Vilhelm Frimann Koren Bjerknes
Vilhelm Bjerknes (1862-1951), a pioneer of modern meteorology, was especially known for his studies in hydrodynamics and thermodynamics and their relation to atmospheric motion. Following the steps of his father and even improving on his work, he devised a program of weather analysis and forecasting and founded the Geophysical Institute and Weather Service of Bergen.
Vilhelm Bjerknes was born on March 14, 1862, to Carl Anton Bjerknes, a respected mathematician and physicist, and Aletta Koren, a minister's daughter, in Kristiania (later renamed Oslo), Norway. Bjerknes' father was a devoted researcher of hydrodynamics. He had been a respected teacher of physics, but turned his focus towards the study of fluid-related movement, and also researched comparable studies in electro-dynamic phenomena. The younger Bjerknes was equally devoted to his father, and started working alongside him early in his scientific career. Although he assisted his father in his research, it was not long before he set out on his own to eclipse his father as a geophysicist.
Bjerknes began his formal education in mathematics and physics at the University of Kristiania in 1880. He studied hydrodynamics until 1887 when he started his M.S. degree. Upon completion of his degree, Bjerknes went to Paris on a state fellowship and began taking lectures by Jules Henri Poincare on electrical wave diffusion. It was then that he became acquainted with Heinrich Hertz's studies on the same subject.
In 1890, Bjerknes traveled to Bonn and attended the university there for two years. He was fortunate enough to become the assistant and first collaborator to Heinrich Hertz himself. Significant research during this period resulted in contributions in resonance and oscillatory circuit theory. Further research with resonance curve experiments also helped to validate Hertz's own theory and experiments. Wanting to return his focus to electrodynamics, Bjerknes returned to Norway in 1892 where he completed his Ph.D. Shortly thereafter, in 1893, he secured a lectureship at Stockholm's School of Engineering. His career further advanced when he procured a position as professor of applied mechanics and mathematical physics at the University of Stockholm in 1895. That same year he married Honoria Sophia Bonnevie, a Norwegian science student in Kristiania. Their son, Jacob Aall Bonnevie Bjerknes was born in 1897. Jacob was destined to not only follow in his father's footsteps in the study and discovery of meteorology, but to further his findings and expand on his father's knowledge. While the new family lived in Stockholm, Bjerknes ceased active research in electrodynamics and returned once more to his father's hydrodynamic studies. In 1902, he published Vorlesungenuber hydrodynamische Fernkrafte (1900-1902), a summary of his work in hydrodynamics.
Established Meteorology Foundations
By 1898, Bjerknes had combined personal mechanical research with a general analysis of the two primitive circulation theorems of absolute motion derived by British mathematician and physicist William Thomson Kelvin and German physicist Hermann Helmholtz. These two theorems dealt with velocities of circulation and the conservation of a circular vortex, which describes the remarkable stability of vortex motion. Applying his own changes to these theorems to the atmosphere and the ocean, the world's two biggest fluid systems, Bjerknes devised the theory of physical hydrodynamics. These were important finding as Bjerknes realized that atmospheric motion can be best understood when hydrodynamics and thermodynamics are combined. He knew that the heat of the sun is transformed into motion in our atmosphere. The friction of that atmospheric motion also generates heat, which is also turned into motion. Hence, thermodynamic laws are intertwined with fluid mechanics and this combination is necessary to fully understand the phenomena of the atmosphere.
Because motion in the atmosphere creates weather patterns, Bjerknes' findings entertained tremendous possibilities in meteorological forecasting. Until then, forecasting was unreliable at best, even though certain progressions of weather systems were observable and understood and important in that forecasting. Long-term outlooks were particularly difficult. Bjerknes' discoveries, however, presented a more structured atmospheric dynamic that enabled meteorologists to forecast more predictably and accurately, especially in the longer term. These offerings were based on a detailed three-dimensional analysis of atmospheric conditions. According to Arnt Eliassen, "He put forward the view that weather forecasting should be dealt with as an initial value problem of mathematical physics and carried out by numerical or graphical integration of the governing equations. This is nothing more than treating the atmosphere as a physical system, but at the time it was a revolutionary idea."
