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  • richardmitnick 12:57 pm on October 14, 2017 Permalink | Reply
    Tags: , Hard X-rays, , , Nanoflares, , NASA Sounding Rocket Instrument Spots Signatures of Long-Sought Small Solar Flares, NASA UC Berkeley FOXSI sounding rocket, One of the consequences of nanoflares would be pockets of superheated plasma, Solar Flares,   

    From Goddard: “NASA Sounding Rocket Instrument Spots Signatures of Long-Sought Small Solar Flares” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    Oct. 13, 2017
    Sarah Frazier
    sara.frazier@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    Like most solar sounding rockets, the second flight of the FOXSI instrument – short for Focusing Optics X-ray Solar Imager – lasted 15 minutes, with just six minutes of data collection. But in that short time, the cutting-edge instrument found the best evidence to date of a phenomenon scientists have been seeking for years: signatures of tiny solar flares that could help explain the mysterious extreme heating of the Sun’s outer atmosphere.

    FOXSI detected a type of light called hard X-rays – whose wavelengths are much shorter than the light humans can see – which is a signature of extremely hot solar material, around 18 million degrees Fahrenheit. These kinds of temperatures are generally produced in solar flares, powerful bursts of energy. But in this case, there was no observable solar flare, meaning the hot material was most likely produced by a series of solar flares so small that they were undetectable from Earth: nanoflares. The results were published Oct. 9, 2017, in Nature Astronomy.

    “The key to this result is the sensitivity in hard X-ray measurements,” said Shin-nosuke Ishikawa, a solar physicist at the Japan Aerospace Exploration Agency, or JAXA, and lead author on the study. “Past hard X-ray instruments could not detect quiet active regions, and combination of new technologies enables us to investigate quiet active regions by hard X-rays for the first time.”

    1
    The NASA-funded FOXSI instrument captured new evidence of small solar flares, called nanoflares, during its December 2014 flight on a suborbital sounding rocket. Nanoflares could help explain why the Sun’s atmosphere, the corona, is so much hotter than the surface. Here, FOXSI’s observations of hard X-rays are shown in blue, superimposed over a soft X-ray image of the Sun from JAXA and NASA’s Hinode solar-observing satellite.
    Credits: JAXA/NASA/

    JAXA/NASA HINODE spacecraft


    NASA UC Berkeley JAXA FOXSI sounding rocket

    These observations are a step toward understanding the coronal heating problem, which is how scientists refer to the extraordinarily – and unexpectedly – high temperatures in the Sun’s outer atmosphere, the corona. The corona is hundreds to thousands of times hotter than the Sun’s visible surface, the photosphere. Because the Sun produces heat at its core, this runs counter to what one would initially expect: normally the layer closest to a source of heat, the Sun’s surface, in this case, would have a higher temperature than the more distant atmosphere.

    “If you’ve got a stove and you take your hand farther away, you don’t expect to feel hotter than when you were close,” said Lindsay Glesener, project manager for FOXSI-2 at the University of Minnesota and an author on the study.

    The cause of these counterintuitively high temperatures is an outstanding question in solar physics. One possible solution to the coronal heating problem is the constant eruption of tiny solar flares in the solar atmosphere, so small that they can’t be directly detected. In aggregate, these nanoflares could produce enough heat to raise the temperature of the corona to the millions of degrees that we observe.

    One of the consequences of nanoflares would be pockets of superheated plasma. Plasma at these temperatures emits light in hard X-rays, which are notoriously difficult to detect. For instance, NASA’s RHESSI satellite – short for Reuven Ramaty High Energy Solar Spectroscopic Imager – launched in 2002, uses an indirect technique to measure hard X-rays, limiting how precisely we can pinpoint the location of superheated plasma. But with the cutting-edge optics available now, FOXSI was able to use a technique called direct focusing that can keep track of where the hard X-rays originate on the Sun.

    “It’s really a completely transformative way of making this type of measurement,” said Glesener. “Even just on a sounding rocket experiment looking at the Sun for about six minutes, we had much better sensitivity than a spacecraft with indirect imaging.”

    FOXSI’s measurements – along with additional X-ray data from the JAXA and NASA Hinode solar observatory – allow the team to say with certainty that the hard X-rays came from a specific region on the Sun that did not have any detectable larger solar flares, leaving nanoflares as the only likely instigator.

