"The mean annual G series over Spain shows a tendency to increase during the 1985-2010 period, with a significant linear trend of + 3.9 W m-2 [2.3% more] per decade." This is the main conclusion of a study published in the magazine 'Global and Planetary Change' by researchers from the University of Girona and the Federal Institute of Technology in Zurich (ETH, Switzerland).

The season-by-season data show the same "significant" increase in solar radiation impacting the nation: + 6.5 W/m2 per decade during the summer, + 4.1 W/m2 in autumn, + 3.2 W/m2 in spring and + 1.7 W/m2 in winter.

"These data relate to global solar radiation, in other words the increase in direct radiation reaching us from the Sun plus diffuse radiation which is scattered previously by clouds, atmospheric gases and aerosols," explains one of the authors, Arturo Sanchez-Lorenzo, currently a postdoctoral researcher at the University of Girona.

What is intriguing is that the scientists found a decrease in the diffuse component, because of which direct radiation has increased to a proportionately higher degree. Only in 1991 and 1992 did diffuse radiation rise, and this was due to the ashes from Mount Pinatubo. In general, however, we can observe a downward trend of - 2.1 W/m2 per decade between 1985 and 2010.

"The explanation lies in the fact that in Spain the amount of cloud has decreased markedly since the 1980s - as we have ascertained through other studies - and the tropospheric aerosol load may also have decreased," states Sanchez Lorenzo. "It seems to be very simple: fewer clouds result in higher solar radiation on the surface," he continues.

According to the scientists, this increase may also go hand in hand with more ultraviolet rays, an excess of which presents a health risk, potentially leading to skin cancer.

More global brightening
The increase in global solar radiation is a phenomenon that has been observed in other parts of the world for almost 30 years, especially in developed countries, and it has been named "global brightening". The fall in the diffuse component has also been observed in Central European and Eastern countries.

The team behind the study has not yet analysed the solar radiation data for 2011-2013 provided by the Spanish State Meteorological Agency, but the data from other European weather stations suggests that this brightening is still on the rise.

"Studies such as these may be of interest to the solar energy industry, especially in countries like Spain, where not only do we already have a lot of direct solar radiation but now we are getting even more," affirms one of the other authors, Josep Calbo, who is a professor at the University of Girona.

A. Sanchez-Lorenzo, J. Calbo, M. Wild. "Global and diffuse solar radiation in Spain: Building a homogeneous dataset and assessing their trends". Global and Planetary Change 100: 343-352, 2013.

]]> Wed, 12 JUN 2013 00:36:01 AEST Beijing (UPI) Jun 4, 2013 - Chinese archaeologists say a cluster of ancient tombs in the country's far west are arranged in a manner that implies a sun-worshiping culture.

The tombs were found in Xinjiang's Taxkorgan Tajik Autonomous County, a border region neighboring Afghanistan and Pakistan, China's state-run Xinhua news agency reported Tuesday.

Located on a crossroads of the ancient Silk Road, the tombs have been dated to about 2,500 years ago, or 300 years before China's first emperor established the Qin Dynasty (221-207 B.C.)

Eights tombs, each 6 feet in diameter, were arranged on a 100-yard by 50-yard platform, with lines of black stones and lines of white stones stretching alongside like sun rays, the archaeology team with the Chinese Academy of Social Sciences said.

"The ray-like stone strings might imply sun worship. No similar ones have been detected before in all of Central Asia," team leader Wu Xinhua said.

The people buried in the tombs might have been of high social status, the researchers said, because the black stones lined up with a certain pattern were a rare resource in the area and were likely carried to the tomb site from afar.

]]> Wed, 12 JUN 2013 00:36:01 AEST Greenbelt MD (SPX) Jun 06, 2013 - Lying just above the sun's surface is an enigmatic region of the solar atmosphere called the interface region. A relatively thin region, just 3,000 to 6,000 miles thick, it pulses with movement: Zones of different temperature and density are scattered throughout, while energy and heat course through the solar material.