Bjerknes knew his findings were paramount to weather forecasting and realized that economic support was necessary to both continue and share his research. In 1905, he traveled to the United States to present his program of lectures at the Massachusetts Institute of Technology and to seek funding for continued study. He shared his vision for forecasting and was enthusiastically received. He received a research associateship and was awarded a yearly grant from the Carnegie Institute in Washington, D.C. This was continued until the U.S went to war in 1941. Eliassen explained, "The money could hardly have found a better use; it enabled Vilhelm to employ and educate a considerable number of research assistants, all of whom became well-known geophysicists." It was certainly the case, for Bjerknes was an ideal collaborative partner for younger students, as his history of assistants and their future histories would prove.
Bjerknes moved, in 1907, to the University of Kristiania, where he served as professor of applied mechanics and mathematical physics. In 1909, he began a series of lectures that called for an awareness of the importance of new techniques in the science world as they related to weather forecasting and atmospheric understanding. He wrote and published the first volume of Dynamic Meteorology and Hydrography, that dealt with the fixed state of the atmosphere and fluids, with his new assistant, Johann Wilhelm Sandstrom. Bjerknes published a second volume the next year with his new assistants Theodor Hesselberg and Olav M. Devik. This substantial work dealt with massless movement of fluids and the atmosphere. The third and final volume would not be published until 1951, and was written by Bjerknes' collaborators. In 1911, another collaborator arrived to join his work, Harald Ulrik Sverdrup, a fellow Norwegian who would become an important polymathic geophysicist. German scientists were impressed with Bjerknes' work and, in 1912, they offered him a professorship and a position as director of the new geophysics institute at the University of Leipzig. This recognition made Bjerknes' geophysical work more visible.
At the start of his stay at the German university, research was successful. Bjerknes had brought along T. Hesselberg and H.U. Sverdrup, who worked with him in addition to the several German research assistants and students. When World War I broke out, however, he lost many of his student assistants to war service. He also lost Hesselberg and Sverdrup, which left him in serious need for assistants. His son, Jacob, left his studies in Kristiania to join his father, along with Halvor Solberg. Even with reinforcements to assist, the war made research and living more difficult in Leipzig. About this time, a zoologist and Arctic explorer, Fridtjof Nansen, and oceanographer, Bjorn Helland-Hansen, offered him the opportunity to establish his own geophysical institute at the new University of Bergen. Bjerknes accepted. This would prove to be the most productive season of his career.
Founded the Weather Service of Bergen
Bjerknes and his assistants, including his son Jacob, began immediately with their research programs at the new Weather Service. He started research in the dynamic theory of atmospheric movement, systematic daily observation of the basic meteorological conditions, intensive calculation of predictions and graphic representation of meteorological change, and timely weather forecasts.
By the end of the war it was increasingly clear that Bjerknes' work would be indispensable. The Norwegian government set up a weather observation network based on Bjerknes' applications in response to the need. By July 1918, while the new techniques were still experimental, the Western Bergen Weather Service began reporting daily for the government and military. Once the usefulness of the service was more widely recognized, increasingly refined forecasts became accessible to farmers, fisherman, and the newly developing aviation business.
Besides the growing public need and enthusiasm for the dissemination of forecasts, Bjerknes' team welcomed other major research advances. The group's work resulted in the polar front theory, the theory of motion in cyclone systems, and the elaborate upper front theory. These were all major advances of the time and greatly advanced the science of modern meteorology. Jacob, or Jack as he became known, was instrumental in the developments during this time. Building on the research of his father, he recognized that the air masses named by his father had their own cycle. In a paper, "On the Structure of Moving Cyclones" written in the fall of 1918, he stated that "warm air ascends along the sloping frontal surfaces, causing bands of clouds and precipitation to form along the fronts, whereas the cold air sinks and spreads out along the ground." He also noted that "these vertical motions represent a reduction of the potential energy, which could account for the formation of the cyclone's kinetic energy." Bjerknes also continued to publish abundantly. His crowning achievement, On the Dynamics of the Circular Vortex with Applications to the Atmosphere and to Atmospheric Vortex and Wave Motion, was released in 1921. Another, Physical Hydrodynamics, a work completed with Jacob, Solberg, and Bergeron, was published in 1933. The many collaborators and assistants Bjerknes was fortunate to have with him enthusiastically disseminated the Bergen meteorological approach when they, in their turn, left the team and spread out in different countries, including the United States.
