Raven pins a postcard of a beach to the log. "My cousin says the wind there always blows in from the sea by afternoon."
"Always?" Rocket asks. "Wind cannot have a schedule."
Nova dims her lights. "Think about Wednesday. The sand is land. The sea is water. What happens by afternoon?"
"The land is much warmer than the water," Raven says. "The air over it warms and rises."
"And cooler air from over the sea slides in to replace it," Rocket says slowly. "A breeze from the sea."
Nova brightens. "The National Weather Service calls it a sea breeze. At night, it can run the other way."
"So the land versus water race makes wind," Rocket says. "Every single afternoon."
The National Weather Service explains that the Sun warms ground and ocean at the same rate. But the ground's heat stays near the surface.
That surface heat warms the air above the land. The warm air becomes less dense and forms a weak area of low pressure.
Over the water, cooler, denser air is pulled down by gravity and spreads inland. That inland push is the sea breeze.
At night the land can cool below the sea surface temperature. Then denser air spills from the land onto the water: a land breeze.
Land breezes are most common in fall and winter, when the water is still fairly warm and the nights are cool.
NASA explains that water has a high heat capacity: it absorbs a lot of heat before it begins to get hot.
The ocean covers about 70 percent of the Earth's surface.
The top few meters of the ocean store as much heat as the Earth's entire atmosphere.
That is why temperature swings between day and night are much greater over land than over water.
So a coast often has smaller day-to-night swings than a place far inland. Your own area may show this.
| Statement | True or false? |
|---|---|
| Radiation is how the Sun's energy crosses space to the Earth. | ? |
| The Sun heats the poles more than the equator. | ? |
| The seasons are caused by the tilt of the Earth's axis. | ? |
| Soil warms faster than water in the same sunlight. | ? |
| About 48 percent of incoming sunlight is absorbed by the surface. | ? |
Twice this week you met a "weak area of low pressure" where warm air rose. Next week you find out what pressure is.
Air has weight. You will build a barometer and learn to read pressure as rising or falling.
A whole week of solar energy. Tomorrow is Station Day: the family tracks a shadow.