Discovering the Stratosphere
When dawn broke on 5th November 1895, a crowd had already been gathered in the courtyard of the École Militaire, on the Champ-de-Mars, in Paris to attend a ceremony that was about to take place on this chilly morning. Alfred Dreyfus, a young Jewish artillery officer who had been convicted of treason just days earlier in a rushed and irregular court-martial, would be stripped from his insignia medals and would be marched around the grounds in his ruined uniform. Four months later, Dreyfus began his life sentence at the notorious Devil’s Island Prison in French Guyana.
A few years later, it was disclosed that the evidence against Dreyfus had been forged and the military was forced to order a new court-martial, which took place in 1899. Major Ferdinand Esterhazy, who was implicated as the guilty party, had fled the count, and Dreyfus was again found guilty and sentenced to 10 years in prison. Finally, in 1906; the supreme court of appeals overturned Dreyfus’ conviction. The Dreyfus affair divided French society and greatly shaped France by leading to the reduction in the power of the military and the separation of church and state.
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While Dreyfus’ trial was polarised and convulsed France, in a house in the community of Trappes near Versailles, a man in his forties was designing instruments that would allow him to have written records of the upper atmospheric conditions. Léon-Philippe Teissernenc de Bort was determined to obtain reliable temperature measurements up to a height of 14 kilometers. A few years later, he will discover the stratosphere.
The atmosphere is what keeps our planet alive. Without this pale-blue security blanket that envelops our planet, Earth would be a ball of frozen water and rock with an average temperature of minus 50 degrees Celsius. Life would be impossible. It is only when we view Earth from space that we realise the true nature of our atmosphere, its thinness, and its fragility. As the retired NASA astronauts Scott Kelly said, “When you look at the ... atmosphere on the limb of the Earth, I wouldn't say it looks unhealthy, but it definitely looks very, very fragile and just kind of like this thin film, so it looks like something that we definitely need to take care of." (Buis, 2019)
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In the 17th century, new instruments and inquiry methods, allowed scientists to learn more about the world. The cornerstone of philosophy and science, suggested by ancient philosophers and later enhanced by Aristotle, supported that the space around Earth was filled with different combinations of earth, fire, water, and air. In the 1620s, the Dutch Isaac Beeckman (1588-1637), a remarkable scientist, philosopher, and candle maker, was one of the first scientists to engage with meteorology and atmospheric instruments. In the 1700s, scientists began to launch experiments with balloons and they were surprised to discover that the air was becoming thinner and colder as they rose. This discovery seemed to defy all logic, as they claimed - although the distance between them and the sun didn't change in any meaningful way - the closer you get to a source of heat, that is the sun, the warmer you should feel. So, for the next roughly two hundred years, the dominant belief amongst scientists was that the air got thinner and colder until it completely diminishes. This will change at the beginning of the nineteen century.
Léon-Philippe Teisserenc de Bort was born in Paris in 1855. He joined the meteorological department of the Bureau Central Météorologique (Administrative Centre of National Meteorology) immediately after its foundation in 1880, and a few years later, in 1892, after spending some time in the French colonies in Africa, studying geology and terrestrial magnetism, he was appointed chief meteorologist. He didn’t last long on the job.
Frustrated with the bureaucracy and the Bureau’s unwillingness to support research in the high air, he resigned in 1896. Using his family fortune, he bought a piece of land in Trappes, just outside Paris, and founded a private meteorological observatory. He was now able to devote all his time to his research to predict the weather by carrying out investigations on the movements and altitude of clouds.
Teisserenc de Bort spent the next few years designing instruments that would enable him to make accurate measurements and building unmanned, high-altitude gas balloons with wicker baskets to carry aloft his instrument package, of thermometers and barometers. He even designed a parachute system that was deployed after the wicker basket that carried the instruments was released from the balloon, to land them safely. His balloons were made of materials like paper and silk, and had a volume of 50-60 cubic metres. They were filled with gas, hydrogen, helium or methane. Until 1902, Teisserenc de Bort launched about 238 balloons, day and night.
Evaluating the data recorded in his instruments, he found that at a certain height in the atmosphere the temperature no longer dropped. Instead, at an altitude of between 8 and 13 kilometres, it stayed about the same, after which it started increasing. At first, he thought an error had occurred, but all the balloons told him the same thing. After a certain height, the air got no cooler. Instead, it was warmer.
On April 28, 1902, Teisserenc de Bort presented his conclusions to the French Academy of Sciences on a paper titled, “Variations de la température de l’air libre dans la zone comprise entre 8 km et 13 km d’altitude.” Contrary to the universally held belief that the atmosphere was homogenous and that there was a constant fall in temperature as one went higher, Teisserenc de Bort argued that the atmosphere was composed of separate layers. He called the lower layer, the troposphere, from the Greek word, tropos, which means to turn or stir. The troposphere extends to an altitude of six kilometres over the polar regions and 17 kilometres at the equator. It serves as a trap for water vapour, and that is why there is very little water vapour in the stratosphere. The troposphere is the source of all our weather.
Teisserenc de Bort named the upper part of the atmosphere, the stratosphere, from the Latin word stratum, meaning layer, and argued that temperature differences make gases lie in distinct strata. Today we know that the stratosphere occupies the region of the atmosphere from about 12 to 50 kilometres; its lower boundary is near the poles. The rise in the temperature is caused by the absorption of ultraviolet (UV) radiation from the Sun by the ozone layer which is centered at an altitude of 15 to 25 kilometres. Approximately 90 percent of the ozone in the atmosphere resides in the stratosphere.
At the same time that Teisserenc de Bort was sending his balloons up into the atmosphere from Trappes, in Germany, the scientist and doctor Richard Assmann was also exploring the atmosphere with balloons, made of rubber. Rubber is a stronger material than paper and fabric and therefore Assmann's balloons could fly at a higher altitude. Assmann’s instruments also showed that the air stopped cooling at a certain altitude before it started to warm again from 10 to 15 kilometres in the atmosphere. On May 1, 1902, Assmann announced his findings to the German Academy of Sciences with a report titled “On the existence of a warmer airflow at heights from 10 to 15 kilometres.” He didn’t know that Teisserenc de Bort had presented the same findings three days earlier.
The discovery of the stratosphere was, in the words of the British meteorologist Sir Napier Shaw (1854-1945) “the most surprising discovery in the whole history of meteorology.” It is also one of the most overlooked events in the history of science.
References:
Buis, A. (2019, October 2). The Atmosphere: Earth's Security Blanket. Retrieved from NASA
McAdie, A. (1934, June-July). The Discovery of the Stratosphere. Bulletin of American Meteorological Society, 15(6/7), 174- 177.