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Jacob Bjerknes (1897–1975)

Basic Information

  • Full name: Jacob Aall Bonnevie Bjerknes
  • Born: 2 November 1897, Stockholm, Sweden
  • Died: 7 July 1975 (aged 77), Los Angeles, California, USA
  • Citizenship: Norwegian, later American
  • Fields: Meteorology, atmospheric science, climate science

Family Background

  • Father: Vilhelm Friman Koren Bjerknes (1862–1951), the founder of modern meteorology
  • Paternal grandfather: Carl Anton Bjerknes, professor of mathematics at the University of Christiania
  • Maternal grandfather: Jacob Aall Bonnevie, Norwegian politician (Jacob was named after him)
  • Spouse: Hedvig Borthen (married 1928; 1904–1998)
  • Children: Two

Jacob was born in Stockholm while his father held a professorship there. He grew up immersed in the scientific world that surrounded Vilhelm, and his path into meteorology was virtually inevitable.

Education

  • Studied at the University of Kristiania (Oslo)
  • Ph.D. from the University of Oslo (1924), with research on polar front dynamics and heat transport mechanisms

Career Timeline

Period Position Institution
c. 1917–1918 Research assistant to his father Geophysical Institute, University of Bergen
1919 onwards Meteorologist, Bergen weather service Bergen, Norway
1926 Support meteorologist for Amundsen expedition Norge airship Arctic crossing
1931–1939 Professor of Meteorology Geophysical Institute, University of Bergen
1933–1934 Visiting lecturer Massachusetts Institute of Technology
1939/1940 Emigrated to the United States  
1940 onwards Head of government-sponsored meteorology annex UCLA Department of Physics
WWII Colonel, US Air Force weather service Various
Post-war Founder and Professor UCLA Department of Meteorology (now Atmospheric and Oceanic Sciences)
Until 1975 Professor UCLA

Major Scientific Contributions

1. The 1919 Cyclone Paper and the Norwegian Cyclone Model

In 1918, at age 21, Jacob Bjerknes made the observational discovery that would revolutionise weather forecasting. Analysing data from the dense network of weather stations his father had established across western Norway, he discovered that cyclones are composed of weather fronts – three-dimensional surfaces of discontinuity separating air masses of different origin and physical characteristics.

On 1 February 1919, he published “On the Structure of Moving Cyclones” in Geophysical Publications (Vol. 1, No. 2). This paper described:

  • How cyclones originate as waves on the boundary (front) between polar and tropical air masses
  • The structure of warm and cold fronts within a cyclone
  • The life cycle of cyclones from genesis through intensification to occlusion and decay

This paper is considered the foundation of modern weather forecasting and the birth announcement of the Bergen School of Meteorology.

2. The Term “Fronts”

The term “front” was deliberately borrowed from the military terminology of World War I. Just as battlefronts delineated the boundary between opposing armies, weather fronts marked the boundary between opposing air masses. The meteorological terminology was coined during 1918–1919, while WWI was still fresh in everyone’s minds. The Bergen group explicitly used the military analogy: warm and cold air masses were like opposing forces, and the narrow zones where they clashed were the “fronts.”

3. Polar Front Theory (1922)

Together with Halvor Solberg, Jacob Bjerknes published a key 1922 paper on the dynamics of the polar front, demonstrating that the polar front integrated with the cyclone model provided the major mechanism for north-south heat transport in the atmosphere.

4. The Amundsen Expedition (1926)

Jacob served as support meteorologist for Roald Amundsen’s historic Arctic airship crossing aboard the Norge, providing weather forecasts for the expedition.

5. ENSO Discovery (1969)

In 1969, at age 71, Jacob Bjerknes made his second paradigm-shifting contribution by elucidating the mechanism of the El Nino-Southern Oscillation (ENSO).

He suggested that:

  • Increased sea-surface temperatures in the central and eastern Pacific during El Nino events were caused by a weakening of the trade winds and consequent reduction of equatorial upwelling
  • The atmosphere and ocean form a coupled system: warm SSTs reduce the east-west pressure gradient, which weakens the trade winds, which further reduces upwelling, which further warms the SSTs – a positive feedback loop
  • He proposed the concept of the Walker Circulation as the atmospheric component of the coupled system

This work connected oceanic and atmospheric sciences and opened the entire field of tropical ocean-atmosphere interaction.

Key publication: Bjerknes, J. (1969). “Atmospheric teleconnections from the equatorial Pacific.” Monthly Weather Review 97: 163–172.