Understanding how the energy travels through this region - energy that helps heat the upper layer of the atmosphere, the corona, to temperatures of 1 million kelvins (about 1.8 million F), some thousand times hotter than the sun's surface itself - is the goal of NASA's Interface Region Imaging Spectrograph, or IRIS, scheduled to launch on June 26, 2013, from California's Vandenberg Air Force Base.

"IRIS will extend our observations of the sun to a region that has historically been difficult to study," said Joe Davila, IRIS project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "Understanding the interface region better improves our understanding of the whole corona and, in turn, how it affects the solar system."

Scientists wish to understand the interface region in exquisite detail, because energy flowing through this region has an effect on so many aspects of near-Earth space.

For one thing, despite the intense amount of energy deposited into the interface region, only a fraction leaks through, but this fraction drives the solar wind, the constant stream of particles that flows out to fill the entire solar system. The interface region is also the source of most of the sun's ultraviolet emission, which impacts both the near-Earth space environment and Earth's climate.

IRIS's capabilities are uniquely tailored to unravel the interface region by providing both high-resolution images and a kind of data known as spectra. For its high-resolution images, IRIS will capture data on about 1 percent of the sun at a time. While these are relatively small snapshots, IRIS will be able to see very fine features, as small as 150 miles across.

"Previous observations suggest there are structures in the solar atmosphere just 100 or 150 miles across, but 100,000 miles long," said Alan Title, the principal investigator for IRIS at Lockheed Martin in Palo Alto, Calif.

"Imagine giant jets, like the huge fountains you see in Las Vegas. Except these jets have a footprint the size of Los Angeles, and are long enough and fast enough that they would zoom around Earth in 20 seconds. We have seen hints of these structures, but never with the high resolution or the information about velocity, temperature and density that IRIS will provide."

The velocity, temperature and density information will be provided by IRIS' spectrograph. While ultraviolet images look at only one wavelength of light at a time, spectrographs show information about many wavelengths of light at once. Spectrographs split the sun's light into its various wavelengths and measure how much of any given wavelength is present.

This is then portrayed on a graph showing spectral "lines." Taller lines correspond to wavelengths in which the sun emits relatively more light. Analysis of the spectral lines can also provide velocity, temperature and density information, key information when trying to track how energy and heat moves through the region.

Not only does IRIS provide state-of-the-art observations to look at the interface region, it makes uses of advanced computing to help interpret what it sees. Indeed, interpreting the light flowing out of the interface region could not be done well prior to the advent of today's supercomputers because, in this area of the sun, photons of light bounce around so much that it is difficult to understand the path the photon traveled.

"When you observe the interface region, there is no intuitive approach to understanding the light's path from the sun's surface and that's been a major stumbling block," said Bart De Pontieu, the IRIS science lead at Lockheed Martin. "We're trying to understand something that's hidden in a fog - but now, thanks to the enormous advance of computers and sophisticated numerical models, the fog is lifting."

This modeling of the IRIS data takes place on cutting-edge supercomputers at NASA's Ames Research Center in Moffett Field, Calif. Moreover, science teams at Lockheed Martin and the University of Oslo in Norway have worked over the last year to create and refine the models to interpret the dominant processes expected to be at work in the interface region.

For its launch at the end of June, IRIS will take flight using a Pegasus XL rocket, carried aloft by an Orbital Sciences L-1011 aircraft from Vandenberg. IRIS weighs 400 pounds, and upon deployment, will extend its solar panels to reach 12 feet across. IRIS will travel in a polar, sun-synchronous orbit, traveling around Earth at the globe's sunrise line, ranging from approximately 390 miles to 420 miles above Earth's surface.

Each orbit will take IRIS around 97 minutes to complete. This orbit was selected because it provides nearly eight months of eclipse-free sun viewing and also maximizes IRIS' ability to downlink data, by traveling over several ground receivers.

After launch, the IRIS team will perform post-flight checkouts for about 60 days before the official science campaign begins. Once the campaign starts, IRIS will join a host of other spacecraft currently observing the sun and its effects on Earth. NASA's Solar Dynamics Observatory and the joint NASA-Japan Aerospace Exploration Agency's Hinode, for example, both capture high-resolution images of the sun, but focusing on different layers of the sun.

