AGU Journal Highlights—3 October 2007
Contents
- I. Highlights, including authors and their institutions
- II. Downloading/ordering instructions for science writers and general public
I. Highlights, including authors and their institutions
You may read the scientific abstract for any already-published paper by clicking on the link provided at the end of each Highlight. Or, if links are not active in this email, you can also read the abstract 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., 2007GL030276). The doi is found at the end of each Highlight below. To obtain the full text of the research paper, see Part II.
The following highlights summarize research papers in Geophysical Research Letters (GRL):
- Entering into the “greenhouse century”: A case study from Switzerland
- Changes in tropical precipitation under global warming
- Sea surface temperatures through time: A new sampling method for analyzing corals
- A study in angular momentum: Why and how does El Niño slow the spin of the Earth?
- Long-term drought severity variations in Morocco
- Atmospheric boundary layers muffle signals of volcanic tremor
- Electron spin transitions in lower mantle minerals
- Upper atmosphere lightning: Studying the behavior of halos
- Measuring pollution from ice cores
- Record U.S. warmth in 2006 was due to human influences
- Underwater acoustics: Remote estimates of the sonic layer depth
- Photodissociation of sulfuric acid
- A large terrestrial source of methyl iodide
- Interactions between two subducting plates under Tokyo
- Are Chinese loess deposits essentially continuous?
- Inferring crustal and mantle strength: Observations after a Mojave earthquake
- Particle deposition and clogging: Microstudies of colloids moving through pore spaces
Journalists and public information officers of educational and scientific institutions (only) may receive one or more of the papers cited in the Highlights (including pre-publication copies of articles listed as “in press”) by sending a message to Peter Weiss at pweiss@agu.org, indicating which one(s). Include your name, the name of your publication, and your phone number. The papers will be e-mailed as pdf attachments.
Members of the public can read the abstract of any published paper by clicking on the doi link in the source section, at the end of the highlight. The full scientific article is available for purchase through a link in the abstract.
The Highlights and the papers to which they refer are not under AGU embargo.
1. Entering into the "greenhouse century": A case study from Switzerland
Over the past few years, record-breaking warm seasons have affected many parts of the world, calling into question whether the anomalously warm weather over a relatively short time span is further evidence of global warming. Beniston investigated such warming trends in Switzerland and compared seasonal statistics to those simulated for the end of the 21st century for a "greenhouse gas" climate. The author found that peaks of minimum and maximum temperatures observed during some of the record seasons match well with scenarios for climate simulated by regional climate models, with 25–75% agreement. The author suggests that the anomalously warm seasons can serve as a preview of conditions that may occur with greater frequency in the future. Further, using current data as a proxy for the future allows scientists to assess hazards and risk associated with climate change. With this knowledge, adaptation strategies can be developed to mitigate future changes.
Title:
“Entering into the “greenhouse century”: Recent record temperatures in Switzerland are comparable to the upper temperature quantiles in a greenhouse climate”
Authors:
- Martin Beniston
- Institute for Environmental Science, University of Geneva, Geneva, Switzerland
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030144, 2007
2. Changes in tropical precipitation under global warming
Under global warming conditions, climate models show substantial regional precipitation changes in the tropics, but the spatial distribution of these changes varies significantly among these simulations. Using data from models and observations, Chou et al. sought to determine whether trends in tropical precipitation can be separated by hemisphere. Assuming that average precipitation rates of the past 20 years represent normal tropical conditions, the authors found a clear trend in precipitation changes induced by global warming, where an asymmetric pattern between tropical precipitation changes in the Northern and Southern hemispheres is locked with seasonal cycles of tropical convection. Specifically, during summer in the Northern Hemisphere, the average departure of precipitation rates from normal conditions in the tropics increases while the departure of the Southern Hemisphere's precipitation rates from normal tropical conditions decreases. The reverse happens during winter in the Northern Hemisphere. The authors suggest that their result implies an enhanced seasonal precipitation range between rainy and dry season, and an increased precipitation difference between Northern and Southern hemispheres.
