Highlights in Geophysical Research Letters
I. Highlights, including authors and their institutions
1. Lightning and ice precipitation in harmony
The following highlights summarize research papers in Geophysical Research Letters (GL). The papers related to these Highlights are printed in the next paper issue of the journal following their electronic publication.
You may read the scientific abstract for any of these papers by going to www.agu.org/pubs/search_options.shtml and inserting into the search engine the portion of the doi (digital object identifier) following 10.1029/ (e.g., 2005GL987654). The doi is found at the end of each Highlight, below. To obtain the full text of the research paper, see Part II.
New satellite observations are illuminating the relationship between lightning and the ice content of precipitation. Based on theory and previous observations, Petersen et al. hypothesized that the relationship between the number of lightning strikes per unit area and the amount of ice-phase precipitation in clouds would be the same for different atmospheric environments over oceans, coasts, and continents. To test this, they analyzed lightning and precipitation observations from 1998 to 2000 taken from the Tropical Rainfall Measuring Mission (TRMM) satellite, launched in 1997 by the United States and Japan. They found the amount of lightning corresponded closely with the location of ice precipitation and the size of ice particles, regardless of the environment in which a storm occurred. The relationship between rain and lightning does not show this kind of consistency. The authors say the results, when viewed on a global scale, support previous assumptions about the basic physics of lightning and ice. The density of lightning in a storm may be used in the future to predict the amount of ice present, they suggest.
Title: TRMM observations of the global relationship between ice water content and lightning
Authors: Walter A. Petersen, University of Alabama in Huntsville, Huntsville, Alabama, USA; Hugh J. Christian, NASA Marshall Space Flight Center, Huntsville, Alabama, USA; Steven A. Rutledge, Colorado State University, Fort Collins, Colorado, USA.
Source: Geophysical Research Letters (GL) paper 10.1029/2005GL023236, 2005
2. Muons surge at Earth’s surface during a solar flare
Satellite- and spacecraft-mounted sensors observed a sudden surge in cosmic radiation near Earth on 20 January 2005, caused by a solar flare. At the same time, D’Andrea and Poirier detected a sudden ground-level increase in muons, elementary charged particles similar to electrons but heavier and not found in normal atoms. They observed the muons using Project GRAND, an array of 64 stations of proportional wire detectors in Notre Dame, Indiana. The muons were observed as they passed near the wires and were distinguished from other particles by passing undeflected through a steel plate. The surge of muons peaked between 6:51 and 6:57 Universal Time and coincided with a rise in neutrons reaching detection facilities in New Jersey and Finland. The authors hope to combine their data with that from other muon and neutron detectors around the world to learn more about the particles emitted by the Sun during solar flares.
Title: Ground level muons coincident with the 20 January 2005 solar flare
Authors: C. D’Andrea, J. Poirier, University of Notre Dame, Notre Dame, Indiana, USA.
Source: Geophysical Research Letters (GL) paper 10.1029/2005GL023336, 2005
3. Dense solar winds can reduce auroral electrojet strength
During the spectacular celestial light show called the aurora borealis, intense electric currents known as auroral electrojets form in the Earth’s upper atmosphere. These result from solar winds striking the magnetosphere and connections between the planet’s magnetic field and interplanetary magnetic fields. Previous research suggested that dense solar winds compress the magnetosphere, exciting particles in the ionosphere and strengthening the auroral electrojets. Statistically, however, the evidence only showed a weak relationship between solar wind particle density and auroral electrojet strength. To explore this relationship further, Shue et al. analyzed solar wind and aurora data collected during auroral events from 1978 to 1988 by the Interplanetary Monitoring Platform 8 spacecraft. They isolated solar wind density by discarding events that were overly affected by variations in the interplanetary magnetic fields. Contrary to previous assumptions, the authors found that denser solar winds sometimes weaken auroral electrojets. They say this might be the result of the magnetosphere being "stretched" away from the Earth by the solar wind, which reduces energy in the ionsphere.
