AGU journal highlights -- Aug. 3
The following highlights summarize research papers that have been recently published in Journal of Geophysical Research-Atmospheres (JGR-D), Water Resources Research (WRR), and Geophysical Research Letters (GRL).
In this release:
- Sun's prolonged minimum linked to stretched conveyor belt
- Water globalization can boost drought vulnerability
- Melting floating ice does cause sea level rise
- Identifying oceanic sources of precipitation
- Measuring the Eyjafjallajökull volcanic ash plume
- Bigger role in global carbon cycle found for peatlands
- Study targets atmosphere layer important to climate, ozone
- Sharper look at sprite lightning
- Studying geologic heat transport
Anyone may read the scientific abstract for any already-published paper 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/ 2010GL044143. 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.
1. Sun's prolonged minimum linked to stretched conveyor belt
The Sun goes through cycles lasting approximately 11 years that include phases with increased magnetic activity, more sunspots, and more solar flares, and phases with less activity. The level of activity on the Sun can affect navigation and communications systems on Earth. Puzzlingly, solar cycle 23, which ended recently, lasted longer than previous cycles, with a prolonged phase of low activity that scientists had difficulty explaining.
A new analysis suggests that one reason for the long cycle could be changes in the Sun's conveyor belt. Just as Earth's global ocean circulation transports water and heat around the planet, the Sun has a conveyor belt in which plasma flows along the surface toward the poles, sinks, and returns toward the equator, transporting magnetic flux along the way. Recent measurements show that in solar cycle 23, the poleward flow extended all the way to the poles, while in previous solar cycles the flow turned back toward the equator at about 60 degrees latitude. Furthermore, from mass conservation, the return flow was slower in cycle 23 than in previous cycles.
Dikpati et al. use simulations to model how the solar plasma conveyor belt affects the solar cycle. The authors find that the longer conveyor belt and the slower return flow could have caused the longer duration of cycle 23. The results should help scientists better understand the factors controlling the timing of the solar cycles and could lead to better predictions.
Title: Impact of changes in the Sun's conveyor-belt on recent solar cycles
Authors: Mausumi Dikpati, Peter A. Gilman, and Giuliana De Toma: High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado, USA;
Roger K. Ulrich: Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California, USA.
Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL044143, 2010 http://dx.doi.org/10.1029/2010GL044143
2. Water globalization can boost drought vulnerability
Water is vital for human life. Not only is it used for drinking, water is used for producing electricity, washing, cooking, and growing food. Lately there has been a disproportionate population growth in arid regions, and the demand for water in those regions exceeds the limited supply. However, through the importation of food from other regions, water is virtually transported to arid regions. This exchange allows some societies to thrive in a water deficit state and prevents water wars. However, D'Odorico et al. suggest this increased globalization of water supplies can actually decrease the chance for human societies to rebound from drought-induced crop failure.
The researchers use a simplistic model of population dynamics to study exchanges of virtual water. They consider a situation in which water is shared only locally, a situation in which water is shared globally only when a drought in one region necessitates sharing, and a situation in which water is shared globally at all times.
The authors find that when water is shared globally at all times, populations can grow worldwide, including in arid regions. This works well as a short-term solution, but in the long term, global water supplies are stressed, leaving little extra water capacity to deal with a drought-induced famine in one region and leading to increased mortality during droughts. However, the simulation shows that when water is shared globally only during times of drought, unused water capacity is available and could be shared with the region needing water, thus making society more resilient.
Title: Does globalization of water reduce societal resilience to drought?
Authors: Paolo D'Odorico: Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA;
Francesco Laio and Luca Ridolfi: DITIC, Politecnico di Torino, Turin, Italy.
Source: Geophysical Research Letters (GRL) paper 10.1029/2010 GL043167, 2010 http://dx.doi.org/10.1029/2010GL043167
3. Melting floating ice does cause sea level rise
In recent years, the volume of ice floating in the world's oceans has changed significantly. Some believe that these changes do not affect the sea level, and floating ice loss has often been neglected in studies of sea level rise. However, because ice is fresher (less salty) than seawater, when floating ice melts it causes the ocean to become less dense, and so to expand.
To quantify the global sea level rise due to floating ice loss, Shepherd et al. use satellite observations and an ice-ocean model to estimate changes in the volume of Earth's floating ice. The authors find that overall, the volume of floating ice declined by about 750 cubic kilometers (180 cubic miles) per year during the period from 1994 to 2004, about twice the rate of grounded ice loss over the same period. The greatest reductions were caused by the melting of Arctic Sea ice and the collapse and thinning of small Antarctic ice shelves. Although the net contribution to global sea level has been small?just 50 micrometers (0.002 inches) per year?there are indirect effects to consider too, because ice shelves and sea ice play an important role in global climate.
