Tagged: SDO – NASA’s Solar Dynamics Observatory Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 3:00 pm on April 5, 2019 Permalink | Reply
    Tags: , , , Coronal rain, , Emily Mason, Helmet streamers, , , SDO - NASA’s Solar Dynamics Observatory, ,   

    From NASA Goddard Space Flight Center: Women in STEM “Unexpected Rain on Sun Links Two Solar Mysteries” Emily Mason 

    NASA Goddard Banner
    From NASA Goddard Space Flight Center

    April 5, 2019

    Miles Hatfield
    miles.s.hatfield@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    For five months in mid 2017, Emily Mason did the same thing every day. Arriving to her office at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, she sat at her desk, opened up her computer, and stared at images of the Sun — all day, every day. “I probably looked through three or five years’ worth of data,” Mason estimated. Then, in October 2017, she stopped. She realized she had been looking at the wrong thing all along.

    Mason, a graduate student at The Catholic University of America in Washington, D.C., was searching for coronal rain: giant globs of plasma, or electrified gas, that drip from the Sun’s outer atmosphere back to its surface. But she expected to find it in helmet streamers, the million-mile tall magnetic loops — named for their resemblance to a knight’s pointy helmet — that can be seen protruding from the Sun during a solar eclipse. Computer simulations predicted the coronal rain could be found there. Observations of the solar wind, the gas escaping from the Sun and out into space, hinted that the rain might be happening. And if she could just find it, the underlying rain-making physics would have major implications for the 70-year-old mystery of why the Sun’s outer atmosphere, known as the corona, is so much hotter than its surface. But after nearly half a year of searching, Mason just couldn’t find it. “It was a lot of looking,” Mason said, “for something that never ultimately happened.”

    1
    Mason searched for coronal rain in helmet streamers like the one that appears on the left side of this image, taken during the 1994 eclipse as viewed from South America. A smaller pseudostreamer appears on the western limb (right side of image). Named for their resemblance to a knight’s pointy helmet, helmet streamers extend far into the Sun’s faint corona and are most readily seen when the light from the Sun’s bright surface is occluded. Credits: © 1994 Úpice observatory and Vojtech Rušin, © 2007 Miloslav Druckmüller

    The problem, it turned out, wasn’t what she was looking for, but where. In a paper published today in The Astrophysical Journal Letters, Mason and her coauthors describe the first observations of coronal rain in a smaller, previously overlooked kind of magnetic loop on the Sun. After a long, winding search in the wrong direction, the findings forge a new link between the anomalous heating of the corona and the source of the slow solar wind — two of the biggest mysteries facing solar science today.

    How It Rains on the Sun

    Observed through the high-resolution telescopes mounted on NASA’s SDO spacecraft, the Sun – a hot ball of plasma, teeming with magnetic field lines traced by giant, fiery loops — seems to have few physical similarities with Earth.

    NASA/SDO

    But our home planet provides a few useful guides in parsing the Sun’s chaotic tumult: among them, rain.

    On Earth, rain is just one part of the larger water cycle, an endless tug-of-war between the push of heat and pull of gravity. It begins when liquid water, pooled on the planet’s surface in oceans, lakes, or streams, is heated by the Sun. Some of it evaporates and rises into the atmosphere, where it cools and condenses into clouds. Eventually, those clouds become heavy enough that gravity’s pull becomes irresistible and the water falls back to Earth as rain, before the process starts anew.

    On the Sun, Mason said, coronal rain works similarly, “but instead of 60-degree water you’re dealing with a million-degree plasma.” Plasma, an electrically-charged gas, doesn’t pool like water, but instead traces the magnetic loops that emerge from the Sun’s surface like a rollercoaster on tracks.

    2
    Coronal rain, like that shown in this movie from NASA’s SDO in 2012, is sometimes observed after solar eruptions, when the intense heating associated with a solar flare abruptly cuts off after the eruption and the remaining plasma cools and falls back to the solar surface. Mason was searching for coronal rain not associated with eruptions, but instead caused by a cyclical process of heating and cooling similar to the water cycle on Earth.
    Credits: NASA’s Solar Dynamics Observatory/Scientific Visualization Studio/Tom Bridgman, Lead Animator

    At the loop’s foot points, where it attaches to the Sun’s surface, the plasma is superheated from a few thousand to over 1.8 million degrees Fahrenheit. It then expands up the loop and gathers at its peak, far from the heat source. As the plasma cools, it condenses and gravity lures it down the loop’s legs as coronal rain.

