Grades 3–5 · Earth & Space
Why can a cool breeze blow from the sea on a sunny day?
On a sunny day, a beach can warm much faster than the sea beside it. Land heating is concentrated near the surface. Water stores a great deal of energy, and mixing spreads warming through more water. The two surfaces can therefore warm at different rates.
In the diagramA daytime sea breeze blows toward warmer landOne coastal circulation · wider weather and terrain omittedSea: coolerLand: warmerReturn flow aloftSurface breezeRisingSinkingLand warms faster during a sunny day.
The warmer ground heats the air above it. That air expands and becomes less dense than nearby cooler air under comparable conditions. In the developing coastal circulation, cooler air from over the sea moves inland near the ground and pushes beneath warmer air, which rises.
Higher up, a return flow moves back toward the sea, where air sinks. The surface breeze is one part of this larger circulation. The arrows show how moving air near the ground connects with movement above it; the sea is not simply sending out an endless supply of new air.
After sunset, land can cool faster than the water. A reversed circulation, called a land breeze, may then develop. Neither breeze is guaranteed every day or night: wider weather patterns and the shape of the coast can change or overwhelm the local pattern.
About this explanation
Starting knowledge: Know that sunlight warms surfaces and air can move in different directions at different heights.
Sources
- National Oceanic and Atmospheric Administration — The Sea Breeze
- NOAA National Data Buoy Center — What are sea breezes and why do they occur?