JOURNAL HIGHLIGHTS(202) 777-7507
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| American Geophysical Union JOURNAL HIGHLIGHTS |
Contact: Harvey Leifert (202) 777-7507 hleifert@agu.org |
| 31 July 2003 |
| Contents I. Highlights, including authors and their institutions II. Ordering information for science writers |
| I. 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. 1.Predicting radio wave propagation through forests 1. Predicting radio wave propagation through forests A new prediction of the power of radio signals in forests may allow hikers and mountain climbers to stay in touch by cellular signals and could help firefighters better communicate while battling a blaze. Blaunstein et al. present an analysis of signal propagation through forests that considers the effect of reflectivity from branches and leaves and the signal absorption from vegetation found in the confined environment. Their study is the first to compare actual results from the topography of tree-filled forested areas with theoretical models of such waves through rough terrain. The researchers studied the short-range signal loss in forests, which presents different problems than urban areas. They also created a new model to examine signal propagation in Danish forests and determined the approximate error range in existing models with a degree of accuracy that could help scientists plan a cellular network to reach various forested areas worldwide. Title: Prediction of UHF path loss for forest environments Authors: Natan Blaunstein, Y. Ben-Shimol, D. Katz, Ben Gurion University of the Negev, Beer Sheva, Israel; I. Z. Kovacs, J. Bach Andersen, P. C. F. Eggers, R. Giladi, K. Olesen, Aalborg University, Aalborg, Denmark. Source: Radio Science (RS) paper 10.1029/2002RS002600, 2003
2. Special section on solar energetic particles Geophysical Research Letters features a collection of multidisciplinary papers about solar energetic particles, including analyses of data recently gathered by space- and ground-based instruments and presented during a 2002 NASA workshop. Nat Gopalswamy summarizes the results generated by researchers studying solar cycle 23, which peaked in 2001, and presents the scientific issues and data sets discussed at the meeting. The special section offers the first results from the collective study of solar and geospace connections of large solar energetic particle events, which bombard the Earth with high levels of particles that pose radiation hazards, affect aerospace technology, and have a significant bearing on our understanding of our planet's atmospheric chemistry. Other papers in the special section include a global view of the largest events from the current solar cycle, interactions among solar energetic particles and a study of some specific characteristics of solar particles. Title: Solar and geospace connections of energetic particle events Authors: Nat Gopalswamy, NASA Goddard Space Flight Center, Greenbelt, Maryland. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017277, 2003
3. Creating synthetic goethite Goethite, an iron compound commonly found in soil and sediment, is often used as an indicator of environmental change and for estimating heavy-metal pollution. Researchers have adapted a previously used technique to create nanometer-sized synthetic goethite crystals that can help researchers to create better models to simulate the environmental conditions that lead to the natural formation of the material. Guyodo et al. propose that their extremely small crystals are more like natural goethite particles than larger ones grown by other traditional methods and may allow researchers to better understand the growth and spread of the ubiquitous mineral. The authors' chemically constructed, rod-shaped goethite particles created in the laboratory grow uniformly around newly created crystals and can be readily identified among other minerals by electron microscopy because of their magnetic properties. Title: From nanodots to nanorods: Oriented aggregation and magnetic evolution of nanocrystalline goethite Authors: Yohan Guyodo, Alison Mostrom, R. Lee Penn, Subir K. Banerjee, University of Minnesota, Minneapolis, Minnesota. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017021, 2003
4. Three-dimensional model better simulates fault movement Existing two-dimensional models that simulate fault motion produce much lower estimates for friction than those that look at all three dimensions. Hazzard and Mair present a three-dimensional model of the impact of shear on layers of granular rock within fault zones and suggest that their results can provide a more realistic approximation of the strength and stability in a fault zone. Previous models largely simulated the movement of two-dimensional round particles during laboratory-created shearing conditions, which do not account for the interactions at multiple angles by loose rocks or represent the full range of motion between the materials. The authors suggest that their numerical model highlights the importance of the third dimension on friction in earthquake-prone faults and enables a more complex analysis of fault dynamics. Title: The importance of the third dimension in granular shear Authors: James F. Hazzard, Karen Mair, Lassonde Institute, University of Toronto, Toronto, Ontario, Canada. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017534, 2003
5. Fast-moving water may have created unusual Martian surface features Highly pressurized water spurting from troughs created by volcanic eruptions may have caused the unusual surface features observed on the Cerberus Plains of Mars. Head et al. analyzed the seemingly water-carved channels of Athabasca Valles and suggest that fast-moving water escaping from surface cracks in the past 20 million years can explain the loose rock formations and the dappled structure in the now-frozen terrestrial surface. Previous research had suggested that pressurized subsurface water, possibly raised by regional tectonic movement, could have lead to floods that formed the shapes seen in the Valles and Fossae regions. The authors' model simulated the surface effects from volcanic dikes and found that such activity could produce fractures and cracking capable of releasing groundwater confined beneath the cryosphere [permanently frozen surface] at speeds unprecedented on Earth. Title: Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release Authors: James W. Head, Brown University, Providence, Rhode Island; Lionel Wilson, Karl L. Mitchell, Lancaster University, Lancaster, United Kingdom. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017135, 2003
