Susie Bosse, age 12, of Omaha, Neb., for her question:
WHAT IS A JET STREAM?
Jet streams were not known until World War II, which was waged between 1939 and 1945. During this period of time, American and German pilots encountered jet streams while flying at high altitudes. These strong winds, the pilots discovered, significantly affected the speed of aircraft flying in or near them. It was then discovered jet streams also influence the earth's weather.
A jet stream is a band of fast moving air currents that can be found at high altitudes above the earth. Jet streams flow in wavelike fashion around both the Northern and Southern hemispheres.
Jet streams change position constantly and move both vertically and horizontally.
Strongest winds in the core of a jet stream measure about 60 miles wide and about one mile thick. The length of the core can vary greatly but it usually averages about 3,000 miles.
Winds in a jet stream move at speeds greater than 65 miles per hour and may even exceed 200 miles per hour.
There are three main types of jet streams in the upper troposphere, the layer of the atmosphere nearest the earth. They can be found at altitudes of 10 to 15 miles above the ground. The three are the polar jet, the subtropical jet and the equatorial jet.
The polar jet stream flows from west to east. In the Northern Hemisphere, its position varies a great deal. The subtropical jet also moves in an easterly direction. Both the polar jet and the subtropical jet weaken during the summer and move farther north.
The equatorial jet flows from east to west. Unlike the subtropical and polar jets, it does not circle the earth. You'll find the equatorial jet only over Southeast Asia and Africa, and only in summer. Other jet streams can be found at higher altitudes than those found in the troposphere. The polar night jet, for examlle, is in the stratosphere, the atmosphere layer that is located above the troposphere. It moves in an easterly direction and happens only during the winter.
Jet streams definitely influence the earth's weather. These fast moving air currents are often associated with storms and even tornadoes.
Warm air that has traveled from the equator loses much of its heat in the polar region. Then it sinks and joins the cold polar air mass that pushes against fresh, warm air arriving from the subtropics.