ACCUWEATHER READY Updated Feb. 25, 2020 1:38 PM
In ancient Greece, it was believed that the winds were caused by four gods, Boreas, Eurus, Notus, and Zephyrus, each brother controlling a different cardinal direction on the compass. Boreas was the god of the North wind which brought winter down over the greek city-states. Eurus was the god of the east wind, a bringer of bad luck and rain. Notus was the god of the south wind which brought with it storms and the summer sun. Finally, Zephyrus was the god of the west wind, a gentle and life-giving wind. Today, we understand that the wind is not something dictated by four deities that are often depicted as four horses.However, you yourself may not know what causes wind and find yourself asking “where does wind come from?”Wind, in the simplest of terms, is caused by the sun, the sea, and the Earth’s rotation.
Photo by Georgi Petrov
1- The Sun
The sun is the Earth’s main source of heat. Our protective atmosphere filters out some of the more harmful aspects of the sun and lets in the heat that warms our lovely planet to make it both livable and comfortable for living things. Our atmosphere also traps the heat fairly well so while the warm rays of the sun hit the surface and reflect back off because heat rises, most of that heat is kept. Still, the sun doesn’t heat the Earth evenly which creates pockets of high pressure and low pressure. This difference in atmospheric pressure is key to understanding what causes wind and we will get to it in just a moment.
Photo by Manuel Sardo
2- The Sea
The sun is able to heat the surface of the Earth fairly quickly, but the sea is not so easily persuaded. The sea is massive and, according to Hawai’i Pacific University, takes up more than 70% of the Earth’s surface and contains 97% of Earth’s total water. 97% is so much water, especially when you think of how big the Great Lakes are or how much rainfall a city like Seattle gets. It’s nothing compared to the sea. Because the sea is so large, it takes a long time for it to heat up. You may know of areas in the world where the ocean is known to have warm waters, but those kinds of beaches are few and far between. The contrast of the land heating up really fast and the ocean having nearly no change creates diffusion effect (nature seeking balance by having areas of high concentration moving to areas of low concentration) between the high air pressure and the low air pressure that results in wind.
A satellite image shows sunlight and darkness hitting equal amounts of earth.
3- The Earth’s Rotation
The Earth completes a full rotation in a 24 hour period, but different parts of the planet travel at different speeds in that rotation with the Equator moving the fastest and the poles moving the slowest. A weird concept to wrap your brain around, right? This difference in rotation speeds, as well as the contrast between the low air pressure over the land and the high air pressure over the sea, results in the Coriolis effect. The Coriolis effect is defined by National Geographic as “a phenomenon that causes fluids, like water and air, to curve as they travel across or above Earth’s surface”. Cyclones and trade winds are examples of the coriolis effect in motion. Cyclones have an extremely low pressure center with high air pressure surrounding it. The high pressure is drawn to the low pressure center, because of diffusion, but instead of blending, the high pressure is reflected resulting in the spinning motion cyclones are known for. Trade winds are another example. Since heat rises and there is a difference in rotational speed depending on where you are, the heat that rises and moves northward from the equator doesn’t move in a straight line, but slightly to the east in the Northern Hemisphere. The heat is then deflected and the wind that was once moving northeast is now moving southwest. This continuous cycle of heat rising and being deflected is what makes trade winds trade winds.
Photo by Kenrick Mills
4- Air Pressure
Now that we have a basic understanding of all the little things that go into what makes wind what it is, we can put all these elements together. When we combine the effects of the sun, the sea, and the Earth's rotation, we get air pressure. When air is heated, the atoms and molecules move faster and spread out while cold air molecules are more condensed and move rather slowly. The air above land has low pressure because the molecules are spread out. The air about the sea is known to have higher pressure as the molecules hang closer to the surface and are “heavier”. The high air pressure moves to the low pressure, because of that diffusion effect we mentioned earlier, and that rush of the two different air pressures meeting creates what we call wind.
Photo by ActionVance
The larger the contrast between the two pressures, the stronger the wind will be. The daily gusts of winds that come and go and seem ever shifting are because of the spiraling nature of the Coriolis effect. In some instances, the contrast is so sizable it results in a storm and the Coriolis effect is more visible.Of course, we see wind in more areas than just on beaches, but the same truths remain. Areas of high pressure are looking for the yin to their yang in the low pressure areas. When they finally meet, air is pushed out and wind is born. While wind is not caused by any horse-shaped deity, the truth is still just as cool. Earth creates such a unique environment in which scientific phenomenon like wind, atmospheric pressure, and the Coriolis effect is able to flourish.
Check out your local forecast to see if you can predict the severity of the wind in your hometown by looking at the air pressure maps.
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