    “This is a proof of existence for these kinds of events,” said Steve Christe, the project scientist for FOXSI at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and an author on the study. “There’s basically no other way for these X-rays to be produced, except by plasma at around 10 million degrees Celsius [18 million degrees Fahrenheit]. This points to these small energy releases happening all the time, and if they exist, they should be contributing to coronal heating.”

    There are still questions to be answered, like: How much heat do nanoflares actually release into the corona?

    “This particular observation doesn’t tell us exactly how much it contributes to coronal heating,” said Christe. “To fully solve the coronal heating problem, they would need to be happening everywhere, even outside of the region observed here.”

    Hoping to build up a more complete picture of nanoflares and their contribution to coronal heating, Glesener is leading a team to launch a third iteration of the FOXSI instrument on a sounding rocket in summer 2018. This version of FOXSI will use new hardware to eliminate much of the background noise that the instrument sees, allowing for even more precise measurements.

    A team led by Christe was also selected to undertake a concept study developing the FOXSI instrument for a possible spaceflight as part of the NASA Small Explorers program.

    FOXSI is a collaboration between the United States and JAXA. The second iteration of the FOXSI sounding rocket launched from the White Sands Missile Range in New Mexico on Dec. 11, 2014. FOXSI is supported through NASA’s Sounding Rocket Program at the Goddard Space Flight Center’s Wallops Flight Facility in Virginia. NASA’s Heliophysics Division manages the sounding rocket program.

    Related:

    JAXA press release on these findings (Japanese)
    NASA-funded FOXSI to Observe X-rays from Sun
    https://www.nasa.gov/mission_pages/sounding-rockets/index.html

    See the full article here.

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    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.


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  • richardmitnick 9:05 am on March 28, 2016 Permalink | Reply
    Tags: , , , Solar Flares   

    From AAAS: “Could Earth be fried by a ‘superflare’ from the sun?” 

    AAAS

    AAAS

    Mar. 24, 2016
    Daniel Clery

    Solar eruption 2012 by NASA's Solar Dynamic Observatory SDO
    Solar eruption 2012 by NASA’s Solar Dynamic Observatory SDO

    NASA/SDO
    NASA/SDO

    Solar flares on the sun frequently shower Earth with high-energy particles causing the Aurora Borealis and, occasionally, less-welcome disruptions to power networks and communications. But researchers say that there is a chance—though small—that the sun could one day blast us with a solar flare thousands of times as powerful, potentially frying our atmosphere and obliterating life.

    Other stars occasionally produce such superflares, some up to 10,000 times the power of the largest solar flare ever detected. To see whether these are generated by the same process as happens on the sun—the breaking and reconnection of magnetic fields (pictured above)—astronomers studied light from 100,000 stars using China’s Guo Shouiing Telescope [LAMOST].

    LAMOST telescope China
    LAMOST China

    As they report online today in Nature Communications, superflares do seem to be produced by the same process, but they usually occur in stars with much stronger magnetic fields than the sun’s. Still, the researchers found that about 10% of the superflaring stars had magnetic fields similar to or weaker than the sun’s. From evidence in tree rings, the researchers say, it looks like Earth suffered small superflares—10 to 100 times bigger than normal—in 775 C.E. and 993 C.E. We can expect more, they conclude, once per millennium. (As for the chances of an Earth-frying flare, they don’t say.) So, back up your data and stock up on candles.

    See the full article here .

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  • richardmitnick 7:59 am on January 26, 2016 Permalink | Reply
    Tags: , , , , Solar Flares,   

    From SPACE.com: “Mysteriously Powerful Particles from Solar Explosions Unveiled in New Study” 

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    SPACE.com

    January 25, 2016
    Calla Cofield

    Solar eruption 2012 by NASA's Solar Dynamic Observatory SDO
    A photo of a solar eruption from Oct. 14, 2012, as seen by NASA’s Solar Dynamic Observatory. Credit: NASA/SDO

    NASA SDO
    NASA/SDO

    A couple of times a month — sometimes more, sometimes less — an explosion goes off on the surface of the sun, releasing energy that’s equal to millions of hydrogen bombs.

    Mind boggling as that number is, this tremendous energy output cannot explain how material that is spit out by these explosions gets ramped up to nearly the speed of light. It’s like expecting a golf cart motor to power a Ferrari.

