Weather forecasters often reference the Gulf Stream or California Current when talking about upcoming weather. Ocean currents have a significant effect on weather and climate. There are quite a few named ocean currents in different parts of the world, and many of them are part of larger systems of ocean currents called gyres.
What Are Gyres?
Gyres are large systems of rotating ocean currents that move in a circular motion. Ocean currents are created by wind blowing over the ocean's surface, combined with forces created by the Earth's rotation and the shape of the ocean's basin — that is, the landmasses and shapes on the ocean's floor that create obstacles that force water to change direction. In the case of gyres, those landmasses are the coastlines of Earth's continents.
The five major gyres include:
- The North Atlantic Gyre
- The South Atlantic Gyre
- The North Pacific Gyre
- The South Pacific Gyre
- The Indian Ocean Gyre
There are also smaller gyres in the oceans, but these are the largest and most well known. Taken together, the ocean gyres circulate water — and everything in it — around the world, earning them the nickname "the ocean's conveyor belt."
How Are Gyres Formed?
Gyres are created by a combination of prevailing winds, the Earth's rotation, and landmasses. Here's a look at how each contributes to the formation of a gyre:
- The warm temperatures at the equator create a persistent low pressure area where air rises into the atmosphere.
- As the warm air rises, cooler air from north and south of the equator moves in to take its place, creating winds from the north and south, respectively.
- The rotation of the Earth shifts the direction of the winds by about 45 degrees. In the Northern Hemisphere, the winds shift to the right, or clockwise. In the Southern Hemisphere, they shift to the left, or counterclockwise.
- The winds pull the water in the ocean, creating currents that flow in their prevailing directions.
- The ocean currents keep flowing in that direction until they meet an obstacle, such as a landmass or another strong current. Those landmasses and currents form the eastern and western boundaries of a gyre.
Gyres are typically stable, predictable currents that don't move far, though seasonal variations can sometimes occur.
An Example of a Gyre
The North Atlantic Gyre encompasses the Atlantic Ocean from the Intertropical Convergence Zone near the equator to just south of Iceland and from the east coast of the United States to the west coasts of Africa and Europe. It starts with the Gulf Stream, which flows northward along the eastern U.S. coast, then joins the North Atlantic Current to cross the Atlantic Ocean. Along the coast of Europe, the North Atlantic Current meets up with the Canary Current, which flows south along the African coast until it finally joins the Atlantic's North Equatorial Current, which eventually completes the circuit by joining the Gulf Stream.
How Does Wind Control Ocean Patterns?
Let's take a deeper dive into the factors that help shape ocean gyres, which, in turn, affect so much of our weather.
Global Wind Patterns
Your nightly weather forecast — or your home weather station — usually includes a measurement of wind direction, which is important for weather forecasting. On the local level, air can flow in any direction and is affected by a number of factors, including temperature, pressure systems, elevation, or the simple movement of air around objects like buildings and fences.
Because of the shape, rotation, and orbit of Earth, the sun heats the surface of the planet unevenly. Near the equator, the sun is directly overhead most of the year, resulting in warm temperatures. The warm surface air rises, resulting in a low pressure area. Cooler air moves in from the high pressure areas to the north and south to replace the air that has risen. As the warm air rises into the atmosphere, it cools and moves outwards toward one of the poles until it becomes cool enough to sink back to the surface.
This constant rising and cooling of air creates what's called a circulation cell, which creates wind and drags the water in the direction of the wind.
The Earth's Rotation
If the Earth were simply suspended in space, the global winds would blow directly north or south. The Earth doesn't stay still, though — it rotates, which means that as the air moves north or south, the surface of the Earth is moving from west to east. Because of this, the wind actually moves diagonally across the ocean's surface — but it's even more complicated than that.
Because the Earth is spherical, different parts of it move at different speeds. It's a concept called the Coriolis Effect. Here's a quick example of how the Coriolis Effect works: The Earth takes 24 hours to make one full rotation. If you are standing a foot away from the North Pole, you will have traveled around a circle with about a 6-foot circumference. If you spend that same 24 hours at the equator, you will have traveled about 25,000 miles — the entire circumference of the Earth.
Because of the Coriolis Effect, the global winds create curved currents on the ocean's surface that move clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. The combination of these factors creates zones of circulation cells on the Earth's surface.
There are three main circulation cells that span the globe from pole to pole:
- Hadley cells: These cells are closest to the equator. They're areas of low pressure, and the prevailing winds there are tropical easterlies.
- Ferrell cells: Ferrell cells are about 30 degrees out from the equator. The wind patterns in this range are the prevailing westerlies.
- Polar cells: These cells are another 30 degrees further from the equator. The prevailing wind patterns in the polar cells are the polar westerlies.
Landmasses and Boundaries
The third major influence that helps shape a gyre is the shape of the ocean basin, which is the bottom and sides of the ocean's floor. Water will flow in one direction until it meets an obstacle, such as the coast of a continent, or a stronger current. At that point, it will adjust the direction and flow north or south until it meets another mass or stronger current, as noted in the example of the North Atlantic Gyre earlier in the article.
Who Should Know About Gyres?
Understanding how wind helps shape ocean currents is important knowledge for meteorologists and anyone else who tracks weather. It's not unusual to hear weather forecasters talk about the Gulf Stream and other ocean currents when they discuss anything from winter storms to whether or not the hurricane season will be particularly active this year. It's also useful and interesting information to those who enjoy outdoor sports and activities and can give you some insight into the best times and places for that fishing or surfing trip you're planning.
Check out our collection of weather equipment curated especially for outdoor enthusiasts. Along with the necessary equipment, you can find lots of helpful information and tips for monitoring weather patterns on our website to ensure all your outdoor activities will be safe and enjoyable.