Barbara  Krause, age 11, of Freeport, Maine, for her question,  

Can jet streams be explained?

Meteorologists can figure the wild winds of a hurricane, the wilder winds of a tornado and even the wildest winds of a jet stream. But these weather events are merely small local pockets, governed by the turbulent global atmosphere. When we understand how the whole planetary system works, it will be possible to explain jet streams and other weather events in fine detail. It is hoped that improved weather satellites will help to provide this basic background on a global scale.

In the early 1940s, meteorologists thought that the global weather was confined to the troposphere. This lowest layer of the atmosphere reaches up five to about ten miles. It is topped with the slim tropopause layer, and above this the calm stratosphere reaches up 50 miles or so. It was known that the tallest thunderheads extend above the turbulent troposphere. But apart from these rare events, it was assumed that the lofty tropopause is a calm, weatherless realm.

Then came the high flying planes of World War II    and up there in the tropopause they encountered the wildest winds known to man. These lofty jet streams blew away the old notions that all breezy weather events are confined to the lower troposphere. What's more, their patterns and paths were something new. These odd structural details have been tabulated :h detail. It also was learned that jet streams appear to be related to surface weather events, especially cold fronts. But experts cannot explain what causes them or their role in the global weather picture.

The structure of a jet steam is a wavy ribbon of winds, about four miles deep and maybe 300 miles wide, racing eastward at altitudes of four to more than seven miles. Its most remarkable feature is its drafty wind tunnel funnel. At its core, the wind speed may be 100 to 350 miles per hour. Around the core, the winds gradually slacken and those at the rim dwindle to perhaps 50 miles per hour. The breezy wind tunnel swerves north and south as it races around the globe.

The erratic paths seem to coincide roughly with the three climate zones between the equator and the poles. Some experts suspect that the belts between these zones create overlaps in the tropopause, causing turbulence aloft that may give birth to the jet streams. Others suspect that jet streams more likely are triggered by conflicting air masses down in the troposphere. Certainly they seem to be associated with cold fronts advancing into warmer regions of the atmosphere. Their wildest winds occur in winter, when these temperature contrasts are strongest. What's more, where polar fronts bulge southward, the paths of jet streams tend to swerve with them. No doubt all these factors are related. But at present we cannot explain how they, and perhaps unknown factors, trigger and govern the jet streams.

Jet streams may build up local storms below them, but their wild winds do not reach us at ground level. However, they are a problem in high altitude aviation. Flying east, the tail winds of a jet stream boost a pilot's speed. But flying west against its buffeting head winds may be impossible. And the tunnel of contrasting winds may be fatal to a plane that tries to fly across a jet stream. '