1. Oceanic monitor may help predict fish population
A new method to monitor sea surface temperatures and height in the
North Pacific may help in measuring wind patterns and ocean
dynamics and could provide insight into better managing fisheries
located in the mid-latitudes. Robin Tokmakian developed an
algorithm to monitor changes in the sub-surface ocean's heat content
from shifts in the Alaskan and California currents, as the water
follows its circulation pattern over the central and eastern North
Pacific. Such sea temperature and height changes have been shown
to affect the marine ecosystem and fish populations by affecting the
density and mixing of nutrient-rich waters. Tokmakian proposes a
space-based system that can monitor the circulation patterns from
changes in the sea surface height and predict the size of various fish
stocks by observing the North Pacific heat content progression
during its typical southwesterly shift.
Title: Monitoring North Pacific heat content variability: An
indicator of fish quantity?
Author:
Robin Tokmanian, Naval Postgraduate School, Monterey,
California.
Source: Earth Interactions (EI) paper 10.1029/2002EI000063, 2003
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2. Vegetation's affect on summer warming may not last
Surface temperatures in North America and Eurasia are balanced by
atmospheric feedback from increased vegetation during summer,
which lowers the temperature, and reduced snow cover during
winter, which increases annual average temperatures. Kaufmann et
al. analyzed the effect of vegetation on surface temperatures, using
satellite measures of surface greenness in the summer and snow
extent in the winter. Previous research had found that enhanced
vegetation leads to cooler surface temperatures, which the authors
confirmed with their finding that vegetation growth during warm
summer months slowed the ongoing increase in summertime
temperatures. They note, however, that this mechanism for slowing
global climate change may not be effective for much longer, as a
temperature increase by another 3-5 degrees Celsius [5-9 degrees
Fahrenheit] may harm vegetation growth. The browning or loss of
vegetation would then accelerate further climate warming.
Title: The effect of vegetation on surface temperature: A statistical
analysis of NDVI and climate data
Authors:
R. K. Kaufmann, R. B. Myneni, N. V. Shabanov, Boston
University, Boston, Massachusetts;
L. Zhou, Georgia Institute of Technology, Atlanta, Georgia;
C. J. Tucker, D. Slayback, Jorge Pinzon, NASA Goddard Space
Flight Center, Greenbelt, Maryland.
Source: Geophysical Research Letters (GL) paper
10.1029/2003GL018251, 2003
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3. New theory explains meteors' double plumes
A new analysis of double plumes observed behind falling meteors
suggests a new explanation for the phenomenon. Kelley et al. report
on lidar and camera views of the heretofore-mysterious "trains" cast
behind meteors. The authors studied the persistent emissions
commonly left behind by meteors from the 1998 and 1999 Leonid
meteor showers and propose that one of the tails is left by gaseous
vapor emissions, while the other is caused by dust particles. They
note that the two layers are separated by gravitational properties of
the dust that keeps it segregated, evidence that has been confirmed
by rocket-based observations of dust remnants behind other
meteors. The researchers dismiss previous speculation that the
double tails were the result of a hollow cylinder because of
inconsistencies between the theory and observed light emissions
from the plumes. They conclude that their explanation may solve
the long-standing problem of explaining the phenomenon.
Title: A new explanation of persistent double meteor trains
Authors:
M. C. Kelley, C. Kruschwitz, L. Gelinas, S. Collins, Cornell
University, Ithaca, New York;
J. Drummond, Starfire Optical Range, Kirtland Air Force Base,
New Mexico;
C. Gardner, University of Illinois at Urbana-Champaign, Urbana,
Illinois;
J. Hecht, The Aerospace Corporation, Los Angeles, California;
E. Murad, Hanscom Air Force Base, Massachusetts.
Source: Geophysical Research Letters (GL) paper
10.1029/2003GL018312, 2003
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4. Climate models should include carbon dioxide increases
The impact of land cover change in climate models may be
incorrectly interpreted if the vegetation response to greater
atmospheric carbon dioxide concentrations is not taken into
account. Narisma et al. suggest that climate models should include a
measure of vegetation response to natural and man-made carbon
dioxide increases during the 20th century to accurately account for
biospheric feedback. The researchers examined the specific impacts
of elevated atmospheric carbon dioxide concentrations during the
Australian summer and report that the plant response to increased
carbon dioxide influences atmospheric temperatures and the climate
in ways that are not currently captured by climate models. They
conclude that simulations of land cover changes that exclude
biospheric feedback may lead both regional and global models to
overestimate the impact of land cover change on heat flux and
temperatures.