Because oceans are expected to warm considerably over the course of the century, resulting in loss of large volumes of floating ice, the authors suggest that the melting of floating ice should be included in future assessments of rising sea levels.
Title: Recent loss of floating ice and the consequent sea level contribution
Authors: Andrew Shepherd and Venke Sundal; School of Earth and Environment, University of Leeds, Leeds, UK;
Duncan Wingham, David Wallis, Katherine Giles, and Seymour Laxon: Department of Earth Sciences, University College London, London, UK.
Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL042496, 2010 http://dx.doi.org/10.1029/2010GL042496
4. Identifying oceanic sources of precipitation
Ninety percent of water evaporated from the oceans precipitates back to the oceans. The remaining 10 percent is transported to the continents and plays an important role in the land branch of the hydrological cycle. Studies have suggested that rising global temperatures will lead to increased evaporation and precipitation, exacerbating the hydrological cycle. To identify regions that will be vulnerable to these changes in the hydrological cycle, Gimeno et al. use a model to detect major oceanic moisture source areas and the continental regions significantly influenced by each moisture source.
The researchers identify 12 oceanic moisture sources. They find that the supply of water to the continents from the major oceanic sources is highly uneven. Vast continental areas lack a noticeable direct water transport from any major source region. In addition, some land areas obtain moisture from only one or two sources located in the same hemisphere, while others receive moisture from both hemispheres with large seasonal variations. The continental areas characterized by monsoons benefit from a large number of source regions.
The authors note that the continental regions that rely on only one or two moisture source regions could be more exposed to changes in the hydrological cycle due to a changing climate than regions that receive moisture from multiple sources.
Title: On the origin of continental precipitation
Authors: Luis Gimeno, Anita Drumond, Raquel Nieto: EPhysLab, Facultade de Ciencias, Universidade de Vigo, Ourense, Spain;
Ricardo M. Trigo: CGUL, IDL, University of Lisbon, Lisbon, Portugal; Departamento de Engenharias, Universidade Lusófona, Lisbon, Portugal;
Andreas Stohl: Norwegian Institute for Air Research, Kjeller, Norway.
Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL043712, 2010 http://dx.doi.org/10.1029/2010GL043712
5. Measuring the Eyjafjallajökull volcanic ash plume
The 14 April eruption of Icelandic volcano Eyjafjallajökull sent enormous plumes of thick ash over Europe, disrupting air travel for days. Ansmann et al. report lidar (light detection and ranging) and photometer observations of the ash plume over central Europe. The authors' measurements, made at Leipzig, Germany, on 16 April and Munich, Germany, on the following day, provide some of the first quantitative data on the optical properties of the plume, the optically thickest volcanic ash plume ever measured over Germany. The researchers measured optical depth and optical extinction ratios and estimated ash mass concentrations. The photometer measurements indicate the presence of a significant amount of large ash particles (diameters more than 20 micrometers, or 0.0007 inches). The data could be useful for atmospheric modeling and for improving understanding of the role of volcanic ash in weather and climate.
Title: The 16 April 2010 major volcanic ash plume over central Europe: EARLINET lidar and AERONET photometer observations at Leipzig and Munich, Germany
Authors: A. Ansmann, M. Tesche, P. Seifert, A. Hiebsch, J. Schmidt, U. Wandinger, I. Mattis, and D. Müller: Leibniz Institute for Tropospheric Research, Leipzig, Germany;
S. Groß, V. Freudenthaler and M. Wiegner: Meteorological Institute, Ludwig-Maximilians-Universität, Munich, Germany;
J. M. Picone: Department of Physics and Astronomy, George Mason University, Fairfax, Virginia, USA.
Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL043809, 2010 http://dx.doi.org/10.1029/2010GL043809
6. Bigger role in global carbon cycle found for peatlands
Peatlands, lands in which soil has accumulated large amounts of decaying plant matter, play an important role in the global carbon cycle because they contain significant stores of carbon and can release that carbon into the atmosphere. Although previous studies have investigated the dynamics of peatlands within a particular region, few studies have looked at peatland dynamics globally over a long time period, and estimates of the amount of carbon stored in peatlands vary.
In one of the first comparisons of peatland dynamics across different regions, Yu et al. synthesize global peatland data since the Last Glacial Maximum, approximately 20,000 years ago. The authors look at when peatlands formed in different regions and estimated regional averages of peat carbon accumulation rates. The researchers find that northern peatland formation peaked around 11,000,000 years ago, tropical peatland formation began more than 20,000 years ago and peaked about 8,000,000 years ago, and southern peatland initiation peaked about 17,000,500 years ago. The authors also identify the dominant factors controlling peatland formation: climate seasonality in the northern regions and sea level and monsoon intensity in tropical regions.
