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Benioff
particular area showed that they all occurred on a common structure, which he took to be a large inclined fault.
In 1952 he extended this concept to zones of deep earthquakes all around the Pacific Ocean, making many geologists aware of these large and deep structures; when plate
tectonics explained these regions of deep seismicity as
locations of subduction, they came to be called Benioff
zones. While Benioff used his strain-release methodology
to display other patterns of earthquake occurrence, this
approach was not much pursued by other seismologists.
Benioff, in his instrumental work in the 1950s, continued to pursue higher sensitivity at longer periods. One
stimulus for this was the observation on the strainmeter,
following a great earthquake in 1952, of signals with
about a one-hour period, which could be interpreted as
free vibrations of the whole Earth, a phenomenon known
from theory but never observed. Benioff improved the
performance of his strainmeter, and built new instruments
in quieter locations in California and (as part of the International Geophysical Year in 1957–1958) in Peru. When
the largest earthquake of the twentieth century occurred
in Chile in 1960, these instruments gave clear records of
free vibrations at many frequencies, inaugurating a new
branch of seismology. For his accomplishments Benioff
was elected to the National Academy of Sciences in 1953,
and received two awards, the Arthur L. Day Medal of the
Geological Society of America in 1957 and the William
Bowie Medal of the American Geophysical Union in
1965.
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
see what the ear might detect. He put this interest to more
direct use during World War II, when he and his engineering staff worked on radar and acoustics for the Submarine
Signal Company.
Benioff married Alice Silverman in 1929; they had
three children and divorced in 1953, after which he married Mildred Lent, with whom he had one child.
BIBLIOGRAPHY
WORKS BY BENIOFF
“Seismic Evidence for the Fault Origin of Oceanic Deeps.”
Bulletin of the Geological Society of America 60 (1949):
1837–1856.
“Earthquakes and Rock Creep.” Bulletin of the Seismological
Society of America 41 (1951): 31–62.
“Earthquake Seismographs and Associated Instruments.” In
Advances in Geophysics, vol. 2. New York: Academic Press,
1955.
With Frank Press and Stewart W. Smith. “Excitation of the Free
Oscillations of the Earth by Earthquakes.” Journal of
Geophysical Research 66 (1961): 605–619.
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Bergeron
OTHER SOURCES
Goodstein, Judith R. “Waves in the Earth: Seismology Comes to
Southern California.” Historical Studies in the Physical and
Biological Sciences 14 (1984): 201–230.
Press, Frank. “Victor Hugo Benioff.” Biographical Memoirs, vol.
43. Washington, DC: National Academy of Sciences, 1978.
Duncan Carr Agnew
BERGERON, TOR HAROLD PERCIVAL (b. Godstone, Surrey, England, 15 August
1891; d. Uppsala, Sweden, 13 June 1977), synoptic meteorology, cloud and precipitation physics, weather forecasting.
Bergeron was one of the principal scientists in the
Bergen School of Meteorology, which transformed this
science by introducing a new conceptual foundation for
understanding and predicting weather. While developing
innovative methods of forecasting, the Bergen scientists
established the notion of weather fronts and elaborated a
new model of extratropical cyclones that accounted for
their birth, growth, and decay. Bergeron is credited with
discovering the occlusion process, which marks the final
stage in the life cycle of an extratropical cyclone. Bergeron
also contributed to cloud physics, most notably the
description of the Bergeron-Findeisen process by which
precipitation forms inside a cloud containing both ice
crystals and water droplets.
The Early Years. Bergeron was born in England to
Swedish parents Armand Bergeron and Hilda Stawe.
Much later, evidence came to light in Sweden that Bergeron was one of several illegitimate children born to a radical Stockholm intellectual couple who were also owners
of a prominent newspaper. Bergeron, as with the other
children, was given to a well-chosen family abroad, with
money provided for his education in Sweden. His mother
knew Nils Ekholm, director of the Swedish Meteorological Institute (SMI), which proved valuable for the young
Bergeron. After receiving his BSc from the University of
Stockholm in 1916, Bergeron spent the summers taking
observations of visibility at different locations around
Sweden and returning to SMI in Stockholm during the
autumn to complete his research. He found that changes
in visibility seemed to be related to wind-shift lines (what
would be later called fronts). On 1 January 1919, Bergeron received the title of “extra assistant meteorologist” at
the reorganized SMI, later called the Swedish Meteorological and Hydrological Institute (SMHI). Within a few
months, the tiny core of the incipient Bergen School,
father and son Vilhelm and Jacob Bjerknes and Halvor
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Ci
CiStr
A Str
A Str
Ni
Ni
Warm air
Cold air
Cold air
Cold air
arm
W
fron
Cold
air
Cold air
nt
t
fro
Warm
air
(warm sector)
Co
ld
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CiStr
ACu (lent)
Ni
Cold air
ca
9km
A Str
Ni
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
new weather forecasting service.
