AGU journal highlights — April 5, 2010

The following highlights summarize research papers that have recently been published in Geophysical Research Letters (GRL).

In this release:

  1. Prolonged low solar activity will not offset global warming
  2. Heat waves increased in Mediterranean region since 1960
  3. Stirring up the ocean to store carbon?
  4. Wetlands influence rain patterns over large regions
  5. Researchers observe Moon’s minimagnetosphere for the first time
  6. Earthquake history revealed automatically from terrain
  7. Explaining debris distribution near ocean shores
  8. Determining groundwater age in complex systems
  9. Coral carbon ratios reflect fossil fuel use
  10. Model details river delta transformation
  11. Low-atmosphere tide reaches way high

Anyone may read the scientific abstract for any of these papers by clicking on the link provided at the end of each Highlight. You can also read the abstract by going to http://www.agu.org/pubs/search_options.shtml and inserting into the search engine the full doi (digital object identifier), e.g. 10.1029/2010GL042710. The doi is found at the end of each Highlight below.

Journalists and public information officers (PIOs) at educational or scientific institutions, who are registered with AGU, also may download papers cited in this release by clicking on the links below. Instructions for members of the news media, PIOs, and the public for downloading or ordering the full text of any research paper summarized below are available at http://www.agu.org/news/press/papers.shtml


1. Prolonged low solar activity will not offset global warming

Solar activity is known to influence Earth’s temperature, and it has been suggested that the current period of low solar activity will lead into a more prolonged period of low activity, a new “grand minimum” similar to the Maunder minimum that lasted from 1645 to 1715, coinciding with the Little Ice Age. Could low solar activity in the future help offset anthropogenic warming? To determine the potential effects of a prolonged period of low solar activity, Feulner and Rahmstorf run a series of simulations using a coupled climate model that reproduces the cooling during past solar minima. The authors find that a new grand minimum would produce only a minimal amount of cooling — no more than 0.3 degrees Celsius (0.54 degrees Fahrenheit) in 2100. This potential temperature decrease is much smaller than the increase expected from human-induced warming. Furthermore, any cooling effect would be temporary, since the period of low solar activity would last no more than a few decades. The authors conclude that a new grand minimum cannot offset global warming caused by human greenhouse gas emissions.

Title:
On the effect of a new grand minimum of solar activity on the future climate on Earth

Authors:

Georg Feulner and Stefan Rahmstorf: Potsdam Institute for Climate Impact Research, Potsdam, Germany.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL042710, 2010

http://dx.doi.org/10.1029/2010GL042710


2. Heat waves increased in Mediterranean region since 1960

Heat waves have serious impacts on human health, agriculture, water resources, ecosystems, and energy use. Heat waves have been increasing as global temperatures rise, but most studies have focused on changes in maximum or average temperatures. Kuglitsch et al. instead focus specifically on changes in the number, length, and intensity of heat waves in the eastern Mediterranean region, where previous studies had not focused. The authors analyze records of daily maximum and minimum temperatures from 246 stations in the eastern Mediterranean region between 1960 and 2006, adjusting the instrumental measurements for nonclimatic influences. The results indicate that some instrumental measurements in the 1960s were warm-biased. They define heat waves as periods of three or more consecutive hot days and nights when the temperature exceeded a threshold defined for a particular location. Their results indicate that since 1960 the number, length, and intensity of heat waves have increased significantly; the increase was greater than had been estimated using uncorrected temperature data. This new analysis should be useful as scientists and policy makers work to understand and quantify the effects of extreme heat on humans and ecosystems.

