Category: Earth Observation

Scientists from the Lamont-Doherty Earth Observatory (LDEO) at Columbia University and Rensselaer Polytechnic Institute in New York State have developed the first-ever map of water depth in Lake Vostok, which lies between 3,700 and 4,300 meters (more than 2 miles) below the continental Antarctic ice sheet. The new comprehensive measurements of the lake?roughly the size of North America’s Lake Ontario?indicate it is divided into two distinct basins that may have different water chemistry and other characteristics. The findings have important implications for the diversity of microbial life in Lake Vostok and provide a strategy for how scientists study the lake?s different ecosystems should international scientific consensus approve exploration of the pristine and ancient environment.

Michael Studinger, of the Lamont-Doherty Earth Observatory (LDEO) at Columbia University, said that the existence of two distinct regions with the lake would have significant implications for what sorts of ecosystems scientists should expect to find in the lake and how they should go about exploring them.

“The ridge between the two basins will limit water exchange between the two systems,” he said. “Consequently, the chemical and biological composition of these two ecosystems is likely to be different.”

The National Science Foundation (NSF), an independent federal agency that supports fundamental research and education across all fields of science and engineering, supported the work. NSF manages the U.S. Antarctic Program, which coordinates almost all U.S. science on the southernmost continent.

The new measurements are significant because they provide a comprehensive picture of the entire lakebed and indicate that the bottom of the lake contains a previously unknown, northern sub-basin separated from the southern lakebed by a prominent ridge.

Using laser altimeter, ice-penetrating radar and gravity measurements collected by aircraft, Studinger and Robin Bell, of LDEO, and Anahita Tikku, formerly of the University of Tokyo and now at Rensselaer Polytechnic Institute, estimate that Lake Vostok contains roughly 5400 cubic kilometers (1300 cubic miles) of water. Their measurements also indicate that the top of the ridge dividing the two basins is only 200 meters (650 feet) below the bottom of the icesheet. Elsewhere, the water ranges from roughly 400 meters (1,300 feet) deep in the northern basin to 800 meters (2,600 feet) deep in its southern counterpart.

Water that passes through the lake starts on one end as melted ice from the very bottom of the ice sheet, which refreezes at the other end. According to the new measurements, the base of the ice sheet melts predominantly over the smaller northern basin, while the water in the lake refreezes over the larger southern basin. The researchers assert that water takes between 55,000 and 110,000 years to cycle through the lake.

The arrangement of the two basins, their separation and the characteristics of the meltwater may, the scientists conclude, all have implications for the circulation of water within the lake. It is possible, for example, that if the water in the lake were fresh, meltwater in the northern basin would sink to the bottom of that basin, limiting the exchange of waters between the two basins. The meltwater in the adjacent basin likely would be different.

The two lake basins, they argue, could therefore have very different bottoms.

The scientists also point out that the waters of the two basins may, as a result of the separation, have a very different chemical and even biological composition. Indeed, Lake Vostok, is also of interest to those who search for microbial life elsewhere in the solar system. The lake is thought to be a very good terrestrial analog of the conditions on Europa, a frozen moon of Jupiter. If life can exist in Vostok, scientists have argued, then microbes also might thrive on Europa.

The new measurements also indicate that different strategies may be needed to target sampling of specific types of lake sediments. Those released from the ice sheet represent the rocks over which the ice traveled, for example, and would be more prominent in the northern basin. Material in the southern basin would be more likely to represent the environmental conditions before the ice sheet sealed off the lake.

Scientists deciding whether and how to proceed with an exploration of Lake Vostok say a great deal of technological development would likely be needed before a device could be deployed to conduct contamination-free sampling. Currently, no scientific sampling of the lake is being carried out.

The ultimate goal of any sampling would be to obtain water and sediment samples from the lake bottom.

The team published the new maps in the June 19 edition of Geophysical Research Letters, a publication of the American Geophysical Union.