The Bergen School and the Occlusion Process. In 1917,
the Bergen Museum (precursor of Bergen University)
called Vilhelm Bjerknes to a new professorship in meteorology. Bjerknes had been working in Leipzig on a research
program for creating an exact physics of the atmosphere
and ocean. In contrast, meteorologists at the time predicted weather primarily by often inaccurate empirical
rules of thumb and statistical insight. Upon coming to
Bergen in 1918, Bjerknes organized an experimental
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weather prediction service, directing a number of enthusiastic young scientists in developing new forecasting practices based on insight into physical processes. The impact
of the work performed in Bergen, combined with the
incubation of several high-quality scientists, had an
immense impact internationally on the burgeoning scientific field of meteorology.
Much of the earliest work in Bergen focused on
understanding the structure of extratropical cyclones,
storms outside the tropics responsible for most of the
weather in the midlatitudes (not violent tropical storms
like hurricanes). Based on the first summer’s forecasting,
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Jacob Bjerknes proposed in November 1918 a new model
for these disturbances which accounted for their asymmetric 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
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
(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
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 threedimensional representation by which a cold front and
warm front merged, resulting in the previously sandwiched warm air being lifted aloft. Without access to the
warm air fueling the storm, such a cyclone would weaken.
Eventually, Bergeron used the term occlusion for this
process, and the resulting boundary between the two cold
air masses was called an occluded front. By 1922, he convinced Jacob Bjerknes of the importance of this process to
the evolution of extratropical cyclones. This discovery,
along with Solberg’s concept of cyclone families, changed
the Bergen cyclone model from a static conceptualization
(Figure 1) into one that featured the entire life cycle of
birth, maturity, and death (Figure 2). Forecasters and theoreticians now had a model to help them understand the
processes affecting storm intensification and decay.
Occlusion is a seminal feature of the classic 1922
paper by Jacob Bjerknes and Halvor Solberg, “Life Cycle
of Cyclones and the Polar Front Theory of Atmospheric
Circulation,” yet Bergeron was not a coauthor. At the
time, Bergeron was in Stockholm where he was preoccupied with other tasks, including preparation of a supplemental manuscript, which never was completed. Bergeron
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Bergeron
a
b
c
d
e
f
g
h
Figure 2. Schematic life cycle of the extratropical cyclone model
proposed by the Bergen School of Meteorology with Bergeron’s
occluded front shown in panels e and f. Dashed lines represent
surface fronts; arrows represent streamlines of the flow.
was a perfectionist, oftentimes not completing publications for want of further analysis. And whereas Solberg
and the Bjerkneses accepted the need to simplify when
presenting the new findings, Bergeron aimed to depict all
the new insights in their full complexity. By temperament
and principle, he could not easily collaborate with the
others in writing what he considered a much too hastily
prepared publication. Although he was not a coauthor, his
Bergen colleagues always gave him full credit in discovering occlusion, the capstone of the Bergen school’s early
achievements.
Indirect Aerology and Air-Mass Analysis. To convince
others of the reality and importance of fronts, the Bergen
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0° C
ⴚ10° C
Figure 3. Sketch of the conditions (top) not favoring and
(bottom) favoring the Bergeron–Findeisen process. Dotted areas
represent clouds composed of liquid water droplets.
meteorologists needed to create systematic methods to
reproduce them reliably in daily forecasting work.
Although all members of the emerging Bergen school contributed towards this goal, Bergeron played a crucial role
in establishing innovative forecasting practices.
Bergeron collaborated with Swede and close friend
Ernst Calwagen to bring greater clarity to an ever-growing
number of new but elusive phenomena emerging from the
analysis of weather maps. To achieve this goal, they sought
to refine and systematize the Bergen group’s innovative
methods for observing and analyzing weather. They
brought to maturity a method of indirect aerology, to identify fronts and track the life history of large homogeneous
bodies of air called air masses. At a time when direct measurement of the atmosphere through weather balloons and
kites above the surface (aerology) was not available for
daily forecasting, this method combined observation of
the clouds and sky overhead with analyses of phenomena
plotted on the weather map to envision the physical
processes occurring in a three-dimensional atmosphere.
