9.10.3 Effects of the sun Variations in air pressure result from the sun’s heating and the Earth’s rotation. The sun’s warmth changes with the time of day (see FIGURE5 ) and distance from the equator. Temperatures are hotter at midday and warmer at the equator than at the poles. Warm air is less dense than cold air because as the air heats, it expands, causing it to rise. Air pressure is lower at the equator than at the poles. As warm air rises at the equator, cooler air from the poles moves in to replace it. This movement of air around the Earth is called wind.
FIGURE5 This diagram illustrates how the sun creates a sea breeze on a small scale.
Land heats up and cools down more quickly than the sea.
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How sea breezes work 1 Daytime: Air above the land heats up, expands and rises. 2 Sea breeze: Air pressure drops over the land, and air moves in from the sea, where pressure is higher, creating a sea breeze. 3 Evening: Land cools faster than the sea, and the temperature of the land drops. 4 Reversed breeze: Air above the sea becomes warmer and rises, and a breeze flows from land to sea.
TOPIC9 Water in the world 311
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