AGU Journal highlights - 23 March 2005

03/23/05

Highlights, including authors and their institutions

The following highlights summarize research papers in Geophysical Research Letters (GL). The papers related to these Highlights are printed in the next paper issue of the journal following their electronic publication.

You may read the scientific abstract for any of these papers by going to http://www.agu.org/pubs/search_options.shtml and inserting into the search engine the portion of the doi (digital object identifier)following 10.1029/ (e.g., 2004GL987654). The doi is found at the end of each Highlight, below. To obtain the full text of the research paper, see Part II.

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1. Volcanic eruption produces smaller than expected climate effects

A new analysis of the 1991 Mount Pinatubo eruption suggests that volcanic eruptions may have a much smaller effect on the global climate than previously thought. Douglass and Knox quantified climate changes after the eruption in the Philippines and show that worldwide temperature change and the magnitude of climate response following the event are in contrast to most previous studies. The authors report a temperature decrease of approximately 0.5 degrees Celsius [0.9 degrees Fahrenheit] following the eruption and found that the climate effects lasted nearly seven months after the summertime blast. Such volcanic eruptions were previously thought to have much longer-term and widespread significance, with some predictions indicating that the volcanic material would produce effects similar to the accumulation of all man-made greenhouse gases since the industrial revolution. The current study, however, reveals a relatively short atmospheric response with no discernable effects from the volcanic events afterward.

Title: Climate forcing by the volcanic eruption of Mount Pinatubo

Authors: David H. Douglass, Robert S. Knox, University of Rochester, Rochester, New York, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL022119, 2005

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2. Linking North Atlantic Oscillation and greenhouse gases

An analysis using a dozen climate models suggests that the North Atlantic Oscillation (NAO) may intensify with further increases to greenhouse gas concentrations. Kuzmina et al. report on the Coupled Model Intercomparison Project, designed to investigate how the current generation of climate models reproduces the major features of the wintertime North Atlantic Oscillation and how the oscillation may have changed in response to increasing atmospheric carbon dioxide. The North Atlantic Oscillation modulates the jet stream over the Northern Hemisphere, dominating climate and atmospheric conditions over the globe. The researchers explored speculation that changes in greenhouse gas concentrations since the 1960s may have affected the periodic oscillation, using the models to compare theoretical with actual events since that time. They observed trends in recent decades indicating that the North Atlantic Oscillation index has shifted along with the increasing carbon dioxide, providing evidence that they interpret as a possible link between the North Atlantic Oscillation and greenhouse gases.

Title: The North Atlantic Oscillation and greenhouse-gas forcing

Authors: Svetlana I. Kuzmina, Nansen International Environmental and Remote Sensing Center, St. Petersburg, Russia;
Lennart Bengtsson, Max Planck Institute for Meteorology, Hamburg, Germany, and University of Reading, Reading, United Kingdom, and Nansen International Environmental and Remote Sensing Center, Bergen, Norway;
Ola M. Johannessen, Nansen International Environmental and Remote Sensing Center, Bergen, Norway, and University of Bergen, Bergen, Norway;
Helge Drange, Nansen International Environmental and Remote Sensing Center, Bergen, Norway, and University of Bergen, Bergen, Norway, and Bjerknes Center for Climate Research, Bergen, Norway;
Leonid P. Bobylev, Nansen International Environmental and Remote Sensing Center, St. Petersburg, Russia, and Bergen, Norway;
Martin W. Miles, Bjerknes Center for Climate Research, Bergen, Norway, and Environmental Systems Analysis Research Center, Boulder, Colorado, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL021064, 2005

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3. Determining clouds' electrical potential from satellite observations

Observations from instruments aboard the Tropical Rainfall Measuring Mission (TRMM) satellite can help refine existing estimates for the movement of water within clouds and may also allow researchers to remotely probe for electrical activity inside the cloud. Prigent et al. report that reflections from convective cloud systems obtained by the TRMM microwave instrument can provide significantly enhanced resolution over previous data, supplying greater details to help researchers resolve the intracloud structures associated with heat transfer from atmospheric motion. In addition, the authors used a lightning sensor on the satellite to analyze the electrical activity within the clouds, revealing information that could be used to develop and evaluate realistic cloud models that could account for electrical activity. The research may help resolve discrepancies in the small areas within clouds where the strongest heat transfer (convective) updrafts take place.