Title: A systematic study of effects of solar wind density on auroral electrojets
Authors: J.-H. Shue, Institute of Space Science and Department of Atmospheric Sciences, National Central University, Jhongli, Taiwan; Y. Kamide, Solar-Terrestrial Environment Laboratory, Nagoya University, Toyokawa, Japan; P. T. Newell, Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA.
Source: Geophysical Research Letters (GL) paper 10.1029/2005GL023197, 2005
4. Where there’s fire, there’s smoke
Boreal forest fires near Siberia’s Lake Baikal resulted in extremely high concentrations of carbon monoxide (CO) in the upper troposphere, say researchers. Nedelec et al. analyzed rare direct recordings of carbon monoxide taken by sensors on 320 commercial airline flights between Europe and northeast Asia in 2003. The recordings where taken at altitudes from eight to 12.5 kilometers [five to 7.8 miles]. The amount of carbon monoxide in the upper troposphere increased dramatically over a large area of Siberia from April to July, at times reaching concentrations the authors think are the highest ever recorded. This surge in carbon monoxide came from smoke released during summer forest fires near Lake Baikal. From May to June 2003, the mean concentration of carbon monoxide in the upper troposphere over northeast Asia was 30 percent greater than over Europe, and high carbon monoxide concentrations were found over a wide region of Siberia. This, the authors say, suggests that it is common for forest fire smoke to travel to the upper troposphere rapidly on rising warm air currents. They say a better understanding of the processes influencing atmospheric carbon monoxide levels is vital to studies of atmospheric circulation, air pollution, and greenhouse gases.
Title: Extreme CO concentrations in the upper troposphere over northeast Asia in June 2003 from the in situ MOZAIC aircraft data
Authors: Philippe Nedelec, Valerie Thouret, Jerome Brioude, Bastien Sauvage, Jean-Pierre Cammas, Laboratoire d’Aerologie, CNRS, Observatoire Midi-Pyrenees, Toulouse, France; Andreas Stohl, Norwegian Institute for Air Research, Kjeller, Norway.
Source: Geophysical Research Letters (GL) paper 10.1029/2005GL022141, 2005
5. Siberian river isotopes offer insight into global climate change
Measurement of oxygen isotope concentrations in a Siberian river may help researchers understand the impact of global warming on the Arctic hydrological cycle. Welp et al. measured the quantities of the oxygen isotope delta18O in river water samples taken from the Kolyma River of Siberia from September 2002 to April 2004. The delta18O in water from rain is distinguishable from that in snowmelt. This allowed the researchers to determine the percentages of the river water originating from snowmelt and rain water. They found that the river water leaving the basin consisted of 60 percent snow melt and 40 percent rain. The results also suggest that a substantial proportion of spring snowmelt leaves the basin through evapotranspiration by vegetation. As the temperatures in the region continue to rise, river delta18O concentrations are expected to increase, but changes in precipitation, surface vegetation, and permafrost may also affect the Arctic river’s isotopes. The authors say monitoring this type of stable isotope in Arctic rivers will be a useful tool for future climate change studies.
Title: A high-resolution time series of oxygen isotopes from the Kolyma River: Implications for the seasonal dynamics of discharge and basin-scale water use
Authors: L. R. Welp, California Institute of Technology, Pasadena, California, USA; J.T. Randerson, University of California, Irvine, California, USA; J.C. Finlay, University of Minnesota, St. Paul, Minnesota, USA; S.P. Davydov, G.M. Zimova, A.I. Davydova, S.A. Zimov, Russian Academy of Sciences, Republic of Sakha, Yakutia, Cherskii, Russia.
Source: Geophysical Research Letters (GL) paper 10.1029/2005GL022857, 2005
6. Evidence of an ancient crater lake found on Mars
A discovery of sediment fans in a Martian crater associated with two valley systems suggests that water once flowed over and formed lakes on the planet’s surface. Using imaging systems on the Mars Odyssey and Mars Global Surveyor spacecraft, Fassett and Head observed the fan deposits at the margin of a 40 kilometer [25 mile] crater in the Nili Fossae region. The sediment fans appear to have been deposited as deltas in the water-filled crater. The lake overtopped and breached the eastern crater rim, carving an outlet valley east of the crater and dropping the lake level. If water deposited the delta-like features in the crater as the authors believe, it supports the idea that the early Martian environment was characterized by surface liquid water. The authors say that the large amount of water necessary to fill the crater suggests that water existed for an extended period of time on Mars’ surface.