6. Military Service: Atomic Bomb Date Selection

During World War II, Jacob Bjerknes served as a colonel in the US Air Force. In this capacity, he helped determine the best dates for the atomic bombings of Hiroshima and Nagasaki, using his meteorological expertise to identify windows of clear weather over the target cities. Weather conditions were critical – the bombs had to be dropped visually.

7. Research with Holmboe at UCLA

At UCLA, Bjerknes worked with fellow Norwegian meteorologist Jorgen Holmboe on cyclone theory and pressure tendency research. Together they trained a generation of American meteorologists, including influencing the young Jule Charney.

Honours and Awards

Award Year
Honorary Member, Royal Meteorological Society 1932
Member, Norwegian Academy of Science and Letters 1933
Member, Royal Swedish Academy of Sciences 1933
Symons Gold Medal (Royal Meteorological Society) 1940
William Bowie Medal (American Geophysical Union) 1945
Knight 1st Class, Royal Norwegian Order of St. Olav 1947
Vega Medal (Swedish Society for Anthropology and Geography) 1958
International Meteorological Organization Prize (WMO) 1959
Carl-Gustaf Rossby Research Medal (AMS, highest honour) 1960
National Medal of Science (USA) 1966
American Academy of Achievement Golden Plate Award 1967

Personal Characteristics

  • Extraordinarily precocious – made a paradigm-shifting discovery at age 21 and another at 71
  • Deeply loyal to his father’s scientific legacy; continued and extended Vilhelm’s programme throughout his career
  • Generous mentor: Jacob Bjerknes wrote detailed letters of practical advice and career guidance to younger colleagues. His solicitude toward Charney (arranging income for Charney’s wife, suggesting faculty positions) demonstrates warmth beyond professional obligation
  • Worked with Swedish meteorologists Carl-Gustaf Rossby and Tor Bergeron as collaborators at Bergen

Connections to Other NWP Pioneers

  • Vilhelm Bjerknes (father): The two created the Bergen School together. Jacob provided the key observational insights that validated his father’s theoretical programme.
  • Jule Charney: Jacob Bjerknes was the leader of the UCLA meteorology group where Charney studied. Charney was deeply influenced by Bjerknes’s synoptic meteorology, even though Charney preferred more analytical approaches. Bjerknes wrote to Charney in Oslo with practical suggestions and arranged for Charney’s wife to earn money through translation work.
  • Jorgen Holmboe: Fellow Norwegian who was Charney’s direct supervisor at UCLA. Holmboe introduced Charney to meteorology.
  • Carl-Gustaf Rossby: Collaborated with Bjerknes at Bergen before going to the US to build American meteorology programmes.
  • Tor Bergeron: Joined the Bergen group and developed the Bergeron process for precipitation formation.
  • Halvor Solberg: Co-author with Jacob on the polar front dynamics papers.

Legacy

Jacob Bjerknes is one of the very few scientists to have made two completely distinct paradigm-shifting contributions to atmospheric science – the Norwegian cyclone model in 1919 and the ENSO mechanism in 1969, separated by half a century. The UCLA Department of Atmospheric and Oceanic Sciences, which he founded, remains one of the world’s leading centres for climate research.

Sources

  • “Jacob Bjerknes.” Wikipedia. https://en.wikipedia.org/wiki/Jacob_Bjerknes – Accessed: 2026-04-02
  • “Jacob Bjerknes.” Britannica. https://www.britannica.com/biography/Jacob-Bjerknes – Accessed: 2026-04-02
  • “Bjerknes, Jacob Aall Bonnevie.” Encyclopedia.com (Complete Dictionary of Scientific Biography). https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/bjerknes-jacob-aall-bonnevie – Accessed: 2026-04-02
  • “Jacob Aall Bonnevie Bjerknes.” Encyclopedia.com (Encyclopedia of World Biography). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/jacob-aall-bonnevie-bjerknes – Accessed: 2026-04-02
  • “Jacob Bjerknes.” IRI/LDEO Climate Data Library. https://iridl.ldeo.columbia.edu/maproom/ENSO/New/bjerknes.html – Accessed: 2026-04-02
  • “How a Father and Son Helped Create Weather Forecasting as We Know It.” CIRA/RAMMB. https://rammb.cira.colostate.edu/dev/hillger/pdf/Vilhelm_and_Jacob_Bjerknes.pdf – Accessed: 2026-04-02
  • “Bjerknes Discovers Fronts in Atmospheric Circulation.” EBSCO Research Starters. https://www.ebsco.com/research-starters/history/bjerknes-discovers-fronts-atmospheric-circulation – Accessed: 2026-04-02