AGU Journal highlights - 5 January 2005

01/05/05

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 following 10.1029/ (e.g., 2004GL987654). The doi is found at the end of each Highlight, below.

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1. Time to improve GPS accuracy

Correcting for a time lag built into current Global Positioning System satellites can significantly enhance the accuracy of highly detailed GPS observations that are increasingly used to study Earth systems. Choi et al. report that existing satellite techniques often slightly misjudge the location of ground changes, such as seismic activity, ice sheet flow, and volcanic deformation, because researchers used the wrong time delay in the GPS satellites. The authors show that the orbit period varies for each satellite and often differs considerably from what scientists have assumed since the GPS constellation was begun in the late 1970s. The researchers examined, for example, a GPS dataset from the well-observed 2003 San Simeon earthquake and found that high-precision (1 Hertz) GPS data needed to be corrected by nine seconds. They suggest that the improved processing technique would greatly reduce current error rates and make it possible to more accurately measure dynamic ground motion across the globe.

Title: Modified sidereal filtering: Implications for high-rate GPS positioning

Authors: Kyuhong Choi, Andria Bilich, Kristine M. Larson, Penina Axelrad, University of Colorado, Boulder, Colorado, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL021621, 2004

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2. Linking floods and drought across the Atlantic Ocean

The Amazon and Congo basins, two of the major regions where intense storms help shape Earth's climate, share a see-saw pattern wherein one basin experiences drought as the other floods. Eltahir et al. present new satellite observations of tropical rainfall distribution that shows the Amazon often sees extreme dryness while the Congo, across the Atlantic Ocean, is wet, and vice versa. The researchers analyzed the natural variability in historical river flow data describing extreme wet and dry periods over the two basin regions, which also include the world's two largest rivers by discharge, and suggest a significant correlation between their alternating periods. They note that the pattern lasts over several months and can be seen most clearly in the 1940s-1960s. The authors propose that the study presents a new mode of climate variability over the Amazon and Congo basins that has received little attention previously.

Title: A see-saw oscillation between the Amazon and Congo basins

Authors: Elfatih A. B. Eltahir, Brian Loux, Teresa K. Yamana, Arne Bomblies, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL021160, 2004

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3. Explaining ozone reductions in California pine forests

A previously unmeasured type of very reactive particle in California's pine forests may be responsible for enhancing ozone uptake in the forests and affecting the tropospheric chemical composition. Goldstein et al. report that thinning of the forests, which dramatically enhanced natural hydrocarbon emissions from the trees, also stimulated ozone uptake within the forest canopy. They suggest that the observation proves that the unmeasured natural emissions, called biogenic volatile organic compounds, released from pine needles and bark similarly to commonly measured emissions, are so reactive that they are lost via ozone oxidation before they can escape the forest canopy. The authors suggest that the volatile organic compounds may be the dominant cause of ozone deposition in pine forests and should be included in climate models. Such inclusions would affect emission inventories and estimates for ozone and atmospheric chemistry on local, regional and global scales.

Title: Forest thinning experiment confirms ozone deposition to forest canopy is dominated by reaction with biogenic VOCs

Authors: Allen H. Goldstein, M. McKay, M. R. Kurpius, G. W. Schade, A. Lee, R. Holzinger, University of California, Berkeley, California, USA; R. A. Rasmussen, Oregon Graduate Institute, Beaverton, Oregon, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL021259, 2004

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4. Technique improves gas exchange measurement

A new technique to measure dimethyl sulfide (DMS) can allow scientists to vastly improve their estimates of the trace gas exchange over the ocean and identify its effects on the marine environment. Huebert et al. report that by using a modified atmospheric pressure ionization mass spectrometer, they were able to calculate fluctuations in the atmospheric pollutant over a shorter time scale and with greater accuracy than previously possible. Current estimates are often flawed because the slow response time of existing methods cannot measure flux changes during rapidly changing conditions at sea. The authors suggest that the new method will allow them to better investigate the air-sea gas transfer and predict how variables like wind speed, surface films and wave characteristics affect DMS, which can influence marine clouds and climate over the ocean.

Title: Measurement of the sea-air DMS flux and transfer velocity using eddy correlation

Authors: Barry J. Huebert, Byron W. Blomquist, University of Hawaii at Manoa, Honolulu, Hawaii, USA; J. E. Hare, Cooperative Institute for Research in Environmental Studies, University of Colorado, Boulder, Colorado, USA; C. W. Fairall, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA; James E. Johnson, Timothy S. Bates, National Oceanic and Atmospheric Administration, Seattle, Washington, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL021567, 2004

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5. Tracing water flow through Indonesia

Following radioactive tritium in the Pacific has allowed researchers to measure the transport path and speed of water passing through the Indonesian Archipelago into the Indian Ocean. Jean-Baptiste et al. used tritium to trace water movement from the North Pacific in its convoluted passage through the Indonesian islands and investigated the effect of climate patterns on the flow. Tritium was introduced during nuclear testing in the early 1960s and remains easily identifiable in the upper portion of Pacific waters. The authors report that the average speed and transit time for water passage though the region's straits are consistent with previous studies based on moored instruments, although earlier observations produced wide variability in predicting the flow. The researchers suggest that the radioactive tracer can predict long-term changes in the water flow and indicate that fluctuations in earlier estimates likely came from sea surface changes associated with the El Nino oscillation.

