I. Highlights, including authors and their institutions
The following highlights summarize research papers in Geophysical Research
Letters (GL), Global Biogeochemical Cycles (GB) and Journal of Geophysical Research-Planets (JE).
The papers related to these Highlights are printed in the next paper issue of the journal following
their electronic publication.
1. Possible explanation for phenomenon observed prior to solar
storms
2. High frequency sea ice motion may affect Arctic dynamics
3. The connection between drought and global warming
4. Special section on Eastern Turkey Seismic Experiment
5. New method could allow space-based methane analysis
6. Gravity waves can affect large-scale circulation patterns
7. Surface photochemistry may recycle nitrogen compounds back
into atmosphere
8. First analysis of carbon sequestration in saltwater ecosystems
9. Global warming can cause long-term ocean circulation changes
10. Dark Martian dust likely glass particles from impacts
1. Possible explanation for phenomenon observed prior to solar
storms
A theoretical study that simulates the effects of solar materials as
they reach Earth's magnetosphere describes a possible cause for
large magnetic fluctuations observed during the onset of a space
weather substorm. Ji and Wolf suggest that solar plasma ejected
towards Earth can cause a temporary change in the normal incoming
magnetic field, resulting in wild fluctuations that have previously
been observed in near-Earth space early in the violent space weather
phenomenon. The change slows the motion of magnetic waves
coming towards Earth and causes a wrinkle of the magnetic field
lines, termed a firehose instability, that affects the particle
distribution in the region associated with the onset of a solar substorm. The authors conclude that the instabilities, which develop
in only a few seconds, can explain the important and puzzling
phenomenon.
Title: Firehose instability near substorm expansion-phase onset?
Authors:
Shuo Ji and Richard A. Wolf, Rice University, Houston, Texas.
Source: Geophysical Research Letters (GL) paper:
10.1029/2003GL017981, 2003
2. High frequency sea ice motion may affect Arctic dynamics
Satellite observations have confirmed that Arctic sea ice undergoes
slight daily motion in winter. Kwok et al. report ice deformation
estimates from RADARSAT imagery that observed the high Arctic
several times per day. The new data provide evidence of oscillating
ice movement that can add up to 10 centimeters [four inches] of ice
thickness over six months during winter. Earlier studies had
speculated that the ice motion would be inhibited by the strength of
the ice pack during the Arctic winter. The authors note that the
semi-diurnal ice motion observed during winter was not seen prior
to the 1970s, which they suggest may be from a previous lack of
detailed data or could be caused by the recent thinning of the Arctic
ice cover. They conclude that current sea ice dynamics models
should be modified to account for the small time-scale motions,
which can have a significant contribution to the sea ice mass budget
and affect the interactions among the Arctic Ocean and atmosphere.
Title: Sub-daily sea ice motion and deformation from RADARSAT
observations
Authors:
Ron Kwok, Glenn F. Cunningham, Jet Propulsion Laboratory,
California Institute of Technology, Pasadena, California;
William D. Hibler III, University of Alaska, Fairbanks, Alaska.
Source: Geophysical Research Letters (GL) paper:
10.1029/2003GL018723, 2003
3. The connection between drought and global warming
Researchers have identified a mechanism that may play a major role
in determining whether rainfall increases or decreases in a region
because of global warming. Neelin et al. analyzed tropical rainfall
changes associated with El Nino variability and suggest that
tropospheric warming linked with El Nino or global warming
increases the amount of surface moisture contributing to cloud
formation. Precipitation then rises as the moisture increases in the
center of convective regions where small-scale atmospheric motion
lead to cloud formation. The sum of the atmospheric processes leads
to reductions in rainfall at the borders of convection zones that are
near dryer regions. The authors used a climate model to simulate
global warming and note that the mechanism is the leading cause of
tropical drought and closely parallels a similar effect that causes El
Nino drought areas.
Title: Tropical drought regions in global warming and El Nino teleconnections
Authors:
J. D. (David) Neelin, H. Su, Institute of Geophysics and Planetary
Science, University of California at Los Angeles, California;
C. Chou, Institute of Earth Sciences, Academia Sinica, Taipei,
Taiwan, Republic of China.
