What could be more basic to understanding planet Earth than to know what lies between the surface and Earth’s center, or between the surface and outer space? Yet the twentieth century dawned with science having virtually no concept of what the atmosphere was like more than two miles above the earth’s surface.
Teisserenc de Bort was the first to expand science’s knowledge into the upper reaches of Earth’s atmosphere. His discovery provided the first accurate image of our atmosphere and formed the basis for our understanding of meteorological phenomena (storms, winds, clouds, etc.). Teisserenc de Bort was also the first to take scientific instruments into the upper atmosphere.
Born in Paris in 1855, Leon Philippe Teisserenc de Bort was appointed the chief of the Administrative Center of National Meteorology in Paris at the age of 30. There he was frustrated because he believed that science’s inability to understand and predict weather stemmed from lack of knowledge about the atmosphere more than three or four kilometers above the surface.
Certainly, manned balloon flights (both hot air and gas filled) had carried instruments into the atmosphere. But these flights never ventured above four or five kilometers in altitude. There wasn’t enough oxygen up there for people to breathe.
In 1895 Teisserenc de Bort quit his job to devote full time to developing unmanned, high-altitude gas balloons at his Versailles villa (outside of Paris). Over the next five years, Teisserenc de Bort designed an instrument package in a wicker basket that his balloons would carry aloft. Basic thermometers and barometers were connected to recording devices so that he would have written records of upper atmospheric conditions once the balloon returned to Earth.
He also designed a release system and parachute to deploy after the basket released from the rising balloon to bring his instrument package gently back down.
Teisserenc de Bort found that tracking the basket and parachute were more difficult than he first thought, even when he used a telescope. Each launch involved a mad scramble across the countryside to keep the descending package in sight. Even so, a few were never found, some sunk in rivers or lakes, and some were smashed when the parachutes failed.
Still, Teisserenc de Bort persisted, and was amazed at what he discovered. Atmospheric temperature decreased steadily at a constant rate of 6.5°C per kilometer of altitude (19°F per mile). This decrease was expected.
However, at an altitude of around 11 km (7 miles, or about 37,000 feet) the temperature stopped decreasing at all. It remained level at around -53°C up to over 48,000 feet (as high as Teisserenc de Bort’s balloons would fly).
At first Teisserenc de Bort didn’t believe that the temperature could possibly stop decreasing. He suspected that the instruments rose to a height where solar heating warmed the thermometer and compensated for continued atmospheric temperature decrease.
He began to launch at night. It was harder to track the parachute’s descent, but it prevented any possibility of solar heating. Even at night, his results were the same. The temperature above 11 km remained constant.
After 234 tests, Teisserenc de Bort finally concluded that his measurements were accurate and that there were two, separate layers to the atmosphere. Near the surface lay an 11-km-thick lower layer where temperature changes created currents, winds, clouds, and weather. Above that was a region where constant temperature allowed air to settle into quiet, undisturbed layers
He named the lower layer the troposphere, from the Greek words meaning “sphere of change,” and the upper layer the stratosphere, from the Greek words meaning “sphere of layers.”
Teisserenc de Bort’s discovery is still the basis of our understanding of the atmosphere.
Scientists now know that the atmosphere has many layers, but the troposphere is the layer where all of Earth’s weather occurs.