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BERGERON, TOR HAROLD PER- Stimulus for This Was the Observation on the Strainmeter, CIVAL (B ndsbv1_B 9/25/07 4:30 PM Page 245 Benioff Bergeron particular area showed that they all occurred on a com- OTHER SOURCES mon structure, which he took to be a large inclined fault. Goodstein, Judith R. “Waves in the Earth: Seismology Comes to In 1952 he extended this concept to zones of deep earth- Southern California.” Historical Studies in the Physical and quakes all around the Pacific Ocean, making many geolo- Biological Sciences 14 (1984): 201–230. gists aware of these large and deep structures; when plate Press, Frank. “Victor Hugo Benioff.” Biographical Memoirs, vol. tectonics explained these regions of deep seismicity as 43. Washington, DC: National Academy of Sciences, 1978. locations of subduction, they came to be called Benioff zones. While Benioff used his strain-release methodology Duncan Carr Agnew to display other patterns of earthquake occurrence, this approach was not much pursued by other seismologists. Benioff, in his instrumental work in the 1950s, con- tinued to pursue higher sensitivity at longer periods. One BERGERON, TOR HAROLD PER- stimulus for this was the observation on the strainmeter, CIVAL (b. Godstone, Surrey, England, 15 August following a great earthquake in 1952, of signals with 1891; d. Uppsala, Sweden, 13 June 1977), synoptic mete- about a one-hour period, which could be interpreted as orology, cloud and precipitation physics, weather forecasting. free vibrations of the whole Earth, a phenomenon known Bergeron was one of the principal scientists in the from theory but never observed. Benioff improved the Bergen School of Meteorology, which transformed this performance of his strainmeter, and built new instruments science by introducing a new conceptual foundation for in quieter locations in California and (as part of the Inter- understanding and predicting weather. While developing national Geophysical Year in 1957–1958) in Peru. When innovative methods of forecasting, the Bergen scientists the largest earthquake of the twentieth century occurred in Chile in 1960, these instruments gave clear records of established the notion of weather fronts and elaborated a free vibrations at many frequencies, inaugurating a new new model of extratropical cyclones that accounted for branch of seismology. For his accomplishments Benioff their birth, growth, and decay. Bergeron is credited with was elected to the National Academy of Sciences in 1953, discovering the occlusion process, which marks the final and received two awards, the Arthur L. Day Medal of the stage in the life cycle of an extratropical cyclone. Bergeron Geological Society of America in 1957 and the William also contributed to cloud physics, most notably the Bowie Medal of the American Geophysical Union in description of the Bergeron-Findeisen process by which 1965. precipitation forms inside a cloud containing both ice crystals and water droplets. Benioff had a lifelong interest in acoustics and music, which led him to develop novel musical instruments and to experiment with listening to sped-up seismograms to The Early Years. Bergeron was born in England to see what the ear might detect. He put this interest to more Swedish parents Armand Bergeron and Hilda Stawe. direct use during World War II, when he and his engineer- Much later, evidence came to light in Sweden that Berg- ing staff worked on radar and acoustics for the Submarine eron was one of several illegitimate children born to a rad- Signal Company. ical Stockholm intellectual couple who were also owners Benioff married Alice Silverman in 1929; they had of a prominent newspaper. Bergeron, as with the other three children and divorced in 1953, after which he mar- children, was given to a well-chosen family abroad, with ried Mildred Lent, with whom he had one child. money provided for his education in Sweden. His mother knew Nils Ekholm, director of the Swedish Meteorologi- cal Institute (SMI), which proved valuable for the young BIBLIOGRAPHY Bergeron. After receiving his BSc from the University of WORKS BY BENIOFF Stockholm in 1916, Bergeron spent the summers taking “Seismic Evidence for the Fault Origin of Oceanic Deeps.” observations of visibility at different locations around Bulletin of the Geological Society of America 60 (1949): Sweden and returning to SMI in Stockholm during the 1837–1856. autumn to complete his research. He found that changes “Earthquakes and Rock Creep.” Bulletin of the Seismological in visibility seemed to be related to wind-shift lines (what Society of America 41 (1951): 31–62. would be later called fronts). On 1 January 1919, Berg- “Earthquake Seismographs and Associated Instruments.” In Advances in Geophysics, vol. 2. New York: Academic Press, eron received the title of “extra assistant meteorologist” at 1955. the reorganized SMI, later called the Swedish Meteorolog- With Frank Press and Stewart W. Smith. “Excitation of the Free ical and Hydrological Institute (SMHI). Within a few Oscillations of the Earth by