AGU Journal Highlights—31 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):
- Lightning strikes to tall objects
- Ice flow properties just prior to the disintegration of the Larsen B Ice Shelf
- Certain pollutants destroy stratospheric ozone faster than previously thought
- Reorientation of icy satellites by impact basins
- Estimating the size of a planet’s inner core, based on remote observations of its magnetic field
- Freshwater flow from Arctic watersheds may be increasing
- Carbon capture and sequestration are needed in addition to emission reductions to prevent temperature increases from global warming
- Warming temperatures affect seed dormancy, delaying the onset of spring vegetation south of 35 degrees north
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. Lightning strikes to tall objects
Multiple-station lightning detection networks typically locate lightning strikes that occur within tens to hundreds of kilometers [miles] of each station. They also derive peak currents of lightning strokes from measured magnetic field peaks. Because lightning detection networks are originally calibrated via lightning strikes to short objects, estimates of current strength assume that lightning strikes on flat ground. Baba and Rakov have developed a method to estimate lightning current strength from remote fields for strikes to tall structures, taking into account the multiple current waves traveling along the structure and the lightning channel. In particular, they derived far-field-to-current conversion factors for lightning strikes to tall objects for situations where the peak current is (1) the initial peak at the structure's top, (2) the largest peak at the structure's top, and (3) the peak current at the structure's base. The authors use these conversion factors to reexamine data from lightning detection networks and find that their analysis is generally consistent with experimental data, underscoring how such conversion factors are needed for proper interpretation of peak currents reported by lightning detection networks.
Title:
“Lightning strikes to tall objects: currents inferred from far electromagnetic field versus directly measured currents”
Authors:
- Yoshihiro Baba
- Department of Electrical Engineering, Doshisha University, Kyoto, Japan
- Vladimir A. Rakov
- Department of Electrical and Computer Engineering, University of Florida, Gainesville, Florida, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030870, 2007
2. Ice flow properties just prior to the disintegration of the Larsen B Ice Shelf
In 2002, the Antarctic Peninsula's Larsen B Ice Shelf rapidly disintegrated, an occurrence attributed to surface meltwater deepening preexisting crevasses in a progressively thinning ice shelf. Understanding this disintegration, which has been the subject of modeling studies on the fate of ice shelves in a warming climate, requires knowledge of rheology, an important parameter of ice flow, which depends on ice temperature, fabric, impurity, and water content. To better constrain this parameter, Khazendar et al. used satellite-derived observations of ice movement collected in 2000 on the Larsen B Ice Shelf to derive a detailed velocity map of the ice shelf relatively close to the time of its disintegration. From this, they inferred the ice's rheology and found that it exhibited large variability, likely due to the advection of colder ice from tributary glaciers, bottom melting, and the presence of strong shear and fracture zones. The authors demonstrate that variable rheology influences several aspects of ice shelf evolution, most importantly the close relationship among frontal retreat, fracture, ice flow acceleration, and ice shelf destabilization.
Title:
“Larsen B Ice Shelf rheology preceding its disintegration inferred by a control method”
Authors:
- A. Khazendar, E. Rignot, and E. Larour
- Jet Propulsion Laboratory, Pasadena, California, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030980, 2007
3. Certain pollutants destroy stratospheric ozone faster than previously thought
Stratospheric ozone protects our planet from the Sun's ultraviolet rays, which are harmful to biological tissue. In the past few decades, scientists have recognized the role human-made pollutants (e.g., CFCs and HCFCs) play in degrading the ozone layer. Precise knowledge of the rates of chemical reactions that destroy ozone is important to monitoring the effects of these ozone-depleting substances. Kovalenko et al. focus on the rate of formation of HOCl, a by-product of a reaction pathway that destroys ozone; the amount of HOCl in the atmosphere is indicative of the rate of ozone destruction by this pathway. The authors monitored stratospheric HOCl above Fort Sumner, New Mexico., using two balloon-borne instruments that relied on distinctly different measurement techniques. They compared these measurements with model calculations based on reaction rates used in recent ozone assessment studies and found that the model underestimates the observed HOCl abundance by a factor of two. They conclude that current assessment models likely underestimate the rate of stratospheric ozone depletion by this reaction pathway and recommend further study of this pathway.
Title:
“Observed and modeled HOCl profiles in the midlatitude stratosphere: Implication for ozone loss”
Authors:
- L. J. Kovalenko
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, U.S.A.; also at Columbus Technologies, Pasadena, California, U.S.A.
- K.W. Jucks
- Harvard Smithsonian Center for Astrophysics, Cambridge, Massachusetts, U.S.A.
- R. J. Salawitch, G. C. Toon, J.-F. Blavier, A. Kleinbohl, N. J. Livesey, H. M. Pickett, M. L. Santee, B. Sen, R. A. Stachnik, and J. W. Waters
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, U.S.A.
- D. G. Johnson
- NASA Langley Research Center, Hampton, Virginia, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL031100, 2007
4. Reorientation of icy satellites by impact basins
If struck by a large meteor, a planet or a moon can become deformed. This changes the moment of inertia of the planetary body, causing it to reorient itself with respect to its rotation axis. Though scientists have studied the possibility of such reorientations on the Earth, Moon, and Mars, less attention has been paid to reorientations on the outer solar system's icy satellites, many of which house large impact basins. Nimmo and Matsuyama considered these icy satellites and their impact basins, and through theoretical calculations predict that the largest basins on two of Saturn's moons (Tethys and Rhea) and on Uranus's moon Titania caused reorientations of roughly 4 degrees, 7 degrees, and 12 degrees, respectively. These reorientations would have significantly increased global tectonic stresses and along with other factors may complicate interpretation of the satellites' interior structure. The authors also expect that due to their slow rotation, Pluto and Charon, if they possess impact basins comparable in size to those of the Saturnian satellites, are likely to have reoriented 10–20 degrees.
