1. Re-eruption potential of Mt. Etna
2. The "perfect" equatorial typhoon
3. First ground-based measurements of aerosol-cloud interaction
4. Erosion of the Earth's plasmasphere
5. First direct measurement of polar mesospheric clouds
6. Direction of magnetic field can affect radio signals impact on ionosphere
7. Predicting avalanche fracture dynamics
8. Methane hydrates stronger than expected
9. Measuring methane hydrates on the ocean floor
10. Steam removal for electricity generation depleting underground reservoirs

An analysis of Mt. Etna's "plumbing system" suggests that the regularly erupting volcano is again due for another spectacular blowup. Caracausi et al. monitored the gas emissions twice monthly over five years from four stations spaced approximately 60 kilometers [40 miles] apart on opposite sides of the mountain. The authors detected emissions associated with rising magma, suggesting that the volcano's underground system is much more extensive than previously reported. Their gas readings, which they propose can also be used elsewhere to estimate the likelihood of a volcanic eruption, indicated that magma storage inside the volcano is occurring at a shallow depth, a sign that a large quantity of magma has collected near the surface of the volcano and is ready to flow in the event of an eruption. The authors propose that the volcano is again at risk of spewing massive plumes of lava and ash skyward similar to its 2001 eruption that affected Europe and North Africa.

Title: Mount Etna: Geochemical signals of magma ascent and unusually extensive plumbing system

Authors:
Antonio  Caracausi, R. Favara, S. Giammanco, F. Italiano, A.Paonita, G. Pecoraino, A. Rizzo, National Institute of Geophysics and Vulcanology, Palermo Section, Palermo, Italy;
P. M. Nuccio, University of Palermo, Palermo, Italy.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL015463, 2003

An unprecedented typhoon that straddled the equator around Christmas 2001 was made by a confluence of weather conditions that created the "perfect" tropical storm. Chang et al. analyzed the conditions preceding Typhoon Vamei, the first-ever recorded tropical cyclone formed almost directly over the equator, with the 
storm circulation whipping over both the northern and southern hemispheres. Their statistical model showed that such an event occurs only once every 300-400 years. Normally, decreased wind rotation from a weakened Coriolis effect near the equator prevents cyclones from forming there, but the recent typhoon was created by a collision of two powerful systems in the South China Sea. The researchers conclude that an anomalously strong, warm and slow-moving system lingering at the tip of the South China Sea clashed with an equally strong, cold surge from north of the equator. The authors suggest that the combination of the two systems, along with a perfectly placed equatorial wind vortex, created a violent cyclone never seen there before. 

Title: Typhoon Vamei: An equatorial tropical cyclone formation

Authors: 
Chih-Pei Chang Chang, Ching-Hwang Liu, Hung-Chi Kuo, Naval Postgraduate School, Monterey, California.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016365, 2003

The first ground-based measurements of the "Twomey" effect, which hypothesizes that higher atmospheric aerosol concentrations result in higher concentrations of cloud droplets, could provide an easier measure to estimate cloud-aerosol interactions. Feingold et al. used cloud radar, lidar, and other remote-sensing instruments to monitor the aerosol impact on clouds, thus providing a cost-effective alternative to study the effect. Previously, researchers used expensive and complex aircraft studies or satellite remote sensing, which cannot measure the aerosols beneath clouds, to examine the effect of airborne aerosols on clouds. The new method allowed the researchers to estimate changes to the microphysics of non-precipitating, ice-free cloud from changes in aerosol levels. The authors suggest that this new method can be used to measure the long-term effect of the relationship between atmospheric pollutants and climate conditions from ground sensors at a relatively low cost.