    In a new study, researchers provide a first-of-its-kind look under the hood of these solar eruptions, taking specific aim at the physical process that accelerates the superfast particles.

    Explosions on the sun

    There are currently 18 NASA space missions dedicated to studying our nearest star and its effect on the solar system. Some of these satellites stare directly at the sun almost nonstop, providing a 24/7 stream of images of the sun’s swirling, churning surface.

    When a solar eruption happens, these satellites also see the incredibly bright flashes of light that are called solar flares. Occasionally, the eruptions also hurl a cloud of extremely hot and electrically charged gas (called plasma) out into space. The expelled plasma is called a coronal mass ejection, or CME for short.

    A solar explosion releases roughly the same amount of energy that would come from “millions of 100-megaton hydrogen bombs,” according to NASA, where one hundred megatons equal to one hundred million metric tons of TNT.

    While that certainly sounds impressive, it’s hard to imagine something so enormous. The best way to understand the colossal nature of these events might be to consider an image taken by NASA that shows a particularly massive CME. For comparison, a snapshot of the Earth (to scale) is placed next to this great, flaming ribbon. The planet looks like a daisy in the path of a flamethrower.

    A solar explosion releases roughly the same amount of energy that would come from “millions of 100-megaton hydrogen bombs,” according to NASA, where one hundred megatons equal to one hundred million metric tons of TNT.

    Shockingly fast

    When an airplane breaks the sound barrier — physically overtaking the sound waves traveling in front of it — it creates a shock wave, and a deafening sonic boom. The boom is evidence that the shock wave is a source of energy.

    Bin Chen, a researcher at the Harvard-Smithsonian Center for Astrophysics is the lead author on a new research paper that provides the first solid observational evidence that ultraspeedy particles released during a solar eruption are accelerated by a kind of stationary shock wave called a “termination shock.”

    One of the intriguing elements of solar eruptions is that, unlike most explosions on Earth, they aren’t chemically driven. Rather, these sunshine bombs are detonated by a rapid release of magnetic energy. The same force that makes a magnet stick to a refrigerator or makes a compass needle point north is also responsible for these massive belches of light and material.

    The solar eruptions that create solar flares and CMEs occur when one of the sun’s magnetic-field lines break, and rapidly reconnects, near the surface. During the explosion, plasma is flung out into space, but others go back down toward the surface at incredibly high speeds, where they crash into more magnetic-field loops — kind of like a waterfall crashing into the surface of a pond. At the point of collision, a termination shock forms in the electrically charged plasma.

    “Charged particles that cross a [termination] shock can pick up the energy from the shock and get faster and faster. That’s how shock acceleration works,” Bin told Space.com.

    Chen and his coauthors saw evidence of this termination shock during a solar flare on March 3, 2012, using the Karl G. Jansky Very Large Array (VLA) in New Mexico.

    NRAO VLA
    Karl G. Jansky Very Large Array (VLA)

    The recently upgraded telescope was beneficial for two reasons. First, it detects radio waves, which means it isn’t overwhelmed by the brightest flashes of light emitted during a solar flare. But looking at a solar flare radio frequencies does reveal the particles accelerated by the termination shock.

    Second, the telescope can effectively take around 40,000 images per second. It does this by capturing thousands of radio frequencies at the same time. The frequencies are then separated into individual “images.” Chen told Space.com that in order to see termination shock in action, it was necessary to collect that many images for about 20 minutes.

    “So if you do the math, that’s millions and millions of images [you need] in order to extract the information,” Chen said. “That’s a new capability provided by the upgraded VLA.”

    Chen said the new findings don’t necessarily mean that termination shocks are responsible for accelerating particles in all solar flares. He said he and his colleagues would like to conduct further observations to find out if this is the case in all shocks, or only a subset.

    The termination shock explanation has been part of the “standard” solar-flare theory for years, but there hasn’t been “convincing” observational evidence to back it up, Chen said. Chen’s comment was confirmed by Edward DeLuca, a senior astrophysicist at the Smithsonian Astrophysical Observatory, which is part of the Harvard-Smithsonian Center for Astrophysics (DeLuca works in the same department as Chen, but was not involved with the new research.)

    “[The new result] reveals that we’re on the right track with the standard-flare model,” DeLuca said.