Bjerknes accepted a position as professor of mechanics and mathematical physics at the University of Oslo, and left the Geophysical Institute of Bergen to Sverdrup, his son Jacob, and other collaborators he had trained. At the University of Oslo he taught theoretical physics and hoped to write a series of texts on that subject. In 1929, he published his first book on vector analysis and kinematics. In addition, he returned to his father's studies and looked into his hydromagnetic theories. He was unable, however, to resolve the problems with his father's theories.
In addition to his myriad research efforts, he was a powerful spokesman for the theoretical and practical side of meteorology. He remained so even after he retired from the University of Oslo in 1932, at the age of 70. His son, Jacob, continued in the research footsteps of his father grandfather, and furthered the study of modern meteorology. Bjerknes died of heart failure in Oslo, Norway on April 9, 1951
The result of 100 years of research done collectively by Carl, Vilhelm, and Jacob Bjerknes has helped to transform meteorology from a science of random observation to that of data collection and weather forecasting based on physical and mathematical principles.
Friedman, Robert Marc, Appropriating the Weather: Vilhelm Bjerknes and the Construction of a Modern Meteorology, Cornell University Press, 1989.
Notable Twentieth-Century Scientists, Gale Research, 1995.
World of Scientific Discovery, 2nd. ed., Gale Group, 1999.
"Bjerknes, Vilhelm Frimann Koren," http://www.encyclopedia.com/printable/01521.html (11/10/99).
Eliassen, Arnt. "Jacob Aall Bonnevie Bjerknes," http://www.nap.edu/readingroom/books/biomems/jbjerknes.html (11/2/99). □
Bjerknes, Vilhelm Frimann Koren
Bjerknes, Vilhelm Frimann Koren
(b. Christiania [later Kristiania, now Oslo], Norway, 14 March 1862; d. Oslo, 9 April 1951)
Bjerknes was the son of Carl Anton Bjerknes and Aletta Koren. His life and scientific activities were strongly influenced by his father; even in boyhood he became interested in the elder Bjerknes’ hydrodynamic research, especially in the experimental verification of his father’s discovery of the generation of forces between pulsating and rotating bodies in ideal (frictionless) fluids. His collaboration with his father was also necessary because the elder Bjerknes who had never received any formal training in experimental physics, was rather impractical. It should be noted, however, that at an early age Bjerknes was able to give an independent, even critical, evaluation of his father’s research. On the other hand, he defended his father’s memory with great devotion and gave a clearer and more general explanation of his theoretical thinking in Vorlesungen über hydrodynamische Fernkräfte nach C. A. Bjerknes’ Theorie and in Die Kraftfelder.
Bjerknes began his scientific studies at the University of Kristiania in 1880 and in 1888 received the M.S. During the last years of his studies he decided to cease collaborating with his father, a decision that must certainly have been very diffcuilt to make but is a tribute to the maturity and independence with which Bjerknes regarded his possibilities for scientific research. In spite of his great devotion to his father, he was fully aware of the drawbacks to the elder Bjerknes’ scientific isolation and one-sidedness, and feared that he himself could become a victim of the same circumstances. At this time he decided that after completing his education in mathematics and physics and obtaining a position that afforded him comparative peace and security, he would complete his father’s work as far as possible.
After completing his studies, Bjerknes went to Paris on a state fellowship; there he attended Henri Poincaré’s lectures on electrodynamics, during which Heinrich Hertz’s studies on the diffusion of electrical waves were mentioned. He then went to Bonn, where he worked for nearly two years as Hertz’s assistant and first scientific collaborator. For the rest of his life he remained a close friend of the Hertz family and helped Hertz’s widow and daughter in 1933, when they had to flee the Nazis and seek refuge in England. This collaboration with Hertz resulted in some very important scientific publications on resonance in oscillatory circuits; and the theoretical and experimental resonance curves discovered by Bjerknes, along with a work by Poincaré, were of considerable importance for the understanding and final proof of Hertz’s revolutionary experiments.
