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AGU Journal European Highlights - 9 July 2002

July 09, 2002

American Geophysical Union
AGU Journal European Highlights - 9 July 2002

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Contents
I. Highlights, including authors and their institutions
II. Ordering information for science writers

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I. Highlights, including authors and their institutions

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The following highlights are from Geophysical Research Letters
(GRL), the Journal of Geophysical Research-Space Physics
(JGR-A), and the Journal of Geophysical Research-Atmospheres
(JGR-D). The research papers related to these Highlights will be
printed in the next paper issues of the respective journals following
their electronic publication.

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2. Satellite explains lithospheric magnetism

New satellite observations of Earth`s surface magnetic field can
provide insights about the lithosphere and improve regional
magnetic-field models. Purucker et al. analyzed recently created
satellite maps of the lithospheric magnetic field and developed a
global model to explain previously observed phenomena, like
subsurface heat and crustal thickness, in more detail. They focus on
North America, specifically citing the unusually and unexpectedly
large magnetic field centered over Kentucky and spread throughout
the south-central United States. The authors suggest that the
anomaly marks the magnetic edge of the southern portion of thick,
long-stable (cratonic) North America, rather than simply an area of
stronger magnetization, as had previously been speculated. The
new data allows for interpretations of surface magnetism not
tainted by deeper-earth magnetic fields that have clouded previous
research efforts.

Title: "The southern edge of cratonic North America: Evidence
from new satellite magnetometer observations"

Authors:
Michael Purucker, Benoit Langlais, Goddard Space Flight Center,
Greenbelt, Maryland;
Nils Olsen, Danish Space Research Institute, Copenhagen,
Denmark;
Gauthier Hulot, Mioara Mandea, Institut de Physique du Globe de
Paris, Paris, France.

Source: Geophysical Research Letters (GRL) paper
10.1029/2001GL13645, 2002

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7. Listening to falling fireballs

If a meteor fell over Mongolia and no one was there to hear it,
would it still make a sound? Zgarblic et al. provide the beginnings
of an answer to that question, making the first recording of the
mysterious sounds from streaking Leonid fireballs. The researchers
listened to "popping" sounds from a pair of bolides during a 1998
meteor shower, noises that they are unable to fully explain.
Previous research noted the phenomenon of simultaneous sound
and flash in fireballs, which is unexpected because - as thunder
follows lightning - any noise from fireballs should be delayed due
to the speed difference between light and sound. Although the
authors were able to rule out the hypothesis that the sounds were
caused by vibrations from low frequency radio waves, they are
currently trying to determine the cause of the electrophonic sounds.
They speculate that even lower frequency radio waves may be
responsible for their observations.

Title: "Instrumental recording of electrophonic sounds from Leonid
fireballs"

Authors:
Goran Zgrablic, Neven Grbac, University of Zagreb, Zagreb,
Croatia;
Dejan Vinkovic, University of Kentucky, Lexington, Kentucky;
Slaven Garaj, Silvija Gradevcak, Swiss Federal Institute of
Technology (EPFL), Lausanne, Switzerland;
Damir Kovavcic, Scuola Internazionale Superiore di Studi
Avanzati (SISSA), Trieste, Italy;
Nikola Bilivskov, Zeljko Andreic, Rudjer Bovskovic Institute,
Zagreb, Croatia.

Source: Journal of Geophysical Research-Space Physics (JGR-A)
paper 10.1029/2001JA000310, 2002

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10. Humans responsible for most recent global warming

An analysis of more than 130 years of climate data provides the
most conclusive proof to date that humans are responsible for the
majority of the global warming seen during the past 50 years. Tett
et al. simulated natural and man-made temperature changes since
1860, using a detailed model that tracks virtually all major
atmospheric effects, and attribute the observed near-surface
warming trend to human activity. Their model found that natural
factors like solar radiation and volcanic eruptions have had
essentially no net effect on raising temperatures over the past
century and that the recent warming is most likely due to
increasing greenhouses gas concentrations. In fact, they speculate
that the observed increases would likely be greater if not for natural
conditions, such as cooling due to increases in sulphate aerosols
and internal variability, that serve to keep the temperatures lower.
The researchers estimate that the total human-caused warming
trend is approximately 0.5 degrees Kelvin [0.5 degrees Celsius; 0.9
degrees Fahrenheit] per century.

Title: "Estimation of natural and anthropogenic contributions to
twentieth century temperature change"

Authors:
Simon F. B. Tett, Gareth S. Jones, Peter A. Stott, John F. B.
Mitchell, William J. Ingram, Tim C. Johns, Colin E. Johnson,
Andy Jones, David L. Roberts, David M. H. Sexton, Margaret J.
Woodage, Hadley Centre for Climate Prediction and Research, Met
Office, Brackness, United Kingdom;
David C. Hill, University of Oxford, Oxford, United Kingdom;
Myles R. Allen, Rutherford Appleton Laboratory, Chilton, United
kingdom and University of Oxford, Oxford, United Kingdom.

Source: Journal of Geophysical Research-Atmospheres (JGR-D)
paper 10.1029/2000JD000028, 2002.

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American Geophysical Union (AGU)