News Release

AGU journal highlights -- Feb. 1, 2007

Peer-Reviewed Publication

American Geophysical Union

  1. Astrobiology and the Martian radiation environment

    Although the surface of Mars is currently barren, evidence exists that past Martian environments were warmer, wetter, and possibly able to sustain life. Modern Mars lacks, however, a global magnetic field or thick atmosphere, and the surface is exposed to high levels of cosmic radiation. To determine whether life can survive today, Dartnell et al. modeled the propagation of solar energetic protons and galactic cosmic rays through the Martian atmosphere and through several surface scenarios. Their results show that the ionizing radiation environment on or beneath the Martian surface is never lethal to even radiosensitive bacteria, assuming potential life on Mars is similar to that on Earth. The authors note that freezing conditions on the Martian surface imply that any cells must be dormant. Because radiation will eventually deactivate dormant cells, the sampling of any surviving life requires that near-surface cells must periodically revive to repair radiation damage and reproduce and/or be excavated from sufficient depths. Deep rock layers impart their own radiation environments, so promising candidates for such excavation include frozen crater lakes or the putative frozen sea at Elysium.

    [See also AGU Press Release 07-03 of 29 January 2007: http://www.agu.org/sci_soc/prrl/2007-03.html]

    Title: "Modeling the surface and subsurface Martian radiation environment: Implications for astrobiology"

    Authors:
    L. R. Dartnell: Center for Mathematics & Physics in the Life Sciences and Experimental Biology, University College London, London, United Kingdom;
    L. Desorgher: Physikalisches Institut, University of Bern, Bern, Switzerland;
    J. M. Ward: Department of Biochemistry and Molecular Biology, University College London, London, United Kingdom;
    A. J. Coates: Mullard Space Science Laboratory, University College London, United Kingdom.

    Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL027494, 2007


  2. Three-dimensional models help decontaminate tide gauge records for glacial isostatic adjustments

    Determining actual changes in sea level using the globally distributed network of tide gauges requires that data be corrected for ongoing glacial isostatic adjustments ["rebound" of land mass that had been pushed down by the weight of the glacial ice] in response to the last ice age. These corrections, derived from the average of isostatic effects at selected tide gauge sites, yield values between 1.5 and 2.0 millimeters per year [0.06 and 0.09 inches per year]. Since global averages obscure geographic variations in isostatic trends, Kendall et al. investigated the potential impact of lateral variations in viscosity of Earth's mantle and thickness of the lithosphere [Earth's crust and upper mantle] on predictions of present-day sea level change due to glacial isostatic adjustments. They used three models, with differing variables. Through simulations of 300 tide gauges, they found that the difference between one-dimensional and three-dimensional model predictions exceeded 0.5 millimeters per year [0.05 inch per year] at 75 sites. The authors suggest that three- dimensional models of mantle structure should be used to decontaminate tide gauge records for ongoing glacial isostatic adjustment.

    Title: "Decontaminating tide gauge rectors for the influence of glacial isostatic adjustment: The potential impact of 3-D Earth structure"

    Authors:
    Roblyn A. Kendall, Konstantin Latychev, Jerry X. Mitrovica, and
    Jonathan E. Davis: Department of Physics, University of Toronto, Toronto, Ontario, Canada;
    Mark E. Tamisiea: Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, U.S.A.

    Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL028448, 2006


  3. Using seismic noise to image volcanoes in three dimensions

    Piton de la Fournaise, a basaltic volcano located on the Indian Ocean's Réunion island, is one of the most active volcanoes in the world. Over the last two centuries, eruptions have occurred almost every year. Detailed structural images of volcanic interiors can theoretically be constructed through analysis of earthquake data, but are hampered by irregular distributions of earthquake sources. Brenguier et al. sought to dissect seismic noise retrieved from Piton de la Fournaise, in order to gain understanding about the three- dimensional interior of the volcano. By using surface waves extracted from seismic noise, the authors developed a three- dimensional seismic wave velocity model of the volcano. This model agrees well with previous results and allows the authors to image the shape of the magma conduit system. Further, they performed a preliminary study showing that a few months of seismic noise data will yield similar three-dimensional results to that obtained from a full year's data, suggesting that their method could be applied to other volcanoes in order to improve volcanic hazard assessment.

    Title: "3D surface wave tomography of the Piton de la Fournaise volcano using seismic noise correlations"

    Authors:
    Florent Brenguier and Michel Campillo: Laboratoire de Géophysique Interne et Tectonophysique, Université Joseph Fourier, and Centre National de la Recherche Scientifique, Grenoble, France;
    Nikolai M. Shapiro and Alexandre Nercessian: Institute de Physique du Globe de Paris, Centre National de la Recherche Scientifique, Paris, France;
    Valérie Ferrazzini: Observatoire Volcanologique du Piton de la Fournaise-Institute de Physique du Globe de Paris, La Plaine des Cafres, La Réunion, France, and Institute de Physique du Globe de Paris, Centre National de la Recherche Scientifique, Paris, France.

    Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL028586, 2007


  4. Autonomous underwater vehicle maps cold-water coral morphology and distribution

    The study of cold-water corals, which are corals that exist at all latitudes but require no sunlight, has been limited by the coarse resolution of bathymetric surveys taken from the ocean surface. Because understanding the distribution and genesis of cold-water corals requires maps of morphology and oceanographic conditions at the 1-10 meter [3-30 feet] scale, Grasmueck et al. deployed an autonomous underwater vehicle into the waters off the southern coast of Florida at the base of the slope of the Great Bahama Bank. The vehicle, which cruised 40 meters [100 feet] above the seafloor (600-800 meters [2,000-3,000 feet] below sea level) and surveyed a 48 square kilometer [19 square mile] area, acquired acoustic backscatter data, as well as current vectors, salinity, and temperature information. The survey resolved more than 200 coral mounds, and the authors found that mound distribution followed an east-west orientation, despite prevailing tides that move along a north-south orientation, a result that challenges current ideas of coral mound development. The authors suggest that investigations with similar spatial resolution may challenge other existing paradigms about the formation and morphology of cold-water corals.

    Title: "Autonomous underwater vehicle (AUV) mapping reveals coral mound distribution, morphology, and oceanography in deep water of the Straits of Florida"

    Authors:
    Mark Grasmueck, Gregor P. Eberli, David A. Viggiano, Thiago Correa, and Jiangang Luo: Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, U.S.A.;
    Glenda Rathwell: Quester Tangent, Sidney, British Columbia, Canada.

    Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL027734, 2006


  5. Rapid intensification, eyewall contraction and breakdown of Hurricane Charley (2004) near landfall

    Tropical cyclones that rapidly intensify before landfall, such as hurricanes Andrew (1992), Opal (1995), and Charley (2004) have caused tremendous damage to coastal regions of the United States Though sporadic onsite and remote sensing data suggest that the intensification of these hurricanes was accompanied by eyewall contraction, little is known about the exact mechanism that couples eyewall contraction with hurricane intensification, because airborne, onsite, and remote sensing data typically lack adequate spatial resolution. Hurricane Charley was, nevertheless, continuously monitored with Doppler radar in three dimensions every six minutes by stations in Key West and Tampa Bay, Florida. Using these data and a technique to obtain three dimensional kinetic structure from a single station's Doppler radar observations, Lee and Bell analyzed Hurricane Charley's rapid intensification and eyewall contraction. They determined that the hurricane's central pressure dropped significantly over a period of three hours, accompanied by an unstable vortex during eyewall contraction. The vortex became stable after the hurricane reached its peak intensity. The eyewall then broke down during the decaying stage after landfall.

    Title: "Rapid intensification, eyewall contraction and breakdown of Hurricane Charley (2004) near landfall"

    Authors:
    Wen-Chau Lee and Michael M. Bell: Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, Colorado, U.S.A.

    Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL027889, 2007


  6. Predicting geomagnetic storms from the solar wind

    Streams of charged particles ejected from the Sun, known as the solar wind, interact with Earth's magnetosphere to produce geomagnetic storms that can damage power grids and satellites. Predicting geomagnetic activity from upstream solar wind data depends on finding a "coupling function" that correlates solar wind parameters with geomagnetic activity indices. Lyatsky et al. developed a coupling function and tested it against four years of data on the solar wind and interplanetary magnetic fields. They find that their theoretical model correlates well with actual space environment parameters, surpassing other commonly used coupling functions.

    Title: "A coupling function for solar wind effect on geomagnetic activity"

    Authors:
    W. Lyatsky, Sonya Lyatskaya, and Arjun Tan: Department of Physics, Alabama A&M University, Normal, Alabama, U.S.A.

    Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL027666, 2007


  7. Typhoon kicked up solitary waves off Korea's coast

    Satellites frequently observe distinct wave packets superimposed on familiar ocean-current patterns. In September 2003, approximately 19 hours after typhoon Maemi passed across the east coast of Korea, a satellite using synthetic aperture radar observed such waves, known as internal solitary waves, propagating both onshore and offshore. Nam et al. analyze ocean buoy data in the vicinity and hypothesize that the unusual waves formed in response to typhoon winds and downwelling jets of water interacting with sharp variations in the sea floor. The waves could have originated at a series of ridges 28 kilometers [17 miles] off the coast, the scientists propose. If so, then buoy measurements and models of solitary- wave propagation suggest that the waves formed six hours before the satellite detected them, or about 13 hours after the typhoon passed over the area.

