Welcome to You Ask Andy

Mary Fountain, age 13, of Timmonsville, South Carolina for her question:

What is a land breeze?

A land breeze blows from the shore out over the ocean, a sea breeze blows from the ocean toward the shore and over the coastline. The pair of them chase each other like playful puppies, wafting cool morning and evening drafts over the beaches. In the tropics, land and sea breezes are stronger and can be expected throughout the year. In our temperate regions, they are most noticeable in summer; when they refresh our beaches and lake shores.

Land and sea breezes are small local weather events, created by warm air along coasts and shorelines. Actually they are twins; children of the same behavior patterns within the gaseous atmosphere. Basically, warm air expands, thins out and rises. The restless atmosphere strives to stay evenly mixed. When warm air creates a thin pocket, heavier drafts blow in from the cooler air around it. This general rule operates to generate all the wild and gentle winds of the restless global atmosphere.

The land and sea breezes are generated by masses of warm and cooler air, working in harmony with another weather factor. The sun beams down on the earth's surface and the air gets its warmth by touching the surface of the land and sea. But the land and the sea have different rules for absorbing the sun's warmth. For example; en a scorching hot day the land becomes very hot, but after sundown it radiates and loses much of its day's quota of heat. The sea warms up more slowly and retains its heat longer, even after the sun goes down.

These patterns of behavior create conflicts in the air above shorelines, where the land meets the sea. The hot sun doles out equal shares of radiation to both sides of the shore. But because of the different ways water and land hold onto or release their heat when the day is done, an airy see saw is created between cooler, heavier masses and masses of light warmer air, wherever land and water meet. The atmosphere adjusts the balance with alternating land and sea breezes that chase each other back and forth across the shore.

During a scorching summer day, the air above the beaches expands and rises. Into this light pocket flow breezes of heavier air from above the cooler ocean. But after sunset, the land loses its heat faster and the air above it becomes cooler and heavier than the air above the water. Now the breezes reverse, and blow from the land out to sea, taking with them a lot of sticky, stuffy air. Together, during, the hot summer, the alternating land and sea breezes keep the shorelines cooler than the central continents.

These local breezes extend upward only about a quarter of a mile. As a rule: the sea breeze comes to cool ,off the beaches about ten in the morning. It may start ten to 30 miles out to sea and blow another ten to 30 miles inland. As a rule, the gentler land breeze begins to puff an hour or so after sunset. It draws the air from perhaps five miles inland and wafts it about five miles out to sea.

 

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