The following highlights summarize research papers that have been published in Geophysical Research Letters (GRL).
In this release:
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1. Exploring how corals build their skeletons
Despite its long history of study, the mechanism by which corals form their skeletons remains largely unknown. Recently, advances in microanalytical techniques have made it possible for scientists to investigate the variability of trace elements and stable isotopic compositions within coral skeletons. These studies have revealed systematic compositional variations within skeletons that are much too large to be explained by anything but biological activity. Such data complicate the use of corals as proxies for paleoenvironmental change and form a strong basis for fundamental questions about the dynamics of the skeletal formation process and the biological origin of the compositional variations. Houlbrque et al. develop the experimental capability to isotopically label biomineralized carbonate structures under normal (unperturbed) growth conditions. These labeled structures are imaged with an ion microprobe that has a spatial resolution better than 1 micrometer. Applied to corals, these new techniques immediately yield new insights into skeletal formation and hold the potential to rapidly advance the study of marine carbonate biomineralization.
Title: Strontium-86 labeling experiments show spatially heterogeneous skeletal formation in the scleractinian coral Porites porites
Fanny Houlbrque: Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A.; also at Marine Environment Laboratories, International Atomic Energy Agency, Monaco;
Anders Meibom and Yves Marrocchi: Laboratoire de Minralogie et Cosmochimie du Musum, Musum National D'Histoire Naturelle, Paris, France;
Jean-Pierre Cuif: IDES, Universit Paris IX, Orsay, France;
Jaroslaw Stolarski: Instytut Paleobiologii PAN, Warszawa, Poland;
Christine Ferrier-Pags: Centre Scientifique de Monaco, Monaco;
Isabelle Domart-Coulon: Dpartment Milieux et Peuplements Aquatiques, Musum National D'Histoire Naturelle, Paris, France;
Robert B. Dunbar: Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036782, 2009; http://dx.doi.org/10.1029/2008GL036782
2. Earth cyclones may help explain Venusian vortices
At cloud top level, Venus' entire atmosphere circles the planet in just about four Earth days, much faster than the solid planet does. Despite this "superrotation," some dynamical and morphological similarities exist between the vortex organization in the atmospheres of Venus's northern and southern hemispheres and tropical cyclones and hurricanes on Earth. First detected by the Pioneer Venus Orbiter near the northern pole and recently by Venus Express orbiter around the southern pole, an S-shaped feature in the center of the vortices on Venus is also known to occur in Earth's tropical cyclones. Using an idealized nonlinear and nondivergent barotropic model, Limaye et al. show that these S-shaped features are the manifestations of barotropic instability. They find that similar to the S-shapes seen in tropical cyclones, the S-shapes in Venus's vortices are transient. Given the challenges in measuring the deep circulation of Venus's atmosphere, the authors expect that the morphological similarities between vortices on Earth and Venus might help scientists better understand atmospheric superrotation on Venus and guide future observations.
Title: Vortex circulation on Venus: Dynamical similarities with terrestrial hurricanes
Sanjay S. Limaye, James P. Kossin, and Christopher Rozoff: Space Science and Engineering Center, University of Wisconsin-Madison, Madison, Wisconsin, U.S.A.;
Giuseppe Piccioni: ASF, INAF, Rome Italy;
Dmitry V. Titov and Wojciech J. Markiewicz: Max Plank Institute for Solar System Research, Katlenburg-Lindau, Germany.
Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036093, 2009; http://dx.doi.org/10.1029/2008GL036093
3. Model relates South Polar ozone concentrations and wind patterns
The dominant mode of climate variability across the Southern Hemisphere is the Southern Hemisphere Annular Mode (SAM), which describes the strength of the circumpolar zonal winds. Observations and models have linked stratospheric polar ozone depletion with trends in the SAM. However, general circulation models used in the Intergovernmental Panel on Climate Change (IPCC) assessment can only investigate how ozone influences atmospheric circulation, not vice versa. To investigate the two-way ozone-SAM relationship, Fogt et al. analyze records dating from 1962 to 2004. They find that austral spring total column ozone above the South Pole is significantly correlated to the SAM, with delay times of up to four months. The austral spring SAM is also linked to polar ozone concentrations into the early summer. The ozone-SAM relationship is then investigated in a coupled chemistry climate model (CCM), which includes fully interactive stratospheric ozone chemistry. The authors show that the observed relationship can be represented in the CCMs, suggesting CCMs are important tools to investigate future Southern Hemisphere climate change involving ozone recovery and greenhouse gas increases.
