AGU Journal highlights - 10 August 2004

08/10/04

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.

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1. Daily temperature ranges track climate variability

Measuring the daily maximum and minimum temperatures over long periods likely provides more information about climate variability than average daily temperature observations. Braganza et al. analyzed diurnal temperature range data over the past century and suggest that such information can help explain climate trends like the surface warming seen over the past 50 years. The authors report that their data, recorded from above land locations across the globe, show that the range between the maximum and minimum temperatures has decreased due to larger increases in the minimum temperatures compared to the maximum. The 0.4 degree Celsius [0.7 degree Fahrenheit] decrease in daily temperature range over the last 50 years is most likely related to observed changes in cloudiness over the same period. Such changes are consistent with the variations expected from enhanced greenhouse climate change, but are not well simulated by current climate models.

Title: Diurnal temperature range as an index of global climate change during the twentieth century

Authors:
Karl Braganza, Monash University, Clayton, Victoria, Australia;
David J. Karoly, University of Oklahoma, Norman, Oklahoma;
J. M. Arblaster, National Center for Atmospheric Research (NCAR), Boulder, Colorado, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019998, 2004

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2. Cause of New Zealand volcanism

A new seismic velocity model can infer the processes that lead to the formation of the voluminous eruptions of the Taupo Volcanic Zone in New Zealand. Harrison and White propose that material brought down by the subducting Pacific Plate releases water that induces melting of the overlying mantle in the region. The Taupo Volcanic Zone is regarded as one of the largest, most productive volcanic systems on Earth. Relatively little is known, however, about the location or origin of the magma that drives its eruptions. The authors analyzed seismic data from below the volcanic zone and propose that because the melted magma is less dense than the surrounding material, it rises to a depth between 15-30 kilometers [9-19 miles] below the surface. There, interactions with Earth's lower crust change the melt before it moves into the upper crust and forms the source of the volcanic eruptions.

Title: Crustal structure of the Taupo Volcanic Zone, New Zealand: Stretching and igneous intrusion

Authors: A. J. Harrison, R. S. White, University of Cambridge, Cambridge, United Kingdom.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019885, 2004

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3. Robotic aircraft can patrol the ocean

Small, robotic aircraft can provide a new technology that allows improved oceanographic observations in hard-to-reach locations. Inoue and Curry report that a drone aircraft, called the Aerosonde, allows daylong observations of water temperatures along Alaska's Barrow Canyon, an important freshwater conduit into the Arctic Ocean. Such information can improve the resolution and accuracy of oceanographic estimates along the point where warm, fast Alaskan fresh water crosses into the cooler and deeper Arctic Ocean. Most existing monitors are ship-based, which are far more expensive and time-consuming, or satellite-based, which are often blocked by clouds. The authors analyzed Aerosonde data from a 27-hour continuous flight and suggest that the flow pattern through the canyon has a sheared flow into the Arctic Ocean, as evidenced by previous studies. They suggest that the instruments aboard the vehicle improve scientists' knowledge of the small-scale water behavior along the canyon.

Title: Application of Aerosondes to high-resolution observations of sea surface temperature over Barrow Canyon

Authors: Jun Inoue, Judith A. Curry, Georgia Institute of Technology, Atlanta, Georgia, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020336, 2004

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4. Validating the Earth's interior conditions

An X-ray scattering technique has provided an independent confirmation of a common method used to study the high-pressure and high-temperature mineral physics in the Earth's interior. Lin et al. confirmed that their laser-heating system, coupled with nuclear resonant X-ray scattering, confirmed the temperature and pressure conditions previously measured by laser-heated diamond anvil cells. Such measures are useful to understanding the physical properties of materials deep inside Earth's interior. The diamond anvil technique, used since the late 1960s, allows researchers to replicate the extreme conditions inside Earth to test the melting point and to chemically analyze minerals found in the mantle. The authors suggest that the X-ray scattering method can measure the energy in the ground better than a proposed Raman spectra technique and provides data that closely correspond with temperatures determined during laser-heated diamond cell experiments.

Title: Absolute temperature measurement in a laser-heated diamond anvil cell

Authors: Jung-Fu Lin, Ho-swang Mao, Russell J. Hemley, Carnegie Institution of Washington, Washington, D.C., USA; Wolfgang Sturhahn, Jiyong Zhao, Argonne National Laboratory, Argonne, Illinois, USA; Guoyin Shen, University of Chicago, Chicago, Illinois, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020599, 2004

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5. Amplifying seismic waves through the ground

Soft ground and mud may sustain and extend the distance that seismic waves travel on the surface and lead to earthquake hazards far from the location of a quake. Lomnitz and Meas report on data collected at a seismic observation station in Mexico City, indicating that active and passive energy from tremors in the city combined in the soft soil and caused the ground to rock and heave far into central Mexico. The authors note that a layer of mud exists nearly 30 meters [100 feet] below Mexico City from the lake that was drained where the present downtown stands and which could allow seismic activity to transfer over long distances. They suggest that Huygens' coupling, which refers to the combining of two forms of seismic activity into a single, stronger wave, allowed the behavior they observed to occur. The researchers suggest that earthquakes with a magnitude of 7.5 or larger could lead to destruction in remote areas.

