AGU Journal highlights - 26 October 2004

10/26/04

Contents
I. Highlights, including authors and their institutions
II. Ordering information for science writers

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I. Highlights, including authors and their institutions

The following highlights summarize research papers in Geophysical Research Letters (GL), Journal of Geophysical Research--Space Physics (JA), and Journal of Geophysical Research--Atmospheres (JD). 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. Satellite view of ship emissions

A new study presents the first satellite estimate of nitrogen oxide emissions from ships into the atmosphere. Beirle et al. analyzed satellite observations from the open ocean along the congested shipping track between Sri Lanka and Indonesia and report that ship emissions add approximately 23 gigagrams per year of nitrogen oxides into the troposphere [lowest level of the atmosphere] along that route. The authors report that exhaust plumes from ship traffic add a significant amount of trace gases into the atmosphere, and they are the only manmade source of such ozone-producing compounds in the boundary layer above the ocean. They also note that the nitrogen oxides typically don't last long, lingering nearly four hours in the atmosphere. The study confirms existing model results and validates previous observations indicating that ship emissions contribute approximately 15 percent of the worldwide production of nitrogen oxides.

Title: Estimate of nitrogen oxide emissions from shipping by satellite remote sensing

Authors:
Steffen Beirle, U. Platt, R. von Glasow, T. Wagner, Institute for Environmental Physics, Heidelberg University, Heidelberg, Germany;
M. Wenig, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020312, 2004

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2. New seismic method for studying deep Earth motion

A new seismic analysis technique has provided researchers unprecedented high-resolution images of Japan's undersea eastern Nankai subduction system and can be used to study other portions of the Earth's deep crust. Dessa et al. report the first crustal-scale application of two-dimensional full waveform inversion, which uses seismic data to identify anomalies and discontinuities along fault lines that can result from periodic large earthquakes. The authors used an array of 100 ocean-bottom seismometers along the Japanese trench, providing one of the first densely sampled wide-angle marine seismic data sets. They note that the velocity changes their study detected typically indicate the presence of fluid and weakened material that can control ground motion at depth. The researchers suggest that applying the waveform method, particularly to such a well-sampled system, can provide the most accurate estimates of deep crustal structures and the seismic motions that occur there.

Title: Multiscale seismic imaging of the eastern Nankai trough by full waveform inversion

Authors:
Jean-Xavier Dessa, S. Operto, J. Virieux, (French) National Research Council, Ocean Geosciences Division, Villefranche-sur-Mer, France;
S. Kodaira, A. Nakanishi, Y. Kaneda, Institute for Frontier Research on Earth Evolution, Japan Marine Science and Technology Center, Yokahama, Japan;
G. Pascal, (French) National Research Council, Geological Laboratory, Paris, France.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020453, 2004

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3. Circulation shift in the tropical Pacific

Recent observations indicate that the shallow meridional overturning circulation in the tropical Pacific Ocean has rebounded since 1998, following 25 years of significantly weaker flow. McPhaden and Zhang compared the 5-6 year average conditions before and after 1998 in the Pacific and report a recent increase in equatorward flow in the upper ocean linked to a change in the Pacific Decadal Oscillation. The circulation increase is also related to a strengthening of the trade winds, changes in the equatorial sea level, and the development of anomalously cool equatorial Pacific sea surface temperatures. The authors suggest that the changes may have affected the global climate and Pacific marine ecosystems. A pattern of stronger circulation was the norm prior to 1976-77, when weaker overturning flow began to dominate the Pacific. The researchers suggest that the abruptness of the circulation recovery in 1998 obscures presumed manmade warming trends indicated in the instrumental records from the tropical Pacific.

Title: Pacific Ocean circulation rebounds

Authors:
Michael J. McPhaden, NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington, USA;
Donxiao Zhang, Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, Washington, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020727, 2004

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4. Connecting El Nino warm water and Indian monsoon rainfall

The volume of warm water in the tropical Pacific Ocean, which is a key predictor of sea surface temperature anomalies associated with El Nino and La Nina climate fluctuations, may also help predict the amount of rainfall over India during the summer monsoon season. Rajeevan and McPhaden analyzed more than 50 years of ocean thermal field data and report a significant correlation between Pacific warm water volume anomalies and Indian summer monsoon rainfall. Summer monsoon rains contribute up to 90 percent of India's annual rainfall and have a major impact on the country's economy. The authors suggest that using warm water volume in a monsoon prediction model would have provided some advance notice of the unexpected drought over India in 2002, although it would not have foretold the event's severity. They report that the relationship between warm water volume and rainfall could provide a longer lead time than current El Nino indicators, such as sea surface temperature measurements.

