Scientific Weather Prediction:

A Newspaper Article on by V. Bjerknes

In January 1904 Vilhelm F.K. Bjerknes (1862-1951) published a short paper in German in The journal “Meteorologische Zeitschrift”, entitled The Problem of Weather Forecasting from the Standpoint of Mechanics and (Bjerknes 1904a). In this paper Bjerknes introduced hydrodynamics and into and expressed his vision and programme for weather forecasting (Grønås 2005). This well-known paper is often cited as the beginning of modern weather prediction based on physical principles, i.e. prognosis by computing the change of the state of the atmosphere, diagnosed from observations at synoptic times, using the known conservation laws of momentum, mass and energy (e.g. Lynch 2006). In the same month that his scientific journal paper, Bjerknes wrote an article on the same subject in the Norwegian newspaper Aftenposten, published in three parts over three days. The title was Weather Prediction and the Prospect for its Improvement. The article is about 7000 words, more than twice as long as his paper, and contains some interesting additional points not taken up in the paper, such as the problem of acquiring observations aloft, a discussion of possible future predictability for weather forecasting and the importance of predicting seasonal changes in the ocean circulation using similar methods. We have translated the article from Norwegian (rather Danish, since this language – and gothic letters - was used in most Norwegian newspaper at that time). The English version is available at the website of Geofysisk Institutt, University of Bergen (Bjerknes 1904b). In this short paper we summarize the article and make some general comments.

Background Bjerknes studied modern electromagnetic theory with Heinrich Rudolf Hertz (1857-1894) in Bonn, and the title of his doctor thesis at the University of Kristiania in 1892 was “On the motion of electricity in Hertz’s primary conductor”. The following year he obtained an academic position in mechanics and mathematics at Høgskola (College for education of civil engineers), and became a professor there in 1895. In he continued the studies in hydrodynamics that he had started earlier, together with his father (1825-1903), professor in mechanics and physics at the University of Kristiania (Christiania before 1877, from 1925). Carl Anton had ideas on how forces between bodies – like planets – could act at a distance through the ether, which at that time was believed to exist in space. Vilhelm published his findings in 1900/1902 (Bjerknes 1900/1902), in time before the death of his father. Since the idea of ether in space was eventually abandoned, his work got almost no scientific recognition. But since he was forced to consider baroclinic fluids, he was led to discover his famous circulation theorem for baroclinic fluids such as the atmosphere and the ocean. In this way, he generalised the circulation theorem, obtained independently by Kelvin and Helmholz, on the conservation of circulation (vorticity) in barotropic fluids (Bjerknes 1898; 1900; 1902; Thorpe et al. 2002). With this work he also united the disciplines of hydrodynamics and thermodynamics, which until then had developed independently and along separate lines.

Bjerknes’ interest in meteorology probably started when he cooperated with Hertz, who had a keen interest in meteorology, and through his contact with Vilhelm von Bezold (1837-1907), a scientist also credited in the newspaper article. In Stockholm, Bjerknes got to know Nils G. Ekholm (1848-1923) and Johan W. Sandstrøm (1874-1947), who worked in meteorology and oceanography. In the article, Sandstrøm is referred to as a scientist having the kind of practical knowledge that Bjerknes himself, as a theoretician, lacked. With this background Bjerknes was immediately able to apply his theorem to circulations in the atmosphere and the ocean (Bjerknes 1898, Thorpe et al. 2002). Continuing involvement in meteorology led him to his vision of weather forecasting expressed in his journal paper and his long newspaper article.

Bjerknes’ duty and destiny Many years later Bjerknes wrote that in 1904 he had no intention of doing research in meteorology and weather forecasting (Bjerknes 1938). It seems that his vision emerged as a bi-product of his efforts to understand basic questions related to gravitation and electricity. His dedication to meteorology came the next year, he writes, when the Carnegie Institution of Washington offered him a yearly grant, large enough to hire one or two research assistants. The condition for receiving the grant was that his research would focus on the ideas presented in his paper and in lectures on the same topic in Washington. When he accepted the grant, his destiny was sealed.

In his newspaper article, Bjerknes mentions how he was reluctantly drawn towards meteorology. At this time he had gained solid knowledge about weather forecasting, not only about the prognostic equations and how they could be solved, but also about observational methods and how the international observation system could be extended to cover the upper air. He presents his vision with enthusiasm and firm belief in scientific progress. Carl L. Godske, one of his later assistants in Bergen, emphases Bjerknes’ strong conviction of the value of the development of technology and natural science research, and also his sense of philantrophic duty to his country and to mankind (Godske 1956). In his article Bjerknes points to the value for society – the lives of fishermen, sailors and farmers - of improved weather forecasting. He saw what had to be done for better prediction of the weather, and felt a duty for to organise an international network for observations aloft. He already writes like a determined . With the grant from the Carnegie Institution, he dedicated himself for his great vision. In 1910-11 came the first two volumes of Dynamical Meteorology and Hydrography, part I Statics with Sandstrøm and part II Kinematics with his new assistants, O. Devik and Th. Hesselberg. The main title represented the goal of his work, to compute the change of the weather, a task he never finished.