    Look out for powerful particles

    All those NASA satellites studying the sun are not just working to create mesmerizing images; they’re also there to help protect Earth. Solar flares and coronal mass ejections pose a hazard to the planet. The particles they eject can damage satellites and solar panels, and could pose a serious threat to astronauts doing spacewalks outside the International Space Station, on the moon or Mars.

    They can even cause surges in power grids on the ground. In 1989, a CME caused a blackout across the entire province of Quebec, Canada.

    The superfast particles are of particular worry, because their high speeds mean they can penetrate more layers of material than their “slower” counterparts. When those particles penetrate a piece of solid-state equipment, they can cause a “bit flip” — which could not only damage the equipment but also change what it does.

    “If that little flip of the bit means a computer command that normally says, ‘keep taking snapshots of the sun,’ instead says ‘shut down the spacecraft,’ that’s bad,” Young said. “So a lot of times, if there is a large particle event, spacecraft operators will often put their spacecraft into what’s called a ‘safe mode.'”

    That reaction has to happen fast. Light can travel from the sun to the earth in 8 minutes, so the solar energetic particles can reach an orbiting satellite in about 10 to 20 minutes, Young said. Coronal mass ejections leave a little more time, but a delayed response can mean serious consequences.

    For that reason, scientists are trying to get better at predicting when solar flares and CME’s will occur and how intense they will be.

    DeLuca said the new understanding of termination shock will not, most likely, be immediately useful for improving forecasting of solar explosions. But it is a piece of the solar-flare puzzle, and he said it will be incorporated into “next-generation” solar-weather technology and prediction techniques. It’s one more step toward helping humans ride out the solar storm.

    See the full article here .

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  • richardmitnick 12:36 pm on December 4, 2015 Permalink | Reply
    Tags: , , Solar Flares   

    From Science Times: “Sun’s Superflares Enough To Destroy Modern Civilization” 

    Science Times

    Science Times

    Dec 03, 2015
    Jasper Nikki De La Cruz

    1
    (Photo : Reuters) A typical solar flare on the surface of the Sun.

    Scientists issued a warning that the Sun might emit “superflares.” Superflares have enough power and reach to destroy modern civilization.

    Astronomers have noticed from a star that is similar to the Sun that the former is releasing superflares. Such event should point out that the Sun could have the same and the circumstances is dire the technology and modern civilization.

    Solar flares are flash of light from the Sun’s surface. This is considered as one of the most powerful forces produced within the solar system. Typical solar flares are irregular and few and far between. These energy blasts are equal to 100 million megaton bombs; however, the superflares are equivalent to a billion megaton bombs.

    “If the Sun were to produce a superflare it would be disastrous for life on Earth; our GPS and radio communication systems could be severely disrupted and there could be large-scale power blackouts as a result of strong electrical currents being induced in power grids,” according to Chloe Pugh, the lead scientist of the research from University of Warwick

    Superflares are “extremely unlikely” to occur in the Sun basing on the behavior on the surface of it. The superflare that the astronomers studies occurred on the binary star KIC9655129.

    Solar flares have rapid increase in intensity and then is followed by a slow and gradual decline. This phase is often unstable as it releases pulsations called “quasi-periodic pulsations” (QPP). The flare observed by the astronomers on the binary star has two significant QPPs. Based on the statistics, these dual QPPs are not by chance but are actually independent and overlapping each other.

    “The most plausible explanation for the presence of two independent periodicities is that the QPPs were caused by magnetohydrodynamic (MHD) oscillations, which are frequently observed in solar flares,” according to Anne-Marie Broomhal, co-author of the study.

    See the full article here .

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  • richardmitnick 4:38 pm on January 17, 2015 Permalink | Reply
    Tags: , , Solar Flares,   

    From Stanford: “Artificial intelligence helps Stanford physicists predict dangerous solar flares” 

    Stanford University Name
    Stanford University

    January 14, 2015
    Leslie Willoughby

    Solar flares can release the energy equivalent of many atomic bombs, enough to cut out satellite communications and damage power grids on Earth, 93 million miles away. The flares arise from twisted magnetic fields that occur all over the sun’s surface, and they increase in frequency every 11 years, a cycle that is now at its maximum.

    f
    This solar flare was captured Jan. 12 by NASA’s Solar Dynamics Observatory. Stanford physicists are bringing artificial intelligence techniques to the challenge of predicting such flares. (NASA/SDO and the AIA; EVE; and HMI science teams)

    NASA Solar Dynamics Observatory
    NASA/SDO

    Using artificial intelligence techniques, Stanford solar physicists Monica Bobra and Sebastien Couvidat have automated the analysis of the largest ever set of solar observations to forecast solar flares using data from the Solar Dynamics Observatory (SDO), which takes more data than any other satellite in NASA history. Their study identifies which features are most useful for predicting solar flares.