Together, the observatories will explore how the corona and solar wind are powered - Hinode and SDO monitoring the solar surface and outer atmosphere, with IRIS watching the region in between.

"Relating observations from IRIS to other solar observatories will open the door for crucial research into basic, unanswered questions about the corona," said Davila.

Answering such fundamental physics questions about the sun's atmosphere has applications outside of simply understanding the sun, as well. Explosions in the corona can send radiation and solar particles toward Earth, interfering with satellites, causing power grid failures and disrupting GPS services.

By knowing more about what causes such solar eruptions, scientists can improve their ability to forecast such space weather. Moreover, the better we understand this closest star, the better we can understand how other stars are energized as well.

]]> Wed, 12 JUN 2013 00:36:01 AEST Munich, Germany (SPX) Jun 05, 2013 - After two months of preparations in Kiruna in the north of Sweden, the balloon-borne solar observatory Sunrise is ready for its next flight: only a last ground-based rehearsal is still necessary. As soon as the weather conditions are right, a huge, helium-filled balloon will carry Sunrise to a travelling height of approximately 35 kilometers. Equipped with the largest solar telescope ever to have left the Earth's surface, Sunrise will then turn its unique gaze on the Sun.

The mission is led by the Max Planck Institute for Solar System Research (MPS) in Germany. Four years ago, Sunrise embarked on its first, six-day journey - and delivered the most detailed images of the Sun up to that date. However, contrary to all expectations, the Sun was extremely quiet. Today, it is heading towards its next activity maximum. Sunrise 2 will be a journey to the active Sun.

Sunrise's most unique characteristic is its unusual observation point: carried by a huge, helium-filled balloon, the observatory ascends to a height of approximately 35 kilometers - and thus leaves behind the greater part of the Earth's atmosphere. "Turbulences in the atmosphere inevitably blur all images of ground-based telescopes", explains Dr. Peter Barthol from MPS, Sunrise project manager.

Sunrise's telescope, however, will enjoy a unique look at the Sun - and can therefore discern structures with a size of less than 100 kilometers. Once the observatory reaches its travelling height, polar winds will grasp balloon and gondola and carry them westwards around the North Pole. "Thanks to the midnight sun in these latitudes north of the Arctic Circle, we will be able to look at the Sun nonstop", says Barthol. After six or seven days, Sunrise will then land in the north of Canada with the help of a parachute.

"Sunrise's first mission showed us, that this ambitious concept works", says Prof. Dr. Sami K. Solanki, director at the MPS and scientific head of the mission. Sunrise delivered unique images and was able to resolve the Sun's magnetic building blocks for the first time. Scientists assume that the Sun's complex magnetic fields hold the key to many unsolved questions of solar research - for example, why the outermost layer of the Sun, the corona, is approximately 500 times as hot as the photosphere below.

Another mystery is why the Sun's activity changes in an approximately eleven-year-cycle. When the Sun is very active, dark sunspots cover its visible surface especially abundantly. In addition, in these phase solar eruptions emitting particles and radiation into space are frequent. These can cause power outages on Earth or damage satellites.

"Four years ago, the Sun showed us quite impressively, that this eleven-year-cycle is just a rough rule of thumb", says Solanki. Contrary to all expectations, the Sun remained in an extremely long minimum of solar activity. Hence, Sunrise 1 was not able to observe sunspots or solar eruptions. "For the second mission, this should be quite different", says Barthol. Since the end of 2010, the Sun's activity has been increasing again.

Since the beginning of April, the Sunrise team led by the MPS has been preparing the next mission at ESRANGE Space Center near Kiruna in the north of Sweden. "Two months ago, Sunrise arrived here packed into numerous boxes", Barthol remembers.