Title: Fluvial sedimentary deposits on Mars: Ancient deltas in a crater lake in the Nili Fossae region
Authors: Caleb I. Fassett, James W. Head III, Department of Geological Sciences, Brown University, Providence, Rhode Island, USA.
Source: Geophysical Research Letters (GL) paper 10.1029/2005GL023456, 2005
7. Plasma suddenly penetrates Saturn’s magnetosphere
Spacecraft observations show it is common for energized charged particles from Saturn’s outer space environment to suddenly enter the inner portion of the planet’s magnetosphere, with its huge magnetic field that tries to repel such particles. Mauk et al. in July 2004 observed clouds of energetic particles penetrating toward the planet’s surface into the interior regions of Saturn’s magnetosphere. These particles were detected by sensors on the orbiting Cassini-Huygens spacecraft. The injected particles left behind a path as they traveled through the pre-existing populations of electrons and ions in the magnetosphere. In the hours following the particle injections, Cassini’s sensors observed spiral-like patterns the particles left behind. From these observations, the authors were able to determine the character of plasma flow within these regions. They found that energized particles suddenly enter Saturn’s inner magnetosphere frequently, just as they do in the magnetospheres of Earth and Jupiter. The authors say a better understanding of the flow of electrons and ions around the planet would improve calculations of when and where the energized particles penetrate Saturn’s magnetosphere.
Title: Energetic particle injections in Saturn’s magnetosphere
Authors: B. H. Mauk, J. Saur, D. G. Mitchell, E. C. Roelof, P. C. Brandt, S.M. Krimigis, S. A. Livi, C. P. Paranicas, Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland, USA; T. P. Armstrong, J. W. Manweiler, Fundamental Technologies, Lawrence, Kansas, USA; D. C. Hamilton, Department of Physics, University of Maryland, College Park, Maryland, USA; N. Krupp, Max-Planck Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany.
Source: Geophysical Research Letters (GL) paper 10.1029/2005GL022485, 2005
8. Climate alters water transport between Pacific, Indian oceans
An oceanic link, known as the "throughflow," carries warm and fresh waters from the Pacific Ocean to the Indian Ocean. Conditions in the area vary due to transient ocean currents, seasonal climate, and long-term climate cycles such as El Nino, making it difficult to determine how much and what kind of water the throughflow carries annually between the two oceans. Fieux et al. collected samples of water from a research ship in 2004 at locations where the throughflow exits the Pacific Ocean and enters the eastern Indian Ocean. The water samples were analyzed for salinity, oxygen content, and temperature, and compared to samples taken in other sections of the throughflow in 1982 and 1992. The results were used to paint an overall picture of water transport between the two oceans. The authors found that El Nino events and northwestern monsoons tended to decrease transport between the Pacific and Indian oceans, probably by weakening the Pacific tradewinds. La Nina events and northeastern monsoons, on the other hand, tended to increase transport by strengthening the winds. The authors say the extreme climatic events that took place during their research allowed them to observe the maximum variability of throughflow transport.
Title: Variability of the throughflow at its exit in the Indian Ocean
Authors: M. Fieux, R. Molcard, A. Kartavtseff, Université Pierre et Marie Curie, Paris, France; R. Morrow, Laboratoire d’Etudes en Geophysique et Oceanographie Spatiales, GRGS, Toulouse, France; A. G. Ilahude, Puslitbang Oseanologi, Research and Development Center, LIPI, Jakarta, Indonesia.
Source: Geophysical Research Letters (GL) paper 10.1029/2005GL022836, 2005
II. Ordering information for science writers and general public
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Harvey Leifert | AGU -presscenter