Scientist of the Decade Jacob Bjerknes

The Norwegian meteorologist Jacob Aall Bonnevie Bjerknes was born November 2, 1897, to modern meteorology's founder, Vilhelm Bjerknes, and Honoria Sophia Bonnevie in Stockholm, Sweden, where his father was a physics professor. Young Jacob was surrounded by an academic family—his aunt Kristine Bonnevie (1872-1948) was a zoologist and the first female professor in Norway.

Moving with his family to Christiania (later Oslo), where his father had been offered a professorship, Jacob remained in Norway to finish school when his father accepted the directorship of the Leipzig Geophysical Institute in Germany. When Vilhelm needed Jacob's assistance in Leipzig, the 19-year-old took over research on wind field convergence and published his first scientific paper ("Uber die Fortbewegung der Konvergenz—und Divergenzlinienjust" [On the movement of convergence and divergence lines]) before turning 20. Returning to Norway in 1917, Jacob took over forecasting for the west coast of Norway as he continued his research on convergence lines. Within the year, he published yet another important paper, this one on cyclone structure ("On the structure of moving cyclones"). His research on cyclone structure and development, and associated weather phenomena, continued throughout the 1920s and culminated in yet another often-cited paper ("Life cycle of cyclones and the polar front theory of atmospheric circulation"), which detailed his ideas on air mass and frontal analysis. Before he was 30, Jacob Bjerknes had an international reputation in meteorology.

Leaving forecasting behind in the 1930s, Bjerknes became a meteorology professor at the Bergen Museum so that he could concentrate on theoretical research. He was in demand as a speaker and traveled throughout Europe and to the United States lecturing on frontal dynamics. One of these lecture trips to the United States took place in July 1939. Bjerknes, his wife, Hedvig, and their children had anticipated being in the United States for eight months. Less than two months after their arrival, World War II started. Shortly thereafter, Germany invaded Norway. The Bjerknes family remained in the United States and became U.S. citizens.

Unable to return to Norway, Bjerknes needed a job in the United States. At the same time, the United States military needed thousands of trained meteorologists. Bjerknes was asked to lead a meteorological training program for the U.S. Air Force at the University of California, Los Angeles. Taking over the meteorological section of the physics department, he oversaw the training of servicemen and served as a consultant to the U.S. Army Air Corps.

After the war ended, the meteorology section expanded to become the meteorology department. With Bjerknes in charge, the department

As formal meteorological education became more available, national and international professional organizations became more organized. The International Meteorological Organization (IMO) had been active on an informal basis since 1880. By the end of the 1920s, the IMO was working to standardize the meteorological codes that were used to record and transmit observations via telegraph and teletype, the units of measure for observational elements such as pressure and temperature, and the symbols that were used on weather maps. Code standardization was a major achievement in promoting grew very rapidly and was soon a leading international center for teaching and research in the atmospheric sciences. He continued his work on cyclones and expanded it to include research on the general circulation of the atmosphere. By the end of the 1950s, Bjerknes decided to turn his attention to a relatively new field: air-sea interaction.

In his first investigations, Bjerknes examined the changes in sea surface temperature in the North Atlantic Ocean and determined that the sea surface temperature was tied to the strength of the westerly wind. In years when the westerlies were particularly strong, the water south of Iceland and Greenland would be exceptionally cold and the Gulf Stream outside the Grand Banks would be much warmer. After publishing several studies on the Atlantic, Bjerknes turned his attention to the Pacific.

The eastern Pacific Ocean, particularly the coastal waters near Peru, was known to be subject to an oceanographic phenomenon called El Niño—the change in sea surface temperature from cool to warm every two to five years. The nutrient-rich cool waters supported a strong fisheries industry, but when they were replaced by sterile warm waters the industry temporarily collapsed. Bjerknes turned his attention to determining the mechanism behind El Niño. He discovered that the local change in sea surface temperature was actually part of a change that affected the ocean and atmosphere of the entire equatorial Pacific.

Bjerknes also discovered that a very large expanse of the middle and eastern equatorial waters of the Pacific became almost 3.6°F (2°C) warmer than normal. This was a major difference. The increased temperature added heat and moisture to the atmosphere, significantly increasing rainfall on nearby land. The effects extended well beyond a few ocean islands. El Niño increased westerly winds in the northern Pacific that affected weather all across North America and into Europe.

As he continued his investigations of the connections between El Niño and global weather, Bjerknes discovered a tie between El Niño and the Southern Oscillation. The Southern Oscillation, originally discovered in the 1920s by the British scientist Sir Gilbert Walker (1868-1958), is a pulse of atmospheric pressure that occurs irregularly between the Pacific and Indian Oceans. Because of Bjerknes's investigations, meteorologists and oceanographers have a basic understanding of how the Southern Oscillation and El Niño processes affect the equatorial Pacific. Furthermore, the theoretical ideas behind these processes continue to affect the development of climate change theories.

Although he made lasting contributions in many areas of meteorology, perhaps Jacob Bjerknes made his most enduring, and lifesaving, contribution with his frontal cyclone model and its associated forecasting techniques. He continued his work as an active scientist until his death at age 77 on July 7, 1975.

the international nature of a discipline that does not respect political boundaries.

In the United States, the American Meteorological Society (AMS) had been established in 1920; it was open to both professional meteorologists and amateurs, who included anyone who had an interest in the weather. The mission of the AMS was to promote research and instruction in meteorology. Shortly after its founding, members formed 11 committees to address two areas: "the advancement and diffusion" of meteorology and "the development of numerous applications of meteo-

rology to human affairs." As reported in the first issue of its official publication, the Bulletin of the American Meteorological Society, committee chairmen actively sought to put both meteorology and climatology on a firm scientific footing through education from primary through graduate school.

Compared to more established scientific communities, meteorology and climatology remained small in the early 20th century. Basic and applied research on the atmosphere took on increased importance as the general public became more aware of commercial and military aviation, automobile travel, commercial shipping, agriculture, and the health-related effects of the weather. As the 1920s ended, research on atmospheric problems was about to pay off.

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  • futsum
    Why did Jacob Aall Bonnevie Bjerknes want to disciver the water cycle?
    7 months ago

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