In addition, the scientists estimate that 547 gigatons of carbon are stored in northern peatlands, more than previously estimated. Furthermore, they estimate that 50 Gt of carbon are stored in tropical peatlands and 15 Gt are stored in southern peatlands. The analysis shows that peatlands have been an even more important player in the global carbon cycle than had been previously thought.
Title: Global peatland dynamics since the Last Glacial Maximum
Authors: Zicheng Yu, Julie Loisel, Daniel P. Brosseau, and Stephanie J. Hunt: Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania, USA;
David W. Beilman: Department of Geography, University of Hawai'i at Mānoa, Honolulu, Hawaii, USA.
Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL043584, 2010 http://dx.doi.org/10.1029/2010GL043584
7. Study targets atmosphere layer important to climate, ozone
The tropical tropopause transition layer (TTL), starting at about 12 kilometers (7.5 miles) in altitude, is a transition layer between the tropical troposphere (the layer nearest Earth) and the stratosphere above. The TTL can influence the chemistry of the stratosphere, including the global ozone budget. In addition, understanding how water and other greenhouse gases behave in the TTL is important to understanding the greenhouse effect and global climate change. To better understand the TTL and the role the TTL plays in Earth's climate and atmospheric chemistry, the Tropical Composition, Cloud and Climate Coupling (TC4) experiment was conducted. The large-scale study, which ran during July and August 2007, combined ground-based, balloon-based, aircraft, and satellite observations to investigate a variety of topics, including humidity in the upper troposphere and lower stratosphere, the properties of thin cirrus clouds, ozone in the TTL, how short-lived chemical compounds are transported into the TTL and what happens to those compounds, the properties of anvils (the flattened tops of cumulus clouds), and how space-based atmospheric measurements can be validated. Toon et al. describe the planning, implementation, and some preliminary results of the TC4 experiment.
Title: Planning, implementation, and first results of the Tropical Composition, Cloud and Climate Coupling Experiment (TC4)
Authors: Owen B. Toon: Department of Atmospheric and Oceanic Sciences and Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, Colorado, USA;
David O. Starr: Laboratory for Atmospheres, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA, and others (for a complete list of the authors, see http://dx.doi.org/10.1029/2009JD013073)
Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2009JD013073, 2010 http://dx.doi.org/10.1029/2009JD013073
8. Sharper look at sprite lightning
Sprite lightning, a striking and unusual type of lightning that occurs in the upper atmosphere above thunderclouds, consists of a main portion, which is usually red, and thin tendril-like streamers that emanate from the main portion. The streamers have a streamer head, followed by a column-shaped glow. Kanmae et al. captured several sprite streamers using a high-speed spectrograph at 10,000 frames per second in August 2009. The new observations have greater spatial, temporal, and spectral resolution than previous studies. The researchers observed strong blue light emissions from the streamer heads but less blue emissions from the column-shaped glows. The authors use their data to estimate the electric fields in the streamer head and in the glows and confirm that the streamer heads are much more energetic than the glows.
Title: Observation of blue sprite spectra at 10,000 fps
Authors: Takeshi Kanmae and Hans C. Stenbaek-Nielsen: Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA;
Matthew G. McHarg: Space Physics and Atmospheric Research Center, U.S. Air Force Academy, Colorado Springs, Colorado, USA;
Ryan K. Haaland: Physics and Engineering Department, Fort Lewis College, Durango, Colorado, USA.
Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL043739, 2010 http://dx.doi.org/10.1029/2010GL043739
9. Studying geologic heat transport
Environmental and industrial applications such as oil drilling, geothermal engineering, and radioactive waste storage rely on knowledge of heat transport through geological environments. It is often assumed that heat transfer is governed by a simple equation known as the Fourier transport equation, but there is evidence that heat flow in some media is in fact non-Fourier.
To explore the issue, Geiger and Emmanuel conduct simulations of heat flow in geologically realistic fractured porous domains. The authors find that heat transport in a well-connected fracture network is "Fourier-like," but in the poorly connected fracture network in the more heterogeneous material, heat transfer is non-Fourier; the simple classical model does not capture the main features of heat transfer.
However, the researchers find that the non-Fourier heat transport in those poorly connected materials could be accurately modeled using a method known as a continuous time random walk model, in which simulated packets of heat move randomly through the material. The continuous time random walk model has been applied in fields ranging from ecology to economics to physics to computer science; the new work represents one of the first applications of the model to geologic heat transport.
Title: Non-Fourier thermal transport in fractured geological media
Authors: Sebastian Geiger: Institute of Petroleum Engineering, Heriot-Watt University Edinburgh, UK;
Simon Emmanuel: Institute of Earth Sciences, The Hebrew University of Jerusalem Givat Ram, Jerusalem, Israel.
Source: Water Resources Research (WRR) paper 10.1029/2009WR008671, 2010 http://dx.doi.org/10.1029/2009WR008671