AGU journal highlights — May 4, 2010

The following highlights summarize research papers that have been recently published or are “in press” (accepted, but not yet published) in Water Resources Research (WRR) and Geophysical Research Letters (GRL).

In this release:

  1. Satellite study verifies reductions in air pollutant emissions in China
  2. Predicting the evolution of central Pacific El Niño events
  3. Sunlight reflection confirms liquid lake on Titan
  4. Sediment layers could provide insight into Mars’s climate history
  5. Rivers rebound as woodland replaces degraded grassland
  6. Simplified description of atmospheric organic aerosol evolution to help climate models
  7. New finding to improve understanding of large-scale atmospheric turbulence and climate
  8. Correcting model imperfections

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. 10.1029/2010GL042594. 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 .Please note that papers not yet published (i.e. “in press”) are available only to journalists and public information officers.


1. Satellite study verifies reductions in air pollutant emissions in China

A new satellite study verifies that Chinese emission control efforts did reduce power plant emissions of sulfur dioxide, a harmful gas that causes acid rain and can form sulfate aerosols, which play an important role in the climate system by affecting clouds and precipitation patterns and altering the amount of sunlight that is reflected away from Earth. Using a satellite-based monitoring instrument, Li et al. observed increases in sulfur dioxide and nitrogen dioxide from 2005 to 2007 over areas where large coal-fired power plants were built during that time period. In 2008, the authors found little change in nitrogen dioxide, which is consistent with steady output from those power plants. However, in 2008 the researchers observed dramatic reductions in sulfur dioxide, likely because power plants had begun to use desulfurization devices more extensively in response to government policy. The study demonstrates that satellites can be useful in monitoring air quality and air pollutant emissions.

Title:
Recent large reduction in sulfur dioxide emissions from Chinese power plants observed by the Ozone Monitoring Instrument

Authors:
Can Li: Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, USA and NASA Goddard Space Flight Center, Greenbelt, Maryland, USA;

Qiang Zhang: Center for Earth System Science, Tsinghua University, Beijing, China and Decision and Information Sciences Division, Argonne National Laboratory, Argonne, Illinois, USA;

Nickolay A. Krotkov: NASA Goddard Space Flight Center, Greenbelt, Maryland, USA and Goddard Earth Sciences and Technology Center, University of Maryland, Baltimore County, Baltimore, Maryland, USA;

David G. Streets: Decision and Information Sciences Division, Argonne National Laboratory, Argonne, Illinois, USA;

Kebin He: State Key Joint Laboratory of Environment Simulation and Pollution Control, Department of Environmental Science and Engineering, Tsinghua University, Beijing, China;

Si-Chee Tsay and James F. Gleason: NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL042594, 2010

http://dx.doi.org/10.1029/2010GL042594


2. Predicting the evolution of central Pacific El Niño events

El Niño events, in which warmer than usual sea surface temperatures occur in the equatorial Pacific Ocean, are known to have a major influence on weather patterns worldwide. Yu and Kim categorize the ways in which certain types of El Niño events evolve. The authors focus on an El Niño known as the central Pacific (CP) type, in which sea surface temperature warming occurs mainly in the central Pacific Ocean, rather than in the eastern Pacific where most common El Niño sea surface temperature warming occurs. The two types of El Niño events have different effects on weather patterns and may respond differently to global warming. The CP type has occurred more frequently in recent decades.

On the basis of events that occurred between 1958 and 2007, the researchers identify three distinct patterns through which central Pacific El Niño events evolve. They also show that the pattern of evolution is linked to the depth of the thermocline, the transition layer where the temperature drops sharply between surface waters and deep waters. The researchers find that in general during a CP-type El Niño, if the thermocline was at a shallower than normal depth, then eastern Pacific cooling was likely to occur, ending the El Niño abruptly. If the thermocline was at normal depth, the El Niño would likely decay about as quickly as it grew. If the thermocline was deeper than normal depth, then eastern Pacific warming would likely occur, slowing the ending of the El Niño. The results could be useful for predicting the duration of CP-type El Niño events.

