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When the Sun’s rays beat down on the land near a coastal area, the
rays heat the air over the land quicker than the air over the oceans.
Circulation is started when a "sea breeze" of cool air sweeps
in from the ocean, pushing up the air warmed by the land which then
rises (less dense) and streams out toward the ocean. Air cooled by the
sea sinks and flows landward to fill the area of low pressure created by
the warm land, causing onshore breezes. At night, the land loses its
heat more rapidly than the water. The air above it is chilled, while the
ocean air is relatively warm. The colder air now sweeps from the land to
the water, producing the "land breeze."
This is best illustrated in the San Francisco area in California
where you can see the wind blow the fog toward the hotter land. East of
San Francisco the land gets very hot. The cold Pacific water is to the
west. As the land heats up, the wind moves the fog quickly into
San Francisco. It is very dramatic because there are coastal mountains
that prevent the fog from going through most of the areas, so the fog
rolls in through the Golden Gate bridge. Many people have never seen
such a sight.
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