Title:
Heat wave changes in the eastern Mediterranean since 1960

Authors:
F. G. Kuglitsch: Institute of Geography, Climatology and Meteorology, University of Bern, Bern, Switzerland and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland;

A. Toreti: Institute of Geography, Climatology and Meteorology, University of Bern, Bern, Switzerland and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland and Istituto Superiore per la Protezione e la Ricerca Ambientale, Rome, Italy;

E. Xoplaki: Institute of Geography, Climatology and Meteorology, University of Bern, Bern, Switzerland and The Cyprus Institute, EEWRC, Nicosia, Cyprus;

P. M. Della-Marta: Federal Office for Meteorology and Climatology, MeteoSwiss, Zurich, Switzerland;

C. S. Zerefos: Biomedical Research Foundation, Academy of Athens, Athens, Greece;

M. Türke?: Physical Geography Division, Department of Geography, Faculty of Sciences and Arts, Çanakkale Onsekiz Mart University, Çanakkale, Turkey;

J. Luterbacher: Department of Geography, Climatology, Climate Dynamics and Climate Change, Justus-Liebig University of Giessen, Giessen, Germany.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041841, 2010

http://dx.doi.org/10.1029/2009GL041841


3. Stirring up the ocean to store carbon?

With carbon dioxide levels rising and the planet warming, various solutions are being considered to reduce atmospheric carbon dioxide levels. One suggested geoengineering approach is to increase carbon sequestration by stirring up the oceans. Artificial upwelling would be induced by placing pipes in the ocean to bring cold, nutrient-rich deeper waters to the surface. The nutrient-rich waters would fertilize the ocean and stimulate the growth of plankton that could absorb more carbon dioxide from the atmosphere. Artificial upwelling would also cool the Earth’s surface by bringing up cold water from the ocean interior. Oschlies et al. run coupled carbon-climate model simulations to evaluate the efficacy of a potential artificial ocean upwelling plan. The authors find that under the most optimistic assumptions, artificial upwelling could sequester carbon dioxide at the rate of 0.9 billion metric tonnes (.99 billion tons (U.S.)) of carbon per year, a significant percentage of the carbon dioxide emitted by anthropogenic fossil fuel burning. However, the researchers find, oddly, that about 80 percent of the additional carbon would be sequestered by land ecosystems, not in the oceans. This would make it hard to monitor the effectiveness of the artificial upwelling program. Furthermore, the simulations show that if artificial upwelling were stopped, the planet’s temperature would increase even more than it would in the control case in which no artificial upwelling was ever attempted, leaving fewer options in the future.

Title:
Climate engineering by artificial ocean upwelling: Channeling the sorcerer’s apprentice

Authors:
A. Oschlies and M. Pahlow: Leibniz-Institut für Meereswissenschaften an der Universität Kiel (IFM-GEOMAR), Kiel, Germany;

A. Yool: National Oceanography Centre Southampton, Southampton, UK;

R. J. Matear: CSIRO Marine Laboratories, Hobart, Tasmania, Australia.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041961, 2010

http://dx.doi.org/10.1029/2009GL041961


4. Wetlands influence rain patterns over large regions

Changes to water use upstream of wetlands could influence weather region-wide. One example is the Niger Inland Delta, a network of tributaries, channels, lakes, and swamps located in Mali just south of the Sahara desert. These wetlands typically appear in September when the Niger River floods due to upstream rainfall. This flooding can then influence regional rain patterns through feedback with the atmosphere. Human activity that affects the wetland could therefore also affect rainfall hundreds of kilometers away.

To explore land-atmosphere feedbacks in the Niger Inland Delta, Taylor uses satellite thermal infrared imagery spanning 1982? to look at wetland extent and differences in cloud cover before and after wetland inundation. The author finds that during periods of inundation, daytime cloud cover in the vicinity was more than 50 percent higher than during periods when the wetland was not flooded. The increased cloud cover spreads hundreds of kilometers westward, due to an increase in the number of long-lived traveling storms. The author finds that this is consistent with a “wetland breeze” effect, a circulation driven by heat transferred between land and air due to surface temperature differences. The study provides some of the first observational evidence that a wetland can influence weather over a larger region.
The results suggest that water use changes upstream of the wetland could influence weather region-wide. For instance, a proposed hydroelectric dam in Guinea would decrease water flow to the wetland, which could result in reduced rainfall over a wide region.