With the help of the Norwegian military air forces Calwagen began to supplement the indirect aerological methods
with direct vertical measurements in the atmosphere.
While taking observations on 10 August 1925, Calwagen
was killed along with the pilot after their airplane fell
apart in midair. Calwagen’s death deeply affected Bergeron—he never flew again. Bergeron took over his friend’s
work, integrated it with his own, and helped bring the
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Bergeron
methods of air-mass analysis to maturity. Indirect aerology
enabled the Bergen meteorologists to achieve more accurate and detailed predictions, as well as to gain insight into
the nature of fronts, cyclones, and air masses. For Bergeron as well as other members of the Bergen school, synoptic meteorology, or the study of the state of the
atmosphere at a specific moment in time on scales with a
range of several hundred kilometers, was a legitimate
means for winning new knowledge of the atmosphere, an
equal partner to theoretical and mathematical study.
The Bergeron-Findeisen Process. When Bergeron
returned to Bergen in 1922, he stopped for several weeks
at a health resort at Voksenkollen, a hill north of Oslo
often enclosed by fog. Bergeron noted that when the temperature was well below freezing the roads through the
forest were clear of fog. When the temperature was above
freezing, however, the fog would extend down to the
ground. Bergeron recognized that the saturation watervapor pressure over water is higher than that over ice at
temperatures below freezing. Thus, he surmised that diffusion of water vapor from evaporating supercooled liquid-water droplets in the fog to frost growing on the trees
might have been occurring to disperse the fog. Although
Alfred Wegener had already argued in 1911 that such
growth was possible in a cloud with both ice and water
droplets, Bergeron was the first to recognize that this
growth of the ice crystals to precipitation-sized particles at
the expense of the supercooled liquid-water droplets could
lead to precipitation. These ideas would be briefly developed in his doctoral thesis in 1928, and presented more
fully in 1933. Coupled with experimental confirmation
by the German Walter Findeisen in 1938, this process of
forming precipitation in a cloud possessing both ice crystals and supercooled liquid-water droplets was eventually
called the Bergeron-Findeisen process (sometimes called
the Wegener-Bergeron-Findeisen process). This discovery
promoted the subsequent growth of cloud physics as a
vital subdiscipline, not the least by providing a means to
dissipate fog and a physical mechanism for precipitation
enhancement through cloud seeding.
Apostle of the Bergen School. More than any other member of the Bergen School, Bergeron conducted the
detailed case studies, lectures, and travel needed to
develop grassroots support abroad for the Bergen School
concepts and methods. His role as apostle was facilitated
by his linguistic talents: he spoke seven languages and
knew some of three others.
While employed during the early and mid-1920s by
the Norwegian Meteorological Institute, Bergeron spent
time in Leipzig, working with Gustav Swoboda to demonstrate the applicability of the Bergen School concepts in
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an analysis of a weather event over Europe. “Wellen und
Wirbel an einer quasistationären Grenzfläche über
Europa” [Waves and vortices at a quasi-stationary frontal
surface over Europe] (1924) was the first detailed publication to use the methods developed in Bergen. Bergeron
wrote part 1 of his “Über die dreidimensional
verknüpfende Wetteranalyse” [Three-dimensionally combining synoptic analysis] in 1928, for which he received a
doctoral degree from the University of Oslo. That paper
covered many disparate topics, including air-mass analysis
and frontogenesis (the process of forming and strengthening a front). Bergeron recognized that fronts were found
in regions where the horizontal flow was confluent. What
had been considered an uninteresting singularity in the
field of flow—the neutral point or col—held the key for
understanding where and when fronts form. Bergeron
showed that such flows tended to occur between the semipermanent highs and lows, explaining the climatological
locations of fronts around the world.
After completing his doctorate, Bergeron traveled to
Malta and the Soviet Union to lecture on the Bergen
School methods. Part 2 of his doctoral thesis on fronts and
their perturbations was published in Russian in 1934. But
his overly critical demands prevented him from publishing his own research and completing several books. Still,
he produced several texts that played critical roles in the
diffusion of the Bergen meteorology. Although many of
Bergeron’s papers remained unpublished into the early
2000s, his popular lecture notes served as foundations of
major textbooks on synoptic meteorology written by his
colleagues in Russian, English, and German.
