Sea Breezes              Home Page

Nature and Causes
Sea breezes are caused by the unequal temperatures of adjacent land and sea surfaces.  During the day, especially in summer, solar radiation causes the land surface to become warmer than the sea surface.  The ideal conditions for a sea breeze are given by a light offshore gradient wind (@ 700 metres height) which blows the rising warmed air offshore.

The warmed air rises over the land by convection and is blown offshore by the gradient wind, and cool air from the sea at high pressure is drawn over the land to fill the low pressure area, setting up the sea breeze.  The rising warmed air cools and forms a cloud front inland which is a characteristic feature of a sea breeze.

Sea Breeze Development and direction

With weak wind circulations (eg around the centre of a high), a sea breeze will start over the coastline soon after the land temperature begins to exceed the sea temperature (late morning to early afternoon).  As the temperature difference increases, the sea breeze increases and extends further inland. A sea breeze in early summer may reach 10 M inland during the afternoon, and in favourable conditions the sea breeze may reach 30M inland.  Maximum wind speed (Force 4) will occur during the hours after maximum land temperature has been reached, generally during the mid to late afternoon.

A weak sea breeze will die away soon after sunset, but a developed sea breeze will be maintained at the coast till late evening, then dying away rapidly at the coast and moving seawards.

With stronger general wind circulations, coupled with the required temperature gradient, the development of the sea breeze may be complicated.  A moderate to strong off-shore surface wind will delay the onset of the sea breeze and may prevent the sea breeze from developing at all.  On-shore surface winds are usually reinforced by the sea breeze.

A sea breeze will generally start up as a light onshore surface wind, at roughly right angles to the coast, before veering in a clockwise (northern hemisphere) direction as the breeze increases in strength.

A land breeze develops at night as the land cools relative to the sea and an opposite circulation is set up.  The temperature difference is much less than during the day and the breeze strength is much less.

sea breeze gradient wind geostrophic wind  posted 5th April 2011