Cindy Krauszer, age 15, of Metuchen, New Jersey, for her question:
What is the scientific explanation of the jet stream?
In the 1940s, high altitude planes were designed for long distance bombing missions. It was hoped that they would fly in calm air that was supposed to exist above the blustery weather. Instead, they bashed smack into unexpected streams of super winds. Since then, weather scientists have been straining their brains to ex¬plain these amazing jet streams. They now know some of the answers, but many myster¬ies still remain.
A jet stream is weird in every way. It has a shape of its own and it blows near the top of the troposphere, where the wild weather is supposed to subside. Actually it is a flattish wind tunnel, perhaps 300 miles wide. Its wind speeds in¬crease toward the center of the tunnel, where they surpass the wildest hurricanes. It whizzes along a wavy path near the tropopause, a slim layer of calm air between the weathery troposphere and the peaceful stratosphere.
The tropopause is the roof of the global weather system. It sits about eight miles above the equator and slopes down to about four miles above the poles. One big question is how a jet stream musters the enormous energy to blow up through this roof. Weather scientists think that it feeds on two sources of solar energy, one near the surface and another high in the atmosphere. However, the suggestions involve highly complicated equations based on geometry and aerodynamics.
Apparently the average jet stream originates near the Equator. There the sunny surface warms the air above it and bubbles of light air rise in convection currents above the trade winds. There they turn in opposite directions toward the poles. This is usual. It takes some unusual factors to change a parcel of this warm surface air into a high flying jet stream.
Weather events are hard to understand because the air is invisible. Numerous measurements are necessary to pinpoint important factors such as temperature and pres¬sure. It may help to visualize the weathery atmosphere as a tumultuous battlefield, where mountainous masses of light air conflict with troughs of heavier air. Masses of high pressure tend to blow toward zones of low pressure. And north of the equator, the spinning earth veers all the winds to the right.
These are the normal factors that influence our embryo jet stream. But during the winter, steep slopes tend to form along certain weather fronts, where temperatures and pressures change very suddenly. They are called steep gradients of temperature or pressure. Meteorologists suspect that these sudden changes help to mold a budding jet stream. They increase the wind speed and shrink the size of our original parcel of air. This intensifies its energy and the spinning earth adds an extra swirl to complete its tunnel of winds.
A jet stream snakes around masses of high and low pressure. It creates a ridge of high pressure below, which helps to hold it aloft and may push it through the roof. The upper air releases energy when it absorbs ultraviolet from solar radiation and this gives a boost to the jet stream. Dozens of these wild wind tunnels whizz east¬ward across North America, though so far nobody knows enough to predict exactly when or where to expect them.