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.
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.
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.