Teisserenc De Bort, Léon Philippe

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TEISSERENC DE BORT, LéON PHILIPPE

(b. Paris, France, 6 November 1855;

d. Cannes, France, 8 January 1913), meteorology, aerology.

Teisserenc de Bort is famous in meteorology for his discovery of the stratosphere, “the most surprising discovery in the whole history of meteorology” (Shaw, 1926, p. 225), but also for his works on dynamic meteorology (the science that attempts to explain atmospheric motions), on the classification of clouds, and on the general circulation of the atmosphere.

He was born to a prominent and wealthy family, never got married, and devoted his fortune to atmospheric research. Suffering from poor health, he was taught at home by a private tutor who gave him his taste for sciences. For the same reason he made several long stays in Grasse, in the hinterland of Cannes, France, where he started meteorological observations that were sent for publication to the Société météorologique de France (French Meteorological Society). He joined the staff of the newly created Bureau central météorologique (BCM) in 1898 and became the chief of its general meteorology department the following year. When his father died, in 1892, he was left with a substantial income and he requested a long-term leave from BCM, which was granted, in order to devote his free time to the exploration of the atmosphere. After 1904, his poor health prevented him from traveling to foreign countries to attend meetings or participate in the scientific cruises or experiments he co-organized.

The BCM Years. At BCM Teisserenc de Bort made extensive studies concerning the distribution of temperature and pressure at the surface of Earth. In 1879 he established the empirical “law” of isanomals (an isanomal is a line joining the points where the difference between a meteorological parameter and its zonal mean is constant), which relates the anomaly of the monthly mean temperature relative to its zonal mean, to the mean surface pressure: the minima (respectively maxima) of thermal isanomals are associated with pressure maxima (resp. minima). In 1886 he also introduced the concept of centre d’action(center of action) seasonal or permanent, in order to explain the character of seasons, mainly winters, He identified five of these centers of action, the most popular being the anticyclones of the Azores and Siberia, and the Icelandic low, which explain the cold and warm winters in Western Europe.

Concerning the general circulation of the atmosphere, he drew mean isobars at the mean sea level and also in altitude including the 4,000-meter level, the elevation of the Pike’s Peak, Colorado, observatory. He also made a tentative sketch of how the cloud distribution would be seen from space for both hemispheres.

After his years at the BCM, during which he mainly conducted theoretical research, Teisserenc de Bort shifted to problems associated with the design and construction of kites, balloons, and instruments specially built for his researches. In his observatory were developed very interesting devices concerning practically all the technological aspects of these activities, for instance insulating the thermometer from the unwanted influence of the sounding device. His work in this area attracted in Trappes a lot of foreign scientists such as Richard Assmann and Arthur Berson in 1899.

The Dynamic Meteorology Observatory. In 1896 Teisserenc de Bort founded the Observatoire de météorologie dynamique (Dynamic Meteorology Observatory) in Trappes (not far from Versailles, in the western suburbs of Paris) in order to participate in the International Cloud Year (ICY). One of the goals of the ICY was to measure the altitude and displacement of clouds to have a global view of the atmospheric circulation. For this purpose, Teisserenc de Bort installed two photographic theodolites 1,300 meters apart and connected by telephone. Later he also used also this device to measure the altitude of his sounding balloons and compare it with the one computed using the barometric formula, the validity of which was disputed; he proved that it was a reasonable estimate of the altitude, the barometer being slightly delayed during the ascent and the descent.

Under the auspices of the International Meteorological Organization (IMO), Teisserenc de Bort participated in the ICY in 1896–1897, serving together with Hugo Hildebrand Hildebrandsson and Albert Riggenbach on a committee charged with the publication of an international cloud atlas. Teisserenc de Bort eventually financed the project because the IMO had provided no funds for the publication.

After the conclusion of the ICY in 1897, Teisserenc de Bort started the vertical exploration of the atmosphere using kites, following the ideas of his friend Abbott Lawrence Rotch, the director of the Blue Hill Observatory, near Boston, whom he had met in Paris in 1896 during the International Meteorological Conference. At the observatory Teisserenc de Bort installed a workshop in order to build kites, a laboratory for building and calibrating meteorological instruments, and a rotating electrical winch to operate the kites. He invented a line of kites connected by piano wires with diameters decreasing with altitude, a device that was also adopted by the other meteorological observatories, and which allowed his instruments to reach their highest altitude of 5,250 meters in 1901.

In 1898 he started exploring the atmosphere with sounding balloons, a technique devised a few years before by Gustave Hermite and Georges Besançon (1892), and also adopted by Assmann in Germany and Hugo Hergesell in Strasbourg (then in Germany). Teisserenc de Bort used the same kind of instruments as on his kites, but contrary to what his colleagues did, he launched his instruments with lacquered paper balloons (the others, Assmann and Hergesell for instance, used gold beater skin or silk, much heavier), filled with hydrogen produced by the reaction of sulfuric acid on iron filings, and launched from a rotating shelter. The rotating shelter was necessary to launch the delicate paper balloons in the direction of the wind, while the use of hydrogen, instead of town gas (a gas produced from coal and distributed by pipes to houses and buildings for heating, lighting and cooking) was mandatory to reach higher altitudes. Although this technique did not allow Teisserenc de Bort’s balloons to reach altitudes higher than 20 kilometers, as Assmann had, it was much cheaper and allowed him to perform a very large number of launches compared to his rivals and friends.

