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AGU Journal Highlights - 20 May 2002

May 20, 2002

American Geophysical Union AGU Journal European Highlights - 20 May 2002

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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

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The following highlights are from Geophysical Research Letters (GRL). The research papers related to these Highlights will be printed in the next paper issue of GRL following their electronic publication.

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1. Underwater volcano chain connected by plume pulses

A dating technique that accurately gauges the age of volcanic structures shows that a string of underwater volcanic ridges more than 250 kilometers [160 miles] wide on the South Pacific seafloor are connected by a single, short-lived magma release. O`Connor et al. ["Pulsing of a focused mantle plume: Evidence from the distribution of Foundation Chain hotspot volcanism"] suggest that the individual ridges, or seamounts, of the Foundation Seamount Chain were created approximately every million years as the tectonic plate migrated incrementally westward over a plume pulsing hot matter toward the surface.

The researchers believe that the dimensions of the chain come from a relatively narrow, thin "microplate" over the hotspot plume, indicating that virtually any increase in plate thickness can prevent the plume material from reaching the surface. Their theory helps clarify the previously unexplained connection between the chain`s seamounts and ridges and accounts for recent satellite altimetry observations that indicate scattered volcanic formation in other parts of the Pacific.

Authors: John M. O`Connor, GEOMAR-Research Center for Marine Geosciences, Christian-Albrechts University, Kiel, Germany; Peter Stoffers, Christian-Albrechts University, Kiel, Germany; Jan R. Wijbrans, Vrije Universiteit, Amsterdam, The Netherlands.

Source: Geophysical Research Letters (GRL) paper 10.1029/2001GL014681, 2002

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2. Saharan dust plumes over Germany profiled

Advanced measurements of desert dust particles over Germany may help explain the properties of airborne dust and provide new information about the transport and distribution of atmospheric particles. The study by Mattis et al. ["Dual-wavelength Raman lidar observations of the extinction-to-backscatter ratio of Saharan dust"] describes the optical properties of desert dust in the visible and ultraviolet spectrums, which allowed the researchers to better infer particle characteristics. The authors analyzed observations from lidar (laser-sensing radar) to reveal the atmospheric height of dust transported over Europe from two major dust plumes that originated in the Sahara desert. The dust affects the amount of heat absorbed and sunlight reflected by the particles and in turn influences climate. The study provides key information to derive the dust particles` distribution, shape, and composition, which could provide more accurate assessments of the long-term influence of dust on Earth`s climate and energy balance.

Authors: Ina Mattis, Albert Ansmann, Detlef Muller, Ulla Wandinger, and Dietrich Althausen, Institute for Tropospheric Research, Leipzig, Germany.

Source: Geophysical Research Letters (GRL) paper 10.1029/2001GL014721, 2002

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6. Ice angle in cirrus clouds affects climate

The orientation of ice crystals in cirrus clouds can have a significant effect on global climate due to the crystals` ability to reflect incoming sunlight and trap heat from the ground below. In the first look at the alignment of the crystals in cirrus clouds, Noel et al. ["Analysis of lidar measurements of ice clouds at multiple incidence angles"] use lidar (laser-ranging radar) images to analyze the average ice crystal oscillation angle and the number of crystals aligned in the high-altitude clouds. The height of cirrus clouds typically precludes direct measurement of their ice crystal structure. The lidar images of a low-level ice cloud showed that the average crystal can fluctuate up to 12 degrees from a horizontal orientation and that approximately 20 percent of ice crystals are horizontally aligned (and provide the maximum reflectivity) at any given time. The estimates can be used better model the impact of cirrus clouds on climate change.

Authors: Vincent Noel, Helene Chepfer, Pierre Flamant, Ecole Polytechnique, Palaiseau, France; Gilles Roy, Luc Bissonnette, Defence Research Establishment Vancartier, Val-Belair, Quebec, Canada.

American Geophysical Union (AGU)