Title: First measurements of the Twomey indirect effect using ground-based remote sensors

Authors: 
Graham Feingold, Wynn L. Eberhard, National Oceanic and Atmospheric Administration, Boulder, Colorado; 
Dana E. Veron, Michael Previdi, Rutgers University, New Brunswick, New Jersey.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016633, 2003

Researchers have uncovered new insights into "plasmaspheric erosion" and how it is linked to conditions in the interplanetary magnetic field (IMF). Goldstein et al. analyzed ultraviolet satellite images of the plasmasphere, a semicircular envelope of ionized gas around the Earth, that show the first reported observations of the 
global effects of plasmaspheric erosion. Plasmaspheric erosion occurs when the outer layers of the plasmasphere are stripped away during times of enhanced geomagnetic activity. Their analysis shows that plasmaspheric erosion is directly driven by changes in the IMF, but also noted that there is a 30-minute time delay 
between an IMF change and the onset of plasmaspheric erosion. From the delay, the researchers infer that the IMF doesn't act directly on the plasmasphere, but instead must first affect other regions of the Earth's space environment.

Title: IMF-driven plasmasphere erosion of 10 July 2000

Authors: 
Jerry Goldstein, P. H. Reiff, Rice University, Houston, Texas; 
B. R. Sandel, W. T. Forrester, University of Arizona, Tucson, Arizona.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016478, 2003

The first direct global-scale dynamical analysis of polar mesospheric clouds (PMCs) from satellite observations provides new insight into the variability of their formation. Merkel et al. analyzed cloud brightness data retrieved from the Student Nitric Oxide Explorer satellite's ultraviolet spectrometer, observing a five-day planetary wave from PMC measurements in the northern and southern hemispheres during each hemisphere's high-latitude summer. The short-duration waves are not easily seen from the ground, though the satellite's programming and coverage allowed the authors to find variations in the cloud brightness. The polar cloud's brightness is extremely variable, which is thought to be a direct effect of dynamical changes in the humidity and temperature at mesospheric cloud heights between 80 and 90 kilometers [50-60 miles], according to the researchers. They conclude that the five-day planetary waves contribute to the global variation of PMC development.

Title: Observations of the 5-day planetary wave in PMC measurements from the Student Nitric Oxide Explorer Satellite

Authors: 
Aimee W. Merkel W. Merkel, G. E. Thomas, S. E. Palo, University of Colorado, Boulder, Colorado; 
S. M. Bailey, University of Alaska, Fairbanks, Alaska.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016524, 2003

Altering the direction of radio waves can heat the ionosphere and create effects that can help researchers better understand of the Earth's atmospheric boundary. Pedersen et al. observed a bright spot of "airglow" when a strong radio-wave transmitter's beam was pointed parallel to the Earth's magnetic field. Such a glowing effectresults from electrons excited by the interaction between high-powered waves and the planet's ionosphere. The authors found that the bright spot from the parallel signal was at least ten times brighter than transmissions in other directions during their experiment in Alaska. Currently, most high-powered radio beams 
are directed vertically, regardless of their orientation relative to the planetary magnetic field. In such cases, the waves generally either bounce off the ionosphere or pass through it without exciting the electrons. The researchers conclude that the energy transfer to the ionosphere can be increased and the power of radio wave 
transmitters can be boosted by exploiting the Earth's magnetic field.

Title: Magnetic zenith enhancement of HF radio-induced airglow production at HAARP

Authors:
Todd Ryan Pedersen, Air Force Research Laboratory, Hanscom Air Force Base, Massachusetts; 
M. McCarrick, Advanced Power Technologies, Inc., Washington, D.C.; E. Gerken, STAR Lab, Stanford University, Stanford, California; 
C. Selcher, Naval Research Laboratory, Washington, D.C.; 
D. Sentman, University of Alaska,Fairbanks, Alaska; H. C. Carlson, Air Force Office of Scientific Research, Arlington, Virginia; A. Gurevich, Lebedev Institute of Physics, Moscow, Russia.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016096, 2003

A novel theory about the origins of avalanche initiation may help better predict these life-threatening events and could lead to a better understanding of the causes for mud- and landslides. Bazant et al. derived a new law to describe the effect of structural size on the triggering of fracture in large bodies, which describes the effect of deep snow. The authors analyzed the energy released from a crack at the base of a large snow slab and developed a formula that can estimate the stress required before the snow begins to slide. The law, similar to a known rule derived by the same author for understanding the stress needed to cause failure in solids like concrete, sea ice and ceramics, can help researchers estimate when weak spots at the base of a large snow mass can lead to a destructive energy release. Though further research is needed to confirm their results, their predictions approximate field observations from more than 100 avalanches.

