Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS

NOVA menu (see bottom of page for text links)

NOVA Online
Balloon Race Around The World menu (see bottom of page for text links)


Frequently Asked Questions
About The Jet Stream

(See the jet stream today.)

image of globe with stream circling

How Would You Define a Jet Stream?

The jet stream, one of the most dramatic forces of nature, was discovered during World War II when aviators first tried to cross the Pacific. This strong wind current is often defined as upper atmosphere winds that blow faster than 57 miles per hour.

How High?

At an altitude above 20,000 feet, or between 6 and 9 miles above the Earth's* surface, the jet stream winds make their presence known. This puts the jet stream near the top of the Earth's troposphere, where most of the Earth's weather occurs.

How Fast?

The core of the jet, a fast-moving wind current that blows west to east around the Earth, reaches an average windspeed of about 80 knots, or 92 miles per hour, and can reach speeds upwards of 300 miles per hour in the winter. These winds are stronger during the winter months because at this time of year the surface temperature contrasts are greater. The greater the contrasts in surface temperature, the stronger the jet stream winds blow.

Length, Width, and Thickness?

Although the jet stream may stretch for thousands of miles around the world, it is only a few hundred miles wide and often less than 3 miles thick.

Does it Affect Weather?

This strong current of air pushes weather systems around the world, and greatly affects local weather patterns by propelling them forward.

Does It Ever Blow North or South?

Because the jet stream winds are greatly affected by changes in temperature, their trajectory does not always flow in a uniform west to east direction. Often they might head due north and then arc down in a southerly direction, creating a wavy pattern or what meteorologists call troughs and ridges.

What Does It Have to Do With Global Ballooning?

Most of the teams plan to catch a ride on the jet stream, which will carry the balloons around the Earth. Therefore, for global balloonists, troughs and ridges present the least desirable air flow pattern. In this scenario, the jet stream would propel a balloon on a wavy north-south course, advancing very slowly around the Earth, losing precious time rather than advancing the balloon on an easterly course around the globe.

What is the Jet Stream doing today?

Global Contenders '97/'98 | Expedition '96/'97 | Fossett | Virtual Flight
Science of Ballooning | Teacher's Guide | Resources | Transcript | Balloon Home

Editor's Picks | Previous Sites | Join Us/E-mail | TV/Web Schedule
About NOVA | Teachers | Site Map | Shop | Jobs | Search | To print
PBS Online | NOVA Online | WGBH

© | Updated October 2000

Support provided by

For new content
visit the redesigned
NOVA site