    Mason was looking for coronal rain in helmet streamers, but her motivation for looking there had more to do with this underlying heating and cooling cycle than the rain itself. Since at least the mid-1990s, scientists have known that helmet streamers are one source of the slow solar wind, a comparatively slow, dense stream of gas that escapes the Sun separately from its fast-moving counterpart. But measurements of the slow solar wind gas revealed that it had once been heated to an extreme degree before cooling and escaping the Sun. The cyclical process of heating and cooling behind coronal rain, if it was happening inside the helmet streamers, would be one piece of the puzzle.

    The other reason connects to the coronal heating problem — the mystery of how and why the Sun’s outer atmosphere is some 300 times hotter than its surface. Strikingly, simulations have shown that coronal rain only forms when heat is applied to the very bottom of the loop. “If a loop has coronal rain on it, that means that the bottom 10% of it, or less, is where coronal heating is happening,” said Mason. Raining loops provide a measuring rod, a cutoff point to determine where the corona gets heated. Starting their search in the largest loops they could find — giant helmet streamers — seemed like a modest goal, and one that would maximize their chances of success.

    She had the best data for the job: Images taken by NASA’s Solar Dynamics Observatory, or SDO, a spacecraft that has photographed the Sun every twelve seconds since its launch in 2010. But nearly half a year into the search, Mason still hadn’t observed a single drop of rain in a helmet streamer. She had, however, noticed a slew of tiny magnetic structures, ones she wasn’t familiar with. “They were really bright and they kept drawing my eye,” said Mason. “When I finally took a look at them, sure enough they had tens of hours of rain at a time.”

    At first, Mason was so focused on her helmet streamer quest that she made nothing of the observations. “She came to group meeting and said, ‘I never found it — I see it all the time in these other structures, but they’re not helmet streamers,’” said Nicholeen Viall, a solar scientist at Goddard, and a coauthor of the paper. “And I said, ‘Wait…hold on. Where do you see it? I don’t think anybody’s ever seen that before!’”

    A Measuring Rod for Heating

    These structures differed from helmet streamers in several ways. But the most striking thing about them was their size.

    “These loops were much smaller than what we were looking for,” said Spiro Antiochos, who is also a solar physicist at Goddard and a coauthor of the paper. “So that tells you that the heating of the corona is much more localized than we were thinking.”

    3
    Mason’s article analyzed three observations of Raining Null-Point Topologies, or RNTPs, a previously overlooked magnetic structure shown here in two wavelengths of extreme ultraviolet light. The coronal rain observed in these comparatively small magnetic loops suggests that the corona may be heated within a far more restricted region than previously expected. Credits: NASA’s Solar Dynamics Observatory/Emily Mason

    While the findings don’t say exactly how the corona is heated, “they do push down the floor of where coronal heating could happen,” said Mason. She had found raining loops that were some 30,000 miles high, a mere two percent the height of some of the helmet streamers she was originally looking for. And the rain condenses the region where the key coronal heating can be happening. “We still don’t know exactly what’s heating the corona, but we know it has to happen in this layer,” said Mason.

    A New Source for the Slow Solar Wind

    But one part of the observations didn’t jibe with previous theories. According to the current understanding, coronal rain only forms on closed loops, where the plasma can gather and cool without any means of escape. But as Mason sifted through the data, she found cases where rain was forming on open magnetic field lines. Anchored to the Sun at only one end, the other end of these open field lines fed out into space, and plasma there could escape into the solar wind. To explain the anomaly, Mason and the team developed an alternative explanation — one that connected rain on these tiny magnetic structures to the origins of the slow solar wind.

    In the new explanation, the raining plasma begins its journey on a closed loop, but switches — through a process known as magnetic reconnection — to an open one. The phenomenon happens frequently on the Sun, when a closed loop bumps into an open field line and the system rewires itself. Suddenly, the superheated plasma on the closed loop finds itself on an open field line, like a train that has switched tracks. Some of that plasma will rapidly expand, cool down, and fall back to the Sun as coronal rain. But other parts of it will escape – forming, they suspect, one part of the slow solar wind.

    Mason is currently working on a computer simulation of the new explanation, but she also hopes that soon-to-come observational evidence may confirm it. Now that Parker Solar Probe, launched in 2018, is traveling closer to the Sun than any spacecraft before it, it can fly through bursts of slow solar wind that can be traced back to the Sun — potentially, to one of Mason’s coronal rain events.

    NASA Parker Solar Probe Plus named to honor Pioneering Physicist Eugene Parker

    After observing coronal rain on an open field line, the outgoing plasma, escaping to the solar wind, would normally be lost to posterity. But no longer. “Potentially we can make that connection with Parker Solar Probe and say, that was it,” said Viall.

    Digging Through the Data

    As for finding coronal rain in helmet streamers? The search continues. The simulations are clear: the rain should be there. “Maybe it’s so small you can’t see it?” said Antiochos. “We really don’t know.”

