At the beach on a summer day a cool wind blows in from the sea, but at night it turns around and blows from the land out to sea.
Land has a lower specific heat than water, so it warms up and cools down faster; by day the air over the land rises and leaves low pressure, and at night the opposite happens. Wind always blows from high pressure to low pressure.
Switching between day and night in the diagram flips the whole loop at once: the wind along the ground, the return wind higher up, and the rising and sinking air.
When the same thing happens between a continent and an ocean over the seasons, it is a monsoon; in East Asia, for example in Korea, summer brings a southeast wind and winter a northwest wind.
Why the Wind Blows
🌬️ Temperature Difference → Pressure Difference → Wind
①Warmed air becomes lighter and rises, so the pressure at the ground drops (low pressure)
②Cooled air becomes heavier and sinks, so the pressure at the ground rises (high pressure)
③Air moves from where pressure is high to where it is low, and that movement is wind
④The bigger the pressure difference, the stronger the wind
Sea Breeze and Land Breeze
Day
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A day sea breeze and a night land breeze, with the return wind aloft completing the loop of air
🏖️ Why Sea and Land Breezes Form
①By day the land warms faster than the sea, so there is low pressure over land and high pressure over sea → sea breeze from sea to land
②At night the land cools faster, so there is high pressure over land and low pressure over sea → land breeze from land to sea
③Land warms and cools faster because its specific heat is lower than water's
④Higher up, the wind flows back the opposite way, closing a loop
Monsoons
🗺️ Sea and Land Breezes on a Continental Scale
①Summer: the continent gets hotter than the ocean and becomes a low-pressure area → a hot, humid wind blows from ocean to land (southeast monsoon in Korea)
②Winter: the continent gets colder than the ocean and becomes a high-pressure area → a cold, dry wind blows from land to ocean (northwest monsoon in Korea)
③It is the daily sea and land breeze on a yearly cycle and the scale of a continent
Summary
How wind arises
High pressure (cool place) → low pressure (warm place)
A temperature difference makes a pressure difference, and the pressure difference makes wind
Caused by the difference in specific heat between land and sea
🎯 Common Test Points
①Wind blows from high pressure to low pressure
②By day a sea breeze blows (sea → land); at night a land breeze (land → sea)
③Reason: land has a lower specific heat than water, so it warms and cools faster
④Monsoons in Korea: southeast in summer (hot and humid), northwest in winter (cold and dry)
⑤A monsoon works like a sea and land breeze, only larger in size and longer in period
Examples and Unit Review
Example 1
Which way do the daytime sea breeze and the nighttime land breeze blow at the coast, and why?
1
By day the land, with its lower specific heat, warms faster than the sea, so air over the land rises and leaves low pressure; the wind blows from sea to land (sea breeze).
2
At night the land cools faster, so the land has high pressure and the sea low pressure; the wind blows from land to sea (land breeze).
▸ By day from sea to land (sea breeze), at night from land to sea (land breeze), because land and sea differ in specific heat
Switching day and night in the diagram reverses not only the surface wind but also the return wind aloft and the rising and sinking air.
Example 2
How do Korea's summer and winter monsoons differ in direction and character, and how are they related to sea and land breezes?
1
In summer the continent gets hotter than the ocean and becomes a low-pressure area, so a hot, humid southeast monsoon blows from ocean to land.
2
In winter the continent gets colder and becomes a high-pressure area, so a cold, dry northwest monsoon blows from land to ocean. It is the same principle as a sea and land breeze on a continental scale.
▸ Summer: southeast (hot, humid); winter: northwest (cold, dry). A monsoon is a sea and land breeze scaled up to a continent
The summer monsoon picks up water vapor crossing the ocean and brings heavy rain, while the winter monsoon comes off the continent and is dry.
Unit Test
Which statement about sea breezes and monsoons is correct?
①Wind blows from low pressure to high pressure
②By day a land breeze blows from land to sea
③Sea and land breezes arise from the difference in specific heat between land and sea
④The Korean winter monsoon is a southeast wind
⑤Water has a smaller specific heat than land and warms up quickly
▸ ③ Sea and land breezes arise from the difference in specific heat between land and sea
1
Wind blows from high to low pressure (① wrong), and by day a sea breeze blows from sea to land (② wrong).
2
The Korean winter monsoon is a northwest wind (④ wrong), and water has a large specific heat so it warms slowly (⑤ wrong); sea and land breezes arise from the difference in specific heat between land and sea (③ correct).