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1. Continued emissions from banned chemicals

Although production of ozone-destroying methylchloroform products was banned in the United States after 1996, and government and industry reports have stated that consumption of the material ceased in 1997, new research indicates ongoing emissions of the compound in the United States. Millet and Goldstein present evidence from three observation stations, including one each in the eastern, central and western United States, showing traces of methylchloroform in the atmosphere near urban areas. Their study found a significant decline in the airborne emissions from nearly 19 to approximately 3 gigagrams per year between 1997-2002 after the production ban under the Montreal Protocol. They point out that the compound, used in industrial solvents, aerosol cleaners, and adhesives, can survive in the atmosphere for 5-6 years and destroy ozone through a chemical reaction in the stratosphere. The researchers suggest that the continued emissions are likely from stockpiled and recycled material.

Title:
Evidence of continuing methylchloroform emissions from the United States

Authors:
Dylan B. Millet, Allen H. Goldstein, University of California, Berkeley, California, USA.

Source:
Geophysical Research Letters (GL) paper 10.1029/2004GL020166, 2004

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2. Flowers that destroy high-latitude ozone

Frost "flowers" in sea ice may be responsible for heightened tropospheric ozone depletion in both polar regions, as the flower-shaped ice formations are rich with bromide ions that are blown into the atmosphere. Kaleschke et al. analyzed satellite estimates of worldwide bromine levels and sea ice coverage and found a correlation between frost flowers and ozone depletion. The authors report that water vapor commonly blows over newly formed flowers in the ice, releasing gas-phase bromine molecules that can destroy ozone and create bromine monoxide in the atmospheric boundary layer. They note that the flowers contain nearly triple the sea salt ion concentrations of the high-latitude seawater and can release an explosion of bromine during long polar sunrise periods. The researchers suggest that trace gases produced by frost flowers may explain the huge amounts of aerosols seen in the polar troposphere and the thinning of the ozone layer during the polar sunrise.

Title:
Frost flowers on sea ice as a source of sea salt and their influence on tropospheric halogen chemistry

Authors:
Lars Kaleschke, A. Richter, J. Burrows, O. Afe, G. Heygster, J. Notholt, Institute of Environmental Physics, University of Bremen, Germany;
A. M. Rankin, H. K. Roscoe, British Antarctic Survey, Natural Environment Research Council, Cambridge, United Kingdom;
J. Hollwedel, T. Wagner, Institute of Environmental Physics, University of Heidelberg, Germany;
H.-W. Jacobi, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany.

Source:
Geophysical Research Letters (GL) paper 10.1029/2004GL020655, 2004

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3. Measuring the ionosphere from lower altitudes

A new experiment confirms that the more easily accessible region approximately 150 kilometers above sea level provides a good assessment of electric fields in the Earth's ionosphere. Chau and Woodman show good agreement in wave movement between the two upper atmospheric regions after measuring vertical and zonal wind velocities at 150 kilometers [93 miles] above their observation station in Peru with Doppler radar and comparing that data to extrapolated incoherent scatter radar values and altitude profiles from the ionosphere above the same location. Their study found better agreement in the two measurements in the afternoon than morning, which they attribute to effects from day-night shifts, and shows that seasonal and solar conditions can also affect the waves. The researchers suggest that although further study is needed, their results can be used to measure the electrodynamics at high altitudes and at latitudes close to the magnetic equator.

Title:
Daytime vertical and zonal velocities from 150-km echoes: Their relevance to F-region dynamics

Authors:
Jorge L. Chau, Ronald F. Woodman, Jicamarca Radio Observatory, Geophysical Institute of Peru, Lima, Peru.

Source:
Geophysical Research Letters (GL) paper 10.1029/2004GL020800, 2004

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4. Special section on Saturnian moon Titan prior to Cassini mission

The 16 September 2004 issue of Geophysical Research Letters features a collection of papers presenting the current state of research on Saturn's moon Titan prior to the landing of the Huygens-Cassini mission in January 2005. Imke de Pater introduces the section, the product of a workshop held at the University of California Berkeley in November 2003. That meeting brought together a collection of theoretical and observational results from the recent past in order to set the stage for the analysis of new data from the spacecraft. The joint NASA/ESA mission is intended to probe from Titan's atmosphere to its surface during a four-year orbit and planned landing. De Pater notes that researchers are encouraged to continue to collect data for comparison to the spacecraft's observations during the coming years and suggests that the combined information is necessary to develop detailed atmospheric circulation models that could be used to study the formation and destruction of haze on the moon.