    But then again, if Mason had found what she was looking for she might not have made the discovery — or have spent all that time learning the ins and outs of solar data.

    “It sounds like a slog, but honestly it’s my favorite thing,” said Mason. “I mean that’s why we built something that takes that many images of the Sun: So we can look at them and figure it out.”

    Related:

    IRIS Spots Plasma Rain on Sun’s Surface

    NASA IRIS spacecraft, a spacecraft that takes spectra in three passbands, allowing us to probe different layers of the solar atmosphere


    And the Blobs Just Keep on Coming

    See the full article here.


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.


    NASA/Goddard Campus

     
  • richardmitnick 1:30 pm on October 19, 2018 Permalink | Reply
    Tags: , , , , , NASA ACE Solar Observatory, Screening for the Slow Solar Wind, SDO - NASA’s Solar Dynamics Observatory   

    From AAS NOVA: “Screening for the Slow Solar Wind” 

    AASNOVA

    From AAS NOVA

    19 October 2018
    Kerry Hensley

    1
    This artist’s impression of the solar wind shows a constant torrent of particles filling the heliosphere and streaming past Earth. [NASA Goddard’s Conceptual Image Lab/Greg Shirah]

    The solar wind extends outward from the solar corona, suffusing interplanetary space with plasma and magnetic fields. While the solar wind has traditionally been designated as either “fast” or “slow” based on its velocity, a new study suggests that there may be a better way to characterize this highly variable plasma flow.

    2
    Coronal holes, like the one clearly visible as a dark region in this X-ray image of the Sun from Solar Dynamics Observatory, are thought to be the source of the fast solar wind. [NASA/AIA]

    NASA/SDO

    Slow vs. Fast

    The fast solar wind is thought to originate from coronal holes — regions of open solar magnetic field lines. The slow solar wind has been associated with streams of coronal plasma emitted from near the Sun’s equator, but this source location for the slow solar wind is still up for debate.

    The formation mechanism for the slow solar wind is also uncertain; one of the persistent questions of solar physics is whether the slow and fast solar wind form in fundamentally different ways.

    Solving the mysteries of where and how the slow solar wind forms may rely on first finding a better definition of what constitutes the slow and fast solar wind. While regions of slow and fast solar wind have traditionally been separated based only on velocity, the parameters of the solar wind — such as the density, temperature, and ionization state — vary broadly for a given solar wind speed.

    3
    Comparison of solar wind proton speed, components of the proton velocity, and standard deviation in the components of the proton velocity. HCS and PS mark the times of heliospheric current sheet and pseudostreamer crossings, respectively. Low proton speeds are associated with low fluctuations in the proton velocity, while high speeds are associated with high fluctuations in the proton velocity. [Ko, Roberts & Lepri 2018]

    An ACE up Their Sleeve

    Yuan-Kuen Ko of the Naval Research Laboratory and collaborators argue that there is a better way to distinguish between the different states of the solar wind.

    By analyzing data from NASA’s Advanced Composition Explorer (ACE), a solar and space exploration mission launched more than two decades ago, Ko and collaborators found that the slow and fast solar wind may be better distinguished by the magnitude of their velocity fluctuations rather than their absolute velocities.

    NASA ACE Solar Observatory

    To demonstrate this, the authors compared the velocity fluctuation, δvT, to other observed solar wind properties. With the exception of the plasma beta — the ratio of the thermal pressure to the magnetic pressure — δvT correlates well with all observed solar wind properties.

    Ko and collaborators also explored the effect the phase of the solar cycle has on solar wind parameters by comparing data from two time intervals: one from the period during which solar activity is declining, and one near solar minimum. The authors found that while the absolute values of the solar wind parameters during epochs of low δvT varied between the two phases, their overall behavior did not; parameters that increased with increasing δvT did so during both the declining phase of the solar cycle and solar minimum.

    3
    The three slow-solar-wind formation scenarios implied by the results. [Ko, Roberts & Lepri 2018]

    More Solar Data Headed Our Way

    What does this mean for the formation of the slow solar wind? Ko and collaborators derive three potential slow-solar-wind formation scenarios from their findings, none of which are mutually exclusive.

    Distinguishing between these scenarios will have to wait — but not for long. Luckily, the next decade brings two highly anticipated spacecraft that will increase our understanding of the solar corona and solar wind, including the formation of the slow solar wind: NASA’s Parker Solar Probe, which started its journey to the Sun in August 2018, and ESA’s Solar Orbiter, which is scheduled to launch in February 2020.