    Specifically, their study required analyzing vector magnetic field data. Historically, instruments measured the line-of-sight component of the solar magnetic field, an approach that showed only the amplitude of the field. Later, instruments showed the strength and direction of the fields, called vector magnetic fields, but for only a small part of the sun, or part of the time. Now an instrument on a satellite-based system, the Helioseismic Magnetic Imager (HMI) aboard SDO, collects vector magnetic fields and other observations of the entire sun almost continuously.

    Stanford HMI for SDO
    Stanford HMI for NASA SDO

    Adding machine learning

    The Stanford Solar Observatories Group, headed by physics Professor Phil Scherrer, processes and stores the SDO data, which takes 1.5 terabytes of data a day. During a recent afternoon tea break, Bobra and Couvidat chatted about what they might do with all that data and talked about trying something different.

    They recognized the difficulty of forming predictions when using pure theory and they had heard of the popularity of the online class on machine learning taught by Andrew Ng, a Stanford professor of computer science.

    Machine learning is a sophisticated way to analyze a ton of data and classify it into different groups,” Bobra said.

    Machine learning software ascribes information to a set of established categories. The software looks for patterns and tries to see which information is relevant for predicting a particular category.

    For example, one could use machine-learning software to predict whether or not people are fast swimmers. First, the software looks at features of swimmers – for example, their heights, weights, dietary habits, sleeping habits, their dogs’ names and their dates of birth.

    And then, through a guess and check strategy, the software would try to identify which information is useful in predicting whether or not a swimmer is particularly speedy. It could look at a swimmer’s height and guess whether that particular height lies within the height range of speedy swimmers, yes or no. If it guessed correctly, it would “learn” that the height might be a good predictor of speed.

    The software might find that a swimmer’s sleeping habits are good predictors of speed, whereas the name of the swimmer’s dog is not.

    The predictions would not be very accurate after analysis of just the first few swimmers. The more information provided, the better machine learning gets at predicting.

    Similarly, the researchers wanted to know how successfully machine learning would predict the strength of solar flares from information about sunspots.

    “We had never worked with the machine learning algorithm before, but after we took the course we thought it would be a good idea to apply it to solar flare forecasting,” Couvidat said. He and Bobra applied the algorithms and Bobra characterized the features of the two strongest classes of solar flares, M and X. Though others have used machine learning algorithms to predict solar flares, nobody has done it with such a large set of data and or with vector magnetic field observations.

    M-class flares can cause minor radiation storms that might endanger astronauts and cause brief radio blackouts at Earth’s poles. X-class flares are the most powerful.

    Better flare prediction

    The researchers catalogued flaring and non-flaring regions from a database of more than 2,000 active regions and then characterized those regions by 25 features such as energy, current and field gradient. They then fed the learning machine 70 percent of the data, to train it to identify relevant features. And then they used the machine to analyze the remaining 30 percent of the data to test its accuracy in predicting solar flares.

    Machine learning confirmed that the topology of the magnetic field and the energy stored in the magnetic field are very relevant to predicting solar flares. Using just a few of the 25 features, machine learning discriminated between active regions that would flare and those that would not flare. Although others have used different methods to come up with similar results, machine learning provides a significant improvement because automated analysis is faster and could provide earlier warnings of solar flares.

    However, this study only used information from the solar surface. That would be like trying to predict Earth’s weather from only surface measurements like temperature, without considering the wind and cloud cover. The next step in solar flare prediction would be to incorporate data from the sun’s atmosphere, Bobra said.

    Doing so would allow Bobra to pursue her passion for solar physics. “It’s exciting because we not only have a ton of data, but the images are just so beautiful,” she said. “And it’s truly universal. Creatures from a different galaxy could be learning these same principles.”

    Monica Bobra and Sebastien Couvidat worked under the direction of physicist Phil Scherrer of the WW Hansen Experimental Physics Laboratory at Stanford.