Title:
“Asymmetry of tropical precipitation change under global warming”
Authors:
- Chia Chou
- Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan; also at Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan
- Jien-Yi Tu
- Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan
- Pei-Hua Tan
- Department of History and Geography, National Chiayi University, Chiayi, Taiwan
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030327, 2007
3. Sea surface temperatures through time: A new sampling method for analyzing corals
Coral skeletons have tremendous potential as high-resolution archives of past ocean conditions, but interpretations of skeletal chemistry in terms of ocean temperature are complicated by physiological “vital effects” and complex growth strategies. As a result, different corals growing in the same location can yield a broad range of reconstructed temperatures. Cohen and Thorrold developed a new, potentially more accurate way to extract temperature data from corals. The authors note that growth involves an initial extension (upward growth) of skeletal elements, followed by their subsequent thickening (outward growth). Upward growth is fast, but thickening is slow, often taking many months to a year. They realized that current sampling methods that combine the initial and thickening growth result in highly variable chemical signatures among different corals. The authors analyzed two species of Atlantic corals, selectively targeting the fast growing region at the centers of the skeletal elements. This method yielded similar temperature records from different colonies and different species. Using this approach, corals dating back to the late eighteenth century around Bermuda revealedsea surface temperatures about 1°C [nearly 2 degrees Fahrenheit] cooler than today.
Title:
“Recovery of temperature records from slow-growing corals by fine scale sampling of skeletons”
Authors:
- Anne L. Cohen and Simon R. Thorrold
- Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030967, 2007
4. A study in angular momentum: Why and how does El Niño slow the spin of the Earth?
During an El Niño event, the air around the equator is heated and expands upward, energizing westerly winds (or jet streams) and increasing the atmosphere's angular momentum. Because the angular momentum of the atmosphere-Earth system must be conserved, the solid Earth slows down, increasing the length of the day by roughly a thousandth of a second. However, scientists studying the solid Earth observe a lag of about a couple of months between the peak of an El Niño event and the strongest braking of the Earth's rotation. Dickey et al. sought to understand the reasons behind this lag. Through analysis of atmospheric, oceanic, and geodetic data from 1979 to 2004, the authors found that thermal winds rising from the contrast between tropical and subtropical air temperatures tend to maximize a couple months after the peak of an El Niño event, as the heated air spreads outward from the equator. The authors show that these winds drive the observed change in the length of day and account for the studied lag.
Title:
“Thermal wind forcing and atmospheric angular momentum: Origin of the Earth's delayed response to ENSO”
Authors:
- Jean O. Dickey, Steven L. Marcus, and Toshio M. Chin
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030846, 2007
5. Long-term drought severity variations in Morocco
Since the 1980s, northwestern Africa has experienced drought conditions, resulting in socioecological consequences, including reductions in agricultural productivity and drinking water supplies. Though largely related to precipitation changes, the persistence of this drought also seems to be forced by regional surface warming. Noting that long-term high-resolution records of climate are missing for North Africa, Esper et al. studied tree ring data collected from Atlas cedars in Morocco. Through reanalysis of tree ring data collected in the 1980s, combined with surveys of old growth collected in 2002, the authors identified drought occurrences back to 1049. They found that relatively wet conditions persisted for most of the period between 1450 and 1980, making the recent drought seem exceptional. The wet period was preceded by drier conditions spanning back to 1049. The pattern of dry to wet to recent dry conditions is similar to trends seen in records from North America. The authors suggest that this similarity might indicate global connections, possibly related to changes in solar irradiance or large-scale weather patterns such as El Niño.
Title:
“Long-term drought severity variations in Morocco”
Authors:
- Jan Esper, David Frank, Ulf Büntgen, and Ann Verstege
- Swiss Federal Institute for Forest, Snow and Landscape Research, Birmendsorf, Switzerland
- Jürg Luterbacher and Elena Xoplaki
- Institute of Geography and NCCR (National Centres of Competence in Research) Climate, University of Bern, Bern, Switzerland
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030844, 2007
6. Atmospheric boundary layers muffle signals of volcanic tremor
Acoustic monitoring of volcanic tremor allows scientists to observe changes in eruptive activity, particularly during periods of poor visibility. It complements seismic monitoring by helping scientists differentiate between pressure release near the surface and deeper subsurface activity. To monitor the propagation of low-frequency sound waves (infrasound) from Hawaii's Kilauea volcano, Fee and Garcés analyzed data from an infrasound array about 12.5 km [7.8 miles] from the active vent that continuously emits volcanic tremor at a relatively steady rate. Noting that the propagation of infrasound can be masked and muffled by winds and temperature changes at all altitudes, the authors sought to identify how interfaces in the atmosphere bend infrasonic signals. They found that the array hears more volcanic tremor at night, due likely to a nocturnal atmospheric boundary layer refracting sound back down to the array. Thus, correct interpretation of volcanic eruptions through infrasonic data requires a thorough knowledge of the regional atmospheric patterns that might disrupt the signal.