Title: The role of biospheric feedbacks in the simulation of the
impact of historical land cover change on the Australian January
climate
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
10.1029/2003GL018261, 2003
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5. Identifying source of infrasonic waves from Denali earthquake
The sudden motion of ground rupture during the strong 2002 Denali
earthquake in Alaska likely initiated infrasonic signals that were
recorded approximately 150 kilometers [90 miles]away. Olson et al.
traced the source of acoustic signals associated with the 7.9
magnitude earthquake by estimating the speed of the waves as they
moved eastward along the Denali fault. The authors report that the
large local ground motions produced the unusual infrasonic
signature after the November event. Infrasonic waves are often used
to detect faraway sounds from underground nuclear explosions and
storms. The researchers linked the ground motion from the Denali
temblor with observed infrasound signals and show that the largest
amplitude waves correspond to the regions along the fault line that
showed the largest ground motion. Previous studies had not been
able to identify the direct cause of infrasonic waves, which are made
up of low frequency waves inaudible to humans.
Title: Infrasound associated with the 2002 Denali fault earthquake,
Alaska
Authors:
John V. Olson, Charles R. Wilson, Roger A. Hansen, Geophysical
Institute, University of Alaska, Fairbanks, Alaska.
Source: Geophysical Research Letters (GL) paper
10.1029/2003GL018568, 2003
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6. Emissions from Martian dust storms can be remotely identified
Martian dust devils and dust storms can likely be detected remotely
by their electromagnetic radiation signals, which can be easily read
in Mars' thin atmosphere. Renno et al. present a theoretical study
that suggests that Martian dust storms, like terrestrial dust squalls,
produce strong electrical fields that can be observed from Earth.
They based their analysis on anomalously strong microwave activity
seen in regions known to have enhanced dust activity. The collisions of sand and dust particles produce a static electricity-like
charge among the grains that generates radiation that can be
measured by radio and microwave emissions in the ultra-low
frequency range. Such triboelectric charging of dust is especially
likely to discharge in dust particles because of the low atmospheric
density on Mars. The authors note that Martian dust storms are
much stronger, larger and more frequent than those on Earth and
could thus lead to simple observations of the electromagnetic
emissions on Mars.
Title: Electrical discharges and broadband radio emission by
Martian dust devils and dust storms
Authors:
Nilton O. Renno, Ah-San Wong, Sushil K. Atreya, University of
Michigan, Ann Arbor, Michigan;
Imke de Pater, University of California, Berkeley, California;
Maarteen Roos-Serote, Lisbon Astronomical Observatory, Tapada
da Ajuda, Lisbon, Portugal.
Source: Geophysical Research Letters (GL) paper
10.1029/2003GL017879, 2003
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7. First proof that plants absorb atmospheric nitrogen
Researchers have proven for the first time that vegetation can
directly absorb atmospheric organic nitrogen. Sparks et al. report
that plant leaves can remove organic forms of nitrogen, which could
have a significant effect on atmospheric carbon and nitrogen cycles.
The authors measured the uptake rate in eight plant species
representing vegetation from a range of global climates and found
that the pores on the leaves' surface largely determine a plant's
absorption characteristics. They estimate that plants could remove
enough precursor nitrogen pollutants to cause a three percent
reduction in harmful nitrogen oxides in the troposphere [lowest part
of the atmosphere] worldwide. The study used a more realistic
atmospheric model than previous studies that measured the nitrogen
deposition only during nighttime, when plant absorption would be
minimized. The researchers suggest that the extent of plant uptake
can provide insights on the global and regional budgets of
near-surface carbon and nitrogen.
Title: The uptake of gaseous organic nitrogen by leaves: A
significant global nitrogen transfer process
Authors:
Jed P. Sparks, Cornell University, Ithaca, New York, and
Cooperative Institute for Research in Environmental Science,
University of Colorado, Boulder, Colorado;
James M. Roberts, Aeronomy Laboratory, National Oceanic and
Atmospheric Administration, Boulder, Colorado, and Cooperative
Institute for Research in Environmental Science, University of
Colorado, Boulder, Colorado;
Russell K. Monson, University of Colorado, Boulder, Colorado, and
Cooperative Institute for Research in Environmental Science,
University of Colorado, Boulder, Colorado.
