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How are land breezes and sea breezes formed?

Class 7 ScienceNCERT chapter: Heat Transfer in Natureइसे हिंदी में पढ़ें

Exam-ready answer

Land heats up and cools down faster than water. By day, air over the land becomes warmer and rises, and cooler air from the sea moves in; this is a sea breeze. At night, land cools faster, warmer air over the sea rises, and cooler air from the land moves towards the sea; this is a land breeze.

Explanation

In coastal areas, the Sun shines on both land and sea during the day, but the land gets heated much faster than the water. The air in contact with the hot land also becomes warm. Warm air expands, becomes lighter and rises. As it rises, it leaves room above the land that has to be filled by air from somewhere else.

Air over the sea is cooler and heavier, so it moves towards the land to replace the rising warm air. This flow of cool air from the sea to the land is called a sea breeze, which is why coastal towns often get a cool breeze from the sea in the afternoon. The rising air cools high up and moves back towards the sea, completing a loop of convection in the air.

At night the situation reverses. Land loses heat faster than water, so the land becomes cooler than the sea. Now the air over the sea is warmer; it rises, and cool air from the land flows towards the sea to take its place. This is a land breeze. Both breezes are driven by the same idea: warm air rises and cooler air moves in.

Points to remember

  1. Land heats up and cools down faster than water.
  2. Warm air is lighter and rises; cooler, heavier air moves in to take its place.
  3. Sea breeze: cool air blowing from the sea towards the land during the day.
  4. Land breeze: cool air blowing from the land towards the sea at night.
  5. Both breezes are examples of heat transfer by convection in air.

Exam tip

Draw two labelled diagrams, one for day and one for night, showing land, sea, warm air rising and the direction of the breeze with arrows. Always state the reason first: land heats up and cools down faster than water.

Questions students also ask

Why does land heat up faster than water?
For the same sunlight, the temperature of land rises much more than that of water. Water needs much more heat to warm up by the same amount, and its layers keep mixing, so the sea warms up slowly and also cools down slowly.
In which direction does the wind blow at night near the coast?
At night the wind generally blows from the land towards the sea. Land cools faster, so the air above the sea is warmer and rises, and cooler air from the land flows out to replace it. This is the land breeze.
How are winds formed in general?
Winds form because the Sun heats different parts of the Earth unequally. Air over warmer places rises, and air from cooler places moves in to take its place. This movement of air from cooler regions towards warmer regions is felt as wind.

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