Title:
“Infrasonic tremor in the diffraction zone”
Authors:
- David Fee and Milton Garcés
- Infrasound Laboratory, University of Hawaii at Manoa, Hawaii, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030616, 2007
7. Electron spin transitions in lower mantle minerals
Understanding the high-pressure behavior of ferropericlase (Mg,Fe)O, likely the second most abundant mineral in Earth’s lower mantle, is important for modeling the chemistry and physics of the lower mantle. Previous experiments have shown that ferropericlase undergoes an electron spin transition at high pressures. Noting that the abundance of iron or manganese in the ferropericlase determines the pressure at which spin transitions occur, Fei et al. conducted high-pressure laboratory experiments on ferropericlase to better classify its behavior at lower mantle depths. They found that the pressure-induced spin transition in ferropericlase solid solutions results in a volume contraction at the spin crossover pressure, because of the reduction in the Fe+2 ionic radius at its low-spin state. The required transition pressure increases linearly with increasing ferrous oxide content. The authors also developed equations to determine the changes in bulk modulus seen at this transition, dependent on iron content. They anticipate that such data can be used to better model mantle dynamics, and expect that the existence of low-spin ferropericlase implies that the lower mantle might be denser than previously thought.
Title:
“Spin transition and equations of state of (Mg,Fe)O solid solutions”
Authors:
- Yingwei Fei, Li Zhang, Alexendre Corgne, Heather Watson, and Angele Ricolleau
- Ricolleau: Geophysical Laboratory, Carnegie Institute of Washington, Washington D.C., U.S.A.
- Yue Meng
- Meng: High Pressure Collaborative Access Team, Carnegie Institute of Washington, Argonne, Illinois, U.S.A.
- Vitali Prakapenka
- GeoSoilEnviro-Center for Advanced Radiation Studies, University of Chicago, Argonne, Illinois, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030712, 2007
8. Upper atmosphere lightning: Studying the behavior of halos
Most lightning occurs between clouds and the ground when negative or positive charge in the cloud reequilibrates with opposite charge on the ground (called negative/positive cloud-to-ground lightning), forming a bolt of energy. However, lightning can also propagate upward from the cloud, forming transient luminous events (TLEs). To determine patterns in TLEs, Frey et al. analyzed data over Central America from the Imager for Sprites and Upper Atmospheric Lightning (ISUAL) aboard Taiwan's FORMOSAT 2 spacecraft. The authors specifically focused on halos, a class of transient luminous event consisting of brief, diffuse flashes of light with diameters less than 100 km [60 miles] at about 70–90 km [40-55 miles] in altitude, which are conventionally thought to be residuals of positive cloud-to-ground lightning. Instead, results showed that all halos were created by negative cloud-to-ground lightning that occurred almost exclusively over the open water; only three out of 31 observed events occurred over land. The authors conclude that the Central American region seems to be a location that favors the generation of halos by negative cloud-to-ground lightning.
Title:
“Halos generated by negative cloud-to-ground lightning”
Authors:
- H. U. Frey and S. B. Mende
- Space Sciences Laboratory, University of California, Berkeley, California, U.S.A.
- S. A. Cummer and J. Li
- Electrical and Computer Engineering Department, Duke University, Durham, North Carolina, U.S.A.
- T. Adachi
- Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Japan
- H. Fukunishi and Y. Takahashi
- Geophysics Department, Tohoku University, Sendai, Japan
- A. B. Chen, R.-R. Hsu and H.-T Su
- Physics Department, National Cheng Kung University, Tainan, Taiwan
- Y.-S. Chang
- National Space Program, Hsinchu, Taiwan
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030908, 2007
9. Measuring pollution from ice cores
Organic and elemental carbon in snow and ice can be used as chemical signatures of pollution. While elemental carbon is believed to be stable, the concentration of organic compounds in snow and ice may be affected by postdepositional processes. To study this, Hagler et al. analyzed snow from the Greenland ice sheet's surface and from a 3-m [10-foot] snow pit. Within the snow pit, they found that water-soluble organic carbon comprises about 89% of carbonaceous species, followed by water-insoluble particulate organic carbon (10%) and particulate elemental carbon (1%). The enhancement of organic carbon relative to elemental carbon suggests that gaseous organics are a major source of organic carbon found in snow. Comparisons of summer surface snow in 2006 with summer snows uncovered by the snow pit from 2002 to 2005 reveal that the ratio of organic carbon to elemental carbon decreases significantly for three of the four surveyed years. The substantial loss of organic carbon in aged snow suggests that postdepositional processes, such as photochemical reactions, must be considered before linking ice core records of organics to atmospheric concentrations.
