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The Jet Stream

The Discover and Impact of the Jet Stream

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Jet Stream

The polar jet stream and the subtropical jet stream are shown in the northern and southern hemispheres.

Public doman, National Weather Service
A jet stream is defined as a current of rapidly moving air that is usually several thousand miles long and wide, but is relatively thin. They are found in the upper levels of Earth's atmosphere at the tropopause - the boundary between the troposphere and stratosphere (see atmospheric layers). Jet streams are important because they contribute to worldwide weather patterns and as such, they help meteorologists forecast weather based on their position. In addition, they are important to air travel because flying in or out of them can reduce flight time and fuel consumption.

Discovery of the Jet Stream

The exact first discovery of the jet stream is debated today because it took some years for jet stream research to become mainstream around the world. The jet stream was first discovered in the 1920s by Wasaburo Ooishi, a Japanese meteorologist who used weather balloons to track upper level winds as they ascended into the Earth's atmosphere near Mount Fuji. His work significantly contributed to knowledge of these wind patterns, but was mostly confined to Japan.

In 1934, knowledge of the jet stream increased when Wiley Post, an American pilot, attempted to fly solo around the world. To complete this feat, he invented a pressurized suit that would allow him to fly at high altitudes and during his practice runs, Post noticed that his ground and air speed measurements differed, indicating that he was flying in a current of air.

Despite these discoveries, the term "jet stream" was not officially coined until 1939 by a German meteorologist named H. Seilkopf when he used it in a research paper. From there, knowledge of the jet stream increased during World War II as pilots noticed variations in winds when flying between Europe and North America.

Description and Causes of the Jet Stream

Thanks to further research conducted by pilots and meteorologists, it is understood today that there are two main jet streams in the northern hemisphere. While jet streams do exist in the southern hemisphere, they are strongest between latitudes of 30°N and 60°N. The weaker subtropical jet stream is located closer to 30°N. The location of these jet streams shift throughout the year however and they are said to "follow the sun" since they move north with warm weather and south with cold weather. Jet streams are also stronger in the winter because there is a large contrast between colliding Arctic and tropical air masses. In the summer, the temperature difference is less extreme between the air masses and the jet stream is weaker.

Jet streams typically cover long distances and can be thousands of miles long. They can be discontinuous and often meander across the atmosphere but they all flow east at a rapid speed. The meanders in the jet stream flow slower than the rest of the air and are called Rossby Waves. They move slower because they are caused by the Coriolis Effect and turn west in respect to the flow of air they are embedded in. As a result, it slows the eastward movement of the air when there is a significant amount of meandering in the flow.

Specifically, the jet stream is caused by the meeting of air masses just under the tropopause where winds are the strongest. When two air masses of different densities meet here, the pressure created by the different densities causes winds to increase. As these winds attempt to flow from the warm area in the nearby stratosphere down into the cooler troposphere they are deflected by the Coriolis Effect and flow along the boundaries of the original two air masses. The results are the polar and subtropical jet streams that form around the world.

Importance of the Jet Stream

In terms of commercial usage, the jet stream is important for the airline industry. Its use began in 1952 with a Pan Am flight from Tokyo, Japan to Honolulu, Hawaii. By flying well within the jet stream at 25,000 feet (7,600 meters), the flight time was reduced from 18 hours to 11.5 hours. The reduced flight time and aid of the strong winds also allowed for a reduction in fuel consumption. Since this flight, the airline industry has consistently used the jet stream for its flights.

One of the most important impacts of the jet stream though is the weather it brings. Because it is a strong current of rapidly moving air, it has the ability to push weather patterns around the world. As a result, most weather systems do not just sit over an area, but they are instead moved forward with the jet stream. The position and strength of the jet stream then helps meteorologists forecast future weather events.

In addition, various climatic factors can cause the jet stream to shift and dramatically change an area's weather patterns. For instance, during the last glaciation in North America, the polar jet stream was deflected south because the Laurentide Ice Sheet, which was 10,000 feet (3,048 meters) thick created its own weather and deflected it south. As a result, the normally dry Great Basin area of the United States experienced a significant increase in precipitation and large pluvial lakes formed over the area.

The world’s jet streams are also impacted by El Nino and La Nina. During El Nino for example, precipitation usually increases in California because the polar jet stream moves farther south and brings more storms with it. Conversely, during La Nina events, California dries out and precipitation moves into the Pacific Northwest because the polar jet stream moves more north. In addition, precipitation often increases in Europe because the jet stream is stronger in the Northern Atlantic and is capable of pushing them farther east.

Today, movement of the jet stream north has been detected indicating possible changes in climate. Whatever the position of the jet stream though, it has a significant impact on the world's weather patterns and severe weather events like floods and droughts. It is therefore essential that meteorologists and other scientists understand as much as possible about the jet stream and continue to track its movement, to in turn monitor such weather around the world.

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