Original Source: NSF News Release

Image credit: NASA/JPL
In a study published in Geophysical Research Letters (Vol. 31, No.13), University of South Florida College of Marine Science professor Boris Galperin explained a link between the movement and appearance of ocean currents on Earth and the bands that characterize the surface of Jupiter and some other giant planets.

“The banded structure of Jupiter has long been a subject of fascination and intensive research,”said Galperin, a physical oceanographer who analyzes turbulence theory and applies theory and numerical modeling to analyze planetary processes. “The visible bands on Jupiter are formed by clouds moving along a stable set of alternating flows.”

Galperin and colleagues have discovered that the oceans on Earth also harbor stable alternating bands of current that, when modeled, reveal a striking similarity to the bands on Jupiter due to the same kinds of “jets.”

“We think this resemblance is more than just visual,” he said. “The energy spectrum of the oceanic jets obeys a power law that fits the spectra of zonal flows on the outer planets.”

The observation begs the question of whether the similar phenomena are rooted in similar physical forces.

“To answer this question,” said Galperin, “one needs to determine what physical processes govern the large-scale dynamics in both systems.”

According to Galperin, there is a similarity in the forcing agents for planetary and oceanic circulations. The study maintains that both sets of zonal jets – the ocean’s bands of currents and the bands of Jupiter’s clouds – are the result of an underlying turbulent flow regime common in nature.

Comparing the energy spectra on giant planets and in the Earth’s oceans can yield valuable information about the transport properties of the oceans, said Galperin, especially about the strongest currents in the mid-depth ocean.

“The implications of these findings for climate research on Earth and the designs of future outer space observational studies are important,” he explained.

Galperin (http://www.marine.usf.edu/phy/galperin.html) and colleagues Hideyuki Nakano, Meteorological Research Institute, Ibaraki, Japan; Huei-Ping Huang, Lamont-Dougherty Earth Observatory of Columbia University, Palisades, New York; and Semion Sukoriansky, Center for Aeronautical Engineering Studies, Ben Gurion University of the Negev, Beer-Sheva, Israel, reported their research at the 25th Conference of the International Union of Geodesy and Geophysics’s Committee on Mathematical Geophysics, held June 16-18 at Columbia University.

Funding for the study came from the Army Research Office and the Israel Science Foundation.

Original Source: USF News Release

Image credit: JAXA
The Space Engineering Spacecraft “Hayabusa” (MUSES-C) launched on May 9, 2003, by the Japan Aerospace Exploration Agency (JAXA) has been flying smoothly in a heliocentric orbit for about a year using its ion engines.
On May 19, Hayabusa came close to the Earth, and successfully carried out an earth swing-by to place it in a new elliptical orbit toward the asteroid “ITOKAWA”.

The earth swing-by is a technique to significantly change direction of an orbit and/or speed by using the Earth’s gravity without consuming onboard propellant. Hayabusa came closest to the Earth at 3:22 p.m. on May 19 (Japan Standard Time) at an altitude of approximately 3700 km.

The combination of acceleration by the ion engines and the earth swing-by performed this time was the first technological verification in the world, both in the sense of plot and implementation.
After its precise orbit is determined in a week, Hayabusa will restart its ion engines to fly toward “ITOKAWA”.
Hayabusa acquired earth images using its onboard optical navigation camera (which is for detecting a relative position to an asteroid and for scientific observations) as it neared the Earth. You can find these images at the following websites:

Institute of Space and Astronautical Science (ISAS)
http://www.isas.jaxa.jp/e/index.shtml

Original Source: JAXA News Release

Image credit: NASA/JPL
On June 19, NASA will launch Aura, a next generation Earth- observing satellite. Aura will supply the best information yet about the health of Earth’s atmosphere.

Aura will help scientists understand how atmospheric composition affects and responds to Earth’s changing climate. The satellite will help reveal the processes that connect local and global air quality. It will also track the extent to which Earth’s protective ozone layer is recovering.

