Are you familiar with the jet stream? If you’ve ever watched a weather report, then it is likely you’ve at least heard it mentioned. That’s because jet streams play a major role in shaping weather throughout the world, and forecasters use the strength and location of them to help predict the weather. So just what is the jet stream, and how does it impact weather?
What Is the Jet Stream?
In the United States, people often refer to the jet stream, but actually, there are many jet streams located all over the globe.
Jet streams are fast-flowing, narrow wind currents that occur in the atmosphere. Their paths typically have a meandering shape, and they have the power to push air masses around and affect weather patterns. Jet streams are typically found between 20,000 and 50,000 feet above the surface of Earth, traveling in the troposphere, the lowest layer of Earth’s atmosphere.
In most cases, a jet stream will run from west to east with a relatively narrow width, however, they tend be pretty large in length. Occasionally, a primary jet stream might even break away into smaller streams, sometimes even merging again down the path.
Jet Streams are also not only limited to Earth. They can occur on other planets as well, notably Jupiter and Saturn.
Types of Jet Streams
On Earth, there are two common types of jet streams: polar and subtropical. The Northern Hemisphere and the Southern Hemisphere each have a polar jet stream and a subtropical jet stream.
Polar jets occur some 30,000-39,000 feet above sea level, usually forming 50-60 degrees north and south of the equator. In the Northern Hemisphere, the polar jet flows into the middle to northern latitudes of North America, Europe, Asia, and the oceans in between. The Southern Hemisphere polar jet mostly circles Antarctica all year round.
Subtropical jets occur at higher altitudes (33,000–52,000 feet above sea level) and are generally weaker. These jet streams are typically found between latitudes of 20-30 degrees north and south of the equator.
While these are the primary streams found on our planet, a jet stream can form anywhere in the upper atmosphere winds reach 58 MPH or greater.
What Influences Jet Streams?
Jet streams form between two masses of air that have contrasting temperatures. The bigger the difference in temperature between the air masses, the faster the jet stream. Because of this, jet streams typically form during the winter, when there are greater temperature differences between cold continental air and warm ocean air. This also explains why the subtropical jet is only present in the wintertime; it is the only time of year when temperature differences in the subtropics are strong enough to form a jet stream.
Cold air and warm air masses have different densities, and therefore, have pressure differences between them. At some point, you might have learned that wind typically flows from high to low pressure. Why then, do jet streams not follow this same pattern? Well, the rotation of the Earth causes the air to flow to the right. Jet streams, then, do not flow into air masses, but rather, around them.
How Do Jet Streams Affect Weather and People?
As jet streams flow around the world, they can push weather systems on the surface along with them. When a jet stream is strong, weather on the surface will tend to change rapidly, since the stream is moving these weather patterns away quickly. When a jet stream is weak, weather on the surface tends to remain the same for longer periods of time, sometimes even days or weeks. As you can imagine, during extreme weather events, jet stream strength can have a major impact.
In the Northern Hemisphere, the polar jet moves from west to east, but dips down into middle latitudes in a large wavelike pattern around the globe. These waves can be very large, big enough to cover large portions of the United States. Within these dips (also known as troughs), cold air for the north is able to move further south. Areas within these troughs will have colder temperatures. The opposite happens near the wave peaks (also known as ridges); warm air from the equator is able to move northward. This means areas within the ridges will experience warmer temperatures.
Beyond the obvious impact that they have on weather, jet streams also play a huge role in air travel. Pilots use jet streams in order to help determine flight patterns. When used efficiently, jet streams can help an airplane get where it needs to go much faster while using significantly less fuel. And anything that cuts down on travel time sounds like a good thing to us.