronger the wind.
- Land heats and cools faster than water, because water absorbs much more heat for a given rise in temperature.
- Sea breeze (day): land hotter, air rises over land, low pressure over land, air flows from sea to land.
- Land breeze (night): land cooler, air rises over sea, low pressure over sea, air flows from land to sea.
- The breeze reverses because the relative temperatures reverse. Fishermen go out on the land breeze and return on the sea breeze.
- The monsoon is the same mechanism at continental scale — summer heating of the land draws moist air in from the sea.
- Pressure belts: equatorial low (the doldrums), subtropical highs near , subpolar lows near , polar highs.
- Planetary winds: trade winds from the subtropical highs to the equatorial low, from the north-east in the north and south-east in the south; westerlies from the subtropical highs to the subpolar lows, from the south-west in the north; polar easterlies from the polar highs.
- The Earth's rotation deflects winds to the right in the northern hemisphere and the left in the southern, which is why they are not straight north-south.
- Ocean currents are formed by prevailing winds (the main cause), differences in temperature and salinity, the Earth's rotation, and the shape of coastlines and basins.
- A current from low to high latitudes is warm; from high to low it is cold.
- Warm currents warm a coast and can keep ports ice-free. Cold currents cool and dry a coast, and several coastal deserts lie beside them. Where warm and cold meet, there is fog and good fishing.
- Coastal places have a smaller temperature range than inland places at the same latitude.
- The whole chain: uneven heating gives pressure belts, belts give winds, winds drive currents, and currents redistribute heat from the tropics polewards — which is why the Earth's temperature range is far smaller than its radiation range.
Sketch a coastline and draw the breeze at two in the afternoon and at two in the morning, marking the high and low pressure each time — if the arrows reverse and the pressures reverse with them, the mechanism is yours.