Aura will carry four instruments designed to survey different aspects of Earth’s atmosphere. The instruments will provide an unprecedented and complete picture of the composition of the atmosphere. Aura will survey the atmosphere from the troposphere, where mankind lives, through the stratosphere, where the ozone layer resides and protects life on Earth.

Aura’s space-based view of the atmosphere and its chemistry will complete the first series of NASA’s Earth Observing System satellites. The other satellites are Terra, which monitors land; and Aqua, which observes Earth’s water cycle.

“Gaining this global view of Earth will certainly reap new scientific discoveries that will serve as essential stepping stones to our further exploration of the Moon, Mars and beyond, the basis of the Vision for Space Exploration,” NASA Administrator Sean O’Keefe said.

Aura will help answer key scientific questions, including whether the ozone layer is recovering. Aura data may prove useful in determining the effectiveness of international agreements that banned ozone-depleting chemicals like chlorofluorocarbons (CFCs).

Aura will accurately detect global levels of CFCs and their byproducts, chlorine and bromine, which destroy ozone. Aura will also track the sources and processes controlling global and regional air quality. It will help distinguish between natural and human-caused sources of these gases. When ozone exists in the troposphere, it acts as an air pollutant. Tropospheric ozone is linked to high levels of precursors such as nitrogen dioxide, carbon monoxide and volatile hydrocarbons. Aura will help scientists follow the sources of tropospheric ozone and its precursors.

“Aura, the first comprehensive laboratory in space to help us better understand the chemistry and composition of the Earth’s atmosphere, is fundamentally a mission to understand and protect the very air we breathe, ” said NASA Associate Administrator for Earth Science Dr. Ghassem Asrar. “It is also a perfect complement to our other Earth Observing System satellites that, together, will aid our nation and our neighbors by determining the extent, causes, and regional consequences of global change.”

As the composition of Earth’s atmosphere changes, so does its ability to absorb, reflect and retain solar energy. Greenhouse gases, including water vapor, trap heat in the atmosphere. Airborne aerosols from human and natural sources absorb or reflect solar energy based on color, shape, size and substance. The impact of aerosols, tropospheric ozone and upper tropospheric water vapor on Earth’s climate remains largely unquantified. Aura’s ability to monitor these agents will help unravel some of their mystery.

Aura’s four instruments, the High Resolution Dynamics Limb Sounder; the Microwave Limb Sounder; the Ozone Monitoring Instrument; and the Tropospheric Emission Spectrometer will work together to provide measurements in the troposphere and stratosphere to help answer important climate questions.

The High Resolution Dynamics Limb Sounder was built by the United Kingdom and the United States. The Ozone Monitoring Instrument was built by the Netherlands and Finland in collaboration with NASA. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., constructed the Tropospheric Emission Spectromer and Microwave Limb Sounder. NASA’s Goddard Space Flight Center, Greenbelt, Md., manages the Aura mission.

NASA’s Earth Science Enterprise is dedicated to understanding the Earth as an integrated system and applying Earth System Science to improve prediction of climate, weather, and natural hazards using the unique vantage point of space.

Original Source: NASA News Release

Image credit: ESA
ESA’s Proba satellite here shows a winding segment of the 7240-km long Great Wall of China situated just northeast of Beijing. The Great Wall’s relative visibility or otherwise from orbit has inspired much recent debate.

The 21 hours spent in space last October by Yang Liwei – China’s first ever space traveller – were a proud achievement for his nation. The only disappointment came as Liwei informed his countrymen he had not spotted their single greatest national symbol from orbit.

“The Earth looked very beautiful from space, but I did not see our Great Wall,” Liwei told reporters after his return.

China has cherished for decades the idea that the Wall was just about the only manmade object visible to astronauts from space, and the news disappointed many. A suggestion was made that the Wall be lit up at night so it can definitely be seen in future, while others called for school textbooks to be revised to take account of Liwei’s finding.

However such revisions may be unnecessary, according to American astronaut Eugene Cernan, speaking during a visit to Singapore: “In Earth’s orbit at a height of 160 to 320 kilometres, the Great Wall of China is indeed visible to the naked eye.”