Source: Geophysical Research Letters (GL) paper:
10.1029/2003GL018625, 2003
4. Special section on Eastern Turkey Seismic Experiment
The 15 December 2003 issue of Geophysical Research Letters
features a collection of papers about the Eastern Turkey Seismic
Experiment, which was designed to analyze the early stages and
consequences from the ongoing continental collision occurring
along a major fault line in Turkey. Sandvol et al. summarize the
research efforts to study the movements from shifts among three
converging tectonic plates in the region over the past 10-20 million
years. The seismic models, mapping, and geochemistry studies can
be used to estimate the lithospheric [solid Earth] structure of the
Anatolian plateau and to provide better earthquake hazard
assessments in the highly active area. Some of the new findings in
the papers include a report suggesting that widespread volcanism
has changed the interpretation of the Anatolian plateau's depth.
Title: The Eastern Turkey Seismic Experiment: The study of a
young continent-continent collision
Authors:
Gerry T. Narisma, A. J. Pitman, J. Eastman, I. G. Watterson, R. Pielke Sr., A. Beltran-Przekurat, Macquarie
University, North Ryde, New South Wales, Australia.
Source: Geophysical Research Letters (GL) paper:
10.1029/2003GL018912, 2003
5. New method could allow space-based methane analysis
A newly reanalyzed 20-year record of atmospheric methane levels
may allow researchers to better understand the cause of global
methane trends and indicates a potential method for observing
tropospheric [lower atmospheric] methane from space.
Washenfelder et al. investigated high-resolution near-infrared
spectra from the Kitt Peak National Solar Observatory in Arizona
collected between 1977 and 1995. The authors used the known
relationship between stratospheric methane and another
stratospheric tracer gas to infer tropospheric methane levels from
solar absorption data. The tropospheric methane estimates
determined by their method agreed well with existing hydrocarbon
measurements. Previous methane measurements are accurate, but
are typically limited to smaller coverage areas. The researchers
conclude that their technique may provide a new way to estimate
tropospheric methane abundances from space, which would allow
scientists an improved understanding of current atmospheric
behavior and a technique to infer future methane trends.
Title:Tropospheric methane retrieved from ground-based near-IR
solar absorption spectra
Authors:
Rebecca A. Washenfelder, P. O. Wennberg, California Institute of
Technology, Pasadena, California;
G. C. Toon, Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, California.
Source:
Geophysical Research Letters (GL) paper
10.1029/2003GL017969, 2003
6. Gravity waves can affect large-scale circulation patterns
Small-scale waves in the atmosphere and ocean likely have little
impact on their large-scale flow, but may be able to significantly
affect circulation patterns during unstable transition periods.
Williams et al. analyzed the effects of spontaneously generated
gravity waves on global flow patterns. The authors note that the
ubiquitous waves' interactions with larger atmospheric and oceanic
patterns are usually inconsequential, because of their small
amplitude and fast speed. Their study suggests, however, that the
waves, sustained by gravitational forces and Earth's rotations, can
play a significant role in determining the large-scale atmospheric
and oceanic behavior during transitions between large wave activity.
The researchers used both model and laboratory experiments to
study the affect on gravity waves' impact on ocean and tropospheric
flow and suggest that such data can help refine weather prediction and climate models.
Title: Spontaneous generation and impact of inertia-gravity waves
in a stratified, two-layer shear flow
Authors:
Paul D. Williams, P. L. Read, Clarendon Laboratory, University of
Oxford, United Kingdom;
T. W. N. Haine, Johns Hopkins University, Baltimore, Maryland.
Source: Geophysical Research Letters (GL) paper
10.1029/2003GL018498, 2003
7. Surface photochemistry may recycle nitrogen compounds back
into atmosphere
Sunlight causes nitric acid naturally deposited on ground surfaces
and vegetation to quickly break down and can lead to enhanced
nitrogen oxide concentrations in the overlying atmosphere. Zhou et
al. suggest that photolysis [light-caused chemical decomposition] on
the ground and plant surfaces degrades nitric acid into its
component parts much faster than similar chemical reactions in the
atmosphere. They also suggest that the process could explain the
high nitrogen compounds often observed in remote regions. The
authors note that the compounds emitted during the chemical
breakdown may recycle nitric acid back into the troposphere and
represent a new source of nitrogen oxides, which are a precursor for
ozone. They conclude that their laboratory and field results can help
researchers better understand the atmospheric chemistry in rural
environments.