Title: Temporally integrated estimate of the Indonesian throughflow using tritium

Authors: P. Jean-Baptiste, J. C. Dutay, E. Fourre, Pierre Simon Laplace Institute, Gif-sur-Yvette, France;
W. J. Jenkins, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA;
V. Leboucher, Pierre Simon Laplace Institute, Gif-sur-Yvette, France, and University of Paris, Paris, France;
M. Fieux, University of Paris, Paris, France.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020854, 2004

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6. Atmospheric chemistry's enhanced effect on organic aerosols

Chemical processes in the atmosphere may remove nearly as much organic carbon from the troposphere as rain, which was previously considered the major mechanism for eliminating the pollutant particles. Molina et al. report that organic aerosols, which are abundant in the troposphere and can affect cloud formation and climate, can be quickly broken down after a chemical reaction with ubiquitous hydroxide compounds. The authors show that particles containing compounds such as paraffin wax are readily volatized by these and subsequent reactions, whereas inorganic particles are better able to resist the breakdown. The researchers' laboratory experiments also show the removal rate for organic particles and indicate that other compounds, such as soot, may experience a similar reaction in the presence of hydroxyl radicals. Their results may necessitate the revision of global circulation and atmospheric transport models to account for the changes in the lifespan of pollutant aerosols in the environment.

Title: Atmospheric evolution of organic aerosol

Authors: Mario J. Molina, A. V. Ivanov, S. Trakhtenberg, L. T. Molina, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020910, 2004

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7. Linking Japanese and North American plates

Simultaneous observations of two minor seismic events in Japan indicate that slow slip events and their associated tremors may help indicate stress on the underlying tectonic plate that is capable of producing major earthquakes in the region. Obara et al. used seismic data to investigate the tremor activity and crustal deformation near the Philippine Sea plate in western Japan and suggest that the accumulation of slow slip events may change the angle of the ocean-bottom crust and help initiate larger quakes. The authors report that slow slip events occur nearly every other month near Shikoku and are accompanied by deep tremors similar to minor quakes regularly seen in North America's Cascadia subduction zone. The researchers indicate that although the frequency of the tremors is slightly different in the two regions, the findings from Cascadia can be used to infer information about the frictional properties of the Japanese system that may help predict the earthquake hazards there.

Title: Episodic slow slip events accompanied by non-volcanic tremors in southwest Japan subduction zone

Authors: Kazushge Obara, Hitoshi Hirose, Fumio Yamamizu, Keiji Kasahara, National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020848, 2004

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8. Simulating cloud patterns on Jupiter and Saturn

Researchers have successfully recreated in laboratory experiments the unusual patterns seen in cloud bands circling Jupiter and Saturn. Read et al. suggest that normal planetary rotation creates periodic organized systems of clouds in the planets' turbulent atmospheres that lead to the discolorations seen around the two giants and may explain similar features observed in Earth's oceans. Such banded features and winds have long been observed in telescopic images of the two planets, but their origin has not been conclusively determined. The researchers expanded on previous numerical and theoretical studies by conducting experiments with a 14-meter [46-foot] diameter turntable, on which they generated and maintained zonal jets under simulated rotational conditions. They then studied the patterns over extended periods as the jets evolved and changed in response to experimental variables. The authors confirmed the conditions needed to create and sustain the regional atmospheric patterns and indicate that the new information could allow them to better estimate the circulation patterns in the future.

Title: Jupiter's and Saturn's convectively driven banded jets in the laboratory

Authors: P. L. Read, Y. H. Yamazaki, S. R. Lewis, P. D. Williams, K. Miki-Yamazaki, University of Oxford, Oxford, United Kingdom;
J. Sommeria, H. Didell, A. Fincham, Laboratory of Geophysical and Industrial Coriolis Flows (LEGI), Grenoble, France.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL020106, 2004

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9. Effect of dust layer, dryness on climate patterns

A new method to model the effects from dust storms on the tropical climate has replicated some observed features from Saharan dust storms that have traveled over the Atlantic Ocean. Stephens et al. suggest that their numerical technique to study the effects of dust on the formation and organization of tropical convection could help researchers better examine water pattern changes and the atmospheric results from the storms. Such dust regularly enters the environment from arid regions and results in changes to the normal rain and cloud distribution downwind. The authors report that even a thin layer of stationary dust can significantly influence the initiation of tropical heating and that swirling dust-laden winds can produce local areas of warm air and water similar to a monsoon circulation. The researchers indicate that the dryness of air surrounding the dust layer has an important influence over its ability to affect the ocean environment and atmospheric circulation.

Title: On the radiative effects of dust on tropical convection

Authors: Graeme L. Stephens, Normal B. Wood, Lyle A. Pakula, Colorado State University, Fort Collins, Colorado, USA.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL021342, 2004

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10. Special section on surface ocean-lower atmosphere study

The 16 December 2004 print issue of Geophysical Research Letters features a collection of papers presenting the results from the October-November 2002 research cruise that made up the pilot study for the Surface Ocean-Lower Atmosphere Study (SOLAS) project. Wallace and Bange introduce the eight-paper section that focuses on the biogeochemical interactions between the surface ocean and atmosphere within the tropical North Atlantic. The expedition was part of an international global change research initiative to investigate the interactions and feedback between the ocean and atmosphere, specifically looking at how the coupled system is affected by climate change. Some findings from the section's authors include airborne concentrations of environmentally important trace gases in the tropical Atlantic, which can influence global climate conditions, and chemical profiles of the water at varying depths that can affect biotic growth. The researchers also report their findings on the effects from iron deposition in the open ocean.

Title: Introduction to special section: Results of the Meteor 55: Tropical SOLAS Expedition

Authors: Douglas W. R. Wallace, Hermann W. Bange, Leibniz Institute for Sea Sciences, Kiel, Germany.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL021014, 2004

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