Title:
Three evolution patterns of central-Pacific El Niño

Authors:
Jin-Yi Yu and Seon Tae Kim: Department of Earth System Science, University of California, Irvine, California, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL042810, 2010

http://dx.doi.org/10.1029/2010GL042810


3. Sunlight reflection confirms liquid lake on Titan

A glint of sunlight reflecting from the surface of Saturn’s moon Titan indicates the presence of a lake filled with liquid. Earlier observations showed features that look like terrestrial lakes and seas in Titan’s northern polar region, but the presence of liquid had not been confirmed. Stephan et al. report the first detection of a directly visible glint, also called a specular reflection. A specular reflection occurs when sunlight reflects off a smooth, mirror-like liquid surface. Cassini captured an image of the glint on 8 July 2009, and the researchers determined that it came from Kraken Mare, a large, lake-shaped basin near Titan’s north pole. Until recently the northern polar regions of Titan had been in winter darkness since Cassini’s arrival in 2004; the recent direct illumination by sunlight made it possible to observe these optical reflections for the first time. Titan is the only body other than Earth in the solar system known to have stable liquid on its surface.

Title:
Specular reflection on Titan: Liquids in Kraken Mare

Authors:
Katrin Stephan: Institute of Planetary Research, DLR, Berlin, Germany, and others (for the complete list of authors, please see: http://dx.doi.org/10.1029/2009GL042312).

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL042312, 2010

http://dx.doi.org/10.1029/2009GL042312


4. Sediment layers could provide insight into Mars’s climate history

A new stratigraphic record of Martian polar layered deposits could help scientists shed light on Mars’s climate history. Stratigraphic layers can give scientists important clues about the conditions at the time the layer of rock formed. Fishbaugh et al. present the first high-resolution stratigraphic column of Marian north polar layered deposits. The researchers use a digital elevation model (a representation of topography) derived from images taken by the High Resolution Imaging Science Experiment to identify and classify layers in the 400-meter (1,312-feet) stratigraphic column, including several clearly defined “marker bed” layers. The authors also observe that layers get thinner with depth. Furthermore, they find no immediately obvious cyclic pattern in the stratigraphic layers that could correspond to cyclic climatic conditions, indicating that the relationship between Mars’s polar stratigraphy and cyclic climate forcing is complex and needs further investigation. The new stratigraphic column should be useful for future studies of Mars’s climate history.

Title:
First high-resolution stratigraphic column of the Martian north polar layered deposits

Authors:
Kathryn E. Fishbaugh Patrick S. Russell: Center for Earth and Planetary Studies, Smithsonian National Air and Space Museum, Washington, D. C., USA;

Christine S. Hvidberg, Mai Winstrup: Center for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark;

Shane Byrne: Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA;

Kenneth E. Herkenhoff, Randolph Kirk: U.S. Geological Survey, Flagstaff, Arizona, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041642, 2010

http://dx.doi.org/10.1029/2009GL041642


5. Rivers rebound as woodland replaces degraded grassland

The surprising results of a new study suggest that contrary to previous belief, streamflow can increase when grassland converts to woodland. Wilcox and Huang study trends in the base flow (water supplied by groundwater and springs) and stormflow (water from flood events) components of streamflow of four major rivers in the Edwards Plateau region of Texas over the past 85 years. Before 1890, the Edwards Plateau region was mainly grassland. From the late 1800s to about 1960, severe overgrazing degraded the land, resulting in loss of vegetation. Since about 1960, the land has been recovering and woody plants have been taking over what had been grassland. Because trees and shrubs generally use deeper water than grasses do, it had been thought that growth of woody plants would lead to declining groundwater recharge and streamflow. However, the researchers find that rivers actually rebounded since 1960 as degraded grassland converted to woodland, because base flows have increased significantly. Base flow in all four rivers is now double what it was prior to 1950. Furthermore, rainfall did not increase over the time period studied, but streamflow did increase in three of the four rivers studied, indicating that the conversion of degraded grassland to woodland actually improved streamflow.

See previous press release at:
http://www.agu.org/news/press/pr_archives/2010/2010-06.shtml

Title:
Woody plant encroachment paradox: Rivers rebound as degraded grasslands convert to woodlands

Authors:
Bradford P. Wilcox and Yun Huang: Ecosystem Science and Management, Texas A&M University, College Station, Texas, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL041929, 2010

http://dx.doi.org/10.1029/2009GL041929


6. Simplified description of atmospheric organic aerosol evolution to help climate models

Atmospheric organic aerosol consists of a variety of organic molecules that are either directly emitted into the atmosphere or form through chemical reactions in the atmosphere. Organic aerosol can affect climate by altering the amount of sunlight that is reflected away from Earth. Because the aerosol composition changes as chemical reactions take place in the atmosphere and air masses move and mix, it is difficult and time consuming for atmospheric chemistry models to include the details of the evolution of organic aerosol composition. But a new study shows that it may not be necessary for models to include all the details.