Title:
“Particulate and water-soluble carbon measured in recent snow at Summit, Greenland”
Authors:
- Gayle S. W. Hagler and Eugene A. Smith
- School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia, U.S.A.
- Michael H. Bergin
- School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia, U.S.A.; and School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, U.S.A.
- Jack E. Dibb and Casey Anderson
- Climate Change Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire, U.S.A.
- Eric J. Steig
- Department of Earth and Space Sciences, University of Washington, Seattle, Washington, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030110, 2007
10. Record U.S. warmth in 2006 was due to human influences
Early this year, NOAA issued a statement indicating that 2006 was the warmest in the 112-year record for the contiguous United States. However, it was unclear how much of that warming was due to human influences stemming from increasing greenhouse gases or natural influences stemming from El Niño warming of the equatorial eastern Pacific Ocean. To quantify the degree to which different factors contributed to this record warming, Hoerling et al. analyzed historical records of U.S. temperatures observed during past El Niño years and model simulations of sea surface temperatures under El Niño conditions; they compared these data with last year's estimates of greenhouse gas concentrations. Through statistical methods that yield estimates of temperature anomalies related to each forcing, they found that neither historical data nor model simulations revealed a U.S. warm response to El Niño. Instead, over half of the anomalous warmth in 2006 is attributed to greenhouse gas forcing, whose strength overprints natural fluctuations. The authors conclude that the record warmth was due primarily to human influences.
See also AGU Press Release 07-21 of 28 August 2007.
Title:
“Explaining the record of U.S. warmth of 2006”
Authors:
- Martin Hoerling, Jon Eischeid, Xiaowei Quan, TaiYi Xu
- Earth System Research Laboratory, U.S. National Oceanic and Atmospheric Administration, Boulder, Colorado, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030643, 2007
11. Underwater acoustics: Remote estimates of the sonic layer depth
Accurate use of underwater acoustic data, information critical to generating navigational charts and maps of the ocean floor, requires knowledge of sound speed profiles throughout the water column, in particular the near-surface depth, where sound speed is fastest. Called the sonic layer depth (SLD), this depth determines where sound waves refract; knowledge of SLD location is used to reduce errors in sonar surveys. Since direct observations of SLDs at all locations in the ocean are difficult to obtain, Jain et al. sought to determine whether remote observations could be used to determine SLDs. Using surface measurements and measurements collected from moorings on the Arabian Sea and an artificial neural network (ANN-- an information processing system of highly interconnected pathways inspired by the human brain), the authors estimated SLDs. Their estimates agree well with known vertical profiles of the Arabian Sea and are more accurate than previous methods used to estimate SLD remotely. They anticipate that instead of using data from moorings, future estimates can be generated by ANNs using satellite data.
Title:
“Estimation of sonic layer depth from surface parameters”
Authors:
- Sarika Jain and M. M. Ali
- National Remote Sensing Agency, Hyderabad, India
- P. N. Sen
- University of Pune, Pune, India
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030577, 2007
12. Photodissociation of sulfuric acid
Sulfuric acid, one of the main ingredients in the formation of aerosol particles, affects Earth's climate by scattering incoming solar radiation. The acid is responsible for nucleating aerosols and clouds in the troposphere, stratosphere, and mesosphere. At the top of the stratosphere, sunlight triggers the dissociation of sulfuric acid into sulfur trioxide and water, which descend to lower altitude and upon encountering more moist air, produce aerosols. In a theoretical study, which simulated atmospheric conditions, Miller et al. investigated the photodissociation of sulfuric acid and calculated the yield and rate with which the acid molecules break down as a function of altitude. They found that at higher altitudes in the stratosphere and mesosphere, low-energy sunlight can efficiently dissociate sulfuric acid to satisfy modeling requirements and explain field observations of aerosols, cloud condensation nuclei, and previously measured vertical profiles of sulfur dioxide.
