Bjerknes, Vilhelm

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BJERKNES, VILHELM

(b. Christiania, Norway, 14 March 1862; d. Oslo, Norway, 9 April 1951)

meteorology. For the original article on Bjerknes see DSB, vol. 2.

Frequently called the father of modern meteorology, Bjerknes reluctantly devoted himself to atmospheric science. His scientific career, beginning in the 1890s, reveals an astute scientist willing to overcome professional marginalization by developing skills as a disciplinary entrepreneur. Beginning as a theoretical physicist devoted to a mechanical worldview, he hesitantly turned to creating a physics of the atmosphere and oceans. In 1897 he elaborated a hydrodynamic equation for circulation in fluids in which density could depend upon several variables. He soon understood that motions in the atmosphere and oceans could be comprehended through this theorem: He ultimately developed a physical hydrodynamics that became a basis for dynamic meteorology and oceanography. The capstone of his career, the creation of the so-called Bergen School of meteorology, established a new conceptual foundation for the science while creating innovative predictive practices that enabled greater integration of weather as a resource for agriculture, aviation, and fishery.

Career Strategies. Bjerknes’s professional options in physics were limited by both his disposition and his circumstances. Bjerknes hoped to achieve a mechanical depiction of the ether, which would vindicate his father Carl Anton’s hydrodynamic analogies to electromagnetism and serve as an illustration of the contiguous-action physics proposed by Heinrich Hertz. He thought this research would remain central to European physics and could be his vehicle to prestige and authority, but he was mistaken. He felt helpless in the early 1900s when, to his mind, German-speaking theoretical physicists in a state of mass psychosis abandoned the mechanical worldview for electromagnetic alternatives. In Sweden there was little sympathy for theoretical physics, and as a Norwegian working in Stockholm at a time of tensions between the two nations, he found his options limited.

Bjerknes took a calculated risk and transferred his mechanical physics to the atmosphere and less directly to the oceans. Stockholm colleagues helped Bjerknes understand that his generalized circulation theorem, derived theoretically within his work on hydrodynamic analogies, actually held great promise to comprehend motions in the atmosphere and ocean. Although he and his students achieved some notable early successes in applying the circulation theorem, Bjerknes was well aware that “a physicist who goes into meteorology is lost,” as Berlin physicist Friedrich Kohlrausch had informed him. Even after publishing in 1904 his now classic program for pre-calculating changes of state of the atmosphere, Bjerknes remained hesitant about devoting himself to meteorology. Bjerknes was first willing to focus his professional energies on creating an exact physics of the atmosphere (and oceans) once he understood that the growing “conquest of the air” by aeronautics would make possible a transformation of atmospheric science and would bestow cultural and social value on such a science.

His idea of a physics of the atmosphere was informed by his desire to maintain a mechanical worldview and by his understanding that aeronautics would make possible and require three-dimensional diagnoses and prognoses of conditions in the atmosphere. Bjerknes elaborated a program for creating analytic methods by which physical theory could be applied to depict the state of the atmosphere at a given time and rationally pre-calculate changes several hours later. Bjerknes’s program aimed at providing graphical methods that could be applied in practice immediately even while working towards a distant goal of establishing an exact physics of the atmosphere and oceans.

Move to Leipzig. Bjerknes soon realized he needed data for his project that only the international community of aerologists could provide. His difficulties in influencing this rapidly growing subdiscipline, which aimed at exploring the atmosphere well above the ground, to adopt rational units of measurements led him in turn to realize the necessity of producing a new generation of aerologists to shape the profession. To obtain resources for this task, he accepted a call in 1912 to Leipzig University. The new geophysical institute and the choice of Bjerknes as director were linked with a desire of Leipzig physicist Otto Wiener and the Saxony government to create a rigorous atmospheric science that could serve the budding German commercial and military airship activity. Bjerknes understood that if he did not accept the position, the vast resources of the institute would fall to someone else. Amply supported in Leipzig, Bjerknes began to claim great authority for himself, his project, and his institute. Then came the war. Although Bjerknes had little sympathy for German militarism, he and his work were of significance for the rapidly growing use of weather information in strategic operations, not the least for aerial and gas warfare. German military weather services recruited his students and publications; his institute came to a near standstill. With no end of the war in sight and suffering from malnutrition, he accepted in 1917 a call to the Bergen Museum, where Bjørn Helland-Hansen was establishing a geophysical institute as part of a plan to create a new university for west Norway.