    Title: "Typhoon-induced, highly nonlinear internal solitary waves off the east coast of Korea"

    Authors:
    SungHyun Nam: Seoul National University, Seoul, Korea; now at Agency for Defense Development, Jinhae, Korea;
    Duk-jin Kim: University of Michigan, Ann Arbor, Michigan, U.S.A.;
    Hyoung Rok Kim and Young-Gyu Kim: Agency for Defense Development, Jinhae, Korea.

    Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL028187, 2007


  8. Gas cloud near Saturn squelches electron intensity

    As the Cassini spacecraft orbits Saturn, it passes through a region of high concentrations of neutral atoms and molecules. This neutral gas cloud limits the lifetimes of ions and electrons with energies from a few to hundreds of kiloelectronvolts. This means that many charged particles detected inside the cold gas cloud by Cassini are remnants of populations injected within the previous few days. Paranicas et al. model these injections into the cloud, showing how electron populations disperse in the gas cloud and lose intensity. In one detailed case study, they show that even though the spacecraft encountered electrons at different energies and distances during its closest approach to the planet, those populations can be traced back to a single injection which occurred approximately two Earth days earlier.

    Title: "Energetic electrons injected into Saturn's neutral gas cloud"

    Authors:
    C. Paranicas, D. G. Mitchell, E.C. Roelof, B. H. Mauk, S. M. Krimigis, P.C. Brandt, M. Kusterer, F. S. Turner, and J. Vandegriff: Applied Physics Laboratory, The John Hopkins University, Laurel, Maryland, U.S.A.;
    N. Krupp: Max-Planck-Institut fuer Sonnensystemforschung, Lindau, Germany.

    Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL028676, 2007


  9. First maps of nighttime clouds on Mars

    The first mapping of Mars' nighttime clouds of water ice reveals that they are thicker and more extensive than the planet's daytime clouds. Water-ice clouds form prominent belts over the planet's tropics in the season when Mars is the farthest away from the Sun. Past simulations have highlighted the importance of those clouds to the Martian water cycle and suggested that the cloud belt undergoes daily cycles of opacity. Wilson et al. achieve nighttime-cloud mapping by identifying the clouds' influence on temperatures observed by an instrument aboard the Mars Global Surveyor spacecraft. Maps of atmospheric absorption derived from the spacecraft's laser altimeter corroborate the new mapping technique and show the insulating effect of nighttime clouds, the researchers say.

    Title: "The diurnal variation and radiative influence of Martian water ice clouds"

    Authors:
    R. John Wilson: Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, U.S.A.;
    Gregory A. Neumann and Michael D. Smith: NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A.

    Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL027976, 2007


  10. Will earthquakes cause big breaks?

    The probability of an earthquake fault rupturing along multiple segments affects predictions of earthquake rates and violence. Currently, panels of experts estimate those odds by sharing their opinions. Shaw and Dieterich have devised a way to use numerical simulations to calculate the probability of ruptures jumping from segment to segment. They find that the likelihood of such a jump decreases exponentially as the distance between segments increases. Probabilities determined from their approach, which the researchers continue to develop, may refine seismic hazard maps used by earthquake-prone communities, they suggest.

    Title: "Probabilities for jumping fault segment stepovers"

    Authors:
    Bruce E. Shaw: Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, U.S.A.;
    James H. Dieterich: Department of Earth Science, University of California, Riverside, California, U.S.A.

    Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL027980, 2007


  11. Plasma waves and newly formed ions near Jupiter

    Inside Jupiter's and Saturn's magnetospheres, new ions form when neutral particles are ionized by the Sun's energy, electron impacts, and charge exchange. These new ions interact with the plasma, an electrically conductive ionized gas in the magnetosphere. These interactions generate waves in the plasma, phenomena that have been observed by spacecraft. To understand the degree to which perturbations in plasma affect the space environment, Cowee et al. sought to characterize plasma waves generated by the formation of new ions, specifically sulfur dioxide ions, released from the atmosphere of Jupiter's moon, Io. Previous research had suggested that newly formed ions lose 50 percent of their energy to plasma wave generation, but the authors used simulations to show that at most, about 25 percent of the energy of the newly formed ions is lost to wave growth for conditions at Io. Thus, more ions than previously thought are required to generate the plasma wave energies observed.

    Title: "1D hybrid simulations of planetary ion-pickup: Energy partition"

    Authors:
    M. M. Cowee, C. T. Russell, and R. J. Strangeway: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, U. S. A.;
    D. Winske: Los Alamos National Laboratory, Los Alamos, New Mexico, U.S.A.

    Source: Geophysical Research Letters (GRL) paper10.1029/2006GL028285, 2007

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