    See the full article here.

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  • richardmitnick 9:33 am on October 17, 2014 Permalink | Reply
    Tags: , , , , , Solar Flares,   

    From SPACE.com: “NASA Probe Finds Nanoflares and Plasma ‘Bombs’ on Sun” 

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    SPACE.com

    October 16, 2014
    Nola Taylor Redd

    The first results from a new NASA sun-studying spacecraft are in, and they reveal a complex and intriguing picture of Earth’s star.

    NASA’s Interface Region Imaging Spectrograph probe (IRIS) has observed ‘bombs’ of plasma on the sun, nanoflares that rapidly accelerate particles, and powerful jets that may drive the solar wind, among other phenomena, five new studies report.

    iris
    The completed IRIS observatory with solar arrays destroyed prior to launch. Credit: NASA

    While spacecraft can enter planetary atmospheres, they cannot fly through the outer atmosphere of the sun, where temperatures reach 3.5 million degrees Fahrenheit (2 million degrees Celsius). Probes like IRIS instead must study the star from a safe distance. Unlike previous instruments, IRIS can take far more detailed observations of the sun, capturing observations of regions only about 150 miles (240 kilometers) wide on a time scale of just a few seconds.

    “The combination of enhanced spatial and spectral resolution, [which are] both three to four times better than previous instruments, allows a much closer look [at the sun’s atmosphere],” Hardi Peter of the Max Planck Institute for Solar System Research in Germany told Space.com by email. Peter was the lead author on a study of hot plasma ‘bombs’ on the sun.

    Nanoflare acceleration

    The surface of the sun, or photosphere, is the region visible to human eyes. Above the photosphere lie the hotter chromosphere and transition regions, which emit ultraviolet light that can only be observed from space. This is because Earth’s atmosphere absorbs most of this radiation before it reaches land-based instruments. The outer part of the solar atmosphere is called the corona.

    While much of the sun’s energy is generated in its core through hydrogen fusion, temperatures rise in the exterior layers moving out farther from the heat source. This means that something is powering that outer region, and scientists think the magnetic fields generated by the churning solar plasma provide at least part of the answer.

    In emerging active regions, magnetic fields rise through the surface into the upper atmosphere, like a string pulled upward. When the energy carried by the field lines becomes too great, they snap, disconnecting from one another and reconnecting with other broken field lines in a process known as magnetic reconnection.

    Paola Testa, of the Harvard-Smithsonian Center for Astrophysics, led a team that used IRIS to study the footprints of these loops, where he found that the intensity changed over a span of 20 to 60 seconds. Investigating possible causes, Testa determined that the variations were consistent with simulations of electrons generated from coronal nanoflares.

    “Nanoflares are short heating events releasing amounts of energy about a billion times smaller than large flares,” Testa said.

    fl
    Ultraviolet image of an active region on the sun, showing plasma at temperatures of 140,000 degrees. This image was captured by NASA’s IRIS spacecraft on Dec. 6, 2013.
    Credit: IRIS: LMSAL, NASA. Courtesy Bart De Pontieu, Lockheed Martin Solar & Astrophysics Laboratory

    Although smaller than their larger cousins, nanoflares occur more frequently, likely due to magnetic reconnection. Energy released during magnetic reconnection accelerates some particles to high energies, where they are emitted as radio waves and the highest energy X-rays. Scientists have observed these signals in medium and large flares, but for nanoflares, the rapidly moving electrons are too faint to detect directly using current instrumentation.

    “That is why our observations in the ultraviolet are particularly interesting,” Testa said. “They provide an alternative way to study these accelerated particles, although not directly observing them.”

    Hot bombs in cool regions

    In the cooler photosphere of the sun, where temperatures reach approximately 10,000 degrees F (5,500 degrees C), the magnetic fields convert a huge amount of energy from the magnetic energy stored in the field into thermal energy, heating the plasma. According to Peter, the amount of energy released would be enough to provide electric power to Germany for 8,000 years. The change creates a pocket of gas heated up to 180,000 degrees F (100,000 degrees C) in the middle of the cooler surface region.

    These pockets, or “bombs,” eject plasma. Upward-moving material probably disperses into the hot corona, Peter said, while the downward-moving plasma is quickly cooled to reach the same material as the rest of the photosphere, blending back in to the surrounding material.

