Meteorology

“”Wilhelm von Bezold was the first professor of meteorology in Germany. For all the tremendous attention paid to the atmosphere in the second half of the 19th century, he argued, all the major questions remained unanswered. What drives storms? What is their energetic, their thermodynamic foundation? How do centers of high and low atmospheric pressure interact? How do clouds form, why are there different kinds of clouds and cloud shapes? Why does it rain and snow and hail? Are there rhythms and cycles longer than the seasonal year? Where do tornadoes and waterspouts come from? The questions went on and on. Meteorology as presented by Bezold was about not weather forecasting, but the strugle to create a physics of the atmosphere.

Relation with Astronomy

Astronomy and meteorology were then parts of the same subject. One had to consider atmospheric conditions in every astronomical observation, and especially carefully in positional astronomy, where one was trying to determine where something was as much as what it was. These atmospheric influences meant that would-be astronomers had to learn how to measure and record temperature and humidity to correct for their effects. Moreover, weather prediction and prognostication was also useful to an astronomer. A falling barometer, high cirrus clouds at noon, and a wind backing from the south to the northwest were strong indications in Heidelberg that an evening planned for astronomical observation might well be spent instead working in the darkroom.

Researchers

Around 1900, there were only two real university professorships of meteorology in Germany and Austria. There was Wilhelm von Bezold at Berlin, holding the first and only professorial chair of meteorology in the whole German Empire -- this, in part, as a courtesy appointment befitting his status as head of the Prussian Meterological Institute. There was also the chair in meteorology and geophysics created for Julius Hann at Graz in Austria.

Meanwhile, the other meteorologists in German-speaking academia worked in nonacademic positions in state-supported institutes. Wladimir Koppen at the German Marine Observatory in Hamburg, Hugo Hergesell at Straßburg, Richard Aßmann at the Lindenberg Observatory. Under the direction of these institute leaders were a large number of workers variously styled "collaborators", "assistants", and "helpers". These were modest employements, but often filled by scientists of international distinction, such as the balloonist Arthur Berson, Aßmann's collaborators for twenty years at Berlin and then Lindenberg. The list also includes the Austrian Max Margules who got a staff position as an assistant at the Vienna Zentralanstalt fur Meteorologie.

In England, Russia and Scandinavia, the situation was much the same. For example. Nils Ekholm, a collaborator of Svante Arrhenius and polar traveler, worked as an assistant at Uppsala and Stockholm, until he finally obtained the professorship that went along with the directorship of the Meterological Institute in Stockholm.

Still farther from the ranks of university and government posts, there were independent scientists like French pioneer of upper atmospheric research, Leon Teisserenc de Bort (co-discoverer of the stratosphere) and his American counterpart and friend, A. Lawrence Rotch. They combined personal means and private sponsors (including, in de Bort's case, Prince Albert of Monaco) to erect independent institutes where they pursued their own programs of research.

Development

Balloon flight

With few exceptions, meteorology in the previous fifty years had tried to study the three dimensional structure of the atmosphere using only two-dimensional methods of observation. There was, by 1900, a network of meterological stations in the Northern Hemisphere, but the information it gathered was information about what was happening at the surface of Earth -- or at best a few meters above it. It had been possible to expand this network vertically by building meteorological mountain stations, but there is an influence from the topographical and thermal effects of mountains.

Manned balloon flight would allow the investigation of three dimensional structure of the atmosphere up to very great heights in the free air. Bezold was certain that this information would allow the theoretical unification of meteorology as a physics of the ocean of air. Bezold was president of Berlin Aeronautical Society and was an enthusiastic promoter of manned ballooning for scientific purposes. Working together with Richard Aßmann and Arthur Berson, Bezold had requested a grant from the kaiser of 25,000 marks in 1892 to support manned flights from Berlin. The young kaiser, enthused by the project, gave him 50,000 marks instead. Most of these flights were eventually made by Berson between 1892 and 1898 using Aßmann's instruments.

Discovery of Stratosphere

Teisserenc de Bort designed and built meteorological recording instruments and sent them aloft on balloons and kites of his own design and modification.

On 9 September 1899, he had come briefly into the public eye when one of his kite flights -- a large kite carrying a meteorograph and ten other "helping-kites" supporting the tethering cable --- broke free and, trailing 7 kilometers of cable, cut a narrow but astonishing swath through Paris, where it stopped traffic, disabled a train, and cut off all telegraphic communication with Rennes on the day when all France and most of the rest of the world were anxiously awaiting the result of the famous Dreyfus court-martial at that city.