Title: Tropical Pacific upper ocean heat content variations and Indian summer monsoon rainfall

Authors:
M. Rajeevan, India Meteorological Department, Pune, India;
Michael J. McPhaden, NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020631, 2004

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5. Antarctic glacial changes after Larsen B collapse

Antarctic glaciers that had been blocked behind the Larsen B ice shelf have been flowing more rapidly into the Weddell Sea following the breakup of the shelf, according to two papers published in Geophysical Research Letters. Scambos et al. report a significant increase in the speed of glaciers flowing into the now-collapsed section of the Larsen B ice shelf, implying that the ice shelves likely hold back the glaciers in the Antarctic Peninsula. Their satellite images also suggest that recent climate warming has led to a rapid sea level rise and a thinning of the glacial ice. In addition, Rignot et al. collected data that confirmed the eightfold increase in speed among three nearby glaciers following the Larsen B collapse. The researchers note that while the glaciers close to the Larsen shelf accelerated quickly in the years after the collapse, glaciers further south were buttressed by a remaining ice shelf and did not move appreciably. Both authors report that the magnitude of the glacier changes illustrate the importance of ice shelves on ice sheet mass balance and their contribution to sea level change.

Titles:
1. Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica
2. Accelerated ice discharge from the Antarctic Peninsula following the collapse of Larsen B ice shelf

Authors:
1. T. Scambos, J. A. Bohlander, National Snow and Ice Data Center, University of Colorado, Boulder, Colorado, USA;
C. A. Shuman, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA;
P. Skvarca, Argentinian Antarctic Institute, Buenos Aires, Argentina.

2. E. Rignot, Jet Propulsion Laboratory, Pasadena, California, USA, and Center for Scientific Studies, Valdivia, Chile;
G. Casassa, A. Rivera, Center for Scientific Studies, Valdivia, Chile, P. Gogineni, University of Kansas, Lawrence, Kansas, USA;
W. Krabill, EGG&G Services and NASA Goddard Space Flight Center, Wallops Flight Facility, Wallops Island, Virginia, USA;
R. Thomas, EGG&G Services and NASA Goddard Space Flight Center, Wallops Flight Facility, Wallops Island, Virginia, USA, and Center for Scientific Studies, Valdivia, Chile.

Sources:
1. Geophysical Research Letters (GL) paper 10.1029/2004GL020670, 2004
2. Geophysical Research Letters (GL) paper 10.1029/2004GL020697, 2004

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6. Determining radon levels from the ocean

Improved estimates for the amount of radon gas emitted from the ocean may allow researchers to improve climate and air prediction studies. Schery and Huang modified a commonly used oceanic gas transfer model to produce monthly estimates of changes in radon levels across the global ocean. Currently, most studies presume either an insignificant amount or a constant release of radon from the ocean, unlike the ever-shifting levels the researchers discovered. Understanding background radon levels has been identified as an important factor in improving climate and air quality studies, particularly at coastal and marine locations where observed atmospheric radon levels occasionally conflict with global transport models. The authors found that areas near the equator and the Southern Ocean produce higher than expected radon flux. In addition, they suggest that the total annual transfer of radon over the ocean is smaller than the factor used in many global simulations.

Title: An estimate of the global distribution of radon emissions from the ocean

Authors:
Stephen D. Schery, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA;
S. Huang, Woods Hole Oceanographic Institution, Quissett Campus, Woods Hole, Massachusetts, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL021051, 2004

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7. Measuring ozone inside the polar vortex

Including data from the U.S. Naval Research Laboratory's Polar Ozone and Aerosol Measurement (POAM III) instrument into existing ozone models may significantly increase a forecaster's ability to predict regional ozone profiles in the Antarctic. Stajner and Wargan compared ozone profiles with and without the Polar Ozone and Aerosol Measurement (POAM) III satellite data to measures taken from ground and air stations in the South Pole and surrounding Antarctic and show that the satellite information helps produce a much more accurate estimate of the region's ozone distribution. Their analysis included POAM III data into an atmospheric model for the first time, which then accurately depicted the wintertime ozone accumulation in the lower stratosphere in 1998. The authors suggest that the satellite data may be used to produce an ozone map within the polar vortex, a notoriously difficult area to measure. They also note that assimilating real-time POAM III data into forecast models may allow scientists to produce improved ozone analyses and predictions.

