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AGU journal highlights - 7 June 2004


The following highlights summarize research papers in Geophysical Research Letters (GL) and Space Weather (SW). The papers related to these Highlights are printed in the next paper issue of the journal following their electronic publication.

1. Adriatic likely seismically independent fault system

A series of simple models shows that the Adriatic plate is likely not connected to the Eurasian or Nubian (African) tectonic plates as has been previously thought. Battaglia et al. used geodetic data to constrain the boundaries and seismic potential of the Adriatic fault system in the Mediterranean basin. Their evidence depicts the Adriatic as moving in sharp contrast to the direction of the two larger plates, suggesting that the Adriatic is an independent microplate within the collision zone. The authors used Global Positioning System measurements and modeling techniques to analyze the surface movements within the region, whose tectonics are not well known, and explain deformation previously observed near the Mediterranean Sea. The researchers propose that the Adriatic microplate is blocked within several faults and, although they cannot predict the specific number or location of the faults, find that their estimates agree with previous studies and actual events.

Title: The Adriatic region: An independent microplate within the Africa-Eurasisa collision zone

Maurizio Battaglia, University of California, Berkeley, California, and National Institute for Oceanography and Geophysical Studies, Seismological Research Center, Udine, Italy;
Mark H. Murray, Roland Burgmann, University of California, Berkeley, California;
Enrico Serpelloni, National Institute for Geophysical and Volcanological Study, Bologna, Italy.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019723, 2004

2. Monitoring the seasonal effects from changing photosynthesis

Researchers have found a new technique to monitor global-scale photosynthesis, identifying a way to measure plant physiology changes associated with seasonal climate variations. Bonfils et al. used historical global climate-carbon data to estimate changes in vegetation associated with summertime photosynthesis, including enhanced carbon dioxide and water uptake, and suggest that a better understanding of such climatic signatures can improve atmospheric simulations. The authors note that seasonal changes in plant behavior affect the daily maximum temperature and humidity, along with a range of other climate variables. Their study indicates that photosynthesis responds only to natural climate variability caused by changes in temperature or the water cycle, which can be monitored by satellite observations, although global-scale photosynthesis may also be affected by human inputs, such as the greenhouse effect and increasing agricultural fertilizer usage.

Title: On the detection of summertime terrestrial photosynthetic variability from its atmospheric signature

Celine Bonfils, Inez Fung, Jasmin John, Berkeley Atmospheric Sciences Center, University of California, Berkeley, California;
Scott Doney, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019453, 2004

3. Oxygen isotope analyses may not accurately portray paleoclimate

A team of researchers created an alternate Earth model to show how the assumptions used to estimate ancient climate conditions may not be accurate under different environments. Brown and Simmonds suggest that the temperature and oxygen isotope relationship used to reconstruct the past climate from rainwater chemistry relies on atmospheric conditions that may have changed since the last ice age. The authors tested their theory by modifying a global circulation model and found that the assumed temperature-isotope relationship used in present-day paleoclimate isotopic estimates may not accurately portray past climate conditions. They note that the existing climate reconstruction techniques that contrast current and past oxygen isotope ratios in rainwater can by skewed by introducing a cluster of continent-sized land masses in the mid-latitudes, which changes atmospheric circulation patterns and the source of tropical moisture.

Title: Sensitivity of the (Delta)18 O-temperature relationship to the distribution of continents

Josephine Brown, Ian Simmonds, University of Melbourne, Melbourne, Australia.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019870, 2004

4. Estimating polar ice changes using Global Positioning System data

A new technique to detect Global Positioning System (GPS) signals reflected from Earth may allow researchers an improved method to estimate topographical changes across the globe. Cardellach et al. provide the first analysis suggesting that radio frequency interferometer receivers on low- Earth orbiting satellites can be used to collect detailed topographical information, which would be particularly useful for estimating ice variability. Reflected GPS data was previously tested for its accuracy in predicting altimetry and surface roughness over the oceans, but the satellite information has not been used for other Earth applications. The researchers identified the parameters that could allow them to interpret direct and reflected GPS signals into high- resolution data. They then used their technique to estimate the ice surface height at locations in the North Pole and Greenland from satellite data and report that the new method could provide sub-meter [-yard] estimates of Earth's permanent ice cover.

