Public Release: 

AGU Journal Highlights - 25 May 2004

American Geophysical Union

1. Unexpected frequency of planetary wave reflection

A significant amount of planetary wave activity is reflected, rather than absorbed, in the subtropical upper troposphere, sending the waves beyond the tropics where they can affect weather and climate patterns. Abatzoglou and Magnusdottir analyzed more than 40 years of daily data used to detect planetary wave breaking and found that nearly one-third of all such events result in reflection instead of absorption. They note that nearly all of the breaking events occur in the Northern Hemisphere over the Pacific and Atlantic Ocean basins during spring, summer, and fall. In winter, however, stronger atmospheric winds hinder the absorption of the breaking waves. The authors suggest that a stronger jet stream that reaches closer to the tropics is more likely to cause the planetary waves to reflect from the atmosphere toward the equator. The researchers suggest that the unexpected frequency of reflected events may prompt a re-examination of circulation models that predict seasonal climate changes.

Title: Nonlinear planetary wave reflection in the troposphere

Authors: John T. Abatzoglou, Gudrun Magnusdottir
University of California

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019495, 2004.

2. Estimating phytoplankton cycles in Arctic waters

The disappearance of the annual sea ice in Arctic waters has a significant effect on the phytoplankton [minute, floating plants] growth cycle in the high-latitude sea and can affect the region's food chain and marine ecosystem. Arrigo and van Dijken analyzed the relationship between sea ice coverage and the abundance of living plants in the Canadian Arctic and report that open water enclosed within ice floes, known as a polynya, influences the timing, extent, and intensity of phytoplankton growth. The authors investigated five years of satellite data in the southeastern Beaufort Sea and compared their findings to recently collected information from two similarly large Arctic polynyas. While they found wide year-to-year variability in the seasonal climate and water conditions, they note that the trends of phytoplankton growth were comparable among the three major Arctic polynyas. The researchers propose that their results can be used to improve estimates of the region's ecological conditions.

Title: Annual cycles of sea ice and phytoplankton in Cape Bathurst polynya, southeastern Beaufort Sea, Canadian Arctic

Kevin R. Arrigo, Gert L. van Dijken
Stanford University, Stanford, California

Source: Geophysical Research Letters (GL) paper 10.1029/2003GL018978, 2004

3. Carbon dioxide release may predict tectonic activity

The rate of carbon dioxide release from underground waterways may help researchers understand the initiation of earthquakes in central Italy and could explain the tectonic behavior in similar cases worldwide. Chiodini et al. provide the first regional map of carbon dioxide emitted from below-ground reservoirs and springs and suggest that gas overpressurization may trigger the earthquakes observed in the region's Apennine mountain range. The authors note a connection between the underground carbon dioxide discharge rate and seismic activity in central and southern Italy and propose that the gaseous release is related to the ancient volcanism, seismic activity, and tectonic shifts seen in the area. Their map shows the distribution of dissolved inorganic carbon from deep sources in waterways throughout central Italy, including more than 100 fast-moving springs, which can be used to model the relationship between deep upwelling and crustal deformation.

Title: Carbon dioxide Earth degassing and seismogenesis in central and southern Italy

Giovanni Chiodini, S. Caliro, G. Ventura
National Institute for Geophysical and Vulcanology
Naples, Italy

C. Cardellini, F. Frondini
University of Perugia, Perugia, Italy

A. Amato, E. Boschi,
National Institute for Geophysical and Vulcanology

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019480, 2004.

4. Ionospheric heating likely modifies upper atmosphere

A new technique to measure powerful waves in the upper atmosphere indicates that heat in the ionosphere can stimulate the electrical field and enhance oscillations within the heated region. Hughes et al. present detailed radar observations of electromagnetic emissions detected from the ground and report that high-altitude heating strongly and symmetrically enhances the wave fluctuations at specific, readily monitored frequencies. The authors suggest that even small, temporary heat sources can directly modify the upper atmosphere in local areas and create unusual wave patterns that can be recorded by ground-based monitors as stimulated electromagnetic emissions. Such information is useful in estimating the plasma processes related to warming in the ionosphere, whether from natural or artificial sources. They note that the new data may allow better simulations of the planetary geomagnetic field and improve existing theories on high-frequency wave enhancement.