In 1935, Bergeron failed in his bid to be appointed
professor of meteorology at Uppsala University. Bergeron
and his many supporters from abroad could not overcome
local bias against synoptic meteorology, which was considered inferior to laboratory-based research, as well as a
long-standing resentment against Bjerknes and the “Norwegian” achievements with which he was intimately associated. Bergeron returned to Stockholm in 1936, initially
as a meteorologist, but eventually as scientific chief of
SMHI. He began giving lectures and conducting laboratory exercises in weather-map-analysis techniques based
on the Bergen methods. These proved popular, although
at times his perfectionist goals in map analysis and in the
wording of predictions created tension between him and
his meteorological colleagues working with him at SMHI.
Legend has it that he insisted on the exclusive use of a particular brand of colored pencils if accurate weather maps
were to be drawn. Within two years, however, the quality
of Swedish forecasting had significantly improved. Often
meteorologists came from abroad to Bergeron for training. During this time, Bergeron also served on the Commission of Synoptic Meteorology of the World
Meteorological Organization and was influential in the
development of the international terminology and classification of clouds and precipitation.
N E W D I C T I O N A RY O F S C I E N T I F I C B I O G R A P H Y
Uppsala University. By the time World War II ended,
Sweden had a great shortage of meteorologists, especially
for its rapidly growing aviation interests. Practical weather
forecasting classes were not offered at the universities, and
an official report indicated the need for a professorship in
this subject. Although efforts were underway to create
such a professorship for him in Stockholm, in 1947 Bergeron instead became professor and head of the Department of Synoptic Meteorology at Uppsala University.
Despite Bergeron’s reputation, finding students was difficult, especially after Carl-Gustaf Rossby established an
active department at Stockholm. Nevertheless, Bergeron
persisted in lecturing and writing on the principles of
meteorology.
Slowly he returned to the topic of cloud physics. In
1949, Bergeron posited that ice crystals could fall from
high-altitude clouds into liquid-water clouds below. Such
a seeder-feeder process could enhance precipitation at the
ground. He also wrote about the feasibility of artificially
stimulating the production of precipitation from a synoptic and cloud-physics perspective.
In 1953, Bergeron started Project Pluvius, a research
program designed to understand precipitation better by
establishing high-resolution surface rainfall networks.
Among its rich research results, Project Pluvius showed
that a modest elevation of only 40 to 70 meters could produce orographic precipitation enhancement. During the
last decades of his life, Bergeron wrote many articles and
lectures on the history of meteorology. He seems in part
to have been drawn to history after his unsuccessful bid
for a professorship in Uppsala in the mid-1930s. History
provided a way to set the record straight as to his own and
others’ contributions to the Bergen School, which is not
always clear from the publications. He also sought to show
what the Bergen School actually did accomplish, since the
originality of its contributions was, in part, denied by
some German, Austrian, and Swedish meteorologists. His
most important contribution from this time, “Weather
Forecasting: Methods in Scientific Weather Analysis and
Forecasting. An Outline in the History of Ideas and Hints
at a Program” (1959) offers a highly personal, but insightful, essay outlining the development of modern forecasting as the result of improvements in observations,
analytical tools, and models of atmospheric structures.
Bergeron retired in 1961, but continued to work on Project Pluvius, spending his time traveling and lecturing
worldwide, including several trips to the United States.
He died in 1977 of pancreatic cancer, the last of the original Bergen School meteorologists to do so.
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BIBLIOGRAPHY
BERGMANN, ERNST DAVID (b. Karl-
A complete bibliography for Bergeron can be found in Liljequist,
1981a. His correspondence and unpublished manuscripts are
housed in the Department of Meteorology, Uppsala University.
WORKS BY BERGERON
“Wellen und Wirbel an einer quasistationären Grenzfläche über
Europa.Analyse der Wetterepoche 9.–14. Oktober 1923.”
[Waves and vortices at a quasistationary frontal surface over
Europe. Analysis of the Weather Epoch 9-14 October 1923.].
Veröffentlichungen des Geophysikalischen Instituts der
Universität Leipzig, series 2, 3 (1924): 62–172.
Über die dreidimensional verknüpfende Wetteranalyse, I. Teil.
(Three-dimensionally combining synoptic analysis, part 1.)
Geofysiske Publikasjone 5. Oslo: Grøndahl & Sons
boktrykkeri, I kommission hos Cammermeyers boghandel,
1928.
Trechmerno-Svjaznyj Sinopticeskij Analiz, I-II. (ThreeDimensionally Combining Synoptic Analysis.) Moscow,
1934.
