What is the jet stream?

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What is the jet stream?

Photo: NOAA

The jet stream is a narrow current of strong wind that blows through the upper regions of the troposphere, about seven miles above ground. The jet stream generally moves from west to east, but it can meander like a river. The winds can move up to 200 mph and it can be thousands of miles long and a few miles thick. The strongest winds are found in the core of the jet stream.

The jet stream occurs in area where air masses of very different temperatures meet. Over the United States we often find the polar front jet. This jet is found where cold air masses from the polar regions meet warmer air masses originating in the subtropics. The boundary between the air masses is called a front, hence the polar front jet is found around fronts and associated with winter storms. Tracking the movement of the jet stream is one way to track winter storms.

The characteristics of the jet stream were defined near the end of World War II. Fighter planes and bombers flying to Japan sometimes encountered strong headwinds when they flew westward. This headwind was so fast that sometimes felt they weren’t moving at all! When they dropped to a lower altitude, the headwind decreased and they were on their way.

The jet stream remains important in aviation. Flying in the jet stream provides a tailwind that can reduce cross-country flight time and save lots of fuel and money.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.