Title: Carrier phase delay altimetry with GPS-reflection/occultation interferometry from low Earth orbiters

Estel Cardellach, C. O. Ao, M. de la Torre Juarez, G. A. Hajj, NASA/Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019775, 2004

5. Estimating the probability of magnetic storms

A new study evaluates the ability of various disturbances in the solar wind to affect Earth's magnetic field and cause magnetic storms. Echer and Gonzalez report that nearly 80 percent of magnetic clouds are geoeffective, meaning that they have specific features that can change the interplanetary magnetic field and typically cause storms in Earth's magnetosphere that are capable of affecting communications and satellites. In addition, the authors report that more than half of interplanetary shock waves and more than a quarter of solar current sheet crossings initiated geomagnetic storms at the Earth-space boundary. The researchers analyzed approximately three decades of available magnetic field data associated with the regular disturbances and calculated the number and intensity of geomagnetic storms following the events. Their results suggest that compound magnetic structures, like high-speed magnetic clouds and shock wave-carrying magnetic clouds were more geoeffective than single events.

Title: Geoeffectiveness of interplanetary shocks, magnetic clouds, sector boundary crossings and their combined occurrence

Ezequiel Echer, W. D. Gonzalez, National Institute of Space Research, Sao Jose dos Campos, Sao Paulo, Brazil.

Source: Geophysical Research Letters (GL) paper 10.1029/2003GL019199, 2004

6. New pollutant transport path to the stratosphere

A particle-laden plume of air observed in the stratosphere provides evidence for a new transport path from the lowermost troposphere deep into the stratosphere, a feature not fully captured by large-scale atmospheric models. Jost et al. report the first observations from within a carbon monoxide- and particle-enriched plume approximately 16 kilometers [10 miles] above Florida that can be traced to emissions from a forest fire in North America. Previously, most circulation models assumed that lower-level air entered the stratosphere only in the tropics. The authors used asuite of instruments to determine the source of the polluted air in the subtropical stratosphere and discuss its likely transport route. They also note that emissions from a predicted increase in forest fire activity and severity could follow a similar path to the stratosphere, contributing to enhanced aerosol and pollutant levels that could affect the atmospheric chemistry and radiation balance of the ozone layer.

Title: In situ observations of mid-latitude forest fire plumes deep in the stratosphere

Authors:Hans-Jurg Jost, Bay Area Environmental Research Institute, Sonoma, California;
Katja Drdla, Leonhard Pfister, Max Loewenstein, Jimena P. Lopez, T. Paul Bui, NASA Ames Research Center, Moffett Field, California;
Andreas Stohl, Nicole Spichtinger, Technical University Munich, Freising-Weihenstephan, Germany;
Paula K. Hudson, Daniel J. Cziczo, Erik C. Richard, National Oceanic and Atmospheric Administration, Boulder, Colorado, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado;
Daniel M. Murphy, National Oceanic and Atmospheric Administration, Boulder, Colorado;
Michael Fromm, Computational Physics Incorporated, Springfield, Virginia; J. Dean-Day, San Jose State University, San Jose, California;
Christoph Gerbig, Jasna Vellovic Pittman, Elliot M. Weinstock, Irene Xueref, Harvard University, Cambridge, Massachusetts;
M. J. Mahoney, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California;
James C. Wilson, University of Denver, Denver, Colorado.

Source: Geophysical Research Letters (GL) paper 10.1029/2003GL019253, 2004

7. El Nino Oscillation drives Antarctic variability

A new analysis may help resolve the longstanding debate about whether El Nino effects or an eastward propagating wave from the Southern Ocean causes the majority of year-to-year climate and sea ice variability in the Antarctic. Park et al. suggest that the El Nino Southern Oscillation has a major impact on the southern polar variability, while the circumpolar wave has a relatively minor effect. The authors' novel method indicates that the ocean-atmosphere interactions in the tropics that alter the large-scale atmospheric circulation and initiate the El Nino phenomenon are significantly correlated with changes in climate and ice cover around Antarctica. The competing theory, which posits that a self-sustained wave generated within the non-tropical Southern Ocean environment has the greatest effect on the Antarctic variability, is discounted because the recurrent wave is rapidly dissipated and doesn't have enough energy to alter the polar climate.