"Since then, we have calibrated the scientific instruments and the telescope, integrated them into the gondola and tested all systems and the software", he adds. An important aspect in these tests is the so-called pointing: during the flight, the telescope has to find the Sun and align itself accordingly on its own. After first tries with artificial light in the large experimental hall that houses Sunrise tests outside with real sunlight were successful.

When exactly Sunrise will be launched, is still unclear. In the next days the team intends to test the interplay of all the system's components as a last ground-based rehearsal. After that, Sunrise is ready to go. "However, the starting date strongly depends on the weather", says Barthol. Not only rain, but also strong winds forbid a launch. The team therefore will have to be patient and wait - for the right weather and a favorable opportunity for the journey to the active Sun.

The Sunrise mission is led by the Max Planck Institute for Solar System Research in Germany. Further partners are the High Altitude Observatory (Boulder, Colorado), the Kiepenheuer Institute for Solar Physics (Germany), a Spanish consortium led by the Instituto de Astrofisica de Canarias, the Lockheed-Martin Solar and Astrophysics Laboratory (Palo Alto, California), and NASA's Columbia Scientific Ballooning Facility.

]]> Wed, 12 JUN 2013 00:36:01 AEST Greenbelt MD (SPX) Jun 02, 2013 - In late June 2013, NASA will launch a new set of eyes to offer the most detailed look ever of the sun's lower atmosphere, called the interface region. This region is believed to play a crucial role in powering the sun's dynamic million-degree atmosphere, the corona. The Interface Region Imaging Spectrograph or IRIS mission will provide the best resolution so far of the widest range of temperatures for of the interface region, an area that has historically been difficult to study.

"This region is crucial for understanding how the corona gets so hot," said Joe Davila, IRIS project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "For the first time, we will have the capability to observe it at fundamental physical scale sizes and see details that have previously been hidden."

IRIS's capabilities are uniquely tailored to unravel the interface region by providing both high-resolution images and a kind of data known as spectra.

For its high-resolution images, IRIS will capture data on about one percent of the sun at a time. While these are relatively small snapshots, IRIS will be able to see very fine features, as small as 150 miles across.

"We have some great space observatories currently looking at the sun," said Bart DePontieu, the IRIS science lead at Lockheed Martin in Palo Alto, Calif. "But when it comes to the interface region, we've never been able to resolve individual structures. We have been able only to see conglomerates of various structures. Now we will finally be able to observe the details."

IRIS's images will be three to four times as detailed as the images from NASA's Solar Dynamics Observatory - though SDO can observe the whole sun at once. SDO's wavelengths are not tailored, however, to see the interface region. Scientists can use IRIS observations to hone in on smaller details while working with the larger instruments, such as SDO or the Japan Aerospace Exploration Agency's Hinode, to capture images of the entire sun. Together, the observatories will explore how the corona works and impacts Earth - SDO and Hinode monitoring the solar surface and outer atmosphere, with IRIS watching the region in between.

Ultraviolet images look at only one wavelength of light at a time, but IRIS will also provide spectra, a kind of data that can show information about many wavelengths of light at once. Spectrographs split the sun's light into its various wavelengths and measure how much of any given wavelength is present. This is then portrayed on a graph showing spectral "lines" - taller lines correspond to wavelengths in which the sun emits relatively more radiation.

Each spectral line also corresponds to a given temperature, so this provides information about how much material of a particular temperature is present. The images from IRIS' telescope will record observations of material at specific temperatures, ranging from 5,000 kelvins to 65,000 kelvins (8,540 F to 116,540 F) -- and up to 10 million kelvins (about 18 million F) during solar flares -- a range best suited to observe material on the sun's surface and in the interface region.

"By looking at spectra of material in these temperature ranges, we can also diagnose velocity and perhaps density of the material, too," said De Pontieu.

The IRIS instrument will capture a new image every five to 10 seconds, and spectra about once every two seconds. These unique capabilities will be coupled with state-of-the-art 3-D numerical modeling sophisticated enough to deal with the complexity of this region. The modeling makes use of supercomputers at NASA's Ames Research Center, Moffet Field, Calif.

