Are you ready to take flight? Today in Wonderopolis, we're headed up, up, and way high in the sky. How high? We're traveling several miles up into the atmosphere to go sailing on a river of wind. What are we talking about? The jet stream, of course!

A jet stream is a thin current of air that's several thousand miles wide and several thousand miles long. They're found almost seven miles up in the atmosphere where the troposphere meets the stratosphere at a point called the tropopause. Let us explain.

The winds in a jet stream are caused by differences in temperature between two large air masses that border the tropopause. These temperature differences create differences in air pressure between the air masses.

As colder air tries to move toward the warmer air, winds form. Because of the rotation of Earth, these winds begin to move from west to east, creating a jet stream. The greater the difference in temperature, the faster the winds in a jet stream will move.

How fast do the winds in a jet stream usually move? Very fast! Most of the time, a jet stream moves along at over 100 miles per hour. At times, they reach peak speeds of over 200 miles per hour!

Jet streams were first discovered in the 1920s by a Japanese meteorologist named Wasaburo Ooishi. He used weather balloons to track upper level winds high above Mount Fuji. The term “jet stream" wasn't used until 1939, though, when a German meteorologist first used the term in a research paper.

Research and knowledge about jet streams increased during World War II, as pilots noticed variations in winds as they flew between North America and Europe. It didn't take pilots long to figure out that flying with the jet stream could decrease their travel time, while flying against the jet stream could be very difficult — if not impossible — to do.

Although there are jet streams in the Southern Hemisphere, the two strongest jet streams are both in the Northern Hemisphere. Jet streams affect worldwide weather patterns, because the strong winds can rapidly push weather systems from one area to another. Meteorologists track the position of jet streams to help predict the weather.

Jet streams shift throughout the year. In warmer weather, they move north. In colder weather, they move south. They tend to be strongest in winter, because the temperature difference between Arctic and tropical air masses is greatest at that time.

In addition to meteorologists, pilots and airline officials also pay close attention to jet streams. Flying with the jet stream can greatly reduce flight times, as well as fuel consumption. For planes traveling east to west, it's also important to keep an eye on jet streams. Pilots will fly above or below a jet stream to save time and fuel.

Would you believe that there are a few people who have walked in a jet stream? It's true! Mt. Everest is so high that its summit sits in a jet stream. Winds at the top of Mt. Everest routinely blow at over 118 miles per hour. This can make it very dangerous for those who climb all the way to the highest point on Earth!

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