AGU Journal Highlights—06 February 2009

Highlights, including authors and their institutions

The following highlights summarize research papers that have been published in Geophysical Research Letters (GRL) and Journal of Geophysical Research-Atmospheres (JGR-D).

Anyone may read the scientific abstract for 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. 10.1029/2008GL036215. 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/jinstructions.shtml.

Ocean heat transport's health tied to sea level symptoms
Mediterranean cold air surges might cause drought in northern Africa
Scientists find Earth cracks "breathe"
Thick aprons of ice found on Martian slopes
Wildfires in Siberia involved in spring 2008 Arctic haze
New method to measure aerosol properties over land from space
Isotopic composition of potentially harmful organic aerosols

1. Ocean heat transport's health tied to sea level symptoms

Previous studies have raised the possibility that sea levels can diagnose the health of North Atlantic Meridional Overturning Circulation (MOC), the massive "conveyor belt" responsible for distributing heat throughout the world's oceans. To study this further, Bingham and Hughes examine the relationship between MOC and sea level along the east coast of North America using an eddy-permitting ocean model. The authors find a distinctive topography-following pattern of sea level variability in the western North Atlantic that is closely linked to the changing strength of the MOC, with slight drops in sea level associated with a more rapid rate of overturning. Comparing model results with altimetry data revealed a similar pattern of sea level variability that dominates the interannual patterns at tide gauges along the North American east coast between 40 degrees North and 50 degrees North. The authors conclude that sea level along North America's eastern coast may perhaps be a useful indicator of MOC health.

Title:

“Signature of the Atlantic meridional overturning circulation in seal level along the east coast of North America”

Authors:

Rory J. Bingham and Chris W. Hughes: Proudman Oceanographic Laboratory, Liverpool, U.K.

Source:

Geophysical Research Letters (GRL) paper 10.1029/2008GL036215, 2009; http://dx.doi.org/10.1029/2008GL036215

2. Mediterranean cold air surges might cause drought in northern Africa

Because northern African summer monsoons bring much needed rain to arid regions, prolonged dry periods during the monsoon season can lead to crop failure, drought, and famine. Predicting such breaks in monsoon patterns is critical to disaster management preparations. To help improve prediction efforts, Vizy and Cook study how northern African monsoons are affected by cold air surges from the Mediterranean. Using data from the U.S. National Centers for Environmental Prediction and the satellite-based Tropical Rainfall Measuring Mission, the authors found that between 1998 and 2006, 77 cold air surges occurred in the summer months. The surges persisted for 2-10 days and contributed to local cooling of surface temperatures. The influence of cold air surges on rainfall varies regionally. Over the western Sahara, surges are associated with increased rainfall due to enhanced convective instability. Over the eastern Sahel, the passage of surges is associated with the development of stable environments that favor the development of monsoon breaks. The results suggest that some cases of eastern Sahel drought may be related to an increased frequency of cold air surges from the Mediterranean.

Title:

“A mechanism for African monsoon breaks: Mediterranean cold air surges”

Authors:

Edward K. Vizy: Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York, U.S.A.; now at Institute for Geophysics, University of Texas at Austin, Austin, Texas, U.S.A.
Kerry H. Cook: Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York, U.S.A.; now at Jackson School of Geosciences, University of Texas at Austin, Austin, Texas, U.S.A.

Source:

Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2008JD010654, 2009; http://dx.doi.org/10.1029/2008JD010654

3. Scientists find Earth cracks "breathe"

To fully understand global warming and global water cycling, scientists must explore the links between atmospheric conditions, Earth processes, and major global cycles. Noting that the effect of fractures on global dynamics has only been studied in the context of aquifer recharge and contamination, Weisbrod et al. seek to determine how such fractures influence gas exchange between the Earth and the atmosphere. Using field measurements from the Negev desert, the authors show that fractures "breathe" through a daily cycle of convective venting that is more dominant during the winter. In this process, the Sun heats the soil surface, and the heat propagates slowly downward; by nightfall, the crack is warmer below the surface than at the surface. At night, the warm air inside the crack is less dense than the atmospheric air, which causes it to rise and escape the crack. This thermal convection enhances atmospheric exchange of greenhouse gases, including water vapor and carbon dioxide. In places where surface cracks, fractures, and other discontinuities in the Earth's porous membrane exist, gas exchange through cracks may be the prevailing mechanism driving gas escape into the atmosphere.

