Land and sea breezes
The temperature of the sea surface changes only slowly. By comparison, the temperature of the land may change quickly and dramatically between night and day. As the land warms up, the air above it also warms and rises, leaving a local area of low pressure. Cool air from the sea flows in to fill the low, setting up an onshore sea breeze.
As the sea breeze develops, Coriolis effect may become significant, making the sea breeze veer (swing to the right) by 60°-70° until it is almost paralel to the shore.
Sea breezes are most noticeable:
- In summer, especially when clear skies allow the direct rays of the sun to heat the land quickly during the day.
- In the afternoon, when the land has had time to warm up to its maximum temperature.
Sea breezes can reach 20 knots at the coast, and some effect may be felt 10-20 miles offshore.
Small islands (such as Alderney or the Isle of Wight) are not big enough to sustain a sea breeze for long: as soon as the sea breeze starts, it cools the island and kills the sea breeze.
Land breezes are opposite in direction to sea breezes, and are caused by the land cooling at night. This cools the air over the land, which becomes denser and therefore drains downwards towards the sea. Land breezes are generally lighter than sea breezes, and are not felt as far offshore. But extreme versions of this effect can be felt in mountainous regions, where the offshore wind can reach gale force. In such conditions this ‘drainage wind’ is known as Katabatic wind.