Title:
“Photodissociation yields for vibrationally excited states of sulfuric acid under atmospheric conditions”
Authors:
- Yifat Miller
- Department of Physical Chemistry and Fritz Haber Research Center, The Hebrew University, Jerusalem, Israel
- R. Benny Gerber
- Department of Physical Chemistry and Fritz Haber Research Center, The Hebrew University, Jerusalem, Israel; and Department of Chemistry, University of California, Irvine, California, U.S.A.
- Veronica Vaida
- Department of Chemistry and Biochemistry, and the Cooperative Institute for Research in Environmental Science, University of Colorado, Boulder, Colorado, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030529, 2007
13. A large terrestrial source of methyl iodide
It has been known that methyl iodide, a compound that influences ozone chemistry and aerosol formation in the atmosphere, is released primarily from the ocean. Sive et al. recently identified terrestrial sources of methyl iodide using a synthesis of field observations, including research flights over the United States and the North Atlantic, a ground-based atmospheric observation network in New England, and a field campaign at Duke Forest, North Carolina. The authors found that about 2,700 nanograms of methyl iodide per square meter are released each day from midlatitude vegetation and soils, a value similar in magnitude to previous estimates of the oceanic source strength. They expect that similar studies to measure methyl iodide emitted from tropical and boreal areas will improve flux estimates and facilitate the development of a more accurate global budget for methyl iodide.
Title:
“A large terrestrial source of methyl iodide”
Authors:
- Barkley C. Sive, Ruth K. Varner, Huiting Mao, and Robert Talbot
- Climate Change Research Center; Institute for the Study of Earth, Oceans, and Space; University of New Hampshire, Durham, New Hampshire, U.S.A.
- Donald. R. Blake
- Department of Chemistry, University of California, Irvine, California, U.S.A.
- Oliver W. Wingenter
- Department of Chemistry, New Mexico Tech, Socorro, New Mexico, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030528, 2007
14. Interactions between two subducting plates under Tokyo
Japan's Tokyo region has been hit by disastrous earthquakes throughout recorded history. Noting that the Eurasian, Philippine Sea, and Pacific plates meet underneath Tokyo, Wu et al. sought to identify how interactions between these three plates influence regional seismic hazards. Previous studies have shown that the Philippine Sea plate subducts to the north on top of the westward subducting Pacific plate. The authors conducted high-resolution studies of the region underneath Kanto, using tomographic techniques, an imaging method similar to medical CT scans. They found that as the Pacific plate shoals under Japan, the Philippine Sea plate is being forced into an increasingly tighter space between the Pacific and Eurasian plates. As a result, zones of enhanced seismicity appear not only under the top and bottom of the Philippine Sea plate where it contacts the Eurasian and Pacific plates, but also within the Philippine Sea wedge that is being squeezed. The authors indicate that knowledge of such seismic interactions under Tokyo can help explain unique hazards faced by the city.
Title:
“Interaction between two subducting plates under Tokyo and its possible effects on seismic hazards”
Authors:
- Francis Wu
- Department of Geological Sciences, Binghamton University, Binghamton, New York, U.S.A.
- David Okaya
- Department of Earth Sciences, University of Southern California, Los Angeles, California, U.S.A.
- Hiroshi Sato and Naoshi Hirata
- Earthquake Research Institute, University of Tokyo, Tokyo, Japan
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030763, 2007
15. Are Chinese loess deposits essentially continuous?
China's Loess Plateau, composed of alternating deposits of ancient soils and glacial dust (loess) spanning the past 2.6 million years, is one of the most complete terrestrial records of past climate and magnetic field signals. Because scientists cross-reference these records to other known chronologies, it is critically important to establish the precision of Loess Plateau data. Zhu et al. used paleomagnetic techniques to analyze glacial loess of three representative profiles along a transect in the central Loess Plateau. They found that two profiles recorded a known episode of severely weakened magnetic field intensity, called the Laschamp geomagnetic excursion, which occurred between 39,000 and 41,000 years ago. This suggested that sedimentation of glacial loess in the area surveyed was continuous at the timescale equivalent to the Laschamp excursion (about 2,000 years), but probably episodic at finer timescales. No geomagnetic excursion was found in their third profile, where loess accumulation may be discontinuous. The authors recommend that both site location and timescale must be considered when evaluating the continuity of Chinese loess.
Title:
“Are Chinese loess deposits essentially continuous?”
Authors:
- Rixiang Zhu, Rui Zhang, Chenglong Deng, and Yongxin Pan
- Paleomagnetism and Geochronology Laboratory (SKL-LE), Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
- Qingsong Liu
- National Oceanography Centre, University of Southampton, Southampton, U.K.
