Sea breezes are winds that are caused by the differential heating rates of land and sea. During the day the land heats up more rapidly than the sea because:
- land has a lower specific heat than water – it requires less heat to raise the temperature of 1 kilogram of earth by 1 degree than it does for water;
- the incoming heat warms a shallower layer of the land because earth is a poor conductor of heat. In water the heat is sprread through a significant depth by conduction, convection and foced mixing.
Warm air over the land rises creating a lower pressure at the surface and a higher pressure at the altitude that the air is lifted to. Cool air from over the sea which is now at a higher pressure tends to move in to the low pressure area over land. A circulation is established as the air over the sea subsides and warm air from over land moves in to take its place.
Sea breezes tend to be stronger in the tropics where greater temperature differences are established between land and water and there is also a greater tendancy for instability over the heated land.
Lake breezes are also formed around large areas of inland water.
Low level wind shears are often enhanced by sea breeze circulation.
Land breezes because the of reverse situation. Overnight the land cools to be colder than the sea so cold overland air moves to replace warmer the warmer air over the sea.
As clue to the names of sea breeze and land breeze just remember that when we name winds by where they come from! A sea breeze comes from the sea, a land breeze comes from the land, a northerly wind comes from the north.
Further information on sea and land breezes can be found in Bob Tait’s book ‘CPL Meteorology’ in Topic 2 – Local Winds.
BAck to Pilot Exam Help Index
Technical data content credited to Mr Steve Griffin
