A sea-land breeze is a thermal circulation system that develops along shorelines. These breezes are created where there are variations in pressure due to differences in the way both land and water cool. During the day, the land heats faster than the water does under the sunlight, which makes heated air rise. The air over the oceans is a cool high because water does not heat nearly as fast as land. As soon as a big enough difference is reached and there is a significant enough pressure gradient, air will begin to flow from the cooler ocean air to the land, replacing the air rising in the thermal low. This, in turn, causes the heavier, cooler air over the ocean to move toward land, replacing the air rising in the thermal low. This circulation cell is referred to as a sea breeze, because the wind is flowing in from the ocean. A sea breeze usually does not start until midmorning, because the surface of the Earth needs time to heat up and set up the pressure gradient, which triggers the cellular flow. After several hours of heating, sea breezes are strongest by late afternoon, because this is when the greatest temperature and pressure contrasts exist.
Once the Sun sets and the heat source is removed, the land begins to cool down quickly (much quicker than the water, because water retains its heat longer), until both the land and ocean are similar in temperature again. At sunset, the opposite process occurs. During the night, the land cools off more quickly than the ocean, and soon a large enough temperature gradient has again been set up. This time, however, the opposite circulation pattern happens. The land surface is cooler than the water, making it the thermal high pressure area. The ocean now becomes the warm thermal low. The wind now moves from the land to the ocean and is called a land breeze.
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