In combination, IRIS' resolution, fast imaging rate, wide temperature coverage and computer modeling will enable scientists for the first time to track solar material as it is accelerated and heated in the interface region and thus help pinpoint where and how the plasma gains energy and heat along its travels through the lower levels of the solar atmosphere.

IRIS was developed by Lockheed Martin as a NASA Small Explorer mission. The NASA Explorer Program is designed to provide frequent, low-cost access to space for heliophysics and astrophysics missions using small- to mid-sized spacecraft. Goddard manages the Explorer Program for the agency's Science Mission Directorate in Washington. Major contributions for IRIS were provided by Lockheed Martin Sensing and Exploration Systems, NASA's Ames Research Center, Smithsonian Astrophysical Observatory, Montana State University, Stanford University, the Norwegian Space Centre and the University of Oslo.

]]> Wed, 12 JUN 2013 00:36:01 AEST Beijing (UPI) May 31, 2013 - Chinese scientists say they've found a new way to track solar coronal mass ejections, hazardous ejections of matter from the sun that can affect Earth.

Researchers at the Chinese Academy of Sciences, working with colleagues from the United States and Europe, have developed a technique called geometric triangulation that can determine the trajectory and velocity of CMEs in real time as they travel in space, China's official Xinhua news agency reported Friday.

Triangulation, used in fields such as surveying and navigation, involves using observations from two separated points to determine the location of a third point.

Researcher Liu Ying and his fellow researchers said data from NASA's solar observation mission known as STEREO, which utilizes twin spacecraft in Earth orbit -- one slightly ahead of the planet and one slightly behind -- can provide geometric triangulation to determine the trajectory and velocity of CMEs.

That data can allow predictions of when a CME will reach Earth and at what velocity, the researchers said.

"Once a CME has occurred, we will be able to track it continuously and determine its path and velocity with the triangulation measurements, in much the same way the terrestrial weather forecast works," Liu said.

CMEs, when they reach Earth, can be hazardous to spacecraft, satellites and astronauts in orbit and can disrupt power grids, satellite navigation and mobile phone networks.

]]> Wed, 12 JUN 2013 00:36:01 AEST Greenbelt MD (SPX) May 24, 2013 - On May 20, 2013, NASA and NOAA satellites observed the system that generated severe weather in the south central United States and spawned the Moore, Okla., tornado.

The tornado that struck Moore on the afternoon of Monday, May 20, was an F-4 tornado on the enhanced Fujita scale, according to the National Weather Service. F-4 tornadoes have sustained winds from 166 to 200 mph. This tornado was about twice as wide as the tornado that struck Moore on May 3, 1999. Moore is located 10 miles south of Oklahoma City.

Before, during and after the tornado, satellites provided imagery and data to forecasters. The first tornado warning was issued around 2:40 p.m. CDT (local time). By 3:01 p.m. CDT a tornado emergency was issued for Moore, and 35 minutes later at 3:36 p.m. CDT, the tornado spun down and dissipated.

NASA's Aqua satellite captured a visible-light image that provided a detailed look at the supercell thunderstorm. NOAA's GOES-13 satellite provided continuously updated satellite imagery depicting the storm's movement. After the tornado, the NASA-NOAA Suomi National Polar-orbiting Partnership satellite's lightning observations showed that the thunderstorm complex was still active after nightfall.

NOAA's GOES-13 satellite provided forecasters with images of the storm system every 15 minutes. One GOES-13 satellite image was captured at 19:55 UTC (2:55 p.m. CDT) as the tornado began its deadly swath. The tornado was generated near the bottom of a line of clouds resembling an exclamation mark. The GOES-13 satellite imagery from the entire day was assembled into an animation by the NASA GOES Project at NASA's Goddard Space Flight Center in Greenbelt, Md.

Four minutes after the tornado dissipated (19:40 UTC / 3:40 p.m. EDT), the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA's Aqua satellite captured a visible image of the supercell thunderstorm that spawned the Moore tornado. That image was created by the NASA Goddard MODIS Rapid Response Team and Adam Voiland, NASA Earth Observatory.