- Youbin Sun
- State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, China
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030591, 2007
16. Inferring crustal and mantle strength: Observations after a Mojave earthquake
The strength of Earth's outer layers and their ability to resist deformation are important factors in determining earthquake hazards in seismic zones. To study this, Freed et al. sought to infer the strength of the lithosphere under California's Mojave Desert by treating local earthquakes as large rock deformation experiments. Using a wide-ranging network of GPS instruments spanning more than 200 km [120 miles] from the epicenter of the 1999 Hector Mine earthquake, the authors found that a broad pattern of transient deformation occurred in the seven years following the earthquake. These data were compared with predictions from numerical models of various postseismic relaxation mechanisms, including viscous flow in the lower crust and upper mantle, rebound associated with crustal fluids, and after-slip. Only flow in the upper mantle below a depth of 40 km [20 miles] was able to generate the pattern of displacements seen at large distances. This comparison pointed to only one possible scenario: The mantle is weaker than the lower crust (a “crème brûlèe” structure), and the mantle flows over a wide region rather than within a narrow shear zone beneath the fault.
Title:
“Far-reaching transient motions after Mojave earthquakes require broad mantle flow beneath a strong crust”
Authors:
- Andrew M Freed
- Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana, U.S.A.
- Ronald Bürgmann
- Department of Earth and Planetary Science, University of California Berkeley, Berkeley, California, U.S.A.
- Thomas Herring
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030959, 2007
17. Particle deposition and clogging: Microstudies of colloids moving through pore spaces
When small particles are dispersed in a liquid, the resulting mixture is called a colloid. In Earth and environmental science, knowledge of how colloidal particles disperse and settle in porous regions of Earth's crust is important to extracting petroleum, monitoring pollution transport, and treating wastewater. Prior efforts to understand particle deposition processes have been limited by the coarse resolution of measurements, so Gaillard et al. conducted microtomography experiments on an idealized colloid moving through a porous medium of glass beads. By using the sudden increase in the X-ray absorption coefficient that characterizes the presence of an element, the authors were able to visualize particle deposition and the dynamics of clogging. They found that local pore geometry controls particle deposition and that deposits tend to form in a heterogeneous manner.
Title:
“Imaging of colloidal deposits in granular porous media by X-ray difference micro-tomography”
Authors:
- Jean-François Gaillard, Cheng Chen, Susa H. Stonedahl, Boris L. T. Lau, and Aaron I. Packman
- Department of Civil and Environmental Engineering, Northwestern University, Evanston, Illinois, U.S.A.
- Denis T. Keane
- DuPont-Northwestern-Dow Collaborative Access Team Synchrotron Research Center, Advanved Photon Source, Argonne, Illinois, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030514, 2007
II. Downloading/ordering information for science writers and general public
Journalists and public information officers of educational and scientific institutions (only) who have registered with AGU for direct electronic access to selected research papers may download one or more of the reports cited in the Highlights (including pre-publication copies of articles listed as “in press”) by following the direct-access instructions below. Journalists and public information officers who have not registered for direct access may receive papers by contacting Peter Weiss (pweiss@agu.org, +1 202 777 7507), indicating which one(s). Include your name, the name of your publication, and your phone number. The papers will be e-mailed as pdf attachments.
Direct-Access Instructions: Each journalist or public information officer who has requested direct electronic access to selected AGU papers and received a reply email providing a username and password can download pdf files of one or more of the papers cited in the Highlights as follows: Click on the link at the end of the Highlight regarding the paper of interest. When you activate the dx.doi.org link you should be directed immediately to an abstract. Once there, click on the hyperlink at the top of the abstract, which says "Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF." Clicking on it will take you to a page that asks you to log in. There, click on “click here” of the first option. That takes you to another Web page that asks for the username and password. Enter your username and password, then click on Submit. Now you should find yourself at the HTML version of the full article. It has a navigation bar on the left, with a link at the bottom entitled "PDF for Print". Click on that link and you should see the pdf of the selected paper appear on your screen. If you have any questions or problems with downloading, please contact Peter (pweiss@agu.org, +1 202 777 7507).
Anyone not a member of the press can also access any of the already-published AGU papers in this set of Highlights and purchase them for $9.00 apiece. To do so, follow the Direct Access Instructions above to the stage at which a username and password are submitted. At that point, click on the “Purchase Article” link at the bottom of the Web page.