The Bergen Project. To continue his project in Bergen, Bjerknes had to adapt once more to local conditions. He tried to capitalize on wartime exigencies by proposing first a field weather service for neutral Norway’s air defense and then an emergency weather service to assist agriculture, in both cases with an eye toward the opportunities that commercial aviation would create for advancing meteorology at war’s end. During the summer 1918 experiment, Bjerknes’s son, Jacob, continued the work begun in Leipzig by identifying lines of convergence in the horizontal wind field and pre-calculating their movement. These lines were associated with hazardous conditions for flying, such as squall lines, as well as with areas of rain. Although the attempt to put theory directly to practice proved vexing, under his father’s guidance and encouragement Jacob gradually came to realize through the daily forecasting that two such lines of convergence seemed to be a fundamental feature of extra-tropical cyclones (low-pressure systems). Moreover, a tangent to where the front-most line (steering line; later, warm front) meets the other line (squall line; later, cold front) indicates the direction of the cyclone, while the regions of precipitation within the cyclone could be localized to the two lines.

Local conditions again forced a strategy change after the war. The new university was not to be built. Vilhelm Bjerknes saw that his best chance now lay in establishing a permanent practical forecasting service and defining new predictive methods. He set out to integrate an academic research program into a weather bureau. Toward this end, he sought indirect methods of applying physics to practical forecasting as a means to gain new insight, while simultaneously addressing the concerns of aviators, farmers, and fishermen. Although not actually engaged in the daily predictive practices, Bjerknes supervised and discussed regularly with his assistants the insights and problems arising from the forecasting work. In 1919 he and his young assistants abandoned an earlier mode of conceptualizing based on kinematics of the wind flow and instead considered three-dimensional air masses and the physical boundaries separating them, which they called fronts. Using an analogy with wartime skirmishes and stalemates along the fronts separating enemy armies, they gradually articulated a new model of the extra-tropical cyclone based on air masses and fronts. The Bergen scientists extended their cyclone model to hemispheric dimensions by postulating a polar front, upon which cyclones develop as one or the other air mass pushes into the other’s territory. While his younger disciples refined the models and provided practical advice to aviators and seamen through forecasting work, Bjerknes attempted to reproduce the models in theory.

Bjerknes and his school managed to combine the search to know with a need to serve the public interest. Conceptual change and new insight resulted from demands on, and transformation in, practice. New knowledge arose through changes in the practice of weather forecasting. Criteria for using weather in commerce played a role in how meteorologists perceived weather phenomena and conceptualized atmospheric systems. In spite of theoretical and empirical “precursors,” the concept of the front could be articulated and integrated into meteorology only after an overhaul in the observational and predictive practices as international meteorology geared up to satisfy regular commercial flight.

The Bergen group hoped the weather service could continue to serve as a hothouse for deeper inquiry into and understanding of atmospheric processes, but maintaining a balance over time proved difficult. The Bergen School’s claim that its methods and conceptual breakthroughs were derived from physical theory, and in direct contact with theoretical inquiry, contributed to meteorology’s more general claim to greater legitimacy as an academic science.

SUPPLEMENTARY BIBLIOGRAPHY

A complete bibliography can be found in Geofysiske publikasjoner, 24 (1962): “In Memory of Vilhelm Bjerknes on the 100th Anniversary of His Birth,” pp. 26–37. Vilhelm Bjerknes’s unpublished papers and correspondence are deposited at the National Library (formerly University Library) in Oslo.