Liwei may well have been unlucky with the weather and local atmospheric or light conditions ? with sufficiently low-angled sunlight the Wall’s shadow if not the Wall itself could indeed be visible from orbit.

What is for sure is that what the human eye may not be able to see, satellites certainly can. Proba’s High Resolution Camera (HRC) acquired this image of the Wall from 600 km away in space. The HRC is a black and white camera that incorporates a miniature Cassegrain telescope, giving it far superior spatial resolution to the human eye.

So while the HRC resolves mad-made objects down to five square metres, astronauts in low Earth orbit looking with the naked eye can only just make out such large-scale artificial features as field boundaries between different types of crops or the grid shape formed by city streets. They require binoculars or a zoom lens to make out individual roads or large buildings.

China’s Great Wall
Proba (Project for On Board Autonomy) is an ESA micro-satellite built by an industrial consortium led by the Belgian company Verhaert, launched in October 2001 and operated from ESA’s Redu Ground Station (Belgium).

Orbiting 600 km above the Earth?s surface, Proba was designed to be a one-year technology demonstration mission of the Agency but has since had its lifetime extended as an Earth Observation mission. It now routinely provides scientists with detailed environmental images thanks to CHRIS – a Compact High Resolution Imaging Spectrometer developed by UK-based Sira Electro-Optics Ltd – one of the main payloads on the 100 kg spacecraft.

Also aboard is the HRC, a small-scale monochromatic camera made up of a miniature Cassegrain telescope and a 1024 x 1024 pixel Charge-Coupled Device (CCD), as used in ordinary digital cameras, taking 25-km square images to a resolution of five metres. Proba boasts an ‘intelligent’ payload and has the ability to observe the same spot on Earth from a number of different angles and different combinations of optical and infra-red spectral bands. A follow-on mission, Proba-2, is due to be deployed by ESA around 2005.

Original Source: ESA News Release

Image credit: NASA/Hampton University
Two NASA missions to explore the boundaries of Earth’s atmosphere with space are scheduled for launch in 2006. Both have recently completed preliminary design phases and are ready to proceed with hardware fabrication, integration and testing.

The Aeronomy of Ice in the Mesosphere (AIM) Small Explorer will determine the causes of Earth’s highest-altitude clouds, which occur on the very edge of space. These clouds form in the coldest part of the atmosphere, about 50 miles above the polar-regions, every summer. Recorded sightings of these silvery-blue, noctilucent or “night-shining” clouds began in the late 1800’s at high latitudes. They have been increasing in frequency and extending to lower latitudes over the past four decades.

Scientists have hypothesized the more frequent occurrences may be an indicator of global warming, but until now they have not been able to test this idea. Since similar thin high altitude clouds have been observed at Mars, what AIM teaches us about Earth’s noctilucent clouds should help us understand the similarities and differences between the martian and terrestrial atmospheres.

AIM will measure all the parameters important to understanding noctilucent cloud formation. This will help determine the connection between the clouds and their environment and serve as a baseline for the study of long-term changes in the upper atmosphere. Dr. James Russell III of Hampton University in Hampton, Va., leads AIM as Principal Investigator.

The second mission is the Time History of Events and Macroscale Interactions during Substorms mission (THEMIS). A Medium Explorer mission, it will fly five small spacecraft through explosive geomagnetic disturbances to solve the mystery of what triggers the colorful eruptions of the Northern and Southern lights. These violent “substorms” reflect major reconfigurations of near-Earth space and have significant implications for space weather, affecting satellites and terrestrial communications.

Over the years several different hypotheses have been proposed to explain this phenomenon. THEMIS will use five probes, strategically placed in different regions of the magnetosphere, to determine which explanation is correct. THEMIS is led by Dr. Vassilis Angelopoulos of the University of California, Berkeley.

