Sitting in class with the windows open, riding on a motorcycle with your hair flying about, or walking on the road with the wind blowing your dress. Has it ever occurred to you to ask just how winds are formed? Where do they come from? And where are they headed?
Land and Sea Breeze
The energy that drives wind originates with the sun, which heats the Earth unevenly, creating warm spots and cool spots. Two simple examples of this are sea breezes and land breezes.
During the day, the sun heats up both the ocean surface and the land. Water is a good absorber of the energy from the sun, and the land absorbs much of the sun’s energy as well. However, water heats up much more slowly than land, and so the air above the land will be warmer compared to the air over the ocean.
The warm air over the land will rise throughout the day, causing low pressure at the surface. Over the water, high surface pressure will form because of the colder air. To compensate, the wind will blow from the higher pressure over the ocean to lower pressure over the land, which is called sea breeze. A similar effect can occur near big lakes, where the wind is referred to as a lake breeze.
The sea breeze strength will vary depending on the temperature difference between the land and the ocean.
At night, the roles reverse. The air over the ocean is now warmer than the air over the land. This is because the land loses heat quickly after the sun goes down. and the air above it cools too.
This can be compared to a tarred road. During the day, the road heats up and becomes very hot to walk on. At night, however, the tarred road has given up the heat and is cool to the touch. The ocean, however, is able to hold onto this heat after the sun sets and not lose it as easily, because unlike the land, it is heated to very great depths.
This causes the low surface pressure to shift over to the ocean during the night, and the high surface pressure to move over to the land. This causes a small temperature difference between the ocean surface and the nearby land at night and the wind will blow from the land to the ocean creating the land breeze.
Global Wind Pattern
The coriolis effect, makes moving air masses curve, so that the winds converging on the Equator come from the northeast in the Northern Hemisphere and the southeast in the Southern Hemisphere. These winds are called the trade winds.
Farther from the Equator, the winds try to blow toward the Poles, but the coriolis effect bends them the opposite direction, creating westerlies.
At latitudes higher than about 60°, cold surface winds try to blow toward the Equator, but, like the trade winds, they are bent by the coriolis effect, producing polar easterlies.