Title:
Introduction to special section: Titan: Pre-Cassini view

Authors:
Imke de Pater, University of California, Berkeley, California, USA.

Source:
Geophysical Research Letters (GL) paper 10.1029/2004GL020742, 2004

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5. Plumbing the crust-mantle depths

Researchers have used seismic data from the 1996 South Island (New Zealand) geophysical measurement experiments to create a three-dimensional map of the crust-mantle depth boundary across the Australian-Pacific plate. Henrys et al. estimated the location and thickness of Moho, considered the boundary layer between the Earth's crust and mantle, beneath the mountain range in southern New Zealand, where the crust is thicker than at other sections along the tectonic plate. The authors used onshore seismic data and onshore-offshore information to measure the reflection of the iron-rich mantle through the thinner crust in order to estimate the maximum depth of the Moho. They suggest that the three-dimensional map creates a wide-angle view along the depths of the Southern Alps more efficiently than existing tomographic techniques and placed the "root" of the crust at approximately 45 kilometers [28 miles] below the surface and nearly 80 kilometers [50 miles] across.

Title:
Mapping the Moho beneath the Southern Alps continent-continent collision, New Zealand, using wide-angle reflections

Authors:
Stuart A. Henrys, D. J. Woodward, J. Yu, Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand;
D. Okaya, University of Southern California, Los Angeles, California, USA.

Source:
Geophysical Research Letters (GL) paper 10.1029/2004GL020561, 2004

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6. Using GPS to measure remote earthquakes

High-rate Global Positioning System (GPS) observations can complement existing seismic measurement techniques to estimate the fault motion during large earthquakes. Ji et al. compared the data from detailed GPS measurements recorded during the 2003 San Simeon earthquake in California with information from a sensitive motion and seismic network near the well-studied earthquake zone and report that the two sources produced similar results. The authors analyzed data from ground measurement stations and seismic observation platforms along with GPS observations and report that both methods provided evidence that the San Simeon quake ruptured in a fan-shaped pattern around its hypocenter. Based on their findings, the researchers suggest that GPS could be used to produce estimates of the slip history and ground motion of remote earthquakes where geodetic and geological sensors are not available.

Title:
Slip history of the 2003 San Simeon earthquake constrained by combining 1-Hz GPS, strong motion, and teleseismic data

Authors:
Chen Ji, Ying Tan, California Institute of Technology, Pasadena, California, USA;
Kristine M. Larson, Kyuhong Choi, University of Colorado, Boulder, Colorado, USA;
Kenneth W. Hudnut, U.S. Geological Survey, Pasadena, California, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2004GL020561, 2004

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7. "Warming hole" in the midwestern United States

Low-level circulation patterns in the midwestern United States may be responsible for that part of the country's resistance to the recent warming seen over the rest of North America. Pan et al. suggest that a link between atmospheric circulation and precipitation likely replenishes soil moisture during the summer and suppresses daytime maximum temperatures. The researchers report that the feedback in the hydrological cycle creates a regional minimum temperature increase zone within the continent warmed by enhanced greenhouse gases. The authors used a regional climate model to estimate current and future climate scenarios and found a "warming hole" in the central U.S. during June-September that is not reflected in the global climate models they examined. They note that the daily maximum surface air temperature increase in summer was less than 0.5 Kelvin [0.5 degrees Celsius, 0.9 degrees Fahrenheit] in the hole, compared to an average increase of approximately 3 Kelvin [3 degrees Celsius, 5 degrees Fahrenheit] over the rest of the country during the past few decades.

