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Old 05-03-2006, 03:01   #1
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Sea Breezes

A Sea Breeze will generally begin as a light onshore surface wind, at roughly right angles to the coast, before clocking right (clockwise in northern hemisphere), as the breeze increases in strength.

Sea breezes generally occur on days when the wind is initially lighter, and the skies are clear enough for the sun to heat the land (so as to be significantly warmer than the seawater). With light or calm winds the early morning air pressure will be uniform or nearly so over a wide area.

As the sun heats the land, a horizontal pressure gradient is created, initially at a few hundred feet above the surface. This results in a flow of air from land to sea at those heights and a consequent return flow (sea to land) at sea level.

A light off-shore wind, by encouraging the initial outflow helps rather than hinders the process. A light on-shore wind may prevent or delay the sea breeze.

The sea breeze usually sets in more or less directly onshore (from sea to land); but soon, the sea breeze will veer to be nearly along the coast.

An island creates, in effect, its own low pressure area, and the afternoon winds will tend to behave accordingly ie cyclonic around the centre of the island,

For the sea breeze to be able to develop, a shore needs a fairly low coast line. With all their concrete and masonry, large conurbations heat up quicker than grass land and give a stronger sea breeze effect as anyone sailing dinghies in urban harbours will know.

The start-up and final sea breeze direction (and speed) will depend on the orientation of the coastline as well as the complexity of the coastline (steepness, headlands, bays, estuaries, etc). Sea breeze circulation is actually more complex than this, so you should log and study its behaviour, under a variety of conditions.

At night, the land cools a lot more than the ocean. The temperature difference between the land and ocean, though, is not as large as during the day, so the land breeze at night is not as strong as the daytime sea breeze.

For a little more info’, with graphics - goto:
Gord May
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