6. Asian pollution source may be increasing background ozone levels in U.S. Increasing nitrogen oxide emissions crossing the Pacific from Asia may be responsible for a 30 percent increase in background ozone levels on the west coast of the United States. Jaffe et al. found a strong correlation between higher background ozone concentrations in the western United States over the past 20 years and growing nitrogen oxide emissions in Asia. The authors compared multiple ozone records taken from California and along the U.S. Pacific coast to emissions from Asia since the mid-1980s and suggest that increases in ozone precursors like nitrogen from fertilizer and industrial sources are the likely source of the increase. They found that increasing background ozone along the west coast occurred during the same period that Asian nitrogen oxide emissions are known to have increased. Such emissions are known to cause ozone production and are readily transported across the Pacific. Title: Increasing background ozone during spring on the west coast of North America Authors: Daniel Jaffe, Heather Price, University of Washington, Bothell, Washington; David Parrish, Joyce Harris, National Oceanic and Atmospheric Administration, Boulder, Colorado; Allen Goldstein, University of California, Berkeley, California. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017024, 2003
7. Waterways indicate decline in terrestrial carbon levels Carbon dioxide levels have significantly decreased in waterways across the continental United States during the past two decades, indicating a reduction in terrestrial carbon dioxide levels and possible changes in the nation's aquatic carbon cycle. Jones et al. analyzed a 22-year database of carbon dioxide levels in more than 400 streams and rivers in the contiguous U.S. and report nationwide growth in carbon supersaturation, an unbalanced carbon load that they suggest is caused by organic decomposition exceeding natural carbon dioxide uptake. Such saturation also affects inorganic carbon concentrations in the waterways and can change the aquatic carbon cycle by influencing the water's acidity or alkalinity. The authors suggest that changes in microbial activity in soil caused by reductions in groundwater and river flow, increased nitrogen deposition, and the loss of wetlands in the latter part of the 20th century are the likely source of the supersaturation. Title: Long-term decline in carbon dioxide supersaturation in rivers across the contiguous United States Authors: Jeremy B. Jones, Jr. University of Alaska, Fairbanks, Alaska; Emily H. Stanley, University of Wisconsin, Madison, Wisconsin; Patrick J. Mulholland, Oak Ridge National Laboratory, Ok Ridge, Tennessee. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017056, 2003
8. Bias found in borehole climate reconstructions A new analysis of the impact of atmospheric factors on ground temperatures may provide new evidence for interpreting past environmental conditions from boreholes. Mann and Schmidt studied nearly half a century of modern atmospheric changes to the terrestrial Northern Hemisphere and suggest that snow cover, vegetation, and sub-surface thermal properties can skew temperature reconstructions taken solely from borehole measurements. The authors propose that such a bias could affect previous estimates of air temperature trends inferred from borehole samples, particularly temperature variations projected during the continent's cold season when ground temperatures are significantly affected by snow insulation and other air and surface conditions. They propose that surface air temperatures in past centuries may have been warmer than is suggested by borehole-based estimates. Title: Ground vs. surface air temperature trends: Implications for borehole surface temperature reconstructions Authors: Michael E. Mann, University of Virginia, Charlottesville, Virginia; Gavin A. Schmidt, NASA Goddard Institute for Space Studies and Center for Climate Systems Research, Columbia University, New York, New York. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017170, 2003
9. Another type of El Nino pattern? In addition to the well-known El Nino Southern Oscillation, another global-scale climate process may affect sea surface temperatures in the southern Pacific and conditions across the ocean basin. Montecinos et al. found evidence that suggests an interdecadal, basin-wide event from tropical to mid-latitudes in the south Pacific near Peru and Chile may help drive oceanic temperature conditions and the climate from South America to Asia. The authors compared nearly half a century of regional sea surface temperature data from stations along the South American coastline to global measurements, finding a pattern of elevated sea temperatures that could not be explained by known El Nino patterns. While previous analyses had similarly found two possible sources of sea surface temperature variations in the northern Pacific, the researchers propose that the phenomenon also occurs in the south. Title: Interannual-to-interdecadal sea surface temperature variability along the western coast of South America Authors: A Montecinos, S. Purca, O. Pizarro, University of Concepcion, Concepcion, Chile. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017345, 2003
10. Atmospheric dust may affect regional climate Dust transported from storms in the African desert is likely affecting clouds and climate conditions in North America. Sassen et al. collected data in Florida that suggests that Saharan dust is capable of causing an indirect aerosol effect on clouds that could modulate the region's climate. Particles from the African dust storms, which regularly cross the Atlantic and reach the Caribbean and the Southern United States during mid-summer, allow water droplets to freeze in supercooled clouds and form ice crystals at much warmer temperatures than usual. The authors used aircraft and polarization lidar data from the recent CRYSTAL thunderstorm study to identify the particles from Africa and found that the emissions have properties similar to those from Asia's Mongolian Desert, which has been shown to help initiate ice cloud formation in the western United States. Title: Saharan dust storms and indirect aerosol effects on clouds: CRYSTAL-FACE results Authors: Kenneth Sassen, University of Alaska, Fairbanks, Alaska; Paul J. DeMott, Colorado State University, Fort Collins, Colorado; Joseph M. Prospero, University of Miami, Miami, Florida; Michael R. Poellot, University of North Dakota, Grad Forks, North Dakota. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017371, 2003 ***** Journalists and public information officers of educational and scientific institutions (only) may receive one or more of the papers cited in the Highlights by sending a message to Harvey Leifert at hleifert@agu.org, indicating which one(s). Include your name, the name of your publication, and your phone and fax number. State whether you prefer to receive the paper(s) as pdf attachments by email or as a fax. Others should send a request to service@agu.org, citing the doi of the paper (number beginning 10.1029/....), to order a copy of the paper. The Highlights and the papers to which they refer are not under AGU embargo. Contact: Phone (direct): +1 (202) 777-7507 |
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