In 1917, after three years of war, living conditions were deteriorating throughout Europe. Vilhelm Bjerknes, director of the Leipzig Geophysical Institute since 1913, had lost most of his assistants to the German military and many of them had died. He had imported several Norwegians to help, including Jacob, his 19-year-old son, but he was struggling to keep up with his research tying upper-air data and aeronautical activities with a more rational, scientific basis for meteorology. Bjerknes needed to leave Leipzig.
The opportunity to pursue his work in a more conducive location arose on March 17, 1917. The Norwegian oceanographer Bjern Helland-Hansen (1877-1957), the first professor of the Bergen (Norway) Museum, had been leading a research team and providing training in oceanography and marine biology for more than a decade. HellandHansen and his colleagues had gained significant international recognition by the middle of the decade. He saw an opportunity to create a site where oceanographers, meteorologists, and those geophysicists studying terrestrial magnetism and auroras could work together and enhance their individual research projects. In 1916, Helland-Hansen had proposed establishing a geophysical institute at the museum. The museum council's acceptance of the plan inspired many private donations, and the Bergen Geophysics Institute was born. Initially, there would only be two professorships: one in oceanography, filled by Helland-Hansen, and the second in meteorology. Vilhelm Bjerknes was the choice for the second post.
Accepting the offer, Bjerknes returned to Bergen as soon as the semester ended in Leipzig. Upon his arrival, Bjerknes discovered that working space was at a premium. Setting up his temporary research area within a small corner of the museum's oceanographic laboratory, he started seeking a more suitable location that would lend itself to the fulfillment of his ultimate plan: the creation of a Norwegian meteorology school.
Bjerknes knew that he would need the support of geophysicists throughout Scandinavia. His chance to make a fruitful alliance with the Bergen Meteorological Observatory appeared in spring 1918. Norway was experiencing a severe food shortage and the government was supporting a special weather forecasting unit to provide detailed weather information to farmers during the summer growing season. Bjerknes supported the government's goal of increasing crop yields through better weather forecasts. He also intended to use this opportunity to increase forecast precision. Bjerknes and his assistants (his son, Jacob, and the Swedish meteorologist Halvor Solberg [1895-1974]) became a combination theoretical research team and forecasting unit. Their work would lead to advances in both theoretical meteorology and weather forecasting.
Solberg took over forecasting for east Norway, while Jacob assumed responsibility for the west. Their task was hampered by the lack of established weather observation stations and the overall lack of observational data due to the war. During wartime, particularly when the conflict engulfs an entire continent, combatant nations do not share meteorological data that could be used by enemy forces in planning military operations. Before the war, Norway had depended upon weather observations received via telegram from Great Britain, Iceland, and the Faroe Islands. Now the observations were secret and Norway, a long, narrow country whose weather sweeps in off the North Sea, could not create a surface pressure map and plot the track of low-pressure storm systems into the country. If Bjerknes and his assistants were going to aid Norway's farmers, they had to find a way of providing accurate rain forecasts based on local information. To be effective, their new method had to be grounded on a physical understanding of the atmosphere.
Bjerknes increased the number of observation stations from three to 60 by recruiting sailors and fishermen manning the war-related U-boat watch stations scattered throughout the islands composing Norway's extensive North Sea archipelago. These islands were the first to experience stormy weather before it swept over the country, and the sailors and fisherman were already outstanding weather observers because their lives and livelihoods depended upon reading the sky. Bjerknes also recruited lighthouse keepers, farmers, and fishermen living along the coastline.
The island-based stations provided extremely accurate wind reports. Weather observation stations typically reported wind direction by quadrant, for example, north-northwest or east. To meet defense needs, the U-boat lookouts had to provide more precise directions. They reported the wind direction in 5°, not 45°, increments. Wind measurements on exposed islands were also much more accurate than those on
The West Norway Observation Network was critical for both forecasting and theoretical investigation. (Based on figure 3, Robert Marc Friedman, Appropriating the Weather)
the mainland because they were subject to less topographic interference. Bjerknes hoped that the analysis of these accurate wind reports would lead to a new method of rain prediction by identifying lines of convergence, that is, locations where air was rushing into a long, narrow area of the atmosphere.
