JOURNAL HIGHLIGHTS(202) 777-7507
hleifert@agu.org
| American Geophysical Union JOURNAL HIGHLIGHTS |
Contact: Harvey Leifert (202) 777-7507 hleifert@agu.org |
| 22 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.Smoke from forest fires can reach stratosphere 1. Smoke from forest fires can reach stratosphere Smoke from forest fires may have an underappreciated impact on the upper troposphere and a significant effect on atmospheric chemistry. Fromm and Servranckx provide evidence that dense smoke plumes from a Canadian forest fire in 2001 enhanced aerosol levels in the lower stratosphere, causing atmospheric effects similar to those seen after a volcanic eruption. Their report supports a new proposal of atmospheric transport between the troposphere and stratosphere and suggests that such a mechanism could play an important role in the distribution of atmosphere material and affect environmental conditions, including cloud formation and climate change. The authors also show that emissions from fires are capable of long-range transport, by tracing the movement of aerosols and emissions from a previous North American fire to Europe. They propose that the impact of this phenomenon will be heightened with warming temperatures in the high northern latitudes. Title: Transport of forest fire smoke above the tropopause by supercell convection Authors: Michael D. Fromm, Computational Physics, Inc., Springfield, Virginia; Rene Servranckx, Meteorological Service of Canada, Montreal, Canada. Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016820, 2003
2. New model to explain Great Salinity Anomalies A numerical model applied to study the ocean water-sea ice interactions preceding anomalous salinity levels in the North Atlantic may help explain variations in the fresh water supply coming from the Arctic. Haak et al. analyzed more than half a century of sea ice variability within the Arctic Ocean and the North Atlantic, combined with oceanic circulation and temperature data, to study the influence on the North Atlantic of the region's ice formation, propagation, and thickness changes. The authors created a new model that they suggest can explain the chain of processes before the onset of events known as great saltwater anomalies seen in the Labrador Sea during each of the past three decades. They report that the anomalies likely began in the Arctic and were not caused by atmospheric conditions in the Labrador Sea. Such anomalies affect the global thermohaline [vertical] circulation by preventing deep water formation in the Labrador Sea for several years. Title: Formation and propagation of great salinity anomalies Authors: H. Haak, J. Jungclaus, U. Mikolajewicz, Max-Planck-Institute for Meteorology, Hamburg, Germany; M. Latif, Oceanography Institute, University of Kiel, Germany. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017065, 2003
3. Volcanic sulfur released in aerosols from Indonesian forest fires The high sulfur content in smoke from Indonesian vegetation fires likely comes from sulfur emissions contained in volcanic gases that settle into the ground during the country's rainy season. Langmann and Graf suggest that hot and wet weather during the area's rainy season prevents the atmospheric dissipation of sulfur gases and that local rains deposit the chemicals into peat forests. They propose that a large portion of the sulfur accumulates in peat forests, which act as a sponge for rainwater laced with sulfur from the region's permanently degassing chain of island volcanoes. The authors posit that recent land use changes, combined with evaporation during the dry season, removes much of the water from the area's peat forests while leaving the sulfur. The dried peat is particularly flammable and when it ignites, releases vast quantities of sulfur back into the environment. Title: Indonesian smoke aerosols from peat fires and the contribution from volcanic sulfur emissions Authors: Baerbel Langmann, Hans F. Graf, Max-Planck-Institute for Meteorology, Hamburg, Germany. Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016646, 2003