    Previously, scientists spotted no indications that energy-releasing events in the photosphere would result in the high temperature spikes in pockets within the photosphere. The energy output required to heat the dense gas was thought to be too high to be obtainable.

    “With these new results that show the existence of hot pockets in cool gas, we have to either revise the amount of energy that can be supplied deep in the photosphere, or we have to think of a clever yet unknown mechanism to heat the cool, dense gas rapidly to these high temperatures,” Peter said.

    Do the twist

    In addition to disconnecting and reconnecting, the magnetic fields on the sun also twist. As the twisting field lines move away from the surface at 19 to 62 miles (30 to 100 km) per second, the nearby transition regions brighten to temperatures of up to 144,000 degrees F (80,000 C), far above the chromosphere’s average temperature of 7,800 degrees F (4,000 degrees C).

    IRIS’s detailed study of the sun revealed that the twists are far more widespread than suggested by previous studies. These twists occur in every magnetic region, both quiet and active. Observations of twists were made at IRIS’s maximum resolution, but other unresolved small-scale motions in the observations seemed to indicate the presence of even smaller twists in the field lines.

    Although the current data does not allow the scientists to determine the twists’ cause, IRIS science lead and first author Bart De Pontieu, of Lockheed Martin Solar and Astrophysics Laboratory, said that the twisting is most likely a signature of the so-called Alfven waves. These “magnetic waves [are] not unlike the waves that are generated after plucking a guitar string,” he said. The source of these waves also remains unknown.

    Another potential source could be the strong convective, or “boiling,” motions at the sun’s surface.

    “Numerical simulations of the solar convection suggest that torsional [twisting] motions can be generated, kind of like when you drain a bathtub, and you see swirling motions as the water drains out,” De Pontieu said.

    Scientists have several hypotheses for how the solar atmosphere is heated, and De Pontieu said the new observations provide constraints on these theories.

    “In particular, they provide support for models in which Alfven waves do much of the heavy lifting in the solar atmosphere,” he said.

    sun
    In its first released image of the sun, IRIS captured a view of the solar atmosphere. Credit: NASA

    As the closest and brightest star, the sun has been studied throughout history. Based on indirect evidence from Skylab and other missions in the 1970s and 1980s, astronomer Uri Feldman, of the Naval Research Laboratory, proposed the existence of “unresolved fine structures” (UFS), an important solar atmospheric component in the transition region between the chromosphere and the corona. Using IRIS’s instruments, a team lead by Viggo Hansteen, of the University of Oslo in Norway, determined that a series of low-lying magnetic loops constitute these UFS, settling a decades-long debate regarding their existence.

    The loops of the magnetic field light up for short spans of time, perhaps a minute, when the plasma in the loops are heated, either due to magnetic reconnection or the dissipation of Alfven waves. During magnetic reconnection, plasma is accelerated to 2 to 3 times the speed of sound. Sometimes the loops form in isolation; other times they are concentrated in a nest of loops.

    The debate regarding the loops’ existence stemmed in part from questions about the plasma; scientists questioned whether or not all of the plasma in the transition region was thermally connected to the corona. The presence of the low-lying loops in the transition region confirms that plasma reaching temperatures of 180,000 degrees F (100,000 degrees C) are heated by from the loops rather than the corona.

    Although the loops themselves don’t heat the corona, Hansteen said that they are probably heated with the same mechanism, though with a different response due to their higher density.

    “It is likely that these differences will allow us to focus more clearly on the nature of the unknown heating events themselves,” Hansteen said.

    Powering the solar wind

    The solar wind drives particles and plasma from the sun through the solar system. When the particles collide with Earth’s magnetic field, they produce beautiful auroras, and have the potential to interfere with satellites and communication systems. But the source of the solar wind remains a mystery.

    The fast-moving solar wind travels hundreds of kilometers per second, carrying low-density materials. Previous instruments lacked the ability to study the small-scale regions thought to be responsible for the wind with the precision necessary to understand it.

    Scientists suspect that the solar wind originates from the bright network structures on the sun, appearing as bright lanes enclosing dark cells. These lanes flow outward from the sun, funneled by the magnetic structure, and eventually merge together into a single solar wind stream that flows steadily from the sun.