Title: Nitric acid photolysis on surfaces in low-NOx environments:
Significant atmospheric implications
Authors:
Xianliang Zhou, Honglian Gao, Yi He, Gu Huang, Wadsworth
Center, New York State Department of Health, Albany, New York,
and State University of New York at Albany, New York;
Steven B. Bertman, Western Michigan University, Kalamazoo,
Michigan;
Kevin Civerolo, New York State Department of Environmental
Conservation, Albany, New York;
James Schwab, Atmospheric Sciences Research Center, State
University of New York at Albany, New York.
Source: Geophysical Research Letters (GL) paper: 10.1029/2003GL018620, 2003
8. First analysis of carbon sequestration in saltwater ecosystems
Salt marshes and mangrove swamps can store a higher amount of
carbon and release fewer greenhouse gases than equally sized
peatlands and other freshwater wetlands. Chmura et al. compiled
data from more than 150 sites along saltwater coasts and found that
sediment within sheltered mangrove swamps and salt marshes can
maintain a very high carbon content and may thus serve as a viable
potential sink for carbon sequestration. They also found that
although the sequestration rates drop with increasing temperatures,
an abundant quantity of sulfate in saltwater wetlands hinders the
production of methane and other greenhouse gases in the
ecosystems. Although there are still no accurate predictions for the
size of saline wetlands in the Atlantic, Pacific, and Indian oceans,
there were no previous empirical estimates for the carbon storage
potential of such wetlands worldwide.
Title: Global carbon sequestration in tidal, saline wetland soils
Authors:
Gail L. Chmura, Centre for Climate and Global Change Research,
McGill University, Montreal, Quebec, Canada;
Shimon C. Anisfeld, Yale University, New Haven, Connecticut;
Donald R. Cahoon, James C. Lynch, National Wetlands Research
Center, U.S. Geological Survey, Lafayette, Louisiana.
Source: Global Biogeochemical Cycles (GB) paper:
10.1029/2002GB001917, 2003
9. Global warming can cause long-term ocean circulation changes
Increases in carbon dioxide of human origin may have significant
long-term adverse effects on ocean chemistry, potentially causing
substantial reductions in the density of important waters. Matear
and Hirst report that a global doubling or tripling of atmospheric
carbon dioxide levels from pre-industrial levels, followed by an
extended leveling-off period, could remove dissolved oxygen from
the deep ocean and affect ocean circulation patterns. The authors
note that global warming resulting from the elevated carbon dioxide
levels would affect the upper ocean layer over time, changing the depth
of organic particulate-filled subsurface waters and reducing
the overturning circulation that recycles dense deepwater throughout
the ocean. The researchers simulated atmospheric carbon dioxide
increases, followed by several centuries of constant carbon dioxide
levels using an integrated ocean-climate model, and found that the
ocean's response led to progressive changes that would alter the its
ventilation and change its overall circulation.
Title: Long-term changes in dissolved oxygen concentrations in the
ocean caused by protracted global warming
Authors:
Richard J. Matear, CSIRO Marine Research and the Antarctic
Cooperative Research Center, Hobart, Tasmania, Australia;
A. C. Hirst, CSIRO Atmospheric Research, Aspendale, Victoria,
Australia.
Source: Global Biogeochemical Cycles (GB) paper:
10.1029/2002GB001997, 2003
10. Dark Martian dust likely glass particles from impacts
Many of the dark materials seen on Mars and several of the features
found at the Pathfinder and Viking Martian landing sites may be
glass or larger once-molten materials caused by impacts. Schultz
and Mustard counter the widely held view that the mobile dark
materials are volcanically derived windblown particles. The authors
note that many of the materials observed on Mars do not conform to
the absorption properties expected of a granular composition and
suggest that part of the Martian sediment is made up of glass
particles caused by meteor impacts. Field studies on Earth have
shown that such impacts over millions of years have also caused
similar melt-glass materials on the Moon and around terrestrial
craters. The researchers conclude that the Martian atmosphere has
retained the glass particles from historical impacts for billions of
years, although many of the particles are buried or continually
blown across the landscape by winds.
Title: Impact glasses on Mars
Authors:
Peter H. Schultz, John F. Mustard, Brown University, Providence,
Rhode Island.
Source: Journal of Geophysical Research-Planets (JE) paper:
10.1029/2002JE002025, 2004
*****
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