Title: Antarctic stratospheric ozone from the assimilation of occultation data

Authors:
Ivanka Stajner, Krzysztof Wargan, Science Applications International Corporation, Beltsville, Maryland, and NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020846, 2004

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8. Saltwater anomalies likely occur naturally

Changes in the salinity observed over the past four decades in the North Atlantic Ocean, known as Great Salinity Anomalies, are likely not caused by recent global warming. Wadley and Bigg analyzed historical ocean-climate links, using a model that produced examples of repeated occurrences of the anomalies since pre-industrial times. Such water mass changes in the North Atlantic can produce large changes in oceanic variability, affecting the global thermohaline [vertical movement, based on salinity and temperature] circulation and strength, which can then influence regional and worldwide climate. The authors' study of three recent salinity anomalies in the 1970s and 1990s, using coupled climate simulations, show that similar anomalies took place before the current era of enhanced greenhouse gases, strongly suggesting that periodic low salinities in the northern North Atlantic are caused by natural events.

Title: "Great Salinity Anomalies" in a coupled climate model

Authors:
Martin R. Wadley, University of East Anglia, Norwich, United Kingdom;
Grant R. Bigg, University of Sheffield, Sheffield, United Kingdom.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020426, 2004

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9. Setting solar wind speed records

The October-November2003 solar storms touched off some of the fastest solar winds ever recorded, setting speed records for the time between a solar flare and the wind's arrival at Earth. Skoug et al. analyzed solar wind plasma and magnetic field observations from the Advanced Composition Explorer (ACE) spacecraft and report wind speeds exceeding 1850 kilometers [1,150 miles] per second during these geomagnetic events, making them some of the highest solar wind speeds ever measured in space. The authors note that the incident was comparable to the previous fastest solar winds detected in 1972, which took less than 15 hours to reach the Earth; the trip generally takes more than 48 hours. Surprisingly, they found that the disturbance of the Earth's magnetic environment caused by the fast solar winds, although large, was only slightly above average compared to the effects from other large solar events. The researchers suggest that the direction of the interplanetary magnetic field is likely a better indicator of the damage potential from strong solar events than the velocity of the event.

Title: Extremely high speed solar wind: 29-30 October 2003

Authors:
Ruth M. Skoug, J. T. Gosling, J. T. Steinberg, Los Alamos National Laboratory, Los Alamos, New Mexico, USA;
D. J. McComas, Southwest Research Institute, San Antonio, Texas, USA;

C. W. Smith, Institute for Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire, USA;
N. F. Ness, Bartol Research Institute, University of Delaware, Newark, Delaware, USA Q. Hu, Institute of Geophysics and Planetary Physics, University of California, Riverside, California, USA;
L. F. Burlaga, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.

Source: Journal of Geophysical Research--Space Physics (JA) paper 10.1029/2004JA010494, 2004

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10. Effects of wind farms on local meteorology

The spinning rotor of a wind turbine draws in energy from the wind that can affect local meteorological conditions and generates turbulence in its wake that reduces the efficiency of its power generation. Baidya Roy et al. provide the first paper in the field of wind farming, simulating the effects from an array of turbines at a hypothetical wind farm in the Great Plains region of the United States. The authors created a model to represent the effects from the turbines within a regional climate model and found that a wind farm would likely affect the air temperature and moisture, while the turbulence generated by the rotors increased vertical transport of wind momentum, heat and moisture, leading to a warming and drying near the land surface. They also show that reducing rotor-generated turbulence lowered the meteorological impacts while enhancing the operational efficiency of wind farms by harnessing the energy that would otherwise be wasted.

Title: Can large wind farms affect local meteorology?

Authors:
Somnath Baiyda Roy, S. W. Pacala, Princeton University, Princeton, New Jersey, USA;
R. L. Walko, Duke University, Durham, North Carolina, USA.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2004JD004763,

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II. Ordering information for science writers

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 Harvey Leifert [hleifert@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 should send a request to service@agu.org, citing the doi of the paper (number beginning 10.1029/....), to order a copy of the paper.

The Highlights and the papers to which they refer are not under AGU embargo.

Contact:
Harvey Leifert
American Geophysical Union
2000 Florida Avenue, N.W.
Washington, DC 20009
U.S.A.

Phone (direct): 1-202-777-7507
Phone (toll-free in North America): (800) 966-2481 x507
Fax: 1-202-328-0566
Email: hleifert@agu.org

Source: Eurekalert & others

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