Gary Johnson, age 11, of Dallas, TEX., for his question:

Can a pilot always find a jet stream?     

A jet stream is a rushing current of air miles high above the Earth.  It is a tunnel of winds waving like a rippling ribbon thousands of miles around the globe.  Gale winds gallop along the edges of the jet streams.  The winds that rush down the Center of the tunnel are twice as fierce as a howling hurricane high flying pilots discovered the jet streams in World War II. Later these lofty wind tunnels were explored by IGY experts. They seem to blow when and almost where they choose  a jet pilot flying four to 20 miles above the Earth can never count on striking a jet stream. If he finds one flying East, he will use its super hurricane winds to waft him along. If he finds one while flying westward, he will change course. A headwind jet stream can blow a small plane to a standstill.     Though jet streams seem to blow as they choose, they nevertheless follow a Few rough rules. There are four main jet stream paths, two norths and two south of The Equator. The windy tunnels are born aloft when weather conditions are right then off they whiz to weave their snaky trains sometimes clear around the globe. Most jet streams blow from west to East, but in summer the polar jet stream blows From East to West.     A jet stream of speedy breezes is shaped like a flat oval thousands of wavy miles long. Sliced through the middle, the windy tunnel is about four miles from top to bottom and 300 miles from side to side.     The slowest winds are on the outside. They whoop along at 50 miles an hour, which is Equal to a strong gale on the ground. About half way to the center, the winds may rush along at 100 miles an hour, which is 25 miles an hour faster than hurricane winds. Down the center of the tunnel, the winds range from 150 to 300 miles an hour.     Over North America, there are two wavy tracks where the jet streams are likely to blow. The northern track is four to Eight miles high. It loops over Canada and dips down over New England. The other is 10 to 20 miles high. It swoops up from lower California to the Carolinas.     The northern jet streams circle the globe high above the Arctic. During the Winter, when day never dawns in the polar regions, these jet streams blow from west to east. In spring, they turn about and blow from East to west. On the southern track, the jet streams always blow from the West. But in summer, the winds are weaker arid the track moves from Texas northward to the Great Lakes.