“Methods in Scientific Weather Analysis and Forecasting: An
Outline in the History of Ideas and Hints at a Program.” In
The Atmosphere and the Sea in Motion: Scientific Contributions
to the Rossby Memorial Volume, edited by Bert Bolin. New
York: Rockefeller Institute Press, 1959.
“Some Autobiographic Notes in Connection with the Ice
Nucleus Theory of Precipitation Release.” Bulletin of the
American Meteorological Society 59 (April 1978): 390–392.
OTHER SOURCES
Blanchard, Duncan C. “Tor Bergeron and His ‘Autobiographic
Notes.’” Bulletin of the American Meteorological Society 59
(April 1978): 389–390.
Bjerknes, Jacob, and Halvor Solberg. “Meteorological
Conditions for the Formation of Rain.” Geofysiske
Publikasjoner 2, no. 3 (1921): 3–60.
———. “Life Cycle of Cyclones and the Polar Front Theory of
Atmospheric Circulation.” Geofysiske Publikasjoner 3, no. 1
(1922): 3–18.
Eliassen, Arnt. “Tor Bergeron 1891–1977.” Bulletin of the
American Meteorological Society 59 (April 1978): 387–389.
Friedman, Robert Marc. Appropriating the Weather: Vilhelm
Bjerknes and the Construction of a Modern Meteorology. Ithaca:
Cornell University Press, 1989.
Liljequist, Gosta H. “Tor Bergeron: A Biography.” Pure and
Applied Geophysics 119 (1981a): 409–442.
Liljequist, Gosta H., ed. Weather and Weather Maps: A Volume
Dedicated to the Memory of Tor Bergeron (15.8.1891–
13.6.1977). Basel: Birkhäuser, 1981b.
Schwerdtfeger, Werner. “Comments on Tor Bergeron’s
Contributions to Synoptic Meteorology.” Pure and Applied
Geophysics 119 (1981): 501–509.
Robert Marc Friedman
David M. Schultz
250
sruhe, Germany, 18 October 1903; d. Jerusalem, Israel, 6
April 1975), organic chemistry, education, science policy in
Israel.
Bergmann, a German-Jewish chemist, was forced out
of his position in Berlin under Nazi laws and emigrated to
Mandate Palestine in 1934 to become the first director of
what was later the Weizmann Institute of Science. He subsequently aided the British scientific effort during World
War II. He is best known for leading the development of
science in the fledgling State of Israel, including the inauguration of its nuclear research program. Bergmann typified the close involvement of scientists in Israel with
political and defense matters. His research interests in
organic chemistry were extensive. He introduced German-style chemical research and teaching at the Weizmann Institute of Science and then at the Hebrew
University of Jerusalem.
Early Life in Berlin. Bergmann was born into a strongly
Zionist-leaning German family. In 1908, his father, Rabbi
Judah Bergmann, accepted a post in Berlin and moved
there with his mother, Hedwig Rosenzweig Bergmann,
and his brothers, Artur and Felix. Both brothers later held
influential positions in Israel, the latter as a pharmacologist.
Ernst David studied chemistry at the University of
Berlin, where in 1924 he began research for his doctoral
degree under the supervision of Wilhelm Schlenk. His
work involved investigations on polycyclic aromatic compounds, of great interest to the chemistry of synthetic
dyestuffs and, increasingly, in cancer studies. In 1927,
Bergmann was awarded his doctorate and in the following
year was appointed Privatdozent (lecturer) at the university’s chemical institute. In 1928, he married the chemist
Ottilie Blum, a research assistant in the institute. By then,
his outstanding scientific capabilities were widely recognized. In 1929, chemistry Nobel Laureate Richard Willstätter proposed that Bergmann become his successor to
the chair of chemistry at the ETH (Eidgenössische Technische Hochschule, or Federal Institute of Technology) in
Zurich; however, the more renowned Leopold Ruzicka
was appointed instead. With Schlenk, Bergmann in 1932
published the first volume of a textbook on chemistry,
Ausführliches Lehrbuch der Organischen Chemie, and was
the leading candidate for a vacant chair at the Technische
Hochschule in Berlin. Following passage of the antiSemitic Law for the Restoration of the Professional Civil
Service on 7 April 1933 under the Nazi regime, Bergmann
was not appointed to the Berlin position. On the contrary,
he was dismissed from his post as research assistant and
lost his venia legendi—his right to teach at a German university.
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