Upper air observations and analyses Bjerknes writes about the considerable experience that had already been gained to obtain observations aloft, using a variety of methods. He believed that the time had come to organise regular meteorological measurements aloft based on observations of the drift of clouds and measurements of temperature, pressure and humidity from meteorological kites. Bjerknes stresses that, since the observations aloft could be obtained at a few places only, as much as possible should be derived from the observations using existing physical relationships between the parameters. He explains in particular how the thermal wind relation could be used to estimate temperature and temperature advection in deep layers from observations of the drift of clouds. Apparently, several scientists had already been working with clouds along such lines. The geostrophic wind law was already known, but Bjerknes later expressed it using geopotential height. But Bjerknes obviously owes the thermal wind law to Sandstrøm. This law, so easy to derive, was probably discovered and used by several others around the same time.

Bjerknes felt that observations from manned or unmanned balloons were unsuitable for operational weather forecasting. Extensive experiments undertaken in several countries simultaneously had already been made with balloons carrying self-registering instruments. Here the registering meteorographs were parachuted down to the surface when the balloons burst at high levels. In this way the registered data had to be found and picked up, an operation too time-consuming for operational weather forecasting. Bjerknes was familiar with electricity, but we don’t know if he was aware at that time of the resent development of the radiotelegraphic system by Guglielmo Marconi.

Meteorological kites and cloud tracking was what Bjerknes had in mind. At that time kites already provided convincing experimental results at several places around the western world, and two German stations regularly telegraphed their daily results to meteorological offices. The kites could reach 5000 meters, but Bjerknes believed that with further development, such kites could reach the highest cloud layers. He envisaged meteorological kites both on land and at sea, e.g. from liners crossing the North-Atlantic.

Bjerkens had detailed ideas about how the measurements should be processed, coded and telegraphed to meteorological centres. He refers to tables of Sandstrøm, which were already available for much of the post-processing at each station.

According to Bjerknes, sufficient knowledge was already available to start the organisation of an operational international network of upper air observations. Synoptic weather maps at several levels through the troposphere could then be analysed at different operational meteorological offices. In this way the diagnostic part of the problem could be completed. Even without his second prognostic step, he is convinced that upper air analyses would improve weather forecasting using current methods.

The prognosis In both his scientific paper and his newspaper article, Bjerknes mentions the prognostic equations and their variables, and sketches how they could be solved using graphical methods. As pointed out by Eliassen (1999), Bjerknes made a mistake when he included the second law of thermodynamics in his set of equations, en error that later was corrected by Richardson (1922), who set up the primitive equations as we know them today.

Bjerknes gives an introduction to partial differential equations for laymen and explains broadly how the equations could be integrated in time. He rejects more sophisticated methods that had been derived by mathematicians for special cases. His idea is to apply graphical methods directly to the synoptic maps for the different layers of the troposphere.

Bjerknes maintains that a united effort by many scientists over a long time was necessary to solve the prognostic step. However, he indicates how he thinks it could be done. First he will make a dynamical prediction of the change of the wind using the thermodynamic variables from the initial time as a first guess. Then, in a second step, he will obtain final prognosis for the thermodynamic variables, but without changing the wind prognosis. He never completed any such graphical method, and it is unlikely that his ideas would work even if sufficient time were available. In the 1950’s Ragnar Fjørtoft developed a successful graphical method for integrating a barotropic model using a quasi-Lagrangian approach (Fjørtoft 1952). He was proud to be able to integrate faster than the computers of that time. He had ideas to speed up his computations using a set of light filters. However, in the 1960’s he realized that he could not compete with the development of fast computers.

Bjerknes was certainly aware of the large amount of work necessary to solve the equations, even graphically. But his conviction that scientific progress could be made was enormous. He knew that the method he proposed was approximate in nature, but nevertheless he thought it one day would be possible to predict a major weather change days, or perhaps weeks, in advance. In this, his ideas are not far from what we think today is the predictability limit for weather forecasting. However, his article points to a larger degree of determinism of atmospheric motion than what modern chaos theory has shown to be possible. It is interesting to note that Bjerknes also thinks seasonal forecasting is possible, in terms of the sign of the deviation from climatology for temperature, precipitation and storminess, i.e. seasonal forecasting, with targets similar to those of modern seasonal forecasting.