    Citation

    “Boundary of the Slow Solar Wind,” Yuan-Kuen Ko, D. Aaron Roberts, and Susan T. Lepri 2018 ApJ 864 139.
    http://iopscience.iop.org/article/10.3847/1538-4357/aad69e/meta

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 2:14 pm on February 23, 2018 Permalink | Reply
    Tags: , NASA’s SDO Reveals How Magnetic Cage on the Sun Stopped Solar Eruption, SDO - NASA’s Solar Dynamics Observatory   

    From Goddard: “NASA’s SDO Reveals How Magnetic Cage on the Sun Stopped Solar Eruption” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    Feb. 23, 2018
    Lina Tran
    lina.tran@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    A dramatic magnetic power struggle at the Sun’s surface lies at the heart of solar eruptions, new research using NASA data shows. The work highlights the role of the Sun’s magnetic landscape, or topology, in the development of solar eruptions that can trigger space weather events around Earth.

    The scientists, led by Tahar Amari, an astrophysicist at the Center for Theoretical Physics at the École Polytechnique in Palaiseau Cedex, France, considered solar flares, which are intense bursts of radiation and light. Many strong solar flares are followed by a coronal mass ejection, or CME, a massive, bubble-shaped eruption of solar material and magnetic field, but some are not — what differentiates the two situations is not clearly understood.

    Using data from NASA’s Solar Dynamics Observatory, or SDO, the scientists examined an October 2014 Jupiter-sized sunspot group, an area of complex magnetic fields, often the site of solar activity.

    NASA/SDO

    This was the biggest group in the past two solar cycles and a highly active region. Though conditions seemed ripe for an eruption, the region never produced a major CME on its journey across the Sun. It did, however, emit a powerful X-class flare, the most intense class of flares. What determines, the scientists wondered, whether a flare is associated with a CME?

    1
    On Oct. 24, 2014, NASA’s SDO observed an X-class solar flare erupt from a Jupiter-sized sunspot group. Credits: Tahar Amari et al./Center for Theoretical Physics/École Polytechnique/NASA Goddard/Joy Ng.

    The team of scientists included SDO’s observations of magnetic fields at the Sun’s surface in powerful models that calculate the magnetic field of the Sun’s corona, or upper atmosphere, and examined how it evolved in the time just before the flare. The model reveals a battle between two key magnetic structures: a twisted magnetic rope — known to be associated with the onset of CMEs — and a dense cage of magnetic fields overlying the rope.

    The scientists found that this magnetic cage physically prevented a CME from erupting that day. Just hours before the flare, the sunspot’s natural rotation contorted the magnetic rope and it grew increasingly twisted and unstable, like a tightly coiled rubber band. But the rope never erupted from the surface: Their model demonstrates it didn’t have enough energy to break through the cage. It was, however, volatile enough that it lashed through part of the cage, triggering the strong solar flare.

    By changing the conditions of the cage in their model, the scientists found that if the cage were weaker that day, a major CME would have erupted on Oct. 24, 2014. The group is interested in further developing their model to study how the conflict between the magnetic cage and rope plays out in other eruptions. Their findings are summarized in a paper published in Nature on Feb. 8, 2018.

    “We were able to follow the evolution of an active region, predict how likely it was to erupt, and calculate the maximum amount of energy the eruption can release,” Amari said. “This is a practical method that could become important in space weather forecasting as computational capabilities increase.”

    3
    In this series of images, the magnetic rope, in blue, grows increasingly twisted and unstable. But it never erupts from the Sun’s surface: The model demonstrates the rope didn’t have enough energy to break through the magnetic cage, in yellow. Credits: Tahar Amari et al./Center for Theoretical Physics/École Polytechnique/NASA Goddard/Joy Ng.

    Related:

    NASA Watches the Sun Put a Stop to Its Own Eruption
    Two Weeks in the Life of a Sunspot

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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.


    NASA/Goddard Campus

     
  • richardmitnick 3:06 pm on September 8, 2017 Permalink | Reply
    Tags: , Largest Flare of Past 9 Years Erupts from Sun, SDO - NASA’s Solar Dynamics Observatory,   

    From Eos: “Largest Flare of Past 9 Years Erupts from Sun” 

    AGU bloc

    AGU
    Eos news bloc

    Eos

    9.8.17
    Kimberly M. S. Cartier

    1
    NASA’s Solar Dynamics Observatory captured this image, blended from two ultraviolet filters, of (left) the X9.3 class solar flare that erupted from the Sun on 6 September and (right) a simultaneous smaller flare from a different active region. Credit: NASA/Goddard Space Flight Center/Solar Dynamics Observatory

    NASA/SDO

    A flare erupting from the surface of the Sun on Wednesday blocked communications and interfