Wind is air moving from where the pressure is higher to where it is lower. Those pressure differences come from uneven heating: warm air expands and rises, making lower pressure near the ground, while cool, dense air sinks, making higher pressure. It is convection in the air.
Key idea
Uneven heating makes pressure differences, and air flows from high pressure toward low pressure. The bigger the difference over a distance, the stronger the wind. A wind is named for the direction it comes from.
Why it works
At the coast on a sunny day, land heats up faster than water. Air over the land warms, expands and rises, leaving lower pressure near the ground. Cooler, denser air over the sea flows in to replace it: a sea breeze, blowing from sea to land. At night the land cools faster than the water, the pattern flips, and a land breeze blows from land to sea.
Worked example: Naming a wind
A wind blows from the north toward the south. What is it called, and what is its direction in degrees?
- Winds are named for where they come from: a north wind.
- Wind direction is the compass bearing it comes from: north is 0° (or 360°).
Answer: A north wind, from 0°
Worked example: Day or night?
At a beach, a breeze blows from the land out to sea. Is it more likely day or night?
- Air flows from high to low pressure.
- Flow from land to sea means lower pressure over the sea: the sea is warmer than the land, which happens at night.
Answer: Night: a land breeze
Common mistake
Naming a wind by where it is going. A north wind blows from the north, toward the south. Check: weather reports give the direction the wind comes from, and wind vanes point into the wind, toward its source.