- A twenty year reversal in water mass trends in the subtropical North Atlantic
- Variability in solar radiation under cloud-free skies in China
- Solar ultraviolet radiation penetrates deep into the waters of the southeast Pacific Ocean
- Extreme run-up from the 17 July 2006 Java tsunami
- Lack of see-saw response to Southern Ocean wind reduction
- Water dimer absorption helps to heat the atmosphere
- Recent earthquake near southwest Portugal sheds light on 1755 Lisbon tsunami earthquake
- Non-migrating atmospheric tides in the equatorial ionosphere
- Wind-driven countercurrent off the coast of the Iberian Peninsula
- Changes in ocean circulation: A thermodynamics approach
- Detecting silica-mediated dissolution of magnetic grains in sediments
- Dust deposition from disturbed deserts reduces mountain snow cover duration
Three cruises have been conducted to the same area in the North Atlantic: the first in 1959, the second in 1981, and the third in 2005. Through comparisons of data from the first two cruises, previous researchers showed that temperatures decreased in the upper 800 meters of the ocean, and increased at intermediate depths (between 2500 and 800 meters). However, Leadbetter et al. find that data from the most recent cruise show reversals of these trends, with upper waters warming and intermediate waters cooling and freshening over the last 20 years. They propose that the upper ocean was influenced by density surfaces first shifting upwards and then downwards, consistent with temporal changes in the wind fields, as measured by the North Atlantic Oscillation. In contrast, the reversal in the properties of intermediate waters were likely controlled by changes in source waters derived from the Labrador and Mediterranean seas. The reversing changes seen by this data implies that complex mechanisms drive oceanic responses to global warming.
Title: A twenty year reversal in water mass trends in the subtropical North Atlantic
Authors: S. J. Leadbetter and R. G. Williams: Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, U.K.;
E. L. McDonagh and B. A. King: National Oceanography Centre, Southampton, U.K.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029957, 2007
Sunlight that passes directly through the atmosphere to the Earth's surface is called direct solar radiation (DiSR), while the radiation scattered out of the direct beam is called diffuse solar radiation (DfSR); the total of DiSR and DfSR is called Global Solar Radiation (GSR). Qian et al study trends in GSR seen under cloud-free skies over the last four decades in China. They find that between the 1960s and 1980s, China experienced surprisingly significant decreases in GSR and increases in DfSR. The authors suggest that increased aerosol loading from pollutant emissions was most likely responsible for the significant changes of GSR and DfSR seen during that time period. After 1983, both GSR and DfSR show strong variability with no observable trend, though the pollutant emissions continue to increase in China. The authors hypothesize that increased aerosol single scattering albedo, resulting from the change of combustion efficiency of fossil fuel, can partly explain the transition of the GSR trend. In addition, water vapor possibly plays a role in affecting solar radiation reaching the surface of China.
Title: Variability of solar radiation under cloud-free-skies in China: The role of aerosols
Authors:
Yun Qian, Weiguo Wang, and L. Ruby Leung: Pacific Northwest National Laboratory, Richland Washington, U.S.A.;
Dale P. Kaiser: Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL028800, 2007
The surface waters of the southeast Pacific Ocean are poor in nutrients, making the environment inhospitable to life. To determine how solar ultraviolet radiation affects these waters, Tedetti et al. sampled the southeast Pacific in 2004 as part of the Biogeochemistry and Optics South Pacific Experiment. They find that in the extremely nutrient-poor waters of the South Pacific Gyre, located near Easter Island, ultraviolet radiation penetrates up to 100 meters (328 feet) into the top layers of the ocean. These measurements are the highest ever reported for oceanic waters and are equal to those measured in the clearest freshwaters. Because ultraviolet radiation can degrade organic matter and damage DNA, the authors expect that their results will lend insight into marine ecosystem health and the marine carbon cycle.