Title: SuperDARN observations of spectral enhancements excited during an ionospheric heating experiment

J. M. Hughes
W. A. Bristow
R. T. Parris
Geophysical Institute, University of Alaska
Fairbanks, Alaska

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019613, 2004.

5. Revising measure for underground fluid flow

The existing measure used to estimate fluid flow through rocky underground material likely provides a poor projection of the actual flow behavior. Matthai and Belayneh simulated the flow velocity of liquid through fractured underground conditions and suggest that the fractures between rocks, which were thought to enhance or redirect the fluid flow, have a strongly variable effect on perturbing the liquid movement that depends on the fracture geometry and the properties of the rock. The authors used field and laboratory data of fluid flow through tightly packed rocks to construct virtual flow models. Their study indicates that the current field measure, which uses effective rock permeability to project fluid velocity, rarely provides a useful average to estimate the actual flow. They instead note that as the fracture width and number of fractures increases, the liquid flow varies from not being affected to being essentially bottled. Such studies are useful to projecting the liquid motion and potential dangers from hazardous waste storage sites and confined polluted areas.

Title: Fluid flow partitioning between fractures and a permeable rock matrix

Stephan K. Matthai
Madefro Belayneh
Imperial College London
London, United Kingdom

Source: Geophysical Research Letters (GL) paper 10.1029/2003GL019027, 2004.

6. Unexplained low-temperature region in Poland's subsurface

A borehole temperature analysis in central Europe reveals an unexplained low-temperature region deep within the former permafrost that may affect theories of a gradual warming since the last glacial period. Safanda et al. analyzed deep temperature profiles in northeastern Poland, an area that was exposed to extreme cold during the past ice age but was not protected by a huge ice sheet that covered the northern high latitudes. The authors note that the region's temperature-depth profiles indicate that the climate since the last glacial period has risen by nearly 18 degrees Celsius [32 degrees Fahrenheit]. The researchers compared the area's current ground temperatures, including changes attributed to manmade warming, with the estimated temperature increase since the ice age and suggest that, because of the anomalously deep permafrost that reached further than 500 meters [2,000 feet] at the end of the last ice age, it likely took nearly 10,000 years for the frozen ground to melt.

Title: Geothermal evidence of very low glacial temperatures on a rim of the Fennoscandian ice sheet

Jan Safanda
Geophysical Institute
Academy of Sciences of the Czech Republic
Prague, Czech Republic

Jan Szewcyk
Polish Geological Institute
Warsaw, Poland

Jacek Majorowicz
NGC Ltd.
Edmonton, Alberta, Canada
Northern Plains
Climate Research Center
University of North Dakota
Grand Forks, North Dakota

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019547, 2004.

7. Using background noise to improve seismic models

Researchers have devised a new way to interpret natural seismic noise recorded by existing receivers that may improve the accuracy of efforts to map Earth's interior. Shapiro and Campillo show a technique to extract Rayleigh waves, a type of surface wave with known characteristics, from observations of ambient seismic noise caused by oceanic and atmospheric sources. Surface waves produced during earthquakes are commonly used to generate seismic tomographic maps, but such events cannot provide reliable models, because of their wide distribution over the Earth's surface and the difficulty of determining the source of the seismic waves. The authors suggest that a new method can be created to use the surface-wave dispersion characteristics measured from the background seismic noise that will be able to improve the resolution of seismic tomographic models.

Title: Emergence of broadband Rayleigh waves from correlations of the ambient seismic noise

Nikolai M. Shapiro
University of Colorado
Boulder, Colorado

M. Campillo
Joseph Fourier University and French National Research Center
Grenoble, France

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019491, 2004.