Similar to the results of Hermite and Besançon, but unlike Assmann and Hergesell, Teisserenc de Bort found a layer of increasing temperature above 10 kilometers during his very first launches in April 1898. It is not known what he thought about his finding, but it is known that he corrected his measurements of temperature when the temperature increased in the upper atmosphere in order to preserve the same vertical gradient of temperature as under that layer because at that time meteorologists thought the temperature of the high atmosphere always had to decrease with height (arguments in favor of this opinion have been summarized by Ohring, 1964, p. 12) and that the horizontal heterogeneities of temperature generated by the ground disappeared at high altitude, where temperature has to be constant on a constant altitude surface. From the beginning, Teisserenc de Bort launched his sounding balloons during the night in order to avoid solar radiation affecting the temperature measurements. Teisserenc de Bort must have been unsure about the performance of his instruments, so he decided to multiply the launches in order to verify his conclusions: for instance he launched three balloons during the same night. From 1898 to 1902, he alluded only once to this problem during a conference in 1899 when he also explained the large temporal variations of temperature he had measured in the high atmosphere.

The Discovery of the Stratosphere. When he finally decided to publish his findings in 1902, he had launched 236 sounding balloons above 11 kilometers, whereas at the same period Assmann in Berlin had only launched 20. In his paper to the Academie des sciences, Teisserenc de Bort reported that the temperature ceased to decrease in a layer he called the isothermal layer. He was aware that in the isothermal layer temperature increased, but he was unable to explain why. In his report he also presented a climatology of the altitude of the base of this layer that is higher in anticyclonic areas than in cyclonic areas. Ass-mann had reached the same conclusion concerning the existence of what he called the “upper inversion,” and published his results a few days later than Teisserenc de Bort. The two men corresponded and Assmann visited the Trappes Observatory in 1899.

While Hildebrandsson and Teisserenc de Bort were preparing the international cloud atlas, they were also designing a very interesting two-volume book, Les bases de la météorologie dynamique (The basis of dynamical meteorology), which was published, chapter by chapter, between 1898 and 1907, one of the most beautiful books concerning meteorology because it contains a lot of old documents, mainly maps at their original size—a valuable source of information on the history of meteorology.

Exploration of the Polar and Tropical Atmospheres. Even before the publication of the discovery of what is now called the stratosphere, Teisserenc de Bort decided to extend the geographical area of his researches, in order to give a universal range to his upper-air measurements. In 1900 he organized a field experiment in Saint Petersburg and Moscow, Russia, headed by Alfred de Quervain, a Swiss geophysicist who later explored Greenland.

Teisserenc de Bort also cofinanced the establishment in 1902 of a meteorological observatory in Hald, Denmark, with his colleagues Hildebrandsson (Sweden) and Adam Paulsen (Denmark) and the help of Eleuthère Mascart, the head of BCM. Their kites and sounding balloons launched at the observatory were complemented by launches by the Danish navy in the Baltic sea.

With Rotch, Teisserenc de Bort cofinanced in 1905 and 1906 cruises on his ship Otaria, bought to investigate the existence of (westerly) antitrade winds. Hergesell had denied their existence above Tenerife Island in 1905, but observations by kites and balloons confirmed their existence over a large area including Tenerife. The two men also extended their soundings to the equatorial Atlantic, even in the Southern Hemisphere, in the Saint Helena anticyclone where they found stratospheric temperatures much colder than in temperate latitudes at the same altitude.

With his friend Hildebrandsson, Teisserenc de Bort also organized a three-year (1907–1909) expedition to investigate the arctic atmosphere in Kiruna, Lapland. The results were published by his collaborator M. Maurice after his death. The main result of all these expeditions was that the altitude of the base of the isothermal layer is higher in tropical than in arctic or temperate regions, and that at the same altitude this layer is colder in the tropical latitudes than in the others.

Teisserenc de Bort not only discovered the stratosphere but also coined the words stratosphere (sphere of layers) and troposphere (sphere of turning) in 1908. He thought that no vertical motion took place in the stratosphere, in opposition to what occurs in the troposphere where vertical motions are responsible for the existence of the vertical gradient of temperature. The word tropopause was coined later by William Henry Dines (1910).

After his death in 1913, the Dynamic Meteorology Observatory was donated by his heiress, his niece Hermine Teisserenc de Bort, to the French army, after first being refused by the French Academy of Sciences. Into the twenty-first century the observatory continues to exist, belonging to Météo-France, the French meteorological service, and still launches balloons carrying radiosondes not unlike those that were first invented at the observatory in 1929 by Robert Bureau.

BIBLIOGRAPHY

The correspondence between Hildebrandsson and Teisserenc de Bort is available both at the Uppsala observatory (Sweden) and at Météo-France (Paris).

WORKS BY TEISSERENC DE BORT

With Hugo Hildebrand Hildebrandsson and Albert Riggenbach. Atlas international des nuages [International cloud atlas]. Paris: Gauthier-Villars, 1896.

With Hugo Hildebrand Hildebrandsson. Les bases de la météorologie dynamique: historique—État de nos connaissances. 2 vols. Paris: Gauthier-Villars, 1898–1907.

“Résultats sommaires des ascensions de trois ballons-sondes exécutées à Trappes.” Comptes rendus de l’Académie des sciences 133 (13 June 1898): 1754–1755.

“Variations de la température de l’air libre, dans la zone comprise entre 8 et 15 kilomètres d’altitude.” Comptes rendus de l’Académie des sciences 134 (28 April 1902): 987–989.

Notice sur les travaux scientifiques de M. Léon Teisserenc de Bort. Paris: Imprimerie générale Lahure, 1906. Analysis of his own works with an extensive bibliography. A five-page supplement to the notice was published in 1909.