Public Release: 

AGU journal highlights -- Jan. 28, 2009

American Geophysical Union

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

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 and inserting into the search engine the full doi (digital object identifier), e.g. 10.1029/2008GL036119. 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

1. Natural oil leakage into the Gulf of Mexico occurs frequently

Crude oil from natural seeps accounts for about half of the oil entering the marine environment. However, our knowledge of when, where, and how frequently seeps occur is still poor. Most past studies have used synthetic aperture radar (SAR), which is costly and limited by coverage. Instead, Hu et al. use data from the Moderate Resolution Imaging Spectroradiometer (MODIS) to detect and quantify oil slicks. The satellite sensors provide several images per week at no cost to the public. Focusing on the northwestern Gulf of Mexico, the authors conclude that the slicks were the result of natural seepage from the ocean floor. They also find a much higher occurrence of oil slicks than was previously thought. Over 160 slicks were seen in one image from May 2006. Their proof-of-concept study shows the unique value of MODIS in observing natural oil slicks under Sun glint even in the clearest ocean waters. The authors expect that such research will help coastal communities improve their management of resources as well as aid responders after oil spills caused by ship or oil platform accidents.

Title: Detection of natural oil slicks in the NW Gulf of Mexico using MODIS imagery

Authors: Chuanmin Hu: College of Marine Science, University of South Florida, St. Petersburg, Florida, U.S.A.;

Xiaofeng Li: IMSG at NOAA/NESDIS, Camp Springs, Maryland, U.S.A.; William G. Pichel: NESDIS, NOAA, Camp Springs, Maryland, U.S.A.;

Frank E. Muller-Karger: School for Marine Science and Technology, University of Massachusetts Dartmouth, New Bedford, Massachusetts, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036119, 2009;

2. Freak waves may be sinking ships off the coast of Japan

On 23 June 2008, the Suwa Maru No. 58, a fishing boat with 20 crew members, sank in seemingly moderate sea conditions of Cape Inubosaki, Japan. Reports from the investigators indicated that although reported wave heights were between 2 and 3 meters (6.5 and 9.8 feet), the ship may have encountered abnormal waves twice, sinking the ship about 10 minutes after being hit by the initial wave. Other possibilities, such as improper use of an anchor or an encounter with an unidentified submerged object, were suggested, but no definitive conclusion has been reached as to why the Suwa Maru sank. Noting that a number of ships have been wrecked in this region, which is notorious for abnormal waves, Tamura et al. seek to determine the state of the sea at the time of the shipwreck. Using a hindcast wave simulation using a model driven by wind and ocean current, the authors find that at the time of the accident wave steepness increased and waves became long crested, creating a sea state favorable for freak wave occurrence. Under the influence of rising wind speed, the swell system grew exponentially, dangerously churning the waters and creating a freakish sea state.

Title: Freakish sea state and swell-windsea coupling: Numerical study of the Suwa-Maru incident

Authors: H. Tamura and Y. Miyazawa: Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan;

T. Waseda: Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan; also at Department of Ocean Technology Policy and Environment, Graduate School of Frontier Sciences, University of Tokyo, Chiba, Japan.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036280, 2009;

3. Weather can be modeled as a cascade process

Numerical weather forecasting typically involves complex and nonlinear calculations, although many have theorized that there must be a simpler way to model terrestrial weather. To help search for this way, Lovejoy et al. hypothesize whether simplicity can be reached through seeing weather dynamics as cascade processes in which large structures modulate smaller ones and the process repeats to smaller and smaller scales, generating extremely variable fractal structures. The authors analyze data from 1000 orbits of the Tropical Rainfall Measuring Mission satellite and find that shortwave and longwave radiance and reflective properties planet-wide follow predictions of cascade models with good agreement from planet scales down to 10 kilometers (6.21 miles). Because radiances and atmospheric dynamics are strongly coupled, the authors conclude that weather can be accurately modeled as a cascade process.

Title: Atmospheric complexity or scale by scale simplicity?

Authors: S. Lovejoy, V. Allaire, S. King, J. Pinel, and J. Stolle: Physics, McGill University, Montreal, Quebec, Canada;

D. Schertzer: CEREVE, Université Paris, Est, Mare-la Vallée, France; also at Météo France, Paris, France;

T. Bourgeois: CEREVE, Université Paris, Est, Mare-la Vallée, France.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL035863, 2009;

4. The fate of climate feedbacks as temperatures warm

Small disturbances to climate can be quantified in terms of "climate sensitivity," a marker that combines how changes in water vapor, cloud cover, reflectance, and other properties affect ground temperatures and vice versa. To better understand how climate feedbacks respond to a full spectrum of changes, Colman and McAvaney couple an atmospheric general circulation model with a mixed layer ocean model and subjected it to a range of between 1/16 and 32 times the current CO2 concentration in the atmosphere. They find that as climate warms, climate sensitivity weakens, although not linearly. Further, the feedback whereby solar heat absorption by the planet changes surface cover to allow more solar radiation to be absorbed also weakens. However, some feedbacks strengthen, such as the one by which increased humidity from higher temperatures fosters higher atmospheric water vapor concentrations. The authors conclude that such studies can provide the scientific community with a benchmark for investigating what physical processes appear important in determining feedback strengths and how these systematically vary across a broad range of climate changes.

Title: Climate feedbacks under a very broad range of forcing

Authors: Robert Colman: Centre for Australian Weather and Climate Research, Melbourne, Victoria, Australia;

Bryant McAvaney: Formerly at Bureau of Meteorology Research Centre, Melbourne, Victoria, Australia.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036268, 2009;



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