Later as the storm system continued through the region, another satellite captured an image of the storm at night that showed it was still powerful. The Visible Infrared Imaging Radiometer Suite aboard Suomi NPP observed lightning in a nighttime image on May 21 at 07:27 UTC (3:27 a.m. EDT). Lightning appeared as rectangular shapes in the image. The VIIRS imagery showed the city lights in the Oklahoma City area, but there was reduced light output in Moore as a result of tornado damage.

The Suomi NPP satellite carries an instrument so sensitive to low light levels that it can detect lightning in the middle of the night. The Day/Night band on Suomi NPP produces nighttime visible imagery using illumination from natural (the moon, forest fires) and man-made sources (city lights). The data were captured by the direct broadcast antenna at University of Wisconsin.

]]> Wed, 12 JUN 2013 00:36:01 AEST Baltimore MD (SPX) May 27, 2013 - When a solar flare filled with charged particles erupts from the sun, its magnetic fields sometime break a widely accepted rule of physics. The flux-freezing theorem dictates that the magnetic lines of force should flow away in lock-step with the particles, whole and unbroken. Instead, the lines sometimes break apart and quickly reconnect in a way that has mystified astrophysicists.

But in a paper published in the May 23 issue of the journal Nature, an interdisciplinary research team led by a Johns Hopkins mathematical physicist says it has found a key to the mystery. The culprit, the group proposed, is turbulence-the same sort of violent disorder that can jostle a passenger jet when it occurs in the atmosphere. Using complex computer modeling to mimic what happens to magnetic fields when they encounter turbulence within a solar flare, the researchers built their case, explaining why the usual rule did not apply.

"The flux-freezing theorem often explains things beautifully," said Gregory Eyink, a Department of Applied Mathematics and Statistics professor who was lead author of the Nature study. "But in other instances, it fails miserably. We wanted to figure out why this failure occurs."

The flux-freezing theorem was developed 70 years ago by Hannes Alfven, who later won a Nobel Prize in physics for closely related work. His principle states that magnetic lines of force are carried along in a moving fluid like strands of thread cast into a river, and thus they can never "break" and reconnect. But scientists have discovered that within violent solar flares, the principle does not always hold true.

Studies of these flares have determined that their magnetic field lines sometimes do break like stretched rubber bands and reconnect in as little as 15 minutes, releasing vast amounts of energy that power the flare.

"But the flux-freezing principle of modern plasma physics implies that this process in the solar corona should take a million years!" Eyink said. "A big problem in astrophysics is that no one could explain why flux-freezing works in some cases but not others."

Some scientists suspected that turbulence was playing havoc with the behavior predicted by this principle. To find out, Eyink teamed up with other experts in astrophysics, mechanical engineering, data management and computer science, based at Johns Hopkins and other institutions. "By necessity, this was a highly collaborative effort," Eyink said. "Everyone was contributing their expertise. No one person could have accomplished this."

The team developed a computer simulation to replicate what happens under various conditions to the charged particles that exist in a plasma state of matter within solar flares. "Our answer was very surprising," Eyink said.

"Magnetic flux-freezing no longer holds true when the plasma becomes turbulent. Most physicists expected that flux-freezing would play an even larger role as the plasma became more highly conducting and more turbulent, but, as a matter of fact, it breaks down completely.

"In an even greater surprise, we found that the motion of the magnetic field lines becomes completely random. I do not mean 'chaotic,' but instead as unpredictable as quantum mechanics. Rather than flowing in an orderly, deterministic fashion, the magnetic field lines instead spread out like a roiling plume of smoke."

Although some scholars may still believe there are other explanations for solar flares, Eyink said, "I think we made a pretty compelling case that turbulence alone can account for field-line breaking."

The way the researchers from different disciplines teamed up with Eyink to solve the solar flare puzzle was particularly noteworthy. "We used ground-breaking new database methods, like those employed in the Sloan Digital Sky Survey, combined with high-performance computing techniques and original mathematical developments," he said. "The work required a perfect marriage of physics, mathematics and computer science to develop a fundamentally new approach to performing research with very large datasets."