The Explorer Program is designed to provide frequent, low-cost access to space for physics and astronomy missions with small to mid-sized spacecraft. NASA’s Goddard Space Flight Center, Greenbelt, Md., manages the Explorer Program for the Office of Space Science, Washington.

For information and artists’ concepts of the AIM mission on the Internet, visit:
http://aim.hamptonu.edu/

For Information and artists’ concepts of the THEMIS mission, visit:
http://sprg.ssl.berkeley.edu/themis/

For information about the Explorer program on the Internet, visit:
NASA News Release

For information about NASA and agency missions on the Internet, visit:
http://www.nasa.gov

Original Source: NASA News Release

Image credit: NASA/JPL
Contrary to historical observations, sea ice in the high Arctic undergoes very small, back and forth movements twice a day, even in the dead of winter. It was once believed ice deformation at such a scale was almost non-existent.

According to a recent NASA-funded study, the finding is significant. Such movements may substantially increase the production of new ice and should be factored into Arctic climate models. The phenomenon of short-period Arctic sea ice motion was investigated in detail in 1967 and has been the subject of numerous research studies since.

A 1978 study found short-period ice motions disappeared almost entirely during the winter once the Arctic Ocean froze. A subsequent investigation in 2002, conducted using measurements from ocean buoys spaced hundreds of kilometers apart, found sea ice movement occurs during all seasons.

Since buoy observations are poor for understanding short-length-scale motion and deformation, researchers Ron Kwok and Glenn Cunningham of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and William Hibler III of the University of Alaska, Fairbanks, set out to examine the phenomenon in greater detail.

The researchers used high-resolution synthetic aperture radar imagery from Canada’s RADARSAT Earth observation satellite, which can image the region up to five times a day. Their findings were published recently in Geophysical Research Letters. The researchers studied an approximate 200 by 200 kilometer (124 by 124 mile) area in the Canada Basin region of the high Arctic for about three weeks in May 2002 and in February 2003.

This region is representative of the behavior of the central Arctic Ocean ice cover due to its location and thickness. The time frame was selected because Arctic sea ice motion is least expected during those times of year.

The study provided a more detailed picture of the phenomenon reported in the 2002 buoy research. It found sea ice moved back and forth and deformed slightly in a persistent 12-hour oscillating pattern. Subtle motions triggered by the Earth’s rotation rather than by tidal movement likely caused the pattern. In the absence of external forces, any object will move in a circular motion due to the Earth’s rotation. The researchers attributed the winter behavior of the ice cover, not observed in studies before 1970, to either a previous lack of detailed data or perhaps an indication of recent thinning of the Arctic ice cover.

“If Arctic pack ice is continually opening and closing during the Arctic winter on a widespread basis, it could significantly increase the rate of Arctic ice production and therefore increase the total amount of ice in the Arctic,” Kwok said. “A simple simulation of this ice production process shows that it can account for an equivalent of 10 centimeters (4 inches) of ice thickness over 6 months of winter. That’s approximately 20 percent of the base growth of thick ice during the central Arctic winter.”

Kwok said current models of the dynamics of Arctic sea ice typically don’t take into account processes occurring at short, 12-hour time scales, and the impact of such processes must be assessed. “As climate models continue to get better and better, it becomes increasingly important to understand the physics of small-scale processes so that we can understand their large-scale consequences,” he said. “If these Arctic sea ice processes are indeed important over the entire Arctic basin, their contribution to the overall amount of ice in the Arctic should be included in simulations of the interactions that take place between the Arctic’s ice, ocean and atmosphere to create the overall Arctic climate.

“If such oscillations in Arctic sea ice increase as the sea ice cover thins due to warmer atmospheric temperatures, then this mechanism of ice production may actually serve to slow down the overall depletion of ice in the Arctic Ocean,” he added. Kwok said other parts of the Arctic Ocean would be analyzed in future studies.

For more information about the study on the Internet, visit http://www.earth.nasa.gov/flash_top.html.

For information about NASA on the Internet, visit http://www.nasa.gov/home/index.html.

