Marine Glossary

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sea breeze

A coastal local wind that blows from sea to land, caused when the temperature over the land is higher than that over the adjacent water. The warmer air creates a local low pressure (since warm air is lighter) and then wind blows from high to low. See AM-1106 for a discussion of why land heats more rapidly than water when exposed to the sun. At night the process usually reverses to form a land breeze (see G121). But whereas sea breezes can become quite strong, up to 20 knots in some cases, land breezes are usually very light unless accelerated by some other force such as in a fall wind.

Sea breeze along a coast generally starts as a light on-shore breeze in the mid morning and then (in the Northern Hemisphere) slowly veers (shifts to the right) toward having an along shore component. In the Southern Hemisphere, the sea breeze backs (shifts to the left) as it builds.

Sea breeze is a fundamental concept of marine weather in the presence of land. They exist and behave universally, throughout the world. It is discussed in ART-4 on wind and terrain. There is especially good treatments of sea breezes in the books of Houghton (Wind Strategy) and Bernot (Bernot on Breezes). See WXT and textbook references.

The state of the sea breeze depends on what other weather patterns happen to be in the coastal region at the time. They could either help or hinder it. Consequently, the state of the sea breeze can be used as an indicator of what is going on weatherwise that we might not yet detect. See discussion in G245.

When sea breezes get focused into a gap wind they can be very strong, Examples from San Francisco Bay and the Strait of Juan de Fuca are illustrated in G123.

Note that sea breezes veer as they build (NH) essentially due to the Coriolis force, but one can picture the process a little less abstractly, in that the breeze actually starts on the surface and then builds down from higher elevations. At higher elevations the wind is veered relative to the surface, hence as it lowers it veers. Also, as the circulation develops, there is generally a High offshore and some form of Low on the land (see World Atlas). The general circulation around this pattern would be to cause an on-shore breeze to veer as it fell more in line with the larger scale circulation. The same arguments apply to either coast of the NH and SH.

Sea breezes need not be associated with a sea or even with a coast. In Puget Sound and adjacent Lake Washington that runs parallel to it in the north-south direction, for example, there is a marked "sea breeze" throughout the summer. The building northerly comes from having more water (Admiralty Inlet, Strait of Juan de Fuca, Georgia Strait) to the north and all land to the south of it. The northerly gently builds during the day and then dies off like clockwork at dark. Such an "inland sea breeze" does not, however, tend to veer much over the water itself as it builds since it is channeled along the valley. In more open area measurements from SeaTac airport, the clockwise rotation of the wind throughout the day is more apparent.

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"Sea breeze" could generically be any wind blowing from sea to land, just as "land breeze" could be any wind from land to sea, but it would be incongruous and misleading to refer to a known gradient wind blowing onshore as a "sea breeze," which would best be restricted to thermal winds. In other words, if the Biloxi Sun Herald reported that the picnic took place on the beach in a warm sea breeze, we will know what they meant, and not hold them accountable to the actual driving force of that picnic wind.