Rocket holds a strip of tissue paper above the warm vent in the lab. It lifts and flutters, though every window is shut.
"There is wind inside!" he says. "Where is it coming from?"
Raven holds her hand over the vent. "The air here is warm. What do you notice about the tissue? It only lifts over the warm spot."
Nova dims her light and hovers lower. "Warm air and cool air do not weigh the same," she says. "Which one do you think rises?"
"The warm air," Rocket says. "And something has to fill the space it leaves."
Raven grins. "So the Sun is a giant vent, and the whole sky is the tissue paper."
"Then the sea breeze at the beach is the same trick," Rocket says. "Big heat, big wind."
The source of the Earth's heat is the Sun. Sunlight heats the ground, and the ground heats the air above it.
Warm air is less dense than the cooler air around it. Gravity pulls the cooler, denser air down, and that lifts the warm air up.
Air rushing in to replace the rising air is what we feel as wind. Whenever you feel wind, air is rising somewhere.
This rising of warm air and sinking of cool air is called convection. It drives the wind patterns we experience.
Water and land heat differently. Sunlight passes deep into clear water, and wind keeps mixing the water, so the heat spreads through a huge volume.
On land, the Sun's heat stays in the top few inches of soil. So land warms much more during the day and cools much more at night.
By day, the warm land heats the air above it, and that air becomes less dense. A weak low pressure area called a thermal low forms over the land.
Over the water, cooler and denser air is pulled down by gravity and spreads inland. That inland flow is the sea breeze.
The sea breeze pushes under the warm land air and forces it up. Its leading edge is called a sea breeze front.
When a sea breeze front passes, the temperature can drop sharply, sometimes 15 to 20 degrees Fahrenheit, and the wind shifts.
A sea breeze can form on the shore of any large body of water, not just the ocean.
| Surface | Where the heat goes | Daytime result |
|---|---|---|
| Water | Spread deep and mixed through a large volume | Stays cooler |
| Land | Stays in the top few inches of soil | Heats up fast |
| Statement | True or false? |
|---|---|
| Sunlight stays in the top few inches of soil on land. | ? |
| Water heats up faster than land during the day. | ? |
| A daytime sea breeze blows from the water onto the land. | ? |
| A sea breeze can only form at the ocean. | ? |
| The temperature can drop sharply when a sea breeze front passes. | ? |
Nice thinking. Tomorrow is Station Lab: you will build a wind flag and a paper compass and take your first wind readings.