Title:
Feedbacks on convection from an African wetland

Authors:
Christopher M. Taylor: Centre for Ecology and Hydrology, Wallingford, UK.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041652, 2010

http://dx.doi.org/10.1029/2009GL041652


5. Researchers observe Moon’s minimagnetosphere for the first time

New observations using energetic neutral atoms show a minimagnetosphere on the Moon. Unlike Earth, the Moon does not have a global magnetic field and therefore does not have a magnetosphere surrounding it. However, the Moon does have small regions of magnetization, called magnetic anomalies. These small areas of locally strong magnetic field can create minimagnetospheres that deflect the solar wind in the same way that Earth’s magnetosphere shields most of the planet from the solar wind.
Wieser et al. have observed a minimagnetosphere on the Moon. When solar wind protons hit the surface of the Moon, some are scattered back as energetic neutral hydrogen atoms. Using spacecraft observations, the researchers identify a region above a strong magnetic anomaly where the number of backscattered energetic hydrogen atoms was lower than in surrounding areas. This indicates that the region was shielded from solar wind particles by a minimagnetosphere. The minimagnetosphere was about 360 kilometers across at the time of observation. The study provides direct evidence for the formation of a minimagnetosphere on the Moon.

Title:
First observation of a mini-magnetosphere above a lunar magnetic anomaly using energetic neutral atoms

Authors:
Martin Wieser, Stas Barabash, Yoshifumi Futaana, and Mats Holmström: Swedish Institute of Space Physics, Kiruna, Sweden;

Anil Bhardwaj, R. Sridharan, and M. B. Dhanya: Space Physics Laboratory, Vikram Sarabhai Space Center, Trivandrum, India;

Audrey Schaufelberger and Peter Wurz: Physikalisches Institut, University of Bern, Switzerland;

Kazushi Asamura: Institute of Space and Astronautical Science, Sagamihara, Japan.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041721, 2010

http://dx.doi.org/10.1029/2009GL041721


6. Earthquake history revealed automatically from terrain

Fault scarps, the visible topographic features caused by the motion of faults, can tell researchers about the history of fault motion. Fault scarps formed more recently tend to be sharper; older ones tend to have softened over time. Mapping fault scarps has been a time-consuming, labor-intensive process requiring ground surveying, often on terrain that is difficult to access. Hilley et al. have found an easier way of mapping fault scarps, using high-resolution digital topography from airborne laser mapping data. The authors fit a scarp-like template to the topography data to identify scarps in the data. By modeling the erosion of the scarp as a diffusive mass transport process, the researchers can determine scarp ages. The authors apply their method to fault scarp structures at three sites along the San Andreas Fault. They show that their method can automatically identify scarp features within the topographic data and extract the ages of the fault scarps. Knowing the relative ages of fault scarps in a region can help scientists reconstruct the record of fault activity over the past several hundred to several tens of thousands of years. The method also provides a way of automatically analyzing a large volume of laser mapping data and could be useful for other studies of fault zone structure.

Title:
Morphologic dating of fault scarps using airborne laser swath mapping (ALSM) data

Authors:
G. E. Hilley: Department of Geological and Environmental Sciences, Stanford University, Stanford, California, USA;