    A team lead by Hui Tian, of the Harvard-Smithsonian Center for Astrophysics, identified high-speed, intermittent jets in what scientists think is the solar wind source region, making these jets likely candidates for the initial stage of the solar wind. Rather than producing a steady outflow, the jets are sporadic, accelerating particles to speeds up of to 155 miles per second (250 km/s).

    “If these jets really are the nascent solar wind, then solar wind models must be updated to produce these intermittent, high-speed and small-scale outflows in the interface region,” Tian said.

    “If the answer is no, at least the impact of these jets on the still-not-observed nascent solar wind outflow should be carefully evaluated, because these jets are the most prominent dynamic feature in the believed solar wind source region,” he said.

    All five papers, along with a perspective piece by Louise Harra of the University College London, were published online today (Oct. 16) in the journal Science.

    See the full article, with video, here.

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  • richardmitnick 3:02 pm on August 13, 2014 Permalink | Reply
    Tags: , , , , Solar Flares,   

    From SPACE.com: “Tiny ‘Nanoflares’ May Solve Sun Mystery” 

    space-dot-com logo

    SPACE.com

    August 13, 2014
    Jesse Emspak

    Small “nanoflares” erupting from the sun might be the key to unlocking a cosmic mystery, according to a new study.

    Scientists have found that the sun’s outer atmosphere, or corona, can reach temperatures 1,000 times higher than those at the surface of the star, but solar physicists previously had no explanation for why this temperature discrepancy is so great. Now, researchers think the relatively tiny flares may be the “smoking gun” that explains this mysterious cosmic occurrence.

    corona
    During a total solar eclipse, the solar corona can be seen by the naked eye.

    The new study provides the first direct proof that nanoflares keep the sun’s corona at a temperature of millions of degrees, far hotter than the sun’s visible surface, which is about 6,000 degrees Kelvin (10,000 degrees Fahrenheit).

    sun
    Scientists think that smaller solar flares called “nanoflares” are responsible for the extreme heating of the sun’s outer atmosphere.
    Credit: NASA’s Goddard Space Flight Center

    “The nanoflare model has been around for a while,” said Jeffrey Brosius, a solar physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland “With better instrumentation, we were hoping to find the evidence that was predicted by the model.”

    Nanoflares happen because of huge magnetic fields located throughout the sun’s corona. These loops are anchored in the photosphere, the sun’s visible surface, but move around due to turbulence in the photosphere. Sometimes the field lines cross, and they become twisted and tangled.

    When this happens in the presence of plasma, current sheets form, and the “stress” builds until the magnetic field “breaks,” releasing lots of energy very quickly. This kind of crossing of magnetic fields can happen thousands of times a second over the whole solar surface, and this transfers energy to the plasma in the corona. That energy transfer could explain the corona’s extra heat.

    Earlier evidence for this, though, was indirect. While other models didn’t fit observations, the model based on nanoflares was still missing a piece of the puzzle. That missing evidence came from the Extreme Ultraviolet Normal Incidence Spectrograph mission, which picked up light emitted by a special kind of ionized iron, called Fe XIX. (The Roman numeral describes how highly ionized the iron is, and thus the temperature of the plasma, which was about 8.9 million degrees Kelvin, or about 16 million degrees Fahrenheit.)

    The EUNIS instruments also spotted another form of ionized iron, Fe XII, which occurs at a temperature of 1.6 million degrees Kelvin, or about 2.9 million degrees Fahrenheit.

    The ratio of the two ions showed that the corona is heated by short bursts, rather than a continuous input of energy, because that ratio — the brightness of Fe XIX relative to its cousin Fe XII — would only occur under certain physical conditions. “One of the predictions of the nanoflare model is there should be fairly widespread but faint emission of plasma at about 10 million Kelvin [18 million degrees Fahrenheit],” Brosius told Space.com.

    James Klimchuk, a research astrophysicist at Goddard who was not involved in the study, said what’s new in the Brosius results is the detection of plasma hot enough to produce Fe XIX. Before the EUNIS findings scientists thought it was very likely that nanoflares existed, the case for them wasn’t ironclad.

    One reason for this doubt is that the emission from the ionized iron was so hard to see because it was faint. Another is that the corona is “optically thin,” meaning that at some wavelengths, it’s basically translucent, like stained glass. So the nanoflares, many occurring simultaneously and overlapping, tend to “wash out.”

    The study appears in the August issue of the Astrophysical Journal.

    See the full article here.

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