8. Plasma plumes may be more common than expected

Plasmaspheric plumes, made up of dense patches of charged particles outside of Earth's plasmasphere, were found to be a common feature near the edges of the planetary shield. The plasmasphere is a region of cold and dense plasma surrounding the Earth. Moldwin et al. report that the plumes tend to appear in the aftermath of enhanced geomagnetic activity outside the main plasmasphere, which can upset satellite and radio communications and affect the development of solar storms. The authors analyzed the distribution and properties of the previously little-studied plumes observed outside the plasmapause using data from the Combined Release and Radiation Effects Satellite program and found that the plasma can exist under all levels of geomagnetic activity. They suggest that the dense plasma bulges likely escape Earth's plasmasphere as the planet rotates, leaving plumes that are swept toward the Sun by the combination of solar winds and the Earth's magnetic field.

Title: Plasmaspheric plumes: CRRES observations of enhanced density beyond the plasmapause

Mark B. Moldwin
Institute of Geophysics and Planetary Physics
University of California
Los Angeles, California

J. Howard
J. Sanny
Loyola Marymount University
Los Angeles, California

J. D. Bocchicchio
H. K. Rassoul
Florida Institute of Technology

R. R. Anderson
University of Iowa
Iowa City, Iowa
Kanazawa University
Kanazawa, Japan

Source: Journal of Geophysical Research-Space Physics (JA) paper 10.1029/2003JA010320, 2004.

9. Seasonality of volcanic eruptions

An analysis of volcanic activity over the past 300 years indicates that eruptions tend to occur seasonally during periods of local or regional surface and subsurface movements. Mason et al. report that such enhanced volcanism frequently happens seasonally in response to Earth changes related to the global water cycle. The authors point out, for example, that far more eruptions in Central America and the Alaskan Peninsula follow the annual sea level changes in the regions. They suggest that such sea level changes influence the regional atmospheric pressure and that such effects account for nearly half of all eruptions worldwide, providing a potential measure for improving volcanic eruption risk estimates. The researchers speculate that the previously identified slow deformation of Earth's surface that accompanies the annual movements of water circulation acts as a boundary on volcanoes, so that eruptions tend to be concentrated during specific seasons rather than randomly distributed throughout the year.

Title: Seasonality of volcanic eruptions

Ben G. Mason
D. M. Pyle
Cambridge University
Cambridge, United Kingdom

W. B. Dade
Institute of Theoretical Physics
Cambridge University
Cambridge, United Kingdom

T. Jupp
BP Institute for Multiphase Flow
Cambridge University
Cambridge,United Kingdom

Source: Journal of Geophysical Research-Solid Earth (JB) paper
10.1029/2002JB002293, 2004.

10. Tsunami "shadows" may allow remote detection of tidal waves

The recent observation of a tsunami "shadow," an extended dark strip on the ocean surface preceding a Hawaiian tsunami, suggests that tsunamis in the deep ocean could be remotely detected through changes in the water's surface. Oleg A. Godin suggests that the dark shadow seen during a weak tsunami in 1994 was caused by an air-sea interaction induced by tsunami-related atmospheric disturbances. Godin's theory demonstrates that a tsunami can increase the wind speed in the atmospheric boundary layer above the water, stirring up rougher seas in advance of the wave and causing a change in the water's appearance that can be detected by satellites or airplanes. Such shadows have been previously observed, but earlier studies were not able to fully explain the cause of the deep-sea discoloration. Godin reports that tsunami detection using the shadows can provide significantly more reliable and earlier warning before the large waves strike vulnerable shores and allow scientists to better study the phenomenon.

Title: Air-sea interaction and feasibility tsunami detection in the open sea

Oleg A. Godin
Cooperative Institute for Research in Environmental Sciences
University of Colorado, and National Oceanic and Atmospheric Administration
Boulder, Colorado.

Source: Journal of Geophysical Research-Oceans (JC) paper 10.1029/2003JC002030, 2004.


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