Under the circumstances, de Bort suspended kite flying for a while and return to a series of upper-air experiments with free balloons. He preferred working with those made of kerosened paper. These were filled with hydrogen and trailed a very short cable holding the meteorograph and a bag of sand ballast, which dribbled out at a steady rate to control the balloon's rate of ascent. de Bort's aim was to get these all up as high as possible, often over 11 kilometers and occasionally as high as 14 kilometers. When the balloon reached its maximum altitude, the instrument pack was parachuted back to earth.

When de Bort looked at the temperature records on flights that reached altitudes of 10 kilometers or greater, he noted that the recorded air temperatures failed to decrease with altitude, though theory predicted that they should. The measurement performed by James Glaisher in the 1860s and corrected by Aßmann some years later showed that the temperature should decrease by about 6 C with each kilometer of ascent. In de Bort's records, however, the temperature showed no such decrease between 10 and 14 kilometers.

Aßmann had measured this effect several times between 1894 and 1897 in manned balloon ascents, but he was reasonably sure that it was due to the warming of instrument packet by solar radiation. He was delighted to treat the phenomenon as another problem in instrument design. Hergesell agreed that the phenomenon was probably due to instrument warming, and so did de Bort. All of them tried various ways to shield their thermometers from reflecting or absorbing surfaces on the instrument packets that contained them, in order to keep the thermometers from false readings.

De Bort took the investigation further. He solved all the instrumental problems he could think of. Aware of the possibility of a radiation effect, he began to fly balloons at night. When these night flight also showed a steady temperature around 11 kilometers, he began a systematic program to see whether there was a seasonal variation. The radiation effect should be smaller in the winter than the summer.

The problem was difficult because the effect was elusive. The zone of steady temperature moved up and down between 8 - 12 kilometers, though it was most often at 11 kilometers. It was stronger and weaker over a range of many degrees. By 1900, he had the record of 146 ascents to report to the Academia des Sciences in Paris, but he still postponed conclusions concerning his measurements of temperatures at altitudes above 10 kilometers, unsure as to the character of what he was seeing.

He worked for two more years on the problem, and in 1902, with an accumulation of 236 ascents to support his argument, he made the plunge and publicly rejected the prevailing theory of temperature decrease with altitude. He asserted the existence of an isothermal zone with varying thickness, in which the adiabatic lapse rate (of temperature with altitude) diminished to zero, usually at an altitude of 11 kilometers after which the temperature would remain constant for several kilometers. The layer was higher over high-pressure centers (anticyclones) and lower over low-pressure centers (cyclones). He suggested the problem of the general circulation of the atmosphere would have to be reconsidered, such such an isothermal layer meant the atmosphere as a whole was not in convective equilibrium, but only that part bounded above by this "isothermal zone".

Aßmann realized immediately what he had missed and rushed to claim a share of it for himself, based on the analysis of six balloon ascents at Berlin in 1901. He endorsed de Bort's results, but modified them by asserting that his own superior rubber-balloon technology, with a controlled rate of ascent and more sensitive recorders could prove that this was not simply an isothermal zone, but a true "inversion zone". The temperature not only stopped decreasing in this region, but actually increased for several kilometers before decreasing again. Moreover, he thought he could detect an upper boundary to the region of temperature shift in a layer at about 15 kilometers, meaning that there was both a "lower inversion" and an "upper inversion".

The discovery that the atmosphere was distinctly layered, with a permanent boundary layer near 11 kilometers was momentous. It required a new picture of the vertical structure of the atmosphere. In the new picture there was, between the surface of Earth and the altitude where the lapse of temperature diminished to zero, a shell of turbulent air, soon named the troposphere. This therm was de Bort's, coined in 1908. The "sphere of change", of rising and descending air, of precipitation and clouds. It was the zone of weather. Its upper bound was a mobile surface, later named the "tropopause". Above that boundary surface was the "stratosphere", a zone of stable or rising temperature, without clouds, moisture, turbulence, or convective mixing. It characterized by a laminar airflow.

The atmosphere's weather zone had thus a ceiling as well as floor. Storm systems might now be seen as coherent masses of air, trapped between the boundaries of Earth's surface below and the tropopause above.

It meant that the atmosphere had to be "remapped" from pole to equator and through its full vertical height. No one knew how the tropopause changed with latitude, or how it differed over land and over the oceans, or even why it was there. Was it a matter of temperature and pressure alone, or was it the result of a chemical differentiation of the atmosphere with altitude?