Eyink added that the research could lead to a better understanding of solar flares and mass ejections of material from the sun's corona. Such powerful "space weather" or geomagnetic storms can endanger astronauts, knock out communications satellites and even lead to massive blackouts of electrical power grids on Earth, he said.

The turbulence data on which the analysis relies are publicly available here.

Co-authors of the Nature study from Johns Hopkins's Whiting School of Engineering and Krieger School of Arts and Sciences were Cristian Lalescu and Hussein Aluie, from the Department of Applied Mathematics and Statistics; Kalin Kanov and Randal Burns, from the Department of Computer Science; Charles Meneveau, from the Department of Mechanical Engineering; and Alexander Szalay, from the Department of Physics and Astronomy. Aluie is also affiliated with the Los Alamos National Laboratory. The authors of this study are also affiliated with Johns Hopkins' Institute for Data Intensive Engineering and Science (IDIES), which has been facilitating groundbreaking research based on big data The co-authors from other institutions were Ethan Vishniac, from the Department of Physics and Engineering Physics, University of Saskatchewan, Canada; and Kai Burger, from Fakultat fur Informatik, Technische Universitat Munchen, Munich, Germany.

]]> Wed, 12 JUN 2013 00:36:01 AEST Leeds, UK (SPX) May 24, 2013 - Researchers at the Universities of Leeds and Chicago have uncovered an important mechanism behind the generation of astrophysical magnetic fields such as that of the Sun.

Scientists have known since the 18th Century that the Sun regularly oscillates between periods of high and low solar activity in an 11-year cycle, but have been unable to fully explain how this cycle is generated.

In the 'Information Age', it has become increasingly important to be able to understand the Sun's magnetic activity, as it is the changes in its magnetic field that are responsible for 'space weather' phenomena, including solar flares and coronal mass ejections. When this weather heads in the direction of Earth it can damage satellites, endanger astronauts on the International Space Station and cause power grid outages on the ground.

The research, published in the journal Nature, explains how the cyclical nature of these large-scale magnetic fields emerges, providing a solution to the mathematical equations governing fluids and electromagnetism for a large astrophysical body.

The mechanism, known as a dynamo, builds on a solution to a reduced set of equations first proposed in the 1950s which could explain the regular oscillation but which appeared to break down when applied to objects with high electrical conductivity. The mechanism takes into account the 'shear' effect of mass movement of the ionised gas, known as plasma, which makes up the Sun. More importantly it does so in the extreme parameter regime that is relevant to astrophysical bodies.

"Previously, dynamos for large, highly conducting bodies such as the Sun would be overwhelmed by small-scale fluctuations in the magnetic field. Here, we have demonstrated a new mechanism involving a shear flow, which served to damp these small-scale variations, revealing the dominant large-scale pattern", said Professor Steve Tobias, from the University of Leeds' School of Mathematics, a co-author of the research.

What is more, this mechanism could be used to describe other large, spinning astronomical bodies with large-scale magnetic fields such as galaxies.

The dynamo was developed through simulations using the high-performance computing facilities located at the University of Leeds.

"The fact that it took 50 years and huge supercomputers shows how complicated the dynamo process really is." said Prof Fausto Cattaneo, from the University of Chicago's Department of Astronomy and Astrophysics.

The presence of spots on the Sun has been known since antiquity, and further analysed after the invention of the telescope by Galileo in the 16th Century. However, their cyclic nature, with periods of high activity (lots of sunspots) and low activity (few sunspots) following each other, was not identified until the 18th Century.

At the start of the 20th Century it was then recognised that these sunspots were the result of the Sun's magnetic field. Since then much effort has been devoted to understanding what processes lead to the formation of sunspots and the origin of their cyclic behaviour.

Shear-driven dynamo waves at high magnetic Reynolds Number by S.M. Tobias and F. Cattaneo is published in the journal Nature on 23rd May 2013.

