AGU journal highlights - 15 September 2005

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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.

You may read the scientific abstract for any of these papers 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., 2005GL987654). The doi is found at the end of each Highlight, below. To obtain the full text of the research paper, see Part II.

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1. Climate model predicts declining air quality in Texas, western U.S.

Computer simulations have offered glimpses into the effects that global climate change due to increased emissions of greenhouse gases will have on water resources, agriculture, and ecosystems. They are also beginning to forecast future changes in regional air quality. Leung and Gustafson used a regional climate model to predict future regional rainfall, air temperature, and meteorological conditions that affect air quality across the United States. They compared a simulation of climate patterns for 1995–2005 to the patterns the model predicted for 2045-2055. Atmospheric conditions change markedly in three regions: Texas, the Midwest, and the western U.S. Texas and the West became warmer, received more downward solar radiation, and experienced less rainfall in the summer. Both regions also saw an increase in stagnation frequency, which suggests the likelihood of increased ozone, a pollutant harmful to human health and crops. The Midwest, in contrast, was predicted to receive more rain, less downward solar radiation, lower temperatures, less frequent stagnation, and increased ventilation--changes that would probably mean that ozone levels would remain the same or drop slightly.

Title: Potential regional climate change and implications to U.S. air quality

Authors:
L. Ruby Leung and William I. Gustafson Jr., Pacific Northwest National Laboratory, Richland, Washington, USA

Source: Geophysical Research Letters (GL) paper 10.1029/2005GL022911, 2005

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2. Satellite takes the temperature of Earth's ring current

The ring current is formed above Earth's equator by the longitudinal drift of charged particles trapped on field lines from Earth's magnetic field. The movement of the particles along the ring increases dramatically during geomagnetic storms. Zhang et al. used data extracted from energetic neutral atom (ENA) images obtained by the HENA imager on the IMAGE satellite to estimate the plasma ion temperature in the ring current during the early recovery phase of a strong storm on 12 August 2000. To do this they collected images of ENA, which are unaffected by magnetic fields and so travel straight from their site of origin to the imaging device. The ion temperatures of the ring current were found to be consistent with in situ measurements and with analysis using ENA images. The ion temperatures peak in the post-midnight/pre-dawn region coincident with the peaks in the equatorial ion flux. The results indicate that ion density variations make the major contribution to pressure gradients in the energy range 10-60 thousand electron volts for this storm.

Title: Proton temperatures in the ring current from ENA images and in situ measurements

Authors:
X. X. Zhang, T. Chen, and C. Wang, Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, China;
J. D. Perez, Physics Department, Auburn University, Auburn, Alabama, USA;
P. C. Brandt and D. G. Mitchell, Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA;
Y. L. Wang, Space Science and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2005GL023481, 2005

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3. Earth pulsates as the Amazon ebbs and flows

Earth's crust pulsates up and down in the center of the Amazon basin, new research suggests. A GPS station located next to the Amazon and Rio Negro rivers in Brazil recorded the station's altitude from 1995 to 2002. During that period the station oscillated up and down within a range of about 75 millimeters [3 inches], which was 3-9 times larger than observed at GPS stations around the world. Bevis et al. compared vertical crustal displacement with the fluctuation of the water level in the river and found an almost perfect anti-correlation. As the river rises, the ground sinks. Conversely, as the river level falls in the dry season, the solid Earth rebounds. The authors argue that the motion of the GPS station changed due to elasticity in the planet's crust in the region; the crust was responding to changes in the amount of water loading the riverbeds within about 200 kilometers [120 miles] of the station.

Title: Seasonal fluctuations in the mass of the Amazon River system and Earth's elastic response

Authors:
Michael Bevis and Eric Kendrick, Geodetic Science, Ohio State University, Columbus, Ohio, USA;
Douglas Alsdorf, Geological Sciences, Ohio State University, Columbus, Ohio, USA;
Luiz Paulo Fortes, Instituto Brasileiro de Geografia e Estatistica, Rio de Janeiro, Brazil;
Bruce Forsberg, Department of Ecology, Instituto Nacional de Pesquisas da Amazonas, Manaus, Brazil;
Robert Smalley Jr., Center for Earthquake Research and Information, University of Memphis, Memphis, Tennessee, USA;
Janet Becker, Hawaii Institute for Geophysics and Planetology, University of Hawaii, Honolulu, Hawaii, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2005GL023491, 2005