Title: High penetration of ultraviolet radiation in the South East Pacific waters
Authors:
Marc Tedetti, Richard Sempéré, Bruno Charrière, and David Nérini: Laboratoire de Microbiologie Géochimie et Ecologie Marines (LMGEM), Centre d'Océanologie de Marseille, Université de la Méditerranée, Marseille, France;
Alexander Valsilkov: Science systems and Applications, Inc., Lanham, Maryland, U.S.A.;
William L. Miller: Department of Marine Sciences, University of Georgia, Athens, Georgia, U.S.A.;
Kimitaka Kawamura: Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan;
Patrick Raimbault: Laboratoire d'Océanographie et de Biogéochimie, Centre d'Océanologie de Marseille, Université de la Méditerranée, Marseille, France;
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029823, 2007
On 17 July 2006, an earthquake (magnitude = 7.8) ruptured off the coast of western Java, Indonesia, generating a tsunami that affected more than 300 kilometers (186 miles) of coastline and killed more than 600 people. Hardly felt on the island of Java, the earthquake occurred slowly and breaking, wind-driven waves masked the harbinger withdrawal of water from the shoreline, making this tsunami difficult to detect before impact. Fritz et al. surveyed the 600 kilometers (372 miles) of affected coastline a few days after the tsunami to record eyewitness accounts and measure the height of the tsunami wave when it crashed on land. They find that most areas of the coastline experienced run-up of five to eight meters (20-30 feet). However on the south coast of Nusa Kambangan, the tsunami carved a sharp trimline in a forest at an elevation of 21 meters (69 feet) and up to 1 kilometer (0.6 miles) inland. Due to this pronounced tsunami wave height, the authors suspect that the earthquake might have triggered a local submarine slump that in turn triggered the tsunami.
Title: Extreme run-up from the 17 July 2006 Java tsunami
Authors:
Herman M. Fritz: School of Civil and Environmental Engineering, Georgia Institute of Technology, Savannah, Georgia, U.S.A.;
Widjo Kongko and Sungsang Sujoko: Coastal Dynamic Research Center, Agency for the Assessment and Application of Technology, Yogyakarta, Indonesia;
Andrew Moore: Department of Geology, Kent State University, Kent, Ohio, U.S.A.;
Brian McAdoo: Department of Geology and Geography, Vassar College, Poughkeepsie, New York, U.S.A.;
James Goff: National Institute of Water and Atmospheric Research, Christchurch, New Zealand;
Carl Harbitz: Norwegian Geotechnical Institute, Oslo, Norway;
Burak Uslu: Tsunami Research Center, Verbi School of Engineering, University of Southern California, Los Angeles, California, U.S.A.;
Nikos Kalligeris: Department of Environmental Engineering, Technical University of Crete, Chanea, Greece;
Debora Suteja, Kenia Kalsum, Aditya Gusman, Hamzah Latief, Dodi Djulkarnaen, and Haris Sunendar: Department of Oceanography, Center for Coastal and Marine Development, Institute of Technology Bandung, Bandung, Indonesia;
Vasily Titov: Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington, U.S.A.;
Eko Santoso: Center of Technology for Land Resources and Disaster Mitigation, Agency for the Assessment and Application of Technology, Jakarta, Indonesia;
Costas Synolakis: Tsunami Research Center, Verbi School of Engineering, University of Southern California, Los Angeles, California, U.S.A.; also at Department of Environmental Engineering, Technical University of Crete, Chanea, Greece.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029404, 2007
The global ocean conveyor transports heat and nutrients to the different layers of the ocean. An important arm of this is the Atlantic Meridional Overturning Circulation (AMOC), which moves warm water from the equator to the North Atlantic; water later sinks, driving a deepwater current. Because future climate change has theorized AMOC slowdowns, scientists wonder what would happen to oceanic heat during such a scenario. Most ocean-atmosphere climate models have suggested that the North Atlantic will cool and the southern ocean will warm. However, a refined climate model used by Levermann et al shows both northern and southern cooling in the Atlantic Ocean under such conditions. The lack of a "bipolar see-saw" is due to reduced wind stress in the Southern Ocean. In fact very reduced wind stresses limits sea ice export from the Southern Ocean, causing sea ice extent to increase. This also decreases the amount of solar radiation absorbed by the Earth, further cooling the region. The authors suggest that such a phenomenon could help explain past and future climate sensitivities.
Title: Lack of bipolar see-saw in response to Southern Ocean wind reduction
Authors:
A. Levermann and J. Schewe: Earth System Analysis, Potsdam Institute for Climate Impact Research, Potsdam, Germany;
M. Montoya: Departmento Astrofísica y Ciencias de la Atmósfera, Universidad Complutense, Madrid, Spain
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030255, 2007
Water vapor is the most important radiatively active gas in the Earth's atmosphere, absorbing across visible and infrared wavelengths. In particular, the water dimer, a complex consisting of two weakly bonded water molecules, is thought to play an important role in Earth's energy balance, but firm evidence for absorption of radiation by dimers in near-atmospheric conditions is lacking. Paynter et al. conducted the first high-resolution laboratory measurements of infrared and microwave light absorption by water vapor at a range of near-room temperatures. Their analysis indicates that dimers contribute greatly to radiation absorption by water vapor, significantly in excess of that predicted by other studies. The temperature dependence of this absorption, derived for the first time in this spectral region, corresponds well with theoretical predictions.
Title: Pure water vapor continuum measurements between 3100 and 4400 cm-1:Evidence for water dimer absorption in near atmospheric conditions
Authors:
D. J. Paynter and K. P. Shine: Department of Meteorology, University of Reading, Reading, U.K.;
I. V. Ptashnik: Atmospheric Spectroscopy Division, Institute of Atmospheric Optics, Tomsk, Russia;
K. M. Smith: Space Science and Technology Department, Rutherford Appleton Laboratory, Didcot, U.K.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029259, 2007
On 12 February 2007 an earthquake (magnitude = 6.0) occurred in the Atlantic Ocean about 200 kilometers offshore of southwestern Portugal. Stich et al. study this earthquake with the hope of learning more about the 1755 magnitude 8.5-8.7 Lisbon tsunami earthquake, which is thought to have occurred at the same location. Both earthquakes are special because their unique tectonic environment: Although active subduction is likely not occurring at this location, brittle plate convergence in old oceanic lithosphere can account for the occurrence of great earthquakes along moderate-length faults. Unlike the 1755 earthquake, the 2007 earthquake occurred in a time when global and regional seismic broadband networks continuously monitor the Earth’s interior, allowing the authors to estimate parameters for the recent earthquake. The authors find that it originated 40 kilometers beneath the seafloor with an oblique reverse faulting source; they also identify the preferred fault plane. Scaling the source characteristics to the size of the 1755 earthquake suggests a fault length of 230 to 315 kilometers (143 to 196 miles), compatible with the lengths of mapped faults in the area.
Title: Source analysis of the February 12th 2007 Mw 6.0 Horseshoe earthquake: Implications for the 1755 Lisbon earthquake
Authors:
Daniel Stich and Silvia Pondrelli: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Bologna, Bologna, Italy;
Flor de Lis Mancilla: Seismological and Computational Rock Physics Laboratory, School of Geological Sciences, University College Dublin, Dublin, Ireland;
Jose Morales: Instituto Andaluz de Geofísica, Universidad de Granada, Granada, Spain.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030012, 2007
Non-migrating tides occur in the atmosphere on a 12-hour cycle, but are not pulled by attraction to a celestial body. Rather, they occur in the troposphere over tropical regions as longitudinal global-scale waves, possibly produced by the latent heat release in tropical cloud formation. Through analysis of data from the recently launched FORMOSAT-3/COSMIC satellite constellation, Lin et al observe signatures of these non-migrating tides in the equatorial ionosphere. This observation, from data collected near the solar minimum, matches well with similar observations from the IMAGE satellite near solar maximum. It also provides the first altitudinal distribution of this fascinating ionospheric feature and gives hints to better understand the underlying physical mechanism. Specifically, the global three-dimensional ionospheric electron density seen by the authors shows a prominent four-peaked wave-like longitudinal enhancement in the equatorial ionization anomaly, a region where ions from lower in the ionosphere fountain into the upper ionosphere. The authors expect that these enhancements result from yet unknown physical processes that boost ionic fountaining above 250 kilometers in altitude.
Title: Plausible effect of atmospheric tides on the equatorial ionosphere observed by the FORMOSAT-3/COSMIC: Three-dimensional electron density structures
Authors:
C. H. Lin and C. C. Hsiao: National Space Organization, Hsinchu, Taiwan;
W. Wang and M. E. Hagan: High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado, U.S.A.;
T. J. Immel: Space Sciences Laboratory, University of California, Berkeley, Berkeley, California, U.S.A.;
M. L. Hsu and J. Y. Liu: Institute of Space Science, National Central University, Chung-Li, Taiwan;
L. J. Paxton: Space Department, Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, U.S.A.;
T. W. Fang: High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado, U.S.A.; also at Institute of Space Science, National Central University, Chung-Li, Taiwan;
C. H. Liu: Academia Sinica, Taipei, Taiwan.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029265, 2007
Off the southwestern coast of the Iberian Peninsula, summer conditions can give rise to the onset of a warm countercurrent along the shelf of the Gulf of Cadiz. This current frequently turns northward, extending along the western coast of Iberian Peninsula. A powerful mechanism of water exchange between the south and west coasts of Iberian Peninsula, the countercurrent influences larvae transport and recruitment on the southwestern coast. Teles-Machado et al. investigate this countercurrent and develop both realistic and idealized numerical configurations of the system, with the aim of partitioning the different processes that contribute to its circulation. Through comparisons with satellite data, the authors find that their realistic model simulates in great detail a warm countercurrent that occurred in August 2000. Further analyses of realistic and idealized models show that in all scenarios, a warm countercurrent can be generated except in those where zonal winds are suppressed. The authors conclude that the countercurrent is mainly wind-driven in response to short but strong easterlies that blow over the western Mediterranean Sea and the Gulf of Cadiz.