Title: Quasi-stationary ENSO wave signals versus the Antarctic Circumpolar Wave scenario

Young-Hyang Park, Fabien Roquet, National Museum of Natural History, Paris, France;
Frederic Vivier, Marie and Pierre Curie University, Paris, France.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019806, 2004

8. First gravity results from GRACE

The first results from the Gravity Recovery And Climate Experiment [GRACE] mission satellites to analyze the Earth's gravitational field have provided data that will allow researchers to determine global gravity with approximately an order of magnitude better accuracy than previous studies. Tapley et al. report that gravity models using the newly available data are significantly more accurate over the land and ocean. The greatest improvement is from the globally homogeneous data obtained by the satellite pair, launched in 2002 to map the gravity field every 30 days. The enhanced data acquisition largely stems from an antenna on each satellite

that allows each to accurately measure their relative motion and transmit the measurements to ground receivers, where the combined information removes errors that hindered previous efforts. The researchers note that although the largest improvement in model accuracy for oceanographic research occurs in the low and middle latitudes, the increased coverage in the polar regions provides important new measurements to support polar studies.

Title: The gravity recovery and climate experiment: Mission overview and early results

Byron D. Tapley, S. Bettadpur, Center for Space Research, University of Texas, Austin, Texas;
M. Watkins, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California;
C. Reigber, GeoforschungsZentrum (GFZ), Potsdam, Germany.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019920, 2004

9. First turbidity measurements from inside strong California current

The first measurements of turbidity currents from inside the deep Monterey Submarine Canyon off the California coast provides details of the currents that drive sediments into the open ocean. Xu et al. present preliminary data from their experiment that placed three Doppler current profile instruments at depths between approximately 800-1500 meters [3,000-5,000 feet]. The authors observed maximum velocities of more than 190 centimeters [6.2 feet]per second, or slightly over six kilometers [4 miles] per hour, during four turbidity currents, including two that coincided with surface storms between 2002 and 2003. The fast-moving, destructive currents had hampered previous attempts to monitor the canyon currents by damaging or burying the sensors designed to measure water velocity and dynamics generated by the sediment-laden water. Their findings show that although the current turbidity was confined to within 50 meters [200 feet] of the canyon floor, the sediment plumes from the underwater currents reached more than 170 meters [560 feet] above the floor.

Title: In-situ measurements of velocity structure within turbidity currents

Jingping Xu, M. A. Noble, U.S. Geological Survey, Menlo Park, California;
L. K. Rosenfeld, Naval Postgraduate School, Monterey, California.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019718, 2004

10. Measuring radiation onboard a commercial flight

The flight crew of a commercial airliner operated instruments to estimate the radiation levels on a Los Angeles-New York passenger flight during a strong solar storm in 2003. Ian L. Getley reports the enhanced radiation and X-ray exposure felt onboard the aircraft from the coronal mass ejections during a period of high solar activity. The passengers, crew, and aircraft electronics were exposed to the equivalent of 12 microSieverts of radiation on the 4.5-hour transcontinental flight, far less than the 6 milliSievert per year human safety limit and below the 1 milliSievert threshold for pregnant females. Getley notes that the radiation exposure on the mid-latitude North American flight fits between a higher dose rate for high-latitude transcontinental flights and lower radiation levels on flights closer to the equator. The observations represent the first records of cosmic ray dosage taken onboard a commercial flight and, combined with the fortuitous coincidence of a solar storm, can be used to monitor the radiation hazard for flyers.

Title: Observations of solar particle event on board a commercial flight from Los Angeles to New York on 29 October 2003

Ian L. Getley, University of New South Wales, Sydney, Australia.

Source: Space Weather (SW) paper 10.1029/2003SW000058, 2004

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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