Source: Geophysical Research Letters (GL) paper
10.1029/2003GL018578, 2003
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8. GRACE may provide unprecedented ocean current data
The initial gravity model of the recently launched GRACE [Gravity
Recovery and Climate] mission has been combined with results
from satellite altimeter missions to study ocean surface currents.
The preliminary results from this effort provide a dramatic
improvement over previous observations. Tapley et al. show that
ocean topography data from the GRACE global gravity model
closely correspond with surface observations and note that, for the
first time, all major current systems can be clearly observed from
space. Previous satellite data produced a higher error level that
prevented the accurate resolution of global ocean circulation
patterns. The authors note that little highly detailed information
exists in remote ocean regions and that the new data will potentially
allow oceanographers to accurately map surface and subsurface
currents worldwide. The researchers note that while the model
requires further validation, the GRACE mission will likely provide
a minimum of a ten-fold increase in the accuracy of the Earth's
gravity model.
Title: Large scale ocean circulation from the GRACE GGM01 Geoid
Authors:
B. D. Tapley, D. P. Chambers, S. Bettadpur, J. C. Ries, Center for
Space Research, The University of Texas at Austin, Austin, Texas.
Source: Geophysical Research Letters (GL) paper
10.1029/2003GL018622, 2003
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9. Coastal mixing enhances mercury levels in coastal ecosystems
The mixing processes in estuaries may contribute to elevated
concentrations of reactive mercury in coastal ecosystems. Rolfhus et
al. collected multiple samples from the Connecticut River estuary
and found that the reactive mercury content increased with
increasing salinity. Mercury is a potent human and wildlife
neurotoxin found in lakes, rivers, and oceans worldwide; numerous
health agencies warn against the consumption of fish and seafood
contaminated with the element. The authors note that mercury's
reactive form may enhance the availability of mercury to the aquatic
food chain, yet little is known about how it is transformed in the estuarine environment. Their study simulated the mixing processes
between salt and freshwater, which they suggest dilutes and/or alters
the chemical compounds that strongly bind with mercury. The
researchers conclude that ions exchanged during saltwater mixing
alter the organic metal content in water and help spread readily bioaccumulated mercury in coastal ecosystems.
Title: Evidence for enhanced mercury reactivity in response to estuarine mixing
Authors:
Kristofer R. Rolfhus, University of Wisconsin-La Crosse, La
Crosse, Wisconsin;
Carl H. Lamborg, William F. Fitzgerald, Prentiss H. Balcom,
University of Connecticut, Groton, Connecticut.
Source: Journal of Geophysical Research-Oceans (JC) paper
10.1029/2001JC001297, 2003
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10. Effects of sea ice keels on polar surface waters
The keels of sea ice contribute to the heat flux of Arctic waterways
by enhancing the underwater mixing of warmer and cooler waters.
Skyllingstad et al. simulated the effects from varying ice keel
depths
on the upper ocean during summer and winter, when the changes in
ice thickness affect the polar oceans' flow patterns and ice coverage.
The authors note that shallow ice keels (one meter [three feet] or less) seen during summer generate a turbulent wake below the ice sheets that extend hundreds of meters [yards] downstream and help mix warmer fresh meltwater with cooler saltwater. They then analyzed the strong differences estimated to occur between the summertime ice keels and the deeper wintertime keels, which can
reach up to 10 meters [30 feet] below the surface, and propose that
the shallower keels generate stronger mixing closer to the ice and
increased ice melting rates. Conversely, the deeper keels follow a
similar pattern but mix the water further from the surface and force
ice bottom melting during the winter when new ice is usually
forming.
Title: Effects of keels on ice bottom turbulence exchange
Authors:
Eric D. Skyllingstad, Clayton A. Paulson, W. Scott Pegau, Oregon
State University, Corvallis, Oregon;
Miles G. McPhee, McPhee Research Company, Naches,
Washington;
Timothy Stanton, Naval Postgraduate School, Monterey, California.
Source: Journal of Geophysical Research-Oceans (JC) paper
10.1029/2002JC001488, 2003
Journal
Geophysical Research Letters