After his return to Norway, Bjerknes continued his studies, obtaining the Ph.D. in 1892 on the basis of the dissertation “Elektricitetsbevaegelsen i Hertz’s primaere leder.” It was his research in this field that especially qualified him for appointment as lecturer in applied mechanics at Stockholm’s Högskola (School of Engineering) in 1893 and his appointment as professor of applied mechanics and mathematical physics at the University of Stockholm in 1895. Even though he abandoned experimental research in this field fairly soon, he retained a deep interest in the problems of electrodynamics for the rest of his life.
During the following years Bjerknes worked on his father’s theories of hydrodynamic forces, which he succeeded in explaning in a simpler form than that based on his father’s calculations of such specific examples as forces between pulsating balls in frictionless fluids. These investigations resulted in the two-volume work Vorlesungen über hydrodynamische Fernkräfte nach C. A. Bjerknes’s Theorie (1900–1902). Later he often returned to the problem of force fields, which he treated in a simple, clear-cut fashion in two books published in 1906 and 1909.
During the period of his hydrodynamic studies, Bjerknes generalized on the well-known propositions of Lord Kelvin and Hermann Helmholtz concerning the so-called velocities of circulation and conservation of the circular vortex. He then applied this generalization to the movements in the atmosphere and the ocean.
Bjerknes’ generalization depended on the introduction of a broader interpretation of the concept of fluids than that normally used in classical hydrodynamic theory, which assumes that a unique relationship exists between pressure and the specific volume (the volume of a unit mass). He perceived the fluids as thermodynamic systems, which made it necessary to renounce such an unambiguous relationship, and was led to the formulation of the theory of physical hydrodynamics.
In this connection, however, reference should be made to the contribution made in 1896 by L. Silberstein, at that time unknown to Bjerknes, who developed one of Bjerknes’ two circulation theorems with out comprehending its far-reaching implications. The atmospheric movements that cause weather changes result from the radiation of heat from the sun, and the atmosphere thus works as a sort of thermodynamic heat engine that is constantly converting heat to mechanical energy; it also emits heat because of the friction resulting from atmospheric movements. It is therefore necessary, when atmospheric movements are described, to produce the synthesis of classical hydrodynamics and thermodynamics that results from the formulation of the theory of physical hydrodynamics.
Although he realized that it would not be completed in the future, Bjerknes planned an ambitious program as the final goal of this research: he hoped to be able, with the help of the hydrodynamic and thermodynamic theories, to use knowledge of the present conditions of the atmosphere and hydrosphere to calculate their future conditions. During a visit to the United States in 1905 he presented these plans, and received from the Carnegie Foundation an annual stipend to support his research in this field. The grant continued until 1941.
During his period as professor at the University of Stockholm, Bjerknes began collaboration with various scientists, for which he was eminently suited because of his stimulating intellect and deep understanding of his associates’s need for independent development and research. Of special importance was his collaboration with J. W. Sandström, with whom he wrote the first volume of Dynamic Meteorology and Hydrography (1910). The second volume (1911), dealing with kinematics, was written with Th. Hesselberg and O. Devik. The projected third volume, dealing with dynamics, was completed by associates, but he lived to see its publication in 1951. In 1933 he co-authored a book with his son, Jack, and a friend of the son, H. Solberg, Physikalische Hydrodynamik mit Anwendung auf die dynamische Meteorologie.
After his return from Stockholm in 1907 Bjerknes became professor of applied mechanics and mathematical physics at the University of Kristiania, where he collaborated with Sandström, Hesselberg, Devik, and H. U. Sverdrup in developing dynamic meteorology. In 1912, when he was offered the professorship of geophysics at the University of Leipzig and the chairmanship of the newly organized geophysical institute, he decided to accept the offer, in the hope of better prospects. The new institute was stared under the best possible conditions: Hesselberg and Sverdrup followed him to Leipzig, and a few years later both his son and Solberg joined them.
