Land and sea breeze

At a beach in Kerala, Palden noticed that during the day the sand is hotter than the sea water, but at night the sand is cooler. Different things heat up and cool down at different speeds.

Activity 7.4 tests this. Two identical bowls, one half-filled with soil and one with water, each with a thermometer whose bulb is under the surface but not touching the sides, are put in sunlight. Temperatures are written down every 5 minutes for 20 minutes.

After 20 minutes the soil's temperature has risen more than the water's: soil heats up faster than water. Bring both indoors to cool for 20 minutes, and the soil also cools down faster.

Now picture a coast by day. The land heats up faster than the sea, so the warm air above the land rises. Cooler air from over the sea moves in to take its place. This movement of cooler air from sea to land is called a sea breeze. In hot places it brings relief, which is why houses on the coast have their windows facing the sea.

At night it turns around. Without sunlight, the land cools faster than the sea. Now the air over the sea is warmer and rises, and cooler air from the land moves towards the sea: a land breeze.

So people by the sea feel the wind change direction between day and night. Land and sea breezes are convection on a giant scale.