Title: Huygens' Principle: The capture of seismic energy by a soft soil layer

Authors:
Cinna Lomnitz, Institute of Geophysics, National University of Mexico, Mexico City, Mexico;
Yunny Meas, Investigative Center for Technical Design, Queretaro, Mexico.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019910, 2004

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6. Measuring airborne water-soluble carbon

A new sampling technique can be used to easily measure the water-soluble organic carbon portion of airborne pollution, providing a method for researchers to determine the makeup of aerosol particles. Sullivan et al. present a sampling instrument that can provide continuous detailed measurements of organic carbon in the air. Such carbon particles could affect the water content of existing atmospheric aerosols and their ability to condense into cloud condensation nuclei, and thus have implications for changing regional air quality and affecting the global climate. The authors used their monitor to estimate the ratio of water-soluble carbon and organic carbon in summer and fall measurements of the air in St. Louis, Missouri, USA. The researchers suggest that their method provides unique information about the water-soluble compounds in airborne aerosols.

Title: A method for on-line measurement of water-soluble organic carbon in ambient aerosol particles: Results from an urban site

Authors:
A. P. Sullivan, R. J. Weber, Georgia Institute of Technology, Atlanta, Georgia, USA;
A. L. Clements, J. R. Turner, Washington University, St. Louis, Missouri, USA;
M. S. Bae, J. J. Schauer, University of Wisconsin, Madison, Wisconsin, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019681, 2004

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7. Evolution of undersea tectonic plates

Reconstructing the movement of the ancient seafloor in the Pacific can allow researchers to better understand the formation and evolution of tectonic plate boundaries. Taylor and Goodliffe analyzed new geophysical data of the West Philippine Basin and note that the direction of its opening rotated approximately 100 degrees counterclockwise between 49 and 33 million years ago. The authors report that the basin began to open at the same time as the beginning of subduction that formed a new western boundary to the Pacific Plate, although the new plate's boundaries and its associated volcanic activity did not follow along the lines of preexisting structures. The researchers state that their study provides a well-constrained example of initial subduction whose explanation will require revisions to existing models.

Title: The West Philippine Basin and the initiation of subduction, revisited

Authors:
Brian Taylor, University of Hawaii, Honolulu, Hawaii, USA;
Andrew M. Goodliffe, University of Alabama, Tuscaloosa, Alabama, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020136, 2004

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8. Volcanic motion could initiate tsunami waves

A new report indicates for the first time that rapid and repeated motion along a volcanic caldera can cause the sides of an island volcano to fail and lead to a landslide from its flanks that could spawn a tsunami. Tibaldi and Vezzoli show that the recurrent lateral collapse of huge sections of the Ischia Island Caldera in Italy is likely triggered by instability in the volcano's crater-like resurgent caldera. They also report that periodically throughout the island's history, material from the volcano's sides poured into the sea and initiated damaging tsunami waves. The authors suggest that such a scenario could have caused previously unexplained tidal waves in the region's ancient past. Several previous studies had suggested that seismic activity, land deformation, or magma upwelling may have initiated the lateral collapse of the volcano, but the current research is the first to suggest that the repeated resurgence motion of its caldera could launch an avalanche and start a hazardous wave.

Title: A new type of volcano flank failure: The resurgent caldera sector collapse, Ischia, Italy

Authors:
Alessandro Tibaldi, University of Milan-Bicocca, Milan, Italy;
Luigina Vezzoli, University of Insubria, Como, Italy.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020419, 2004

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9. New Guinea Trench is active inter-plate boundary

Recent seismic tomography imaging shows clear evidence for southwestward subduction along the entire length of the New Guinea Trench in Indonesia and Papua New Guinea. Viewed in conjunction with large thrust earthquakes that are known to have occurred in the trench, Tregoning and Gorbatov confirm the conclusions of earlier studies that the New Guinea Trench is an active interplate boundary. The Pacific and Australian plates converge in the region at a rate of more than 110 millimeters [4.3 inches] per year across the New Guinea land mass, but the location of the convergence was not accurately located. In addition, conclusions from existing studies conflicted as to whether active subduction occurred on the New Guinea Trench. By using a more accurate data set of seismic observations and earthquake hypocenters, the authors have imaged the subducting slab and produced estimates of the variations in the dip angle of subduction along the trench.

Title: Evidence for active subduction at the New Guinea Trench

Authors:
Paul Tregoning, The Australian National University, Canberra, ACT, Australia;
A. Gorbatov, Institute for Frontier Research on Earth Evolution, Japan Marine Science and Technology Center, Yokohama, Japan.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020190, 2004

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10. Watching the Everglades flow from space

New satellite observations of South Florida have provided detailed images of the water levels in the Everglades and may provide information to improve water management and wetlands restoration. Wdowinski et al. report interferometric synthetic aperature radar (InSAR) observations that recorded the water levels changes in the Florida Everglades. The Everglades region is a wetlands habitat that is currently undergoing extensive repair to restore its natural conditions. The authors suggest that the satellite-based radar system can measure the water's vertical and horizontal levels with unprecedented resolution, providing details more than two orders of magnitude better than existing ground monitors and hydrologic models. Their analysis also shows some previously unrecognized water flow features and quantifies the radial and unidirectional water movement within the wetlands, which can further aid efforts to better understand the water flow within the unique ecosystem.

Title: Space-based measurements of sheet-flow characteristics in the Everglades wetland, Florida

Authors: Shimon Wdowinski, University of Miami, Miami, Florida and Tel Aviv University, Ramat Aviv, Israel;
Falk Amelung, Tim Dixon, University of Miami, Miami, Florida, USA;
Fernando Miralles-Wilhelm, University of Miami, Coral Gables, Florida, USA;
Richard Carande, Vexcel Corporation, Boulder, Colorado, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020383, 2004

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