Title: Size effect law and fracture mechanics of the triggering of dry snow slab avalanches

Authors: 
Zdenek P. Bazant, Goangseup Zi, Northwestern University, Evanston, Illinois; 
David McClung, University of British Columbia, Vancouver, British Columbia, Canada.

Source: Journal of Geophysical Research-Solid Earth (JGR-B) paper: 10.1029/2002JB001884, 2003

The first test to measure the ductile strength of pure methane hydrates has found that the material is far stronger than originally expected. Durham et al. found that methane hydrates are approximately 20 times stronger than water ice. The increased strength will affect estimates of the temperature and convection properties where hydrates are found, including the terrestrial ocean floor and the frozen moons of other planets. The new information can also help predict how hydrate formations might respond to natural or artificial loads placed on them, and could perhaps explain some elements of the historical methane release linked to an early episode of global warming. The researchers' testing method differed from previous efforts because of their ability to synthesize pure hydrates at high pressures, preventing water contamination and fracturing that affected other test results.

Title: The strength and rheology of methane clathrate hydrate

Authors: 
William B. Durham, We Zhang, Lawrence Livermore National Laboratory, Livermore, California; 
Stephen H. Kirby, Laura A. Stern, U.S. Geological Survey, Menlo Park, California.

Source: Journal of Geophysical Research-Solid Earth (JGR-B) paper: 10.1029/2002JB001872, 2003

A team of researchers has used nuclear magnetic resonance to estimate the quantity of methane hydrates in rock and sand samples under seafloor conditions. Kleinberg et al. propose a new method to measure the concentration of hydrates from borehole measurements on the ocean floor. Such a procedure could allow scientists a technique to measure the quantity and location of methane trapped in seafloor formations, where they are known. Although seismic surveys have located widespread hydrate deposits under permafrost and beneath continental slopes, there is currently no convenient or accurate measure of hydrate concentrations The authors suggest that the nuclear magnetic resonance assay can measure the exact quantity and location of gashydrates in earth formations and may provide insight into how the frozen hydrates, well known as a possible energy source or a potential reservoir of greenhouse gas, grow within sediments.

Title: Seafloor nuclear magnetic resonance assay of methane hydrate in sediment and rock

Authors: 
Robert L. Kleinberg, C. Flaum, C. Straley, Shlumberger-Doll Research, Ridgefield, Connecticut; 
P. G. Brewer, G. E. Malby, E. T. Peltzer III, G. Friederich, Monterey Bay Aquarium Research Institute, Moss Landing, California; 
J. P. Yesinowski, Naval Research Laboratory, Washington, D.C.

Source: Journal of Geophysical Research-Solid Earth (JGR-B) paper: 10.1029/2001JB000919, 2003

Steam removed from below one of California's hot geysers to generate electricity is depleting the underground reservoirs, according to an analysis by Gunasekera et al. The researchers used a surface monitoring system to study the subterranean environment below The Geysers geothermal area in northern California, where 
steam is harvested to provide a portion of the electricity for the area. The authors used seismic tomography, a process similar to a CAT scan for the Earth, to provide below ground images of the hot water reservoir. Their study showed a decrease in the amount of water contained in the reservoir between 1991 and 1998, evidenced by an increasing volume filled only with steam. The three-dimensional images, recorded from a system that monitored small quakes likely caused by the vast water removal, potentially can be used to estimate the properties and potential hazards in places where subsurface changes and from water, magma, steam or other geological processes affect the surface.

Title: Reservoir depletion at The Geysers geothermal area, California, shown by four-dimensional seismic tomography

Authors: 
Rashmin C. Gunasekera, B. R. Julian, U.S. Geological Survey, Menlo Park, California; 
G. R. Foulger, University of Durham, Durham, United Kingdom.

Source: Journal of Geophysical Research-Solid Earth (JGR-B) paper: 10.1029/2001JB000638, 2003

*****
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 Emily Crum at ecrum@agu.org, indicating which one(s). Include your name, the name of your publication, and your phone and fax number. State
whether you prefer to receive the paper(s) as pdf attachments by email or as a fax.

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.
###