Title: Relations of polarized scattering signatures observed by the TRMM Microwave Instrument with electrical processes in cloud systems

Authors:
Catherine Prigent, National Center for Scientific Research, Paris Observatory, Paris, France;
Eric Defer, National Observatory of Athens, Athens, Greece;
Juan R. Pardo, Center for Scientific Research, Madrid, Spain;
Cindy Pearl, William B. Rossow, NASA Goddard Institute for Space Studies, New York, New York, USA;
Jean-Pierre Pinty, Aerology Laboratory, Toulouse, France.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL022225, 2005

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4. Recent solar storms likely led to Northern Hemisphere ozone reduction

The bombardment of Earth's space boundary by charged particles during the exceptionally strong solar storms of late 2003 likely led to a temporary increase in high-latitude nitrogen oxides in 2004 and enhanced ozone depletion. Randall et al. report that energetic particles stimulated nitrogen oxide production in the upper atmosphere in late 2003-early 2004 that later descended into Earth's stratosphere. Energetic particles have long been considered a stimulant for nitrogen oxide production in the upper atmosphere, which plays a major role in atmospheric chemistry. The authors suggest that energetic particles from the "Halloween" storms may have resulted in the fourfold increase in nitrogen compounds observed between March and July 2004. They note, however, that unusual meteorological conditions in the upper atmosphere or particle precipitation unrelated to the storms also contributed to the increase. The researchers confirm that the enhanced nitrogen led to significant reductions in ozone, with some Northern Hemisphere locations recording an approximate 60 percent decrease, amounts unprecedented since at least 1985.

Title: Stratospheric effects of energetic particle precipitation in 2003-2004

Authors: Cora E. Randall, V. L. Harvey, University of Colorado, Boulder, Colorado, USA;
G. L. Manney, NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA, and New Mexico Highliands University, Las Vegas, New Mexico, USA;
Y. Orsolini, Norwegian Institute for Air Research, Kjeller, Norway;
M. Codrescu, NOAA Space Environment Center and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA;
C. Sioris, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA;
S. Brohede, Chalmers University of Technology, Goteborg, Sweden;
C. S. Haley, York University, Toronto, Ontario, Canada;
L. L. Gordley, GATS, Inc., Newport News, Virginia, USA;
J. M. Zawodny, NASA Langley Research Center, Hampton, Virginia, USA;
J. M. Russell III, Hampton University, Hampton, Virginia, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL022003, 2005

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5. Simplified modeling method to estimate lava flow

A newly created two-dimensional lava flow model may be able to quickly estimate the direction and potential damage from magma following a volcanic eruption and serve as a warning system to residents near an active volcano. Costa and Macedonio created a relatively simple numerical model that can produce early predictions for the projected path of lava flow far sooner than traditional three-dimensional simulations. The researchers propose a generalized set of equations to describe lava flow propagation, overcoming more complicated and time-consuming methods typically used to model liquid flow. The authors' modeling technique was confirmed through testing by using real data from the 1991-1993 Mount Etna eruption in Italy, where it effectively reproduced the actual lava flow following the volcanic blast. They suggest that the preliminary results from their method indicate that the model may be a useful tool for forecasting lava flow paths for risk mitigation and predicting the damage from future eruptions.

Title: Numerical simulation of lava flows based on depth-averaged equations

Authors: Antonio Costa, Giovanni Macedonio, National Institute of Geophysics and Volcanalogy, Naples, Italy.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL021817, 2005

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6. Overestimating air pollution near forests

A finding that nitrous acid is formed during the daytime in forest environments and is broken down when it escapes the forest canopy may force researchers to revise their estimates for airborne pollutant concentrations near such areas. Kleffmann et al. provide one of the first analyses to measure a range of atmospheric hydrocarbons inside a forest, using data recorded during a 2003 field campaign in Germany. The authors found evidence of a large and unexplained daytime source of nitrous acid, a trace gas capable of enhancing the chemical breakdown of naturally produced emissions like volatile organic compounds, and propose that the unexpected nitrous acid may have a major impact on reducing air pollutant levels. The researchers suggest that if their observations are applicable to other forested areas, future models will likely need to modify their tropospheric assumptions in order to prevent overestimating air pollution estimates.