Earthquakes.” Journal of months, the tiny core of the incipient Bergen School, Geophysical Research 66 (1961): 605–619. father and son Vilhelm and Jacob Bjerknes and Halvor NEW DICTIONARY OF SCIENTIFIC BIOGRAPHY 245 ndsbv1_B 9/25/07 4:30 PM Page 246 CiStr Ci A Str A Str Ni Warm air Ni Cold air Cold air Cold air W ar m front Cold air Cold air Warm air front (warm sector) Cold Ci CiStr ACu (lent) A Str ca Ni Ni 9km Cold air Warm air Warm air Cold air Ni ca 70km ca 200km ca 300km ca 500km Figure 1. Schematic of the extratropical cyclone model proposed by the Bergen School of Meteorology. Solberg, recruited Bergeron to Bergen, Norway, to join a weather prediction service, directing a number of enthusi- new weather forecasting service. astic young scientists in developing new forecasting prac- tices based on insight into physical processes. The impact The Bergen School and the Occlusion Process. In 1917, of the work performed in Bergen, combined with the the Bergen Museum (precursor of Bergen University) incubation of several high-quality scientists, had an called Vilhelm Bjerknes to a new professorship in meteor- immense impact internationally on the burgeoning scien- ology. Bjerknes had been working in Leipzig on a research tific field of meteorology. program for creating an exact physics of the atmosphere Much of the earliest work in Bergen focused on and ocean. In contrast, meteorologists at the time pre- understanding the structure of extratropical cyclones, dicted weather primarily by often inaccurate empirical storms outside the tropics responsible for most of the rules of thumb and statistical insight. Upon coming to weather in the midlatitudes (not violent tropical storms Bergen in 1918, Bjerknes organized an experimental like hurricanes). Based on the first summer’s forecasting, 246 NEW DICTIONARY OF SCIENTIFIC BIOGRAPHY ndsbv1_B 9/25/07 4:30 PM Page 247 Bergeron Bergeron Jacob Bjerknes proposed in November 1918 a new model for these disturbances which accounted for their asym- metric distribution of precipitation (Figure 1). The basic structure was described as a counterclockwise swirl of air around the low-pressure center. Warm air advancing from the south rose up over cold air retreating northward on ab the east side of the low center. The boundary between the two was ultimately called a warm front. On the southwest side of the low center, dense cold air advancing from the north lifted the warm air, forming a boundary later called a cold front. The recently ended World War I inspired using the word front to describe battle lines of advancing and retreating air masses. Bergeron would later suggest the symbols that came to be used for cold and warm fronts cd (lines with filled triangles and semicircles, respectively) on a postcard to Jacob Bjerknes on 8 January 1924. During the fall of 1919, Bergeron noticed that the cold front at times seemed to catch up to and overtake the warm front, what he dubbed sammenklapping (roughly “coming together” or “closing up”). He intuited that the cold front probably rode aloft over the warm front, but he remained puzzled over the nature and significance of this finding. It was not clear whether sammenklapping entailed ef an evolutionary component of extratropical cyclones or simply a local geographical effect. Furthermore, Jacob Bjerknes resisted changes to his model. While in Stockholm and Bergen, Bergeron returned on occasion to this baffling phenomenon. International efforts to increase the amount and frequency of weather data enabled Bergeron to bring into clearer focus the cyclone’s structure. He arrived at a convincing three- dimensional representation by which a cold front and gh warm front merged, resulting in the previously sand- wiched warm air being lifted aloft. Without access to the Figure 2. Schematic life cycle of the extratropical cyclone model warm air fueling the storm, such a cyclone would weaken. proposed by the Bergen School of Meteorology with Bergeron’s Eventually, Bergeron used the term occlusion for this occluded front shown in panels e and f. Dashed lines represent process, and the resulting boundary between the two cold surface fronts; arrows represent streamlines of the flow. air masses was called an occluded front. By 1922, he con- vinced Jacob Bjerknes of the importance of this process to the evolution of extratropical cyclones. This discovery, was a perfectionist, oftentimes not completing publica- along with Solberg’s concept of cyclone families, changed tions for want of further analysis. And whereas Solberg the Bergen cyclone model from a static conceptualization and the Bjerkneses accepted the need to simplify when (Figure 1) into one that featured the entire life cycle of presenting the new findings, Bergeron aimed to depict all birth, maturity, and death (Figure 2). Forecasters and the- the new insights in their full complexity. By temperament oreticians now had a model to help them understand the and principle, he could not easily collaborate with the processes affecting storm intensification and decay.
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