A visit from Fridtjof Nansen resulted in an offer to Bjerknes to take over a professorship at the University of Bergen and to start a geophysical institute there. He decided to accept the offer after assuring himself that the institute in Leipzig would be carried on. Bjerknes was fifty-five when he started working in Bergen, and he remained there until 1926. His years in Bergen were perhaps the most productive of his life. His main collaborators were again his son and Solberg; later they were joined by S. Rosseland, T. Bergeron, E. Bjørkdal, C. Rossby, and E. Palmén. Bjerknes himself continued to play an active role in both the practical implementation of extensive meteorological services and the work on theoretical meteorological problems. From this period came his now classic work On the Dynamics of the Circular Vortex With Applications to the Atmosphere and to Atmospheric Vortex and Wave Motion(1921). One of his finest books, it contains a clear explanation of the most important basic ideas in his research.
After his appointment as professor of applied mechanics and mathematical physics at the University of Oslo in 1926, Bjerknes continued his studies in dynamic meteorology in cooperation with Solberg, J. Holmboe, C. L. Godske, and E. Høiland. He became involved in the teaching of theoretical physics, but remained within the limits of classical physics, and in 1929 he published a small book on vector analysis and kinematics as the first part of a textbook in theoretical physics. The next volume planned, which was to include an explanation of the elder Bjerknes’ “hydromagnetic” theory, was never completed. Despite intensive efforts, Bjerknes and Høiland never succeeded in finding a satisfactory formulation of this theory, which had occupied Bjerknes from his earliest years. This was a problem from which he could not, and would not, disengage himself.
1. Original Works. A bibliography of Bjerknes’ works is in Geofysiske publikationer, 24 (1962), 26–37. Among his writings are “Über die Dämpfung schneller electrischer Schwingungen,” in Annalen der Physik, 44 (1891), 74–79; and “Über electrische Resonanz,” ibid., 55 (1895), 121–169; Über die Bildung von Cirkulationsbewegungen und Wirbeln in reisbungslosen Flüssigkeiten, no. 5 in Skrifter udgivet of Videnskabsselskabet i Christiania, I (1898), 1–29; “Über einen hydrodynamischen Fundamentalsatz und seine Anwendung besonders auf die Mechanic der Atmosfäre akademiens handlingar, 31 , no. 4 (1898–1899), 1–35; Vorlesungen über hydrodynamische Fernkräfte nach C. A. Bjerknes’s Theorie, 2 vols. (Leipzig, 1900–1902); Fields of Force (New York, 1906); Die Kraftfelder (Brunswick, 1909); Dynamic Meteorology and Hydrography, 2 vols. (Washington, D.C., 1910–1911), Vol. 1 written with J. W. Sandström and Vol. II with Th. Hesselberg and O. Devik, also translated as Dynamische Meteorologie und Hydrographie, 2 vols. (Brunswick, 1912–1913); On the Dynamics of the Circular Vortex With Applications to the Atmosphere and to Atmospheric Vortex and Wave Motion (Kristiania, 1921); C. A. Bjerknes. Sein Leben und seine Arbeit (Berlin, 1933); Teoretisk fysik (Oslo, 1929); and Physikalische Hydrodynamik mit Anwendung auf die dynamische Meteorologie (Berlin, 1933), written with J. Bjerknes, H. Solberg, and T.Bergeron, translated as Hydrodynamique physique avec applications à la météorologie dynamique (Paris, 1934).
II. Secondary Literature. Works on Bjerknes are T. Bergeron, “Vilhelm Bjerknes,” in Smàskrifter udgivet af Universitet i Bergen, no. 11 (1962), 7–30; T. Bergeron. O. Devik, and C. L. Godske, “Vilhelm Bjerknes,” in Geofysiske publikationer, 24 (1962), 6–25; T. Hesselberg, in Norsk biografisk leksikon,, I , 584–588; and Harald Wergeland, “Vilhelm Bjerknes,’ in Det kongelige Norske videnskabers selskabs forhandlinger, 24 , no. 16 (1951), 74–78.
(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.
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.
Friedman, Robert Marc. “Constituting the Polar Front,
1919–20.”Isis 73 (1982): 343–362.
———.Appropriating the Weather: Vilhelm Bjerknes and theConstruction of a Modern Meteorology. Ithaca, NY, and London: Cornell University Press, 1989.
Grønås, Sigbjørn and Shapiro, Melvyn, eds. The Life Cycles of
Extratropical Cyclones. Boston: American Meteorological Society, 1999
Robert Marc Friedman