4. New sulfur measurement from biomass burning The first measurement of a trace gas emitted from biomass burning indicates that enough sulfuric chemicals are released during the burning to affect regional atmospheric conditions. Meinardi et al. conducted the first analysis to estimate the levels of dimethyl disulfide (DMDS) from biomass burning, while also simultaneously estimating the concentrations of other similar gases from bush fires in Australia. The gases are a major source of sulfur-containing compounds in the region and can react in the atmosphere to form sulfuric acid and affect tropospheric chemistry. The researchers found that although DMDS emissions have a relatively short life span, they are produced in such quantity from burning and smoldering fires that they can have a significant effect on cloud formation, particularly when released during the nighttime, when atmospheric nitrogen levels are lower. Title: Dimethyl disulfide (DMDS) and dimethyl sulfide (DMS) emissions from biomass burning in Australia Authors: Simone Meinardi, Isobel J. Simpson, Nicola J. Blake, Donald R. Blake, F. Sherwood Rowland, University of California, Irvine, California. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL016967, 2003
5. New scaling factor may improve global circulation models Plugging a newly modified scaling factor into a commonly used global circulation model can help account for differences between observations and the model's results for determining cloud reflectivity. Peng and Lohmann propose a revised estimate for a variable used to calculate the size of water droplets in clouds, which they suggest may provide an improved method to study the influence of manmade aerosols on cloud physics. Increased aerosols from human activity are thought to reduce the droplet size, causing an effect that changes cloud reflectivity. Scientists have had difficulty projecting the amount of the reflectivity changes in global circulation models, leading to differences between observations and model projections. The authors compared model results using the new scaling factor with data from more than a dozen field studies and found that the revised method of determining the cloud properties more closely matched satellite observations of cloud reflectivity taken during the same time. Title: Sensitivity study of the spectral dispersion of the cloud droplet size distribution on the indirect aerosol effect Authors: Yiran Peng, Ulrike Lohmann, Dalhousie University, Halifax, Nova Scotia, Canada. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017192, 2003
6. Satellites find source of peculiar proton aurora Simultaneous satellite observations of the Earth's magnetic field by multiple spacecraft have provided the first direct link between the glowing northern and southern lights and a magnetospheric process known as magnetic reconnection. Phan et al. report a bright spot in the upper atmosphere seen by NASA's IMAGE spacecraft at the same time as the European Space Agency's four Cluster spacecraft passed through a stream of solar protons leaking through the Earth's magnetic shield. These protons were then funneled into Earth's atmosphere along magnetic field lines to create the unusual proton auroral spot. The authors suggest that the new information can provide a powerful tool to observe "cracks" in the magnetic shield that can be seen as proton aurora in the north and the south. [Note: See also AGU Press Release 03-13: http://www.agu.org/sci_soc/prrl/prrl0313.html] Title: Simultaneous Cluster and IMAGE observations of cusp reconnection and auroral proton spot for northward IMF Authors: Tai Phan, H. U. Frey, S. Frey, L. Peticolas, C. Carlson, S. Mende, J. McFadden, G. Parks, Space Science Laboratory, Berkeley, California; S. Fuselier, S. Petrinec, Lockheed Martin Advanced Technology Center, Palo Alto, California; H. Reme, J.-M. Bosqued, I. Dandouras, J.-A. Sauvaud, Center for Space Studies and Radiation, Toulouse, France; A. Balgh, Imperial College, London, United Kingdom; M. Dunlop, Rutherford Laboratory, Oxford, United Kingdom; L. Kistler, C. Mouikis, E. Moebius, University of New Hampshire, Durham, New Hampshire; B. Klecker, G. Paschmann, Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany; M. Fujimoto, Tokyo Institute of Technology, Meguro, Japan; M. F. Marcucci, Institute of Physics and Interplanetary Space, Rome, Italy; A. Korth, Max-Plack-Institute for Aeronomy, Katlenburg-Lindau, Germany; R. Lundin, Swedish Institute of Space Physics, Kiruna, Sweden. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL016885, 2003
7. New method to detect solar wind flow A new model that simulates the X-ray emissions produced by the interaction between solar winds and neutral hydrogen in the Earth's uppermost atmosphere may help researchers remotely detect the bow shock and the solar wind flow around the planetary magnetic field. Robertson and Cravens demonstrated that X-rays emitted from solar winds are partially diverted by the Earth's magnetic field just outside the magnetosphere. They created a model that shows the intensity of charged particles around the magnetosheath. The authors replicated the flow of particles emitted by the Sun, which react with interstellar space to produce X-rays and provide a constant background of radiation in space, on the planet's outer magnetic boundaries. They suggest that such information can be used to interpret the shape and strength of the magnetic field around the Earth. Title: X-ray emission from the terrestrial magnetosheath Authors: Ina P. Robertson, T. E. Cravens, University of Kansas, Lawrence, Kansas. Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016740, 2003