Title:

“Falling through the cracks: The role of fractures in Earth-atmosphere gas exchange”

Authors:

Noam Weisbrod, Uri Nachshon and Modi Pillersdorf: Department of Environmental Hydrology and Microbiology, Zuckerberg Institute for Water Research, Blaustein Institute for Desert Research, Ben Gurion University of the Negev, Sde Boker, Israel
Maria Inés Draglia: Department of Crop and Soil Science, Oregon State University, Corvallis, Oregon, U.S.A.

Source:

Geophysical Research Letters (GRL) paper 10.1029/2008GL036096, 2009; http://dx.doi.org/10.1029/2008GL036096

4. Thick aprons of ice found on Martian slopes

More than 30 years ago, data from NASA's Viking missions identified unusual surface features on Mars called lobate debris aprons. Draped on Martian slopes and only found at middle to high latitudes, these aprons are masses of material hundreds of meters thick that extend up to several tens of kilometers and terminate in lobate fronts. Their shape and restricted occurrence in latitude have caused many to speculate that the aprons contain water ice, although the amount of ice present has been subject to intense debate. Using subsurface radar sounding data from the Mars Reconnaissance Orbiter (launched in 2005), Plaut et al. find that lobate debris aprons at a location in the middle northern latitudes between the southern highlands and northern lowlands are composed predominantly of water ice and contain only a minor component of soil and rock. Results support the idea that lobate debris aprons may be remnants of much larger glaciers that have been protected from sublimation by a coating of gravel and dust.

Title:

“Radar evidence for ice in lobate debris aprons in the mid-northern latitudes of Mars”

Authors:

Jeffrey J. Plaut and Ali Safaeinili: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, U.S.A.
John W. Holt: Institute for Geophysics, Jackson School for Geosciences, University of Texas at Austin, Austin, Texas, U.S.A.
Roger J. Phillips and Nathaniel E. Putzig: Southwest Research Institute, Boulder, Colorado, U.S.A.
James W. Head III: Department of Geological Sciences, Brown University, Providence, Rhode Island, U.S.A.
Roberto Seu: INFOCOM Department, University of Rome, Rome, Italy
Alessandro Frigeri: Dipartimento di Scienze della Terra, Universitá degli Studi di Perugia, Perugia, Italy

Source:

Geophysical Research Letters (GRL) paper 10.1029/2008GL036379, 2009; http://dx.doi.org/10.1029/2008GL036379

5. Wildfires in Siberia involved in spring 2008 Arctic haze

Arctic haze, regularly observed at northern latitudes since the 1950s, can persist for long periods due to slow removal processes in the Arctic. Thought to be produced mostly from emissions of pollutants from Europe, Asia, and North America, haze can also be caused by episodic plumes released from biomass burning and wildfires. Because fires release smoke that is light absorbing, these episodic haze plumes can also directly affect Arctic climate. Warneke et al. study 50 such plumes encountered during April 2008's Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) airborne field experiment. Chemical analysis of the observed plumes revealed that they originated predominantly from forest fires or agricultural burning. Using a particle dispersion model and satellite data that documented recent fires, the authors found that most of the plumes were emitted by forest fires in the southern Siberia/Lake Baikal region and by agricultural burning in Kazakhstan and southern Russia. The authors noted that the wildfire season started earlier than usual in Siberia, which may help account for the unusually efficient transport of biomass burning emissions into the Arctic.

Title:

“Biomass burning in Siberia and Kazakhstan as an important source for haze over the Alaskan Arctic in April 2008”

Authors:

C. Warneke, R. Bahreini, J. Brioude, J. A. de Gouw, K. D. Froyd, J.S. Holloway, J. Peischl, J. P. Schwarz, J. R. Spackman, and P. Veres: Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, Colorado, U.S.A.; also at Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, U.S.A.
C. A. Brock, D. W. Fahey, A. Middlebrook, D. M. Murphy, and T. B. Ryerson: Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, Colorado, U.S.A.
L. Miller: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, U.S.A.; also at NOAA ESRL Global Monitoring Division, Boulder, Colorado, U.S.A.
S. Montzka: NOAA ESRL Global Monitoring Division, Boulder, Colorado, U.S.A.

