WHY ARE LAND BREEZES
OFTEN WEAKER THAN SEA BREEZES?
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METEOROLOGIST JEFF HABY
A sea breeze is a mesoscale circulation produced by heating differences between the land and water. The
direction of wind flow at the surface in a sea breeze is from the sea and into the land. A sea breeze will
keep temperatures moderated along and near the coast. The strength of the sea breeze will depend on
several factors with the most important being the temperature gradient. The sea breeze may not set up
at all if the synoptic weather pattern overpowers the
mesoscale environment such as the case of a passage of a front. When the synoptic environment
is fairly benign the strength of the sea breeze is going to primarily depend on the temperature difference
between the ocean and land. The strength of the sea breeze tends to be strongest from the late morning
to the late afternoon since at this time the difference in temperature between the land and ocean is
at the greatest. Suppose the land temperature is 90 F and the water temperature is 75 F. Since the
temperature is warmer over the land this air will be less dense and more inclined to rise. The air over the
ocean will flow toward the land to replace the rising air. This sets up a circulation that actually
begins aloft due to the density and buoyancy differences of the air over the ocean and land.
The land breeze develops at night when the temperature pattern between the ocean and land are
reversed. In a land breeze the land will be cooler than the ocean. Suppose the land temperature
is 70 F and the ocean temperature is 75 F. In this case the air over the ocean is warmer and thus
the circulation will reverse to a flow from the land toward the sea at the surface. A land breeze will often
be weaker than a sea breeze since the temperature difference between the land and water is not
as great. In some cases the land does not cool off to being significantly less than the ocean
temperature which results in a slacking of the sea breeze but no well defined land breeze
setting up at night. Along with synoptic conditions, it is important to know the water temperature and the expected high
and low over the land. This will help the forecaster determine how established the sea breeze
and land breeze will be that day.
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