Bonnie Smith, age 12, of Philadelphia, Pennsylvania, for her question:
Is it true that the weather in the stratosphere is calm?
The stratosphere was discovered less than 170 years ago. For a long time, reports from this lofty region of the atmosphere were scanty. The thin air upstairs seemed always calm and cool. Recent reports from above prove that the stratosphere is not always as steady as we thought it was.
The troposphere is the weathery shell of atmosphere next to the globe. Its upper limit varies from four to about 11 miles and its temperature decreases with altitude sharply, at what is called a "lapse rate." Above it stretches the stratosphere to a height of about 50 miles. This upper shell of thin gases, such as ozone, is very different in character from the turbulent troposphere below it. Until satellites were sent aloft, however, the lofty layer was difficult to explore.
Scanty reports from test balloons suggested that this was a region where the lapse rate of the troposphere stopped at around minus 50 degrees. The lofty layer seemed a region of cold, dry atmosphere, windless and weatherless. Compared with the restless troposphere it is indeed a region of quiet calm. High flying jets zoom through its thin air with the greatest of ease. They may be out of sight, but we see their filmy white trails. Heat from their engines leaves vapor that the thin chilly air condenses to crystals of ice.
Later tests revealed that the lapse rate of changing temperature does not actually stogy at the stratosphere. It merely slows down and changes direction. Between altitudes of 10 and 20 miles, the temperature may rise perhaps 10 degrees. Above this level, it rises more sharply and the upper limits may be quite warm. However, the rise is not uniform. Sudden flash warmings occur, especially in summer. Tests in one zone 'recorded a flash temperature rise of 122 Fahrenheit degrees in four days.
The general and gradual warming of the stratosphere is attributed to a high percentage of ozone in its gases. Ozone tends to absorb more heat than oxygen and most other gases. I In any case, there are temperature changes in the lofty region. And ICY scientists shattered the notion that the stratosphere is entirely windless. Teams of researchers were exploring the strange jet streams, those speedy wind tunnels that zoom along in wavy paths at altitudes of 4 to 8 miles. They found one and then another jet stream dashing through stratosphere the lower level of the atmosphere.
In mid winter, the Polar Night Jet stream whirls across Alaska and Northern Canada at an altitude of 16 miles at speeds up to 180 knots. Its breezy wind tunnel circles through the stratosphere above the North Pole. In spring, the pattern changes to the south polar region. So the stratosphere has winds and temperature. But no clouds can form in its `thin gases, no rain and no snow. Its rare ice crystals form from the vapor of high flying bets. It is not entirely weatherless but its weather is milder, much milder than the<tossing turbulence that goes on below it.
The study of the stratosphere is very important to aviation of the future. Planes flying in this region of the air meet less resistance and require less fuel. They can travel faster and cheaper with no risks of sudden storms, no encounters with weathery banks of clouds. Our best researchers in this field are those orbiting weather satellites. The latest models are equipped with instruments to gather data from the stratosphere on a global basis and relay them down to the ground.