Source:

Geophysical Research Letters (GRL) paper 10.1029/2008GL036194, 2009; http://dx.doi.org/10.1029/2008GL036194

6. New method to measure aerosol properties over land from space

Aerosol particles affect the climate of the Earth directly by scattering and absorbing solar radiation, and indirectly by affecting the properties of clouds and their lifetimes. Because aerosols constitute one of the largest sources of uncertainty in assessing the Earth radiation budget, efforts are under way to monitor aerosol properties on a global scale using satellite data. However, retrieving the properties of aerosols over land is difficult because typical variations of land surface reflectance are substantially larger than aerosol reflectance. Waquet et al. present a new approach using highly accurate remote sensing measurements of the polarization of light for a broad range of wavelengths and viewing angles. This approach uses longer-wavelength observations to accurately estimate surface polarization properties, and retrieves the load and the microphysics of the aerosols from shorter-wavelength observations. Testing this approach under pristine and polluted conditions (the latter during a wildfire in California) reveals that the aerosol retrievals are within the uncertainties of those from ground-based Sun/sky radiometer observations. This method will be applied to observations made by the Aerosol Polarimetry Sensor that launches in 2009 on the NASA Glory mission.

Title:

“Polarimetric remote sensing of aerosols over land”

Authors:

F. Waqueti: Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, U.S.A.; now at Laboratoire d'Optique Atmosphérique, Université des Sciences et Technologies de Lille, Villeneuve-d'Ascq, France
B. Cairns, L. D. Travis, and M. I. Mischenko: NASA Goddard Institute for Space Studies, New York, New York, U.S.A.
K. Knobelspiesse and J. Chowdhary: Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, U.S.A.
B. Schmid: Pacific Northwest National Laboratory, Richland, Washington, U.S.A.

Source:

Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2008JD010619, 2009; http://dx.doi.org/10.1029/2008JD010619

7. Isotopic composition of potentially harmful organic aerosols

Secondary organic aerosols (SOAs), formed from the oxidation of volatile organic compounds (VOCs) in the atmosphere, can potentially harm human health and global climate. Despite their importance, understanding of the detailed properties of SOA formation processes, composition, and other VOC by-products is still poor. Because analyzing the ratio of stable isotopes within VOCs and SOAs can provide insight into chemical and physical properties behind VOC oxidation, Fisseha et al. conduct a laboratory experiment to investigate the stable carbon isotope composition of SOAs formed by the oxidation of beta-pinene, a hydrocarbon derived from the resin of conifers, within a sealed chamber. True to theory, the authors found that fractionation of light and heavy isotopes occurs upon oxidation, with light isotopes favoring the SOAs and heavy isotopes remaining in unreacted VOCs. Yet nopinone, a product of the reaction that was present in both gas phases and aerosol phases, fractionated such that its gas phase was slightly heavier than its aerosol phase. The authors expect that knowledge of SOA isotope fractionation rates could, after more study, help scientists evaluate the origin of the VOC that created it.

Title:

“Stable carbon isotope composition of secondary organic aerosol from beta-pinene oxidation”

Authors:

Rebeka Fisseha, Hoger Spahn, Rovert Wegener, Thorsten Hohaus, Gregor Brasse, Holger Wissel, Ralf Tillmann, Andreas Wahner, and Astrid Kiendler-Scharr: Institut für Chemie und Dynamik der Geosphare, ICG 2: Troposphäre, Forschungszentrum Jülich GmbH, Jülich, Germany
Ralf Koppmann: Fachbereich Mathematik und Naturwissenchaften, Fachgruppe Physik, Bergische Universität Wuppertal, Wuppertal, Germany

Source:

Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2008JD011326, 2009; http://dx.doi.org/10.1029/2008JD011326