8. Finding day-night changes in cirrus clouds An analysis of long-term cirrus cloud data collected by ground-based polarization lidar [laser-based radar] reveals new insights into the day-night variability within the clouds that will help refine the results from existing climate models. Sassen et al. probed the ice crystal shape and orientation of the high clouds using seven years of observations, providing information that can be used to monitor the feedback between solar heating and cloud reflectivity. The authors found that laser light depolarization in cirrus clouds is slightly less during the day, indicating that absorption of sunlight changes the basic ice crystal shape, depending on whether the heat comes during the day or night. Their study of the natural and solar-induced orientation of ice crystals within the clouds is important to atmospheric forecasting because cirrus clouds regularly form in the upper troposphere and affect surface temperature and climactic variables. Title: Diurnal effects in the composition of cirrus clouds Authors: Kenneth Sassen, Geophysical Institute, University of Alaska, Fairbanks, Alaska; Kuo-Nan Liou, Yoshihide Takano, University of California, Los Angeles, California; Vitaly I. Khvorostyanov, Central Aerological Observatory, Moscow, Russia. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017034, 2003
9. New method to calculate fault growth A new equation that uses cumulative stress to help estimate the amount of strain needed for a fault to grow can help researchers calculate how much stress is needed to turn a minor quake into a major geologic fault. Richard A. Schultz presents a novel way to predict the total amount of stress that causes a fault to fail (brittle deformation), potentially solving a longstanding problem in Earth and planetary science and geology. His analysis of fracture dynamics ties together two areas that were previously considered unrelated: the connection between the amount of stress needed to cause a single episode like an earthquake and the amount of stress required to cause a larger fault to move, or slip. His formula is based on the ratio of stress on a fault, which has been determined from previous model studies on lithospheric materials, to the amount of movement in that particular fault. The equations, he concludes, can be generically applied to faults and tectonics problems on Earth and on Mars. Title: A method to relate initial elastic stress to fault population strains Authors: Richard A. Schultz, University of Nevada, Reno, Nevada. Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016681, 2003
10. Space shuttle exhaust may be partially responsible for polar clouds Water vapor contained in the exhaust plumes from the space shuttle's main engines can reach the Arctic and form polar mesospheric clouds in the upper atmosphere. Stevens et al. found that the shuttle and other launch vehicles may help explain the formation of the ice clouds. Water is a common effluent in many propellants like the fuel used to power the space shuttle. The authors used high-resolution spectrograph images and ground-based microwave observations to follow the 1,100 kilometer [680 mile] -long plume poleward after a 1997 shuttle launch from Cape Canaveral, Florida, providing a possible new source for the unusual clouds that has not been previously considered. Their findings show that ice clouds appeared in the polar sky approximately one week after the launch and they determined that the water content in the clouds is consistent with that injected by the shuttle exhaust. [Note: See also AGU Press Release 03-16: http://www.agu.org/sci_soc/prrl/prrl0316.html] Title: Polar mesospheric clouds formed from space shuttle exhaust Authors: Michael H. Stevens, Christoph R. Englert, Naval Research Laboratory, Washington, D.C.; Jorg Gumbel, Universities Space Research Association, Washington, D.C.; Klaus U. Grossman, University of Wuppertal, Wuppertal, Germany; Markus Rapp, Leibniz Institute for Atmospheric Physics, Kuhlungsborn, Germany; Paul Hartogh, Max-Planck-Institute for Aeronomy, Katlenburg-Lindau, Germany. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017249, 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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