Heald et al. have found a simplified way to describe the evolution of the organic aerosol composition in the atmosphere by plotting the hydrogen to carbon atomic ratio (H:C) versus the oxygen to carbon atomic ratio (O:C). The authors find that in a number of laboratory and field measurements, the bulk molecular composition of organic aerosol tends to fall roughly along a single line in this diagram. As air masses mix and chemical reactions take place in the atmosphere, the mixture of molecules changes, but the overall elemental composition stays along this line. The results suggest that the chemical evolution of organic aerosol in the atmosphere can be represented simply in atmospheric chemistry and climate models.

Title:
A simplified description of the evolution of organic aerosol composition in the atmosphere

Authors:
C. L. Heald: Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA;

J. H. Kroll: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA;

J. L. Jimenez, K. S. Docherty and D. K. Farmer: CIRES and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA;

P. F. DeCarlo: CIRES and Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA. Now at Paul Scherrer Institute, Villigen, Switzerland;

A. C. Aiken: CIRES and Department of Chemistry and Biochemistry, University of Colorado,
Boulder, Colorado, USA. Now at ETH Zurich, Zurich, Switzerland;

Q. Chen and S. T. Martin: School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA;

P. Artaxo: Instituto de Fisíca, Universidade de São Paulo, Sao Paulo, Brazil.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL042737, 2010

http://dx.doi.org/10.1029/2010GL042737


7. New finding to improve understanding of large-scale atmospheric turbulence and climate

Atmospheric velocity (wind speed) statistics are a key part of weather prediction as well as climate studies. Velocity statistics, which are used in describing atmospheric dynamics as a function of spatial scale, season, or geographic region, are usually calculated on constant pressure levels, but some recent studies have suggested that statistics should instead be calculated on constant altitude levels because there can be large altitude variations in constant pressure surfaces during large-scale atmospheric disturbances. However, Frehlich and Sharman use radiosonde and aircraft meteorological observations as well as numerical weather prediction models to demonstrate that velocity statistics at constant altitude and constant pressure are in fact equivalent as long as the data are taken over a sufficiently long period of time. The study, which is the first observational demonstration of the equivalence of the two statistics, could help improve interpretation of studies of large-scale atmospheric turbulence and climate.

Title:
Equivalence of velocity statistics at constant pressure or constant altitude

Authors:
R. G. Frehlich: CIRES, University of Colorado at Boulder, Boulder, Colorado, USA;

R. D. Sharman: Research Applications Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL042912, 2010

http://dx.doi.org/10.1029/2010GL042912


8. Correcting model imperfections

By their nature, environmental models are unable to perfectly simulate natural phenomena. Misfits between model predictions and field measurements are often characterized by the term “structural noise.” The presence of this noise can adversely affect the estimation of model parameters through the calibration process. This, in turn, can lead to erroneous predictions of future system behavior.

Unfortunately, the characteristics of this noise can be nearly impossible to systematically quantify. Doherty and Welter focus on defect-induced model-to-measurement misfit in the hope of providing a method by which structural noise can be at least partially accommodated during the all-important process of model calibration. Through analyzing streamflow and groundwater models, the authors explore some of the ways in which model imperfections can express themselves. They find that these errors can have complex spatial and temporal correlation structures. However, by processing field measurements and complementary model outputs in certain ways, the calibration process can be granted partial immunity from this noise, thereby increasing the accuracy with which model parameters are estimated.

Title:
A short exploration of structural noise

Authors:
John Doherty: Watermark Numerical Computing, Brisbane, Australia; also at National Center for Groundwater Research and Training, Flinders University, Australia;

David Welter: South Florida Water Management District, West Palm Beach, Florida, USA.

Source:
Water Resources Research (WRR) paper 10.1029/2009WR008377, 2010, in press:

http://www.agu.org/journals/pip/wr/2009WR008377-pip.pdf


The material in this press release comes from the originating research organization. Content may be edited for style and length. Have a question? Let us know.

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