S. DeLong and C. Prentice: U.S. Geological Survey, Menlo Park, California, USA;

K. Blisniuk: Department of Geology, University of California, Davis, California, USA;

JR. Arrowsmith: School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL042044, 2010

http://dx.doi.org/10.1029/2009GL042044


7. Explaining debris distribution near ocean shores

Beachgoers often notice that when debris gets into the ocean at a shore, some can be trapped floating near the shore while some is carried away from the surf zone. The distribution of flotsam is often observed to be patchy near the shore and streaky outside the surf zone. Because circulation off a beach with rip currents (powerful currents flowing away from shore) is complicated, it can be difficult to predict when a floating object or a swimmer will be transported out of the surf zone or explain how such objects are distributed.
Reniers et al. use a numerical model to examine the physical mechanisms behind the distribution of flotsam inside and outside the surf zone. The authors show that the distribution can be explained by structures called Lagrangian coherent structures (LCSs). LCSs are basically filament-like curves hidden in the flow of water that control the motion of floating objects in waters with rip currents. LCSs are not visually obvious, so the authors compute them from a modeled surface velocity field to study transport by rip current pulses. The results show how LCSs can trap objects in patches near shore, or farther out, how several adjacent LCSs may be closely spaced, creating thin streaks of floating material.
The study provides a geophysical explanation of the distribution of flotsam inside and outside the surf zone and could have implications for swimmer safety, pollution, water quality, and sediment transport.

Title:
Rip-current pulses tied to Lagrangian coherent structures

Authors:
A. J. H. M. Reniers: Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA and Department of Hydraulic Engineering, Delft University of Technology, Delft, Netherlands;

J. H. MacMahan: Department of Oceanography, Naval Postgraduate School, Monterey, California, USA;

F. J. Beron-Vera and M. J. Olascoaga: Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041443, 2010

http://dx.doi.org/10.1029/2009GL041443


8. Determining groundwater age in complex systems

Groundwater age, the amount of time groundwater has been in an aquifer, is important because the length of time water spends in an aquifer can influence many geologic processes. However, determining groundwater age — which can be as short as a few days or as long as thousands of years — can be complicated because groundwater basins are large and complex and groundwater age distribution is affected by mixing and transport of different parcels of water.
Hydraulic conductivity, the ease with which water can move through the ground, and porosity, the fraction of pore space available for water to flow, have been observed to vary with depth, but these generally have not been taken into account in groundwater age models. Jiang et al. conduct a numerical simulation to study the age distribution of groundwater in complicated flow systems. The authors show that the age of groundwater in the basin is influenced by depth-dependent hydraulic conductivity and porosity. The researchers’ model indicates that groundwater age distribution is more heterogeneous than had been thought. The study should help scientists interpret complex age distributions in large aquifer systems.

Title:
Simultaneous rejuvenation and aging of groundwater in basins due to depth-decaying hydraulic conductivity and porosity

Authors:
Xiao-Wei Jiang, Li Wan and Xu-Sheng Wang: School of Water Resources and Environment, China University of Geosciences, Beijing, China;

M. Bayani Cardenas: Department of Geological Sciences, University of Texas at Austin, Austin, Texas, USA;

Shemin Ge: Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL042387, 2010

http://dx.doi.org/10.1029/2010GL042387


9. Coral carbon ratios reflect fossil fuel use

Carbon dioxide produced from burning fossil fuels contains lower levels of carbon-13 than naturally occurring atmospheric carbon dioxide contains. Thus, as humans burn fossil fuels, the ratio of carbon-13 to other carbon isotopes in the atmosphere and oceans decreases. New data show that coral skeletons provide a record of this effect, known as the carbon-13 Suess effect. Corals use carbon from water in secreting their skeletons. As corals form annual skeletal bands they provide a snapshot of the isotope ratios in the water at the time the coral died.
Swart et al. present new data on the carbon isotopic composition from 10 coral skeletons collected from the Caribbean. They compare these data with 27 other published coral records from the Atlantic, Pacific, and Indian oceans. The coral skeletons range in age from 96 to 200 years old. Most of the skeletons show a statistically significant decrease in the ratio of carbon-13 to other carbon isotopes over time. The researchers note that the decrease in the ratio of carbon-13 to other carbon isotopes in the Atlantic corals matches this ratio’s decrease in the atmosphere over time, though this ratio’s decrease in the Pacific and Indian ocean corals was more variable.
Previously, it had been suggested that changes in the ratio of carbon-13 to other carbon isotopes in corals could be related to factors such as changes in coral growth rate or changes in the amount of light reaching the corals. This study provides strong evidence that the declining ratio of carbon-13 to other carbon isotopes in corals can be attributed to anthropogenic carbon dioxide.