Title: Daytime formation of nitrous acid: A major source of OH radicals in a forest

Authors: Jorg Kleffmann, Traian Gavriloaiei, Bergische University-Wuppertal, Wuppertal, Germany;
Andreas Hofzumahaus, Frank Holland, Ralf Koppmann, Lutz Rupp, Eric Schlosser, Manfred Siese, Andreas Wahner, Institute for Chemistry and Geosphere Dynamics, Research Center of Julich, Inc., Julich, Germany.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL022524, 2005

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7. Mapping a bend in the Japan Trench

An ocean floor seismograph experiment has identified a bend in a major rupture zone near Japan that may help define the seismic structure around the active plate boundary. Ito et al. investigated the plate structure near the Miyagi forearc region of the Japan Trench, an area that has been responsible for at least three 7.0-magnitude quakes in each of the past three centuries, using a reflection technique to create an image of the subducted oceanic crust. The authors analyzed the subducting angle of the tectonic plate in the 15-kilometer [nine-mile] -deep rupture zone and note a significant shift where it abruptly "bends" downward from a nearly five degree angle to approximately 13 degrees. They also show that the bending point corresponds to one of the edges of the rupture zone, which leads them to propose that changes to the plate geometry may affect the propagation of earthquakes in the direction of the plate convergence.

Title: Bending of the subducting oceanic plate and its implication for rupture propagation of large interplate earthquakes off Miyagi, Japan, in the Japan Trench subduction zone

Authors: Aki Ito, Gou Fujie, Seichi Miura, Shuichi Kodaira, Yoshiyuki Kaneda, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan;
Ryota Hino, Tohoku University, Sendai, Japan.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL022307, 2005

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8. Better images of sprite discharges

High-speed imaging of lightning-like sprite discharges may help researchers better understand the short-lived and relatively rare phenomenon. Marshall and Inan report that detailed video observations of sprites at high frame rates reveal complex structures within the sprite flashes, including streamer-like channels and bead-shaped structures. Sprites are luminous events often observed above thunderstorms; previous research had identified shapes inside the flashes, but such analyses were complicated by technological limitations on the equipment. The authors used telescopic imaging and high-speed cameras able to record the duration of each shape with high-resolution images taken at approximately 1000 frames per second. They note the characteristics of the streamers and beads, including observations ranging from 1-2 millisecond durations for the streamers and up to 10 milliseconds for the beads, and demonstrate that the streamers, for example, show signs of propagation and often contain beads. The researchers suggest that even higher frame rates and resolution are necessary to gain greater knowledge about sprite discharges.

Title: High-speed telescopic imaging of sprites

Authors: Robert A. Marshall, U.S. Inan, Stanford University, Stanford, California, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL021988, 2005

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9. High-pressure tests on materials found in lower mantle

A high-pressure test of an analog for a common deep-Earth mineral may allow researchers to estimate the physical properties of materials in the planet's lower mantle. Liu et al. induced pressures greater than 16 gigapascals--more than 160,000 times the normal atmospheric pressure on the Earth's surface--on a perovskite material with a similar makeup as the ubiquitous deep-mantle perovskite MgSiO3 and analyzed the change in its physical makeup under the stress. The authors observed slight changes to its chemical bonds beginning at 6 gigapascals and a compression that that destroyed the perovskite crystal structure at pressures approaching 20 gigapascals. They suggest that the distinct material created under the extremely high-pressure conditions should be further studied to establish its properties and note that such research could help scientists better understand the mechanisms of perovskite, including the temperatures and pressures required for it to stabilize near the Earth's core.

Title: Octahedral tilting evolution and phase transition in orthorhombic NaMgF3 perovskite under pressure

Authors: H.-Z. Liu, H.-K. Mao, Argonne National Laboratory, Argonne, Illinois, USA, and Carnegie Institution of Washington, Washington, D.C., USA;
J. Chen, C. D. Martin, D. J. Weidner, State University of New York at Stony Brook, Stony Brook, New York, USA;
D. Hausermann, Argonne National Laboratory, Argonne, Illinois, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL022068, 2005

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10. Three-dimensional fault gouge evolution model

A new method to model the fracture of individual particles may allow researchers an improved technique to simulate fault dynamics. Abe and Mair describe a method to implement realistic grain fracture in three-dimensional numerical simulations of granular shear and suggest that such information could elucidate the development of the layer of fragmented rock known as fault gouge. Such gouge commonly exists in natural faults where the rough fault surfaces grind against each other. The researchers note that the evolution of the gouge layer, which influences the frictional strength and stability of faults, is important in understanding the earthquake potential in affected areas and propose that the new technique may be used to study the microprocesses within such fault zones. They present a new three-dimensional model of fault gouge development and confirmed their results with laboratory-created material that compared favorably to the grain fragment size and texture of natural gouge under shear stress.

Title: Grain fracture in 3D numerical simulations of granular shear

Authors:
Steffen Abe, University of Queensland, Brisbane, Australia;
Karen Mair, University of Oslo, Oslo, Norway.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL022123, 2005

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