Title: On the onset of Gulf of Cadiz Coastal Countercurrent
Authors:
Ana Teles-Machado, Álvaro Peliz and Jesus Dubert: Center for Environmental and Marine Studies, Departmento de Física, Universidade de Aveiro, Aveiro, Portugal;
Ricardo F. Sánchez: Spanish Institute of Oceanography (IEO), Santander, Spain.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030091, 2007
As an open dissipative system, the ocean gains heat and salt in the equatorial regions and loses heat and salt in the polar regions. This generates oceanic circulation, which seeks to balance out these inhomogeneities through generating entropy. Shimokawa and Ozawa probe this by focusing on "the principle of maximum entropy production (MEP)," in which a nonlinear system in contact with thermal reservoirs far from equilibrium tends to be in a state with a maximum rate of entropy production representing a thermodynamic potential. By examining the response of oceanic circulation to external fresh water perturbations through a numerical model, the authors find that the ocean tends to respond according to the principle of MEP. They suggest that MEP could become a general thermodynamic principle that determines the behavior of oceanic circulation in response to external perturbations, which could lead to a better understanding of past abrupt cooling and warming events. Additionally, MEP could help anticipate future abrupt ocean circulation changes, which are expected to occur in response to global warming.
Title: Thermodynamics of irreversible transitions in the oceanic general circulation
Authors:
Shinya Shimokawa: National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan;
Hisashi Ozawa: Department of Environmental Sciences, Hiroshima University, Higashi-Hiroshima, Japan.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030208, 2007
The chronological record inherent to ocean and lake sediments makes them ideal candidates for studying past variations in the geomagnetic field. However, any process that alters the magnetic properties of sediments can compromise such analyses and these processes must be fully understood in order to account for the effects of alteration. Noting that magnetite can dissolve in silica-rich environments, Wetter et al. seek to characterize the degree to which this process produces changes in magnetic grain-size distribution by studying sediment samples from eastern Africa's Lake Tanganyika. The authors use the samples to collect data from a class of partial hysteresis curves known as first-order reversal curves (FORCs). Sets of FORCs are combined to generate FORC diagrams which provide information about the size distribution of the magnetic grains and the interactions between them. Through this, the authors find that samples with large amounts of biogenic silica lost some fine-grained magnetic material, whereas those with lower biogenic silica levels showed no such depletion, strongly suggesting that silica-mediated magnetite dissolution preferentially removed magnetic grains.
Title: Detection of silica-mediated dissolution of magnetic grains in sediments using FORC diagrams
Authors:
Laura Wetter and Ken Verosub: Department of Geology, University of California, Davis, California, U.S.A.;
James Russell: Department of Geological Sciences, Brown University, Providence, Rhode Island, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029984, 2007
Dust, when deposited on snow and ice, can enhance absorbed solar radiation and melt rates. To quantify these rates, Painter et al. study Colorado's seasonally snow-covered San Juan Mountains, a region containing headwaters of the Colorado and Rio Grande rivers. Using data they collected on dust deposition to mountain snow and snow energy balance from the past three years, they find with a coupled radiative forcing/snowmelt model that dust deposition at high elevations shortens snow cover duration by 18 to 35 days. In particular, a difference in recent deposition from the Colorado Plateau from four events in 2005 to eight events in 2006 led to a further doubling of radiative forcing by dust and greater melt rates. Because continued agriculture and other soil disturbances in arid regions can enhance dust emission, the authors suggest that the current duration of snow cover represents a dramatic change from that before widespread land-use changes in the late 1800s, and that projected increases in drought intensity in the U. S. desert southwest may further alter mountain snowmelt and snow cover duration.
Title: The impact of disturbed desert soils on duration of mountain snow cover
Authors:
Thomas H. Painter: National Snow and Ice Data Center, University of Colorado, Boulder, Colorado, U.S.A.; now at Department of Geography, University of Utah, Salt Lake City, Utah, U.S.A.
Andrew P. Barrett and Maureen P. Cassidy: National Snow and Ice Data Center, University of Colorado, Boulder, Colorado, U.S.A.;
Christopher C. Landry: Center for Show and Avalanche Studies, Silverton, Colorado, U.S.A.;
Jason C. Neff, Corey R. Lawrence and G. Lang Farmer: Department of Geological Sciences, University of Colorado, Boulder, Colorado, U.S.A.;
Kathleen E. McBride: Department of Geography, Planning, and Recreation, Northern Arizona University, Flagstaff, Arizona, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030284, 2007
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Geophysical Research Letters