Land-Water Breeze

The land-water breeze is a localized land-atmosphere phenomenon that arises due to the differential heating of water and land surfaces. This differential heating creates local atmospheric circulations (i.e., breezes) that can strongly affect weather and climate in coastal regions. The land-water breeze and the differential heating of land and water surfaces are recognized factors in explaining temperature patterns and the differences between coasts and inland locations.

A water breeze, more often called a sea breeze, is a cool breeze blowing off an ocean or body of water onto the adjacent land. This breeze is created by the temperature contrast between the cool body of water and the warm land surface. The temperature contrast is usually greatest during warm, sunny afternoons in spring or summer, as the ocean temperature remains cool but the incoming solar radiation heats the land surface. The increased temperature and radiation at the land surface results in the warming of the air (atmosphere) above the land. Because warm air is less dense than cool air, the warm air expands and rises. This upward movement of air creates a local increase in air pressure aloft as the air “piles up” and creates a pressure gradient aloft between the land and ocean locations (Figure 1). Air flows from the local high pressure to the local low pressure. The removal of air above the land surface then creates a local surface low pressure, and the flow of air toward the ocean creates downward-moving air and a high pressure near the surface. Surface air flows from the high pressure over the ocean to the low pressure over the land, carrying the cooler ocean air with it, resulting in the water or sea breeze. This local circulation forms a convection cell or convection loop.

In the land breeze, the situation is reversed. Land breezes occur mainly on cool, clear nights during the fall and winter, when radiational cooling is strongest and water temperatures are fairly warm. At night, the land surface and the atmosphere above it will cool off due to radiational cooling, while the ocean temperature remains relatively constant. As the air above the land surface becomes denser, the atmospheric column contracts, forming [Page 1748]sinking air and a local area of high pressure. Again, the upper air (aloft) is affected by the heating and cooling of the surface. As the air sinks over the land, a low pressure is created aloft, and a high-pressure center forms over the water. Air aloft flows onshore, which creates further vertical sinking over the land. The onshore flow produces vertical rising over the ocean, creating a local low pressure. The land breeze is produced by offshore flow between the land high and the ocean low pressure.

Figure 1 Land-water breeze: surface and aloft circulation

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