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| American Geophysical Union
JOURNAL HIGHLIGHTS |
Contact: Harvey Leifert
(202) 777-7507 hleifert@agu.org |
| 14 November 2003 |
The following highlights summarize research papers in Geophysical Research
Letters (GL), Journal of Geophysical Research-Oceans (JC), and Space Weather.
The papers related to these Highlights are printed in the next paper issue of the journal following
their electronic publication.
1. Voyager 1 has not left the solar system 1. Voyager 1 has not left the solar system The magnetic field measured by the Voyager 1 spacecraft at its 2002 location approximately 85 times the distance between the Earth and Sun should not be interpreted as its exit from the solar system. Burlaga et al. report that the recent heliospheric measurements do not provide evidence for the spacecraft's exit from supersonic solar wind speeds into a subsonic region. The authors note that such an exit would have enhanced the magnetic field strength by a factor of between 3-6 as Voyager 1 passed through the termination shock, the point where solar winds shift from supersonic to subsonic flow in the region that separates the solar winds from the interstellar medium. Instead, they note, recent observations are similar to magnetic field strengths and fluctuations seen during 2001 and in previous years when changes in the solar wind speeds observed by the spacecraft were controlled by solar activity. Title: Search for the heliosheath with Voyager 1 magnetic field measurements Authors:
Source: Geophysical Research Letters (GRL) paper: 10.1029/2003GL018291, 2003
2. Finding a cause for repeated Arctic Ocean warming A simulation of the events responsible for repeatedly warming the subsurface Arctic Ocean during the past half-century may allow scientists to link surface temperature conditions and water sources to the ocean's recent behavior. Gerdes et al. examined the development of anomalous Arctic Ocean warming in the 1990s to estimate the cause of the below-surface temperature rise, which is believed to be associated with an eastward shift in the divide between waters that originated in the Pacific and Atlantic oceans. The authors analyzed the inflow and outflow of waters to the polar ocean from 1948 until 2002 and the climatic changes during the same period to see if the recent warming was unprecedented in the region's history. They conclude that the 1990s warming was exceptional due to a significant influx of heat from the Nordic Seas, likely caused by abnormally warm water flowing from the Barents Sea into the Arctic Ocean. Title: Causes and development of repeated Arctic Ocean warming events Authors:
Source: Geophysical Research Letters (GRL) paper: 10.1029/2003GL018080, 2003
3. Anomalies in Martian southern hemisphere affect magnetic field A new simulation of Mars' magnetic field indicates that magnetic anomalies in the planet's southern hemisphere create unexpected physical reactions to solar winds. Harnett and Winglee present the results from a magnetic dynamics model of the solar wind's interaction with the magnetic anomalies on Mars. The authors suggest that the unusual magnetic properties alter the planet's magnetic field orientation, pressure, and current in a magnetopause-like structure where the planetary field connects with solar energetic particles. The researchers note that the northern hemisphere's magnetic field behaves as expected, which agrees with calculations from the Mars Global Surveyor data. Their findings can help researchers better understand the effects in the area where the interplanetary magnetic field meets planetary plasma and fast-moving charged solar winds rapidly slow down, known as the magnetic pileup boundary. Title: The influence of a mini-magnetopause on the magnetic pileup boundary at Mars Authors:
Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper: 10.1029/2003GL017852, 2003
4. Deciphering plate collision history A new interpretation of ancient tectonic motions has provided evidence that could help researchers explain the effects from the little-studied collision of the African, Arabian, and Eurasian plates. McQuarrie et al. found that the Arabian plate has moved fairly constantly towards the Eurasian plate since the Cenozoic era, approximately 60 million years ago, while the African and Eurasian plate motions have slowed due to the creation of the Red Sea. The plate collisions and resulting effects also destroyed the historical Neotethys Ocean. Their study suggests that the slow, steady plate subduction speeds during the Cenozoic contrasts with highly variable magma production rates during the same time period, prompting the authors to suggest that magma production is likely not related to plate movement. The researchers conclude that estimating the speed and direction of the various plate motions can allow scientists to better understand the forces that control plate motion on the Earth's surface. Title: Cenozoic evolution of Neotethys and implications for the causes of plate motions Authors:
Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper: 10.1029/2003GL017992, 2003
5. Pollution may increase oceanic photosynthesis Air pollution may help increase photosynthesis of oceanic ecosystems, according to a new study that suggests man-made sulfur dioxide in the air promotes the formation of nutrients from mineral dust. Meskhidze et al. analyzed aircraft data collected over heavily polluted areas of China and propose that sulfur dioxide can enhance the production of bioavailable iron when combined with airborne dust plumes that contain insoluble iron particles. The authors believe that the sulfur dioxide emissions acidify the airborne dust commonly blown from sands and arid regions worldwide and promote the mobilization of the iron contained in the dust. The mobilized iron then acts as a micronutrient to oceanic organisms and enhances the water's productivity, including its uptake of carbon from the atmosphere. The researchers caution that further observations are required to examine whether the same effect occurs in other parts of the world. Title: Iron mobilization in mineral dust: Can anthropogenic SO2 emissions affect ocean productivity? Authors:
Source: Geophysical Research Letters (GRL) paper: 10.1029/2003GL018035, 2003
6. Ice shelf cracks indicate higher Arctic temperatures Rising temperatures in the northern polar region have led to fracture in the largest Arctic ice shelf that caused an ice-dammed lake in the region to drain. Mueller et al. suggest that air temperature increases in the far northern latitudes have accelerated ice sheet deterioration in the recent past. The split of the Ward Hunt Ice Shelf in northern Canada was detected by satellite observations and confirmed with scientific expeditions that concluded that the shelf fractured between the years 2000 and 2002. Due to the fragmentation, a freshwater lake behind the 3,000-year-old ice shelf, containing a unique ecosystem, was drained. Further disintegration of the ice shelf will also lead to ice islands up to 30 meters [100 feet] thick migrating into open waters such as the Beaufort Sea, where they could affect shipping and drilling platforms. [Note: See also AGU Press Release 03-26: www.agu.org/sci_soc/prrl/prrl0326.html.] Title: Break-up of the largest Arctic ice shelf and associated loss of an epishelf lake Authors:
Source: Journal of Geophysical Research-Oceans (JGR-C) paper:
10.1029/2003GL017931, 2003
7. East Anatolian Plateau rests on Earth's hot mantle New seismic data indicates that the base of the East Anatolian High Plateau, which makes up the peaks and mountains of the Alpine-Himalayan mountain system of Europe and Asia, likely rests on the Earth's hot mantle rather than on the planetary crust. Sengor et al. present data from a network of seismic stations in eastern Turkey that show the average thickness of the lithosphere below the mountain range is approximately 45 kilometers [28 miles], or nearly 10 kilometers [six miles] shallower than previously assumed. The findings indicate that there is no lithospheric [outer] mantle below the Anatolian complex plateau. The authors estimate that the high temperatures from direct contact with the mantle melted the material that formed the plateau during a tectonic subduction and subsequent continental collision. They further suggest that the elevated mantle temperatures during its post-collision evolution contributed to the rise and eventual remarkable altitude of the mountain range. Title: East Anatolian high plateau as a mantle-supported, north-south shortened domal structure Authors:
Source: Geophysical Research Letters (GRL) paper: 10.1029/2003GL017858, 2003
8. Where gravity waves break down into turbulent winds A new study that tracks the flow of a gravity wave through the tropopause can help researchers better understand turbulence and air mixing in the lower atmosphere. Whiteway et al. analyzed ground-based radar measurements and high-altitude aircraft data from a breaking gravity wave to study the waves' effect on atmospheric winds. Such waves, along with the prevailing jet stream, have a significant bearing on wind patterns that can influence aircraft flight paths and affect cloud dynamics. The authors found that the gravity wave began to break down into small eddies of air turbulence with an amplitude of approximately 500 meters, between the tropospheric and stratospheric layers, a process that contributes to air mixing at the tropopause. They note that little was previously known about where atmospheric mixing occurred and suggest that their observations can also be used to investigate vertical temperature and ozone profiles. Title: Airborne measurements of gravity wave breaking at the tropopause Authors:
Source: Geophysical Research Letters (GRL) paper: 10.1029/2003GL018207, 2003
9. Atmospheric changes dominate ice movement in Antarctic A study of Antarctic ice drift suggests that interactions between sea ice and winds initiate the seasonal advance and retreat of sea ice. Stammerjohn et al. propose that atmospheric dynamics, more so than temperature, dominate the production of ice-edge anomalies in the western Antarctic Peninsula. Because of its exposure to prevailing westerly winds, the peninsula is a highly dynamic region that reacts quickly to climate changes. The authors analyzed the ice-atmosphere reactions during winter 1992 when the sea ice advanced and retreated exceptionally early and compared their findings to the late advance and retreat observed during the winter of 1990. They attributed the abrupt mid-winter ice edge shifts to changes in meridional winds associated with the polar atmospheric circulation. The researchers conclude that the ice-atmosphere interactions in the western Antarctic Peninsula region respond to changes in the semi-annual oscillation influenced by the tropical Pacific. Title: Ice-atmosphere interactions during sea-ice advance and retreat in the western Antarctic Peninsula region Authors:
Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper: 10.1029/2002JC001543, 2003
10. Measuring radiation on airline flights A new detector can measure the levels of charged particles from the sun on airline electronic systems, passengers and crews. Stassinopoulos et al. developed a new type of spectrometer that can precisely measure cosmic and solar radiation as they strike Earth's atmosphere, providing information that could help plan new aircraft routes. Small amounts of radiation can adversely affect commercial flights and other types of aircraft and their computerized on-board control and navigational systems. Newer aircraft use ever more complicated computer systems that are known to be affected by high radiation levels. The authors tested their Low Linear Energy Transfer Radiation Spectrometer on transcontinental flights and those flown over the Arctic to study the effects of solar and environmental influence on aviation altitudes. Their preliminary study found that radiation levels are more intense at higher altitudes and at higher latitudes, particularly during times of known solar storms. [Note: See also AGU Press Release 03-28: www.agu.org/sci_soc/prrl/prrl0328.html.] Title: A systematic global mapping of the radiation field at aviation altitudes Authors:
Source: Space Weather (SW) paper: 10.1029/2003SW000011, 2003 *****
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