Title:
Altered hydrologic feedback in a warming climate introduces as "warming hole"

Authors:
Zaitao Pan, St. Louis University, St. Louis, Missouri, USA;
Raymond W. Arritt, Eugene S. Takle, William J. Gutowski Jr., Christopher J. Anderson, Moti Segal, Iowa State University, Ames, Iowa, USA.

Source:
Geophysical Research Letters (GL) paper 10.1029/2004GL020528, 2004

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8. Tenuous link between ocean and Europa's surface

The uneven and rough topography of Jupiter's icy moon Europa is likely caused by a folding-type uplift of frozen material from within the moon's thick ice shell. Schenk and Pappalardo analyzed high-resolution stereo images of the satellite's surface and suggest that disrupted terrain seen in Europa's topography are consistent with folding, or diapiric, uplift rather than a refreezing of thin ice by a subsurface ocean. The moon is thought to have a liquid ocean buried beneath its frozen exterior, although researchers have puzzled over the source of its uneven and undulating topography. The authors used Galileo spacecraft observations to study the landforms and possibly determine the thickness of the ice sheet and estimate whether the ocean may be warm enough to potentially sustain biological life. Their report indicates that the ice is likely between 10-25 kilometers [6-16 miles] thick, providing evidence that any link between the ocean and the moon's surface must first pass though the ice.

Title:
Topographic variations in chaos on Europa: Implications for diapiric formation

Authors:
Paul M. Schenk, Lunar and Planetary Institute, Houston, Texas, USA;
Robert T. Pappalardo, University of Colorado, Boulder, Colorado, USA.

Source:
Geophysical Research Letters (GL) paper 10.1029/2004GL019978, 2004

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9. Disaster modeling in the Netherlands

Model predictions of extreme weather along the Dutch coast can allow emergency workers to simulate the effects of rare events like a giant storm surge or long droughts. Van den Brink et al. used a model's assessment of extreme events in the current climate, generated from past seasonal forecasts from the European Centre for Medium-Range Weather Forecasts, to estimate the levels of extreme climate conditions in the Netherlands, approximately 40 percent of whose land mass is below sea level. The seasonal forecast archive contain nearly 1600 years of high-resolution predictions, allowing the researchers to observe the possible causes and effects of disastrous high sea-level flooding from strong winds, as well as other disruptive events like massive precipitation or prolonged high temperatures. The computer simulations provides unprecedented accuracy for events so rare and violent that they occur only once in 1,000 years, which can allow researchers to estimate the best design and protection before a potentially catastrophic episode.

Title:
Improving 10(4)-year surge level estimates using data of the ECMWF seasonal prediction system

Authors:
Henk W. van den Brink, G. P. Konnen, J. D. Opsteegh, G. J. van Oldenborgh, G. Bergers, Royal Netherlands Meteorological Institute, De Bilt, Netherlands.

Source:
Geophysical Research Letters (GL) paper 10.1029/2004GL020610, 2004

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10. Stratospheric winds' influence on the lower atmosphere

New calculations with a simple atmospheric model show how stratospheric conditions can affect weather systems in the troposphere. Wittman et al. found that the presence of a high-latitude stratospheric jet can influence the development of weather systems. While previous research had observed the downward propagation of seasonal circulation patterns like the Arctic Oscillation from the stratosphere to the troposphere, the new calculations provide a possible mechanism for how the stratospheric winds may affect the troposphere. The authors demonstrate that the addition of a strong westerly jet in the stratosphere causes tropospheric weather systems to track further toward the pole, noting that the average of the directional changes resembles the results from the Arctic Oscillation. The modeling experiments can allow researchers to understand how the stratosphere affects the troposphere and may improve efforts to improve seasonal weather forecasts and predict the effects of ozone depletion on the climate.

Title:
Stratospheric influence on baroclinic lifecycles and its connection to the Arctic Oscillation

Authors:
Matthew A. H. Wittman, Lorenzo M. Povani, Andrew J. Charlton, Columbia University, New York, New York, USA;
Richard K. Scott, NorthWest Research Associates, Inc., Bellevue, Washington, USA.

Source:
Geophysical Research Letters (GL) paper 10.1029/2004GL020503, 2004