]]> Wed, 12 JUN 2013 00:36:01 AEST Tokyo, Japan (SPX) May 23, 2013 - A team of astronomers led by Jose Dias do Nascimento (Department of Theoretical and Experimental Physics, Universidade Federal do Rio Grande do Norte [DFTE, UFRN], Brazil) has found the farthest known solar twin in the Milky Way Galaxy -- CoRoT Sol 1, which has about the same mass and chemical composition as the Sun.

Spectra from the High Dispersion Spectrograph (HDS) on the Subaru Telescope showed that CoRoT Sol 1 is about 6.7 billion years old while space-based data from the CoRoT (Convection, Rotation and planetary Transits) satellite indicated a rotation period of 29 +/- 5 days. This newly discovered, evolved solar twin allows astronomers to uncover the near future of our solar system's central star -- the Sun.

Since the Sun is the closest star to Earth, it has been extensively studied in a variety of ways. Despite considerable efforts by astronomers, we do not know yet how typical a star the Sun is. Except for the youngest stars, the true rotation of those similar to the Sun is unknown, and there are few studies of mature solar twins or of more evolved ones.

The mass (the amount of matter) and chemical composition of a star are the main characteristics that determine its evolution. Studying stars with the same mass and composition as the Sun, the so-called "solar twins," can give us more information about our own Sun; solar twins of various ages offer snapshots of the Sun's evolution at different phases (Figure 1).

The satellite CoRoT (Convection, Rotation and planetary Transits) has provided precise space-based data from which it is possible to determine the rotation periods of stars. The current team selected the best solar twin candidates within a range of rotation periods to study the evolution of the Sun's rotation period in detail. Because solar twins are faint, the team initially used the High Dispersion Spectrograph (HDS) on the Subaru Telescope to observe three of their solar twin candidates.

The large size of the Subaru Telescope and the capability of HDS to precisely spread out the stellar light into many constituent colors allowed them to study the stars' characteristics in detail. A meticulous analysis of the data showed that one of the solar twin candidates was truly a star with a mass and chemical composition similar to that of the Sun. The finding was even more precious, because the star is at a more evolved stage and can serve as an indicator of the future of the Sun.

Determining the age of a star is probably one of its most difficult aspects to ascertain, but high quality spectra shed light on stellar ages. CoRoT Sol 1 is about two billion years older than the Sun, but its rotation period is about the same as the Sun's.

Subaru Telescope's HDS spectra of CoRoT Sol 1 show that its overall chemical composition is similar to that of the Sun, but its detailed abundance pattern shows some differences, like most nearby solar twins (Figure 2). For example, the abundance of lithium (Li), an element that decreases with age, is less than that of the Sun.

Team leader Dr. Jose Dias do Nascimento commented on the significance of CoRoT Sol 1's age for understanding the Sun's future: "In two billion years' time, about the solar twin's actual age, the Sun's radiation may increase and make the Earth's surface so hot that liquid water can no longer exist there in its natural state."

In contrast to other solar twins that are relatively bright, CoRoT Sol 1, which is located in the constellation Unicorn (Monoceros), is more than 200 times fainter than the brightest solar twin known.

The large 8.2 m mirror of the Subaru Telescope and the precision of its high dispersion spectrograph made it possible to conduct this detailed study of the spectra of such a faint star.

The team plans to use the Subaru Telescope to continue its research on how typical a star the Sun is; they intend to describe its rotation evolution by finding solar twins representing a broad range of stellar ages and then placing the Sun within this context.

The members of the research team are J-D do Nascimento, Universidade Federal do Rio Grande do Norte (UFRN), Brazil; Y. Takeda, National Astronomical Observatory of Japan (NAOJ), Japan; J. Melendez, University of Sao Paulo, Brazil; J.S. da Costa, UFRN, Brazil; G. F. Porto de Mello, Observatorio do Valongo of the UFRJ, Brazil; and M. Castro, UFRN, Brazil.

The research paper entitled "The Future of the Sun: An Evolved Solar Twin Revealed by CoRoT," on which this article is based, has been accepted and will be published in the Astrophysical Journal Letters (ApJL).

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