News Release

AGU journal highlights -- April 10, 2008

Peer-Reviewed Publication

American Geophysical Union

1. Landslide triggered Italian tsunami previously linked to quake

As coastal settlements expand, locating and monitoring areas threatened by tsunami are concerns for local and international authorities responsible for hazard mitigation. One avenue of study that helps with this involves investigating the mechanisms of historic tsunamis. On 28 December 1908, an earthquake with an estimated magnitude of 7.1 struck the region of southern Italy's Messina Straits, within the Ionian Sea. Within minutes after the passage of the seismic waves, a tsunami with maximum observed runups of about 10 meters (33 feet) hit the coasts of Calabria and Sicily. The earthquake and tsunami caused at least 60,000 deaths. Noting that the sources of the tsunami still remain uncertain, Billi et al. use a simple backward ray-tracing method to convert tsunami travel-time data reported in a 100-year-old paper into distances and find that the sources of the earthquake and tsunami are different. Further analysis of all available tsunami, bathymetric, seismic, and seismological data indicates that the tsunami was generated by an underwater landslide, overturning a long-held assumption about the 1908 event.

Title: On the cause of the 1908 Messina tsunami, southern Italy

Authors: Andrea Billi, Renato Funiciello, Liliana Minelli and Claudio Faccenna: Dipartimento di Scienze Geologiche, Università Roma Tre, Rome, Italy;

Giancarlo Neri, Barbara Orecchio, Debora Presti: Dipartimento di Scienze della Terra, Università di Messina, Messina, Italy.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL033251, 2008; http://dx.doi.org/10.1029/2008GL033251


2. Particle formation in lower atmosphere feeds clouds

Aerosols absorb and scatter radiation and influence the properties of clouds through a subset of the aerosol population, which acts as cloud condensation nuclei (CCN). Such cloud-forming particles originate not only from primary particle sources (i.e., dust storms, sea spray, or industrial particulates) but also from particle formation events, where gas phase species nucleate to form new particles. However, the extent to which CCN concentrations are fueled by particle formation events is currently not known. To study this, Spracklen et al. model particle formation in the lowest part of the Earth’s atmosphere using an observationally derived scheme whereby the formation rate of molecular clusters is directly proportional to the amount of gas phase sulfuric acid present. They find that their method models well the particle size distribution observed over three sites in continental Europe. Further, these particle formation events contribute significantly to CCN concentrations over most continental regions. The current generation of climate models does not include these particle formation events, and the authors expect that further work will better constrain how particles influence climate change.

Title: Contribution of particle formation to global cloud condensation nuclei concentrations

Authors: Dominick V. Spracklen, Kenneth S. Carslaw, Joonas Merikanto, Graham W. Mann, and Martyn P. Chipperfield: School of Earth and Environment, University of Leeds, Leeds, U.K.;

Markku Kulmala, Sanna-Liisa Sihto, and Ilona Riipinen: Department of Physical Sciences, University of Helsinki, Helsinki, Finland;

Veli-Matti Kerminen and Heikki Lihavainen: Finnish Meteorological Institute, Helsinki, Finland;

Alfred Wiedensohler and Wolfram Birmili: Leibniz Institute for Tropospheric Research, Leipzig, Germany.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL033038, 2008; http://dx.doi.org/10.1029/2007GL033038


3. Measuring atmospheric metal to estimate interplanetary debris

Every day, the Earth is hit with about 10,000 kg (22,000 pounds) of interplanetary material, most of which is debris from asteroids and comets. This incoming material heats up and is vaporized in the mesosphere and lower thermosphere, contributing heavily to the supply of metal particles in Earth’s upper atmosphere. Determining the atmospheric metal content helps to estimate the influx of interplanetary dust to the Earth. Using data from the Global Ozone Monitoring Experiment spectrometer on the ERS-2 satellite, Correira et al. determine long-term dayside concentrations and temporal variations of meteoric magnesium particles in a representative upper atmospheric air column during 1996 and 1997. They find that concentrations of magnesium ions peak in the middle latitudes during the summer, although neutral magnesium atoms demonstrate a more subtle maximum during summer. The authors expect that further analyses of magnesium and other metals derived from disintegrated meteorites and interplanetary dust will better constrain the time variation of such material to the Earth.

Title: Seasonal variations of magnesium atoms in the mesosphere-thermosphere

Authors: J. Correira and A.C. Aikin: Department of Physics, Catholic University of America, Washington D.C., U.S.A.;

J. M. Grebowsky and W. D. Pesnell: NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A.;

J. P. Burrows: Institute of Environmental Physics, University of Bremen, Bremen, Germany

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL033047, 2008; http://dx.doi.org/10.1029/2007GL033047


4. Earth hums along with unexpected tune

The Earth undergoes continuous oscillations even during periods devoid of significant earthquakes. Scientists call this the Earth's “hum.” Although seismometers measure both the vertical and horizontal motions of the Earth, only the vertical component of the Earth’s hum, which consists of fundamental spheroidal modes, has been detected so far. To search for the hum within horizontal seismic data, Kurrle and Widmer-Schnidrig analyze horizontal seismic data from four exceptionally quiet stations. They find that in addition to the fundamental spheroidal modes, the data show the existence of a previously undocumented global background of fundamental toroidal modes or equivalently long-period Love (surface) waves. For both types of modes, similar horizontal amplitudes are observed. This is surprising because none of the favored models discussed in the literature so far predicts a significant toroidal mode excitation. The authors expect that the discovery of the toroidal background oscillations will require a significant rethinking of the processes that are responsible for hum excitation.

Title: The horizontal hum of the Earth: A global background of spheroidal and toroidal modes

Authors: Dieter Kurrle: Institute of Geophysics, University of Stuttgart, Stuttgart, Germany;

Rudolf Widmer-Schnidrig: Black Forest Observatory, Wolfach, Germany; also at Institute of Geophysics, University of Stuttgart, Stuttgart, Germany.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL033125, 2008; http://dx.doi.org/10.1029/2007GL033125


5. Revealing Yellow River’s erosion and sediment patterns

Within a watershed, sediment moves from uplands and hillslopes into stream channels on its path to the sea. Gauges at watershed mouths can give a lumped representation of linkages between erosion within the drainage basin and downstream sediment delivery. However, such calculations do not provide information on spatial patterns of sediment mobilization within the basin. Using more than 50 years of data from 269 riverine sediment monitoring stations along China's Huanghe (Yellow) River, Hassan et al. study spatial and temporal variation of sediment yield within a large basin with complex geology, climate, and land use history. They find that declining sediment yield is typical of disturbed agricultural areas, while increasing yields indicate the remobilization of stored sediment by bank and floodplain erosion along major tributaries. Also, dramatic changes in sediment yield at landscape scales occurred within the basin’s Loess Plateau after 1970, indicating that land management may have a major effect on sediment dynamics within a relatively short period of time.

Title: Spatial and temporal variation of sediment yield in the landscape: Example of Huanghe (Yellow River)

Authors: Marwan A. Hassan and Michael Church: Department of Geography, University of British Columbia, Vancouver, Canada;

Jiongxin Xu and Yunxia Yan: Institute of Geographical Sciences and Natural Resources Research, Key Laboratory for Water Cycle and Related Land Surface Processes, Chinese Academy of Sciences, Beijing, China.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL033428, 2008; http://dx.doi.org/10.1029/2008GL033428

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