JPL is managed for NASA by the California Institute of Technology in Pasadena.

Original Source: NASA/JPL News Release

Image credit: NASA
Like thermometers in space, satellites are taking the temperature of the Earth’s surface or skin. According to scientists, the satellite data confirm the Earth has had an increasing “fever” for decades.

For the first time, satellites have been used to develop an 18- year record (1981-1998) of global land surface temperatures. The record provides additional proof that Earth’s snow-free land surfaces have, on average, warmed during this time period, according to a NASA study appearing in the March issue of the Bulletin of the American Meteorological Society. The satellite record is more detailed and comprehensive than previously available ground measurements. The satellite data will be necessary to improve climate analyses and computer modeling.

Menglin Jin, the lead author, is a visiting scientist at NASA’s Goddard Space Flight Center, Greenbelt, Md., and a researcher with the University of Maryland, College Park, Md. Jin commented until now global land surface temperatures used in climate change studies were derived from thousands of on-the- ground World Meteorological Organization (WMO) stations located around the world, a relatively sparse set of readings given Earth’s size. These stations actually measure surface air temperature at two to three meters above land, instead of skin temperatures. The satellite skin temperature dataset is a good complement to the traditional ways of measuring temperatures.

A long-term skin temperature data set will be essential to illustrate global as well as regional climate variations. Together with other satellite measurements, such as land cover, cloud, precipitation, and sea surface temperature measurements, researchers can further study the mechanisms responsible for land surface warming.

Furthermore, satellite skin temperatures have global coverage at high resolutions, and are not limited by political boundaries. The study uses Advanced Very High Resolution Radiometer Land Pathfinder data, jointly created by NASA and the National Oceanic and Atmospheric Administration (NOAA) through NASA’s Earth Observing System Program Office. It also uses recently available NASA Moderate Resolution Imaging Spectroradiometer skin temperature measurements, as well as NOAA TIROS Operational Vertical Sounder (TOVS) data for validation purposes. All these data are archived at NASA’s Distributed Active Archive Center.

Inter-annually, the 18-year Pathfinder data in this study showed global average temperature increases of 0.43 Celsius (C) (0.77 Fahrenheit (F)) per decade. By comparison, ground station data (2 meter surface air temperatures) showed a rise of 0.34 C (0.61 F) per decade, and a National Center for Environmental Prediction reanalysis of land surface skin temperature showed a similar trend of increasing temperatures, in this case 0.28 C (0.5 F) per decade. Skin temperatures from TOVS also prove an increasing trend in global land surface temperatures. Regional trends show more temperature variations.

“Although an increasing trend has been observed from the global average, the regional changes can be very different,” Jin said. “While many regions were warming, central continental regions in North America and Asia were actually cooling.”

One issue with the dataset is that it cannot detect surface temperatures over snow. In winter, most of the land areas in the mid to upper latitudes of the Northern Hemisphere are covered by snow. Of Earth’s land area, 90 percent of it is snow free in July, compared to only 65 percent in January. For this reason, the study only focused on snow free areas. Still, in mountainous areas that are hard to monitor, like Tibet, satellites can detect the extent of snow coverage and its variations.

The satellite dataset allows researchers to also look at daily trends on global and regional scales. The largest daily variation was above 35.0 C (63 F) at tropical and sub-tropical desert areas for a July 1988 sample, with decreasing daily ranges towards the poles, in general. Daily changes were also closely related to vegetation cover. The daily skin temperature range showed a decreasing global mean trend over the 18-year period, resulting from greater temperature increases at night compared to daytime.

Things like clouds, volcanic eruptions, and other factors gave false readings of land temperatures, but scientists factored those out to make the skin temperature data more accurate. Scientists are considering extending this 18-year satellite- derived skin temperature record up to 2003. The mission of NASA’s Earth Science Enterprise is to develop a scientific understanding of the Earth system and its response to natural or human-induced changes to enable improved prediction capability for climate, weather, and natural hazards. NASA funded the study.