Title:
The carbon-13 Suess effect in scleractinian corals mirror changes in the anthropogenic carbon dioxide inventory of the surface oceans

Authors:
Peter K. Swart and Amanda J. Waite: Division of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science, Miami, Florida, USA;

Lisa Greer: Division of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science, Miami, Florida, USA and Department of Geology, Washington and Lee University, Lexington, Virginia, USA;

Brad E. Rosenheim: Division of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science, Miami, Florida, USA and Department of Earth and Environmental Science, Tulane University, New Orleans, Louisiana, USA;

Chris S. Moses: Division of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Science, Miami, Florida, USA and Department of Earth Sciences, Florida International University, Miami, Florida, USA;

A. Winter: Department of Marine Science, University of Puerto Rico, Mayaguez, Puerto Rico, USA;

Richard E. Dodge: Oceanographic Center, Nova Southeastern University, Dania Beach, Florida, USA;

Kevin Helmle: Oceanographic Center, Nova Southeastern University, Dania Beach, Florida, USA and Ocean Chemistry Division, AOML, NOAA, Miami, Florida, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041397, 2010

http://dx.doi.org/10.1029/2009GL041397


10. Model details river delta transformation

Various factors determine the dynamics of river delta systems. To examine in detail how river deltas form and transform, Geleynse et al. develop a high-resolution physics-based computer model. Their model takes into account boundary sedimentary composition, transport of multiple sediment fractions, and feeder channel dynamics, and provides a detailed description of the formation of delta distributary networks. The authors find that their simulated delta system shows a striking similarity with findings from field and laboratory studies.

Title:
Modeling of a mixed-load fluvio-deltaic system

Authors:
N. Geleynse and J. E. A. Storms: Department of Geotechnology, Delft University of Technology, Delft, Netherlands;

M. J. F. Stive: Hydraulic Engineering, Delft University of Technology, Delft, Netherlands
H. R. A. Jagers: Deltares, Delft, Netherlands;

D. J. R. Walstra: Hydraulic Engineering, Delft University of Technology, Delft, Netherlands and Deltares, Delft, Netherlands.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL042000, 2010

http://dx.doi.org/10.1029/2009GL042000


11. Low-atmosphere tide reaches way high

The atmosphere has periodic oscillations that are driven by solar heating of the troposphere, the atmospheric layer closest to Earth’s surface, where weather patterns form. Scientists have now observed that one of these atmospheric tides, known as diurnal wavenumber 3 (DE3), propagates upward to reach the thermosphere. DE3 is a nonmigrating diurnal tide, meaning that it has a frequency of a day but is not tied to local solar time. Instead, it has three wave peaks (wavenumber 3) that travel eastward around the circumference of the Earth.

The extent of DE3 into the thermosphere had been predicted by models but not directly observed until now. Talaat and Lieberman use a wind imaging instrument on board a satellite to observe the DE3 pattern in the range of 90-270 kilometers (56-168 miles) above Earth’s surface. Their observations provide the first direct evidence that the DE3 tide provides a direct link through which the troposphere influences the thermosphere. This could explain the origin of some previously observed oscillations in the plasma in the ionosphere. Understanding DE3 and other atmospheric tides is an important part of understanding atmospheric and ionospheric dynamics as a whole.

Title:
Direct observations of nonmigrating diurnal tides in the equatorial thermosphere

Authors:
E. R. Talaat: Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA;

R. S. Lieberman: Colorado Research Associates Division, Northwest Research Associates, Boulder, Colorado, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041845, 2010

http://dx.doi.org/10.1029/2009GL041845

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