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Name: Cheryl C.
Status: other
Grade: other
Location: N/A
Country: N/A
Date: 9/5/2005


Question:
Why is it that wind blows in land off in the ocean during the day?


Replies:
When the sun heats the surface of the earth, the land heats faster than the water. The warm land heats the air above it and that warm air becomes less dense. It rises just as a hot air balloon. When the warm air rises it draws air in to replace it. Along shorelines the replacement air comes off the water creating what we call sea breezes. Interestingly, at night the reverse happens because the land cools faster and we develop land breezes.

Larry Krengel


Dear Cheryl- The land breezes, and sea breezes are due to pressure differences between the land an ocean. These pressure differences are caused by temperature differences over those areas. The air near the surface is heated by whatever surface is beneath it. Land heats up quicker during the day compared to the ocean, where the surface temperature changes very little from day to night.

As the air heats up in the day, the atmospheric pressure drops, because warm air is less dense than cool air. When the pressure is lower over the land relative to the ocean, the air over the ocean moves towards the lower pressure. This produces what is called the "sea breeze." The sea breeze can extend several miles inland from the ocean. This phenomenon also occurs around the Great Lakes under certain conditions.

At night, the reverse occurs. The land cools faster than the ocean, and the air over the ocean is warm, relative to that over land. Then the breeze blows from the land towards the ocean.

Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO.


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