Original Source: NASA News Release

Image credit: NASA
The time it takes for Earth’s magnetic field to reverse polarity is approximately 7000 years, but the time it takes for the reversal to occur is shorter at low latitudes than at high latitudes, a geologist funded by the National Science Foundation (NSF) has concluded. Brad Clement of Florida International University published his findings in this week’s issue of the journal Nature. The results are a major step forward in scientists’ understanding of how Earth?s magnetic field works.

The magnetic field has exhibited a frequent but dramatic variation at irregular times in the geologic past: it has completely changed direction. A compass needle, if one existed then, would have pointed not to the north geographic pole, but instead to the opposite direction. Such polarity reversals provide important clues to the nature of the processes that generate the magnetic field, said Clement.

Since the time of Albert Einstein, researchers have tried to nail down a firm time-frame during which reversals of Earth’s magnetic field occur. Indeed, Einstein once wrote that one of the most important unsolved problems in physics centered around Earth’s magnetic field. Our planet’s magnetic field varies with time, indicating it is not a static or fixed feature. Instead, some active process works to maintain the field. That process is most likely a kind of dynamic action in which the flowing and convecting liquid iron in Earth’s outer core generates the magnetic field, geologists believe.

Figuring out what happens as the field reverses polarity is difficult because reversals are rapid events, at least on geologic time scales. Finding sediments or lavas that record the field in the act of reversing is a challenge. In the past several years, however, new polarity transition records have been acquired in sediment cores obtained through the international Ocean Drilling Program, funded by NSF. These records make it possible to determine the major features of reversals, Clement said.

“It is generally accepted that during a reversal, the geomagnetic field decreases to about 10 percent of its full polarity value,” said Clement. “After the field has weakened, the directions undergo a nearly 180 degree change, and then the field strengthens in the opposite polarity direction. A major uncertainty, however, has remained regarding how long this process takes. Although this is usually the first question people ask about reversals, scientists have been forced to answer with only a vague ‘a few thousand years.'”

The reason for this uncertainty? Each published polarity transition reported a slightly different duration, from just under 1,000 years to 28,000 years.

“Now, through the innovative use of deep-ocean sediment cores, Clement has demonstrated that magnetic field reversal events occur within certain time-frames, regardless of the polarity of the reversal,” said Carolyn Ruppel, program director in NSF’s division of ocean sciences. “Sediment cores originally drilled to meet disparate scientific objectives have led to a result of global significance, which underscores the value of collecting and maintaining cores and associated data.”

Clement examined the database of existing polarity transition records of the past four reversals. The overall average duration, he found, is 7,000 years. But the variation is not random, he said. Instead it alters with latitude. The directional change takes half as long at low-latitude sites as it does at mid- to high-latitude sites. “This dependence of duration on site latitude was surprising at first, but it?s exactly as would be predicted in geometric models of reversing fields,” Clement said.

Original Source: NSF News Release

Image credit: ESA
The coloured waters shown here in this 21 March Envisat Medium Resolution Imaging Spectrometer (MERIS) image have concluded a long journey across China.

They are surging into the East China Sea from the mouth of the Yangtze River, which at 6300 km long is the longest river in Asia and the third longest in the world.

Rising in the Qinghai-Tibetan Plateau, the Yangtze River snakes through nine provinces and serves as a drain for 1.8 million square kilometres of territory. MERIS is designed to detect ocean colour, and clearly visible here is how the Yangtze’s heavy sediment plume discharges into and colours the waters along the Chinese coast. Its total sediment load is estimated at 680 million tonnes a year ? equivalent in weight to a hundred Great Pyramids.

Shanghai – China’s largest city – is located south of the Yangtze mouth and the 1000-km-long navigable stretch of the Yangtze west of it is a zone of major economic activity. The downside of recent growth has been a decrease in water quality that the Chinese government say it intends to combat. At the start of the month an accidental chemical spill into a tributary of the Yangtze temporarily deprived almost a million people of drinking water.

Original Source: ESA News Release