Bjerknes underlines that prediction of changes in the ocean circulation is necessary for seasonal forecasting, and proposes that ocean prediction should be developed in parallel with weather forecasting. He saw such forecasting as important not only for the sea surface, but also for the ocean itself, mainly for fishing purposes.

The Finmark storms Bjerknes tries to win the reader’s confidence by stating in several ways that there is no difference between common sense and scientific thinking. He gives some examples of sound weather proverbs and explains why they are reliable. At all times, he shows great respect for the reader. He really was able to explain for the layman the importance of weather prediction and how it could be improved. He writes in a straightforward and simple way, but perhaps with more words than are necessary. To keep the readers interest, he several times refers to certain recent storms in the northernmost county of , Finmark, to illustrate his ideas. He points to the large temperature differences in winter between the open sea and the cold interior, the Finmark plateau, with Siberian temperatures. He describes the condition as a machine which always is at work, but with irregular strokes. He explains how storms up here don’t necessarily leave strong signals in the barometer readings, partly because of lack of observations over sea and partly because of the small horizontal scales of the phenomena.

Vilhelm Bjerknes wrote many articles in Norwegian newspapers, e.g. during his period in Bergen when he lead the Bergen School of meteorology. He also wrote articles about science and education policy. In addition, he gave lectures to laymen, e.g. at meetings for fishermen and sailors. He saw himself as a server for the people. The Japanese scientist S. Fujiwara, who stayed with the Bergen School for three months, writes that the lectures Bjerknes gave in Bergen were well prepared and easy to understand, in contrast to some lectures by his young assistants. His skill as a communicator of new ideas is evident in the newspaper articles reviewed here.

References. Bjerknes, V., 1898: Über einen hydrodynamischen Fundamentalsatz und seine Anwendung besonders auf die Mechanik der Atmosphäre und des Weltmeeres. Kongl. Sven. Vetensk. Akad. Handlingar, 31, 1–35.

Bjerknes, V., 1900: Das dynamische Princip der Circulationsbewegungen in der Atmosphäre. Meteor. Z., 17, 97–106.

Bjerknes, V., 1902: Cirkulation relativ zu der Erde. Meteor. Z., 19, 97–108.

Bjerknes, V., 1900/1902. Vorlesungen Über hydrodynamische Fernkräfte nach C.A. Bjerknes’s Theorie. Lpz. 1. Mit vierzig Figuren im Text. 1900 XVI + 388 pp. 2. Mit sechzig Figuren im Text und zwei Tafeln, 1902 XVI + 316 pp.

Bjerknes, V., 1904a: Das Problem der Wettervorhersage, betrachtet vom Standpunkte der Mechanik und der Physik. Met. Zeit., 21, 1-7. Translation by Y. Mintz: The problem of weather forecasting as a problem in mechanics and physics. Los Angeles, 1954. Reprinted (pp 1-4) in Shapiro & Grønås, 1999.

Bjerknes, V., 1904b: Weather prediction and the prospect for its improvement. A newspaper article in three parts, published in Aftenposten, January, 1904 [http://web.gfi.uib.no/...]. The original version in Danish is found at http://www.nb.no TO BE COMPLETED

Bjerknes, V., 1938: Festvortrag zur 25-Jahrfeier des Geophysikalischen Instituts der Univeristät Leipzig. Zeitschrift für Geophysik, 14, 49-62.

Eliassen, A., 1999: ' early studies of atmospheric motions and their connection with the cyclone model of the Bergen School. Pp. 5-13 in Shapiro & Grønås, 1999.

Fjørtoft, R., 1952: On a numerical method of integrating the barotropic vorticity equation. Tellus, 4, 179-194.

Godske, C.L., 1956: Hvordan blir været? J.W. Cappelens forlag, Oslo, pp 258.

Grønås, S, 2005: Vilhelm Bjerknes’ Vision for Scientific Weather Prediction. In: The Nordic Seas: An Integrated Perspective. Geophysical Monograph Series 158, Am. Geophys. Union, 357-366.

Lynch, Peter, 2006: The Emergence of Numerical Weather Prediction: Richardson's Dream. Cambridge University Press, 279pp.

Richardson, Lewis F., 1922: Weather Prediction by Numerical Process. Cambridge University Press. Reprinted by Dover Publications, New York, 1965. Second edn., 2007, Camb. Univ. Press, with a new Foreword by Peter Lynch.

Shapiro, M. A. and S. Grønås, Eds., 1999: The Life Cycles of Extratropical Cyclones, American Meteorological Society, Boston, 355 pp. Thorpe, Alan J., Hans Volkert and Michał J. Ziemiansk, 2002: The Bjerknes' Circulation Theorem: A Historical Perspective. Bull. Amer. Met. Soc., 84, 471-480.

Sigbjørn Grønås