While he was analyzing incoming data and discovering the presence of convergence lines, Jacob also analyzed data collected by Scandinavian climatology stations. He found that lines of convergence were invariably associated with cyclones. Furthermore, Jacob noticed air currents from two different air masses—one warm and one cold— met at the line of convergence running through the cyclone. He began looking for other instances of this phenomenon during the summer of 1918. By summer's end, he suspected that there might actually be two lines of convergence associated with a cyclone. Warm air flowed into the back of one line associated with a broad swath of moderate rain. Cold air flowed into the back of the second associated with a narrow band of intense rain. The "warm" convergence line always seemed to point in the direction that the cyclone was moving. If true, Jacob could use this feature to predict the cyclone's movement and the areas of rain accurately. As he used this new method, Jacob's forecast errors dropped significantly.
Jacob Bjerknes's work on cyclone structure produced this cross section, which shows the movement of air in relation to a low-pressure center. (Based on figure 6, Robert Marc Friedman, Appropriating the Weather)
Jacob Bjerknes's interpretation of data from the closely knit network of observation stations yielded an important breakthrough on both the structure and movement of cyclones. In fall 1919, at age 21, he published his often-cited article "On the Structure of Moving Cyclones" in the Norwegian scientific journal Geofysiske publikas-joner (Geophysics publications); later the article in the U.S. Weather Bureau's publication Monthly Weather Review. Jacob described the structure of the cyclone's surface features and then inferred its three-dimensional structure on the basis of surface evidence and upper-air data—a result that is still found in almost every basic meteorological textbook.
The Bergen School, with its emphasis on using practical weather forecasting as a way to advance both meteorological theory and weather prediction, was an oddity in the early 20th century. Research schools—academic entities focused on one scientific discipline and featuring a charismatic leader surrounded by numerous "disciples"—were not usually known for pursuing practical applications. On the other hand, institutions that focused on practical applications were not generally associated with theoretical development.
Vilhelm Bjerknes did not intend to become involved in practical weather forecasting—it was actually the furthest thing from his mind. Desiring to set up an institution equivalent to the Leipzig Geophysical Institute, Bjerknes had the primary goal of placing meteorology on a firm physical and mathematical footing to allow calculation of future atmospheric conditions. Although he envisioned improved weather forecasts in the distant future, he did not think he would be starting his new research program in Norway with weather forecasting.
Bjerknes discovered that by directly addressing the problems of weather prediction for farmers and aviators he and his assistants quickly learned what aspects of the atmosphere—temperature, pressure, wind velocity, humidity—were critical to understanding physical processes. The necessity of providing these weather services presented Bjerknes with the resources to further his atmospheric studies. Had Norway not been experiencing food shortages, and had it not been preparing to expand its aviation capabilities, Bjerknes might not have received the funding and government cooperation needed to carry out his research plan.
The purpose of theoretical meteorology has always been to define atmospheric motions and phenomena with the rigorous techniques of mathematics and physics. It is possible for meteorologists to develop a wonderful theory that explains current conditions and is unable to predict atmospheric conditions in the next day or two. Most theorists were not concerned with matching their physical understanding to future weather. Jacob Bjerknes was not just developing theory: He wanted to ensure that his theory was predictive. When his agricultural forecasts were not accurate, he examined where his theory might have failed. Jacob's methods moved theory closer to atmospheric behavior, and in turn increased meteorologists' ability to predict weather more accurately.
The Bergen School was the first that fully melded theoretical research with the practice of weather forecasting. In the next decade, the methods they developed spread rapidly through the international meteorological community.
By the end of the decade, the work of Jacob and his father, Vilhelm, attracted the attention of some of the brightest young meteorologists of the century, including the Swedes Carl-Gustav Rossby (1898-1957) and Tor Bergeron (1891-1977), both of whom would make discipline-changing discoveries by midcentury. Students from Denmark, Norway, and Sweden visited Bergen to take courses and return home with the Bjerkneses' methods. Vilhelm Bjerknes's dream of a Norwegian meteorology school was coming to life. The Bergen School of Meteorology, that rare combination of theoretical and practical meteorology, was taking shape.
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