A Weather Moment

A large majority of human populations live on the coast of some sort of large bodies of water, be it either lakes or oceans. Day after day, people living in these areas experience the effects of land and sea breezes. While not a “severe” weather event in any stretch of the imagination, the breezes can become strong in the right conditions, and can provide the trigger required to initiate thunderstorms.

Formation

The land/sea breeze is caused by the land and the water heating up at different rates. It requires less energy to raise the temperature of the land. Since both the land and the water receive the same amount of energy, it makes sense then that the land will end up hotter than the water. As the land heats up, the air over the land heats up and expands, creating lower pressure over the land than over the water. As a result, air from over the lake will move inland in an attempt to fill in that low pressure area.

A Sea Breeze is when the air is moving from the water onto the land, and a Land Breeze is when the air is moving from the land onto the water.

Structure

As the air moves onto the land, it builds up, and as the air leaves the water, it leaves a bit of a hole. Vertical movements are generated to counteract this; over the water, air is pulled down to fill in the void; over the land, with the help of the heating, air is pushed up to reduce the amount near the surface. This creates a cycle, where air from over the water will move onto land, then rise, then move back over the water, then sink.

At night, the land cools faster than the water. What goes up must come down. Overnight, the water is then warmer than the land, and the process reverses. Air moves from the land to over the water, then rises, then moves back over the land, then sinks.

Common Weather

The most common element to the land/sea breeze is, naturally, the breeze. It’s strength is proportional to how different the temperature of the land and the water is (the higher the difference, the stronger the wind), but averages in between 15-30km/h. It is possible, however, with the right conditions for sea breeze winds to reach as high as 60km/h (this sometimes occurs near cliffs on the west coast of the United States where the breeze can be redirected and channeled. A sea breeze creates a weak front inland that can cause the air to rise as fast as about 1m/s, which if there is instability in the low levels, can be enough to create thunderstorms. A land breeze promotes inversions over the land, giving clear skies and light winds at night.