Title: Intra-annual relationships between polar ozone and the SAM
Ryan Fogt: Physical Sciences Division, NOAA Earth System Research Laboratory, Boulder, Colorado, U.S.A.;
Judith Perlwitz: Physical Sciences Division, NOAA Earth System Research Laboratory, Boulder, Colorado, U.S.A.; also at Cooperative Institute for Research in the Environmental Sciences, Boulder Colorado, U.S.A.;
Steven Pawson: Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A;
Mark A. Olsen: Goddard Earth Sciences and Technology Center, NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036627, 2009; http://dx.doi.org/10.1029/2008GL036627
4. Laboratory crystals give clues to deep Earth puzzle
Perovskite is the major mineral phase in the lower mantleit dominates the seismic properties and viscous deformation of the deep Earth. At high pressures and temperatures, perovskite transforms into an altered crystal-packing form called postperovskite. The region where the transformation occurs, known as the D'' layer, is directly above the core-mantle boundary and is distinguished by large seismic velocity jumps. Using forms of a synthetic, solid compound containing calcium, iridium and oxygen as analogs for perovskite and postperovskite, Walte et al. conduct laboratory experiments to simulate the perovskite transitions under high temperatures and pressures. Expanding on past research that demonstrated that crystal lattice orientations in the analog postperovskite alter when deformed, the authors find that the transformation of the analog perovskite to analog postperovskite itself yields a crystal lattice structure different from postperovskite deformation textures. If the analogue between the compound used in the experiments and the perovskite crystal-packing system holds true, such lattice orientation transitions may explain the observed seismic jumps. On a more local level, the fast spikes in certain seismic velocities may be explained by downwelling material that underwent these observed crystal lattice transformations.
Title: Transformation textures in post-perovskite: Understanding mantle flow in the D'' layer of the Earth
N. P. Walte, F. Heidelbach, N. Miyajima, D. J. Frost, and D. C. Rubie: Bayerisches Geoinstitut, Universitt Bayreuth, Bayreuth, Germany;
D. P. Dobson: Department of Earth Sciences, University College London, London, U.K.
Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036840, 2009; http://dx.doi.org/10.1029/2008GL036840
5. Spacecraft characterize perturbations that can affect orbiting satellites
Magnetospheric electric and magnetic perturbations at ultralow frequencies (ULF, between 2 and 25 megahertz) can accelerate energetic particles in the magnetosphere and thus affect orbiting satellites. However, not all classes of ULF waves are important for electron acceleration. To learn more, Sarris et al. study data from an unusual source: the five-probe constellation of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, launched in 2007 to study magnetospheric substorms. Through recognizing that the alignment and orbits of the THEMIS probes, particularly in the first period of its mission, provided unique opportunities to study ULF pulsations in the magnetosphere, the authors identify specific electric and magnetic field disturbances that are shown through modeling and observation to be resonances of the magnetic field lines. They then use phase-difference calculations between probes to estimate the number of fluctuations present at a given time. The authors expect that further research will help understand the dynamics of the Earth's radiation belts.
Title: Characterization of ULF pulsations by THEMIS
Authors: T. E. Sarris: Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, U.S.A.; also at Space Research Laboratory, Demokritus University of Thrace, Xanthi, Greece;
W. Liu, X. Li, S. R. Elkington, and R. Ergun: Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, U.S.A.;
K. Kabin and R. Rankin: Department of Physics, University of Alberta, Edmonton, Alberta, Canada;
V. Angelopoulos: Institute of Geophysics and Planetary Physics, Unitersity of California, Los Angeles, California, U.S.A.;
J. Bonnell: Space Sciences Laboratory, University of California, Berkeley, California, U.S.A.;
K. H. Glassmeier and U. Auster: IGEP, Technical University of Braunschweig, Braunschweig, Germany.
Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036732, 2009; http://dx.doi.org/10.1029/2008GL036732
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American Geophysical Union