Title:
“Reorientation of icy satellites by impact basins”
Authors:
- F. Nimmo
- Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California, U.S.A.
- I. Matsuyama
- Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington D.C., U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030798, 2007
5. Estimating the size of a planet’s inner core, based on remote observations of its magnetic field
Magnetic fields from planetary cores are generated by the planet's dynamo, whereby fluid motions in the liquid outer core stretch and twist existing magnetic fields to create new fields. Stanley et al. used a numerical model of a planetary dynamo to investigate whether distinct magnetic field patterns due to the presence of a solid inner core could be observed at the planet's surface or from an orbiting spacecraft. The authors find that it is possible to determine information on inner core size based on remote observations of intense, small-scale reversed magnetic flux patches. Further, they note that this type of study could help in determining the solid inner core size of Mercury, Ganymede, Jupiter, and Saturn. Particularly for Mercury and Ganymede, the authors anticipate that such knowledge of the inner core size would provide useful constraints on thermal evolution models for these bodies.
Title:
“Using reversed magnetic flux spots to determine a planet's inner core size”
Authors:
- S. Stanley
- Department of Physics, University of Toronto, Toronto, Ontario, Canada
- M. T. Zuber
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, U.S.A.
- J. Bloxham
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL030892, 2007
6. Freshwater flow from Arctic watersheds may be increasing
Streamflow from Arctic river basins has been increasing in recent decades in response to climate warming. Arctic discharge is a critical component of the freshwater budget of the Arctic Ocean, where increasing freshwater flows may slow rates of North Atlantic Deep Water formation and heat transport by the thermohaline circulation. However, quantifying rates for freshwater discharge from the entire Arctic drainage has been difficult using traditional stream gauging methods, because significant volumes of flow may bypass gauging stations and because a large fraction of the region is actually ungauged.. Syed et al. used satellite measurements of variations in continental water storage from the Gravity Recovery and Climate Experiment (GRACE) mission to present first estimates of monthly freshwater discharge from the entire Arctic region for 2003 to 2005. They find that discharge rates for this period are significantly larger than those suggested by gauge-based estimates. Further, results may indicate that discharge rates are accelerating.
Title:
“Contemporary estimates of pan-arctic freshwater discharge from GRACE and reanalysis”
Authors:
- T. H. Syed, J. S. Famiglietti
- Department of Earth System Science, University of California, Irvine, California, U.S.A.
- V. Zlotnicki
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, U.S.A.
- M. Rodell
- Hydrologic Sciences Branch, NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL031254, 2007
7. Carbon capture and sequestration are needed in addition to emission reductions to prevent temperature increases from global warming
After the recent release of the Fourth Intergovernmental Panel on Climate Change's Summary for Policy Makers, the issue of global warming has risen as a high priority within the governments of various cities, states, countries, and confederations. These governing bodies have begun discussing, and in some cases passing, legislation requiring specific greenhouse gas reductions by 2050. Weaver et al. used a coupled atmosphere/ocean/carbon cycle model to examine the long-term climate implications of various 2050 greenhouse gas emission reduction targets. They found that all emission targets considered with less than 60 percent global reduction by 2050 break the 2.0 degree Celsius [3.6 degrees Fahrenheit] threshold warming for this century, which some have argued represents an upper bound on manageable climate warming. Further, even when emissions are stabilized at 90 percent below present levels by 2050, the authors find that the 2.0 degree Celsius [3.6 degrees Fahrenheit] threshold is eventually broken. These results suggest that if a temperature increase of 2.0 degree Celsius [3.6 degrees Fahrenheit] is to be avoided, carbon capture and sequestration projects are needed in addition to sustained emission reductions.
Title:
“Long term climate implications of 2050 emission reduction targets”
Authors:
- Andrew J. Weaver, Kirsten Zickfeld, Alvaro Montenegro and Michael Eby
- School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL031018, 2007 (in press as of date)
8. Warming temperatures affect seed dormancy, delaying the onset of spring vegetation south of 35 degrees north
Warming climates are thought to advance the timing of spring leafing, flowering, and bud-burst in northern areas, but the delayed responses of vegetation phenology to rising temperatures in more southern regimes are poorly understood. Using satellite and climate data from 1982 to 2005, Zhang et al. found that from 40 degrees north northward, spring onset has advanced by 0.32 days each year. These regions have sufficient winter chilling duration, so a decrease in chilling days by warming winter temperatures has little impact on the thermal requirements for spring onset. However, south of 40 degrees north, the shortened winter chilling days are insufficient for certain seeds to overcome their dormancy, causing a delay in the onset of spring conditions. The authors found that vegetation green-up onset changes progressively from an early trend at 40 degrees north to a later trend through a latitude transition zone from 40 degrees to 31 degrees north, with the cusp of this switch occurring around 35 degrees north. Below 31 degrees north, the onset of spring has been delayed by 0.15 days each year. Furthermore, the transition zone shifts poleward by 0.1 latitude degree per year.
Title:
“Diverse responses of vegetation phenology to a warming climate”
Authors:
- Xiaoyang Zhang
- Earth Researches Technology Inc. at the Satellite Applications and Research; National Environmental Satellite, Data, and Information Service, National Oceanic and Atmospheric Administration, Camp Springs, Maryland, U.S.A.
- Dan Tarpley and Jerry T. Sullivan
- Satellite Applications and Research; National Environmental Satellite, Data, and Information Service, National Oceanic and Atmospheric Administration, Camp Springs, Maryland, U.S.A.
Source:
Geophysical Research Letters (GRL) paper doi:10.1029/2007GL031447, 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.