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4. Seismic noise may offer a glimpse inside other planets

Scientists have been using microseismic noise--mild seismic waves generated by ocean waves and atmospheric processes--to image Earth's internal geological makeup. Researchers are now exploring the possibility of using the technique to explore other planets. Larose et al. analyzed microseismic data from the Moon collected by sensors planted in 1972 by the Apollo 17 mission. Although the Moon does not have an ocean or an atmosphere, low-level seismic activity is generated by heat from the Sun. The authors analyzed recordings of this activity, collected by the sensors from April 1976 to April 1977. The information this technique provided about the Moon's interior was in line with that provided by other, more established experimental methods. The authors say this suggests that analysis of microseismic noise can be used to explore other planets that differ in size and origin and have different sources of seismic noise.

Title: Lunar subsurface investigated from correlation of seismic noise

Authors:
E. Larose and M. Campillo, Laboratoire de Geophysique Interne et Tectonophysique, Grenoble, France;
A. Khan, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark;
Y. Nakamura, Institute for Geophysics, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, Austin, Texas, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2005GL023518, 2005

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5. Two distinct source regions found for the 2004 Sumatra tsunami

The devastating tsunami that resulted from the massive 2004 earthquake in the Indian Ocean killed over 225,000 people. Fine et al. used recordings of wave arrival times and the first satellite-based observations of a major tsunami to find the location of the source of the waves. Wave arrival times were recorded at several stations throughout the Indian Ocean in the hours following the earthquake. The satellite observation came from two satellites that passed over the region about 150 kilometers [90 miles] apart about two hours after the quake. The data showed that the source of the tsunami was a 1200 kilometer [750 mile] long, 250 kilometer [160 mile] wide curved region centered over the Sunda trench off the northwest coast of the Indonesian island of Sumatra. In addition, the results showed two distinct "hot spots" within the region that acted as sources for the maximum waves: a northern slow-slip area and a southern fast-slip area. The enormous extent of the source region helps explain why long-period (40-50 minute) tsunami waves from the earthquake were recorded throughout the world.

Title: The dual source region for the 2004 Sumatra tsunami

Authors:
Isaac V. Fine, Alexander B. Rabinovich, and Richard E. Thomson, Department of Fisheries and Oceans, Institute of Ocean Sciences, Sidney, British Columbia, Canada.

Source: Geophysical Research Letters (GRL) paper 10.1029/2005GL023521, 2005

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6. Slow slide for a subduction zone off New Zealand coast

Offshore of the eastern portion of New Zealand's North Island is an earthquake-prone region known as the Hikurangi subduction zone, where the Pacific Plate moves underneath the North Island. Sometimes the plates in this and other subduction zones slide against each other slowly without creating large earthquake tremors. These events, known as slow slip events, can release tension in the fault, so understanding them is important for predicting earthquakes. Douglas et al. analyzed GPS recordings of an altitude change at two stations near the city of Gisborne on the Raukumara Peninsula in October 2002. They determined that the Gisborne stations moved 20-30 millimeters [0.8-1.2 inches] over about ten days and they compared this displacement event to GPS recordings collected in the region from 1995 to 2004. They suggest the movement was due to a slow slip event in the Hikurangi fault; they estimate that these events can be expected to take place every 2-3 years. Through modeling they estimate that the fault slipped by about 18 cm during the 2002 slow slip. The long-term GPS data indicate, however, that the event had little effect on geological strain in the region.

Title: Slow slip on the northern Hikurangi subduction interface, New Zealand

Authors:
A. Douglas and J. Townend, School of Earth Sciences, Victoria University of Wellington, Wellington, New Zealand;
J. Beavan and L. Wallace, Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand.

Source: Geophysical Research Letters (GL) paper 10.1029/2005GL023607, 2005

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II. Ordering information for science writers and general public

Journalists and public information officers of educational and scientific institutions (only) may receive one or more of the papers cited in the Highlights by sending a message to Jonathan Lifland [jlifland@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.

Others may purchase a copy of the paper online for nine dollars:
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2. Paste it into the second-from-left search box at http://www.agu.org/pubs/search_options.shtml and click "Go." 3. This will take you to the citation for the article, with a link marked "Abstract + Article."
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