Onshore/Offshore Breezes


Last night’s Taco Bar and Bonfire was a spectacular success. In addition to the diehard Phase one residents, most of Phase Two as well as the patio home residents turned out to enjoy the mildish evening. During the ensuing bonfire, the question arose as to why the wind direction shifts at night. So I consulted Wikipedia this morning and this is what it said:

“A sea-breeze (or onshore breeze) is a wind from the sea that develops over land near coasts. It is formed by increasing temperature differences between the land and water; these create a pressure minimum over the land due to its relative warmth, and forces higher pressure, cooler air from the sea to move inland. Generally, air temperature gets cooler relative to nearby locations as one moves closer to a large body of water. The sea has a greater heat capacity than land and therefore is more able to absorb heat than the land, so the land so the surface of the sea warms up slower than the land’s surface. As the temperature of the surface of the land rises, the land heats the air above it. The warm air is less dense and so it rises. This rising air over the land lowers the sea level pressure by about 0.2%. The cooler air above the sea, now with higher sea level pressure, flows towards the land into the lower pressure, creating a cooler breeze near the coast. The strength of the sea breeze is directly proportional to the temperature difference between the land and the sea. At night, the land cools off quicker than the ocean due to differences in their heat capacity, which forces the dying of the daytime sea breeze. If the land cools below that of the adjacent sea surface temperature, the pressure over the water will be lower than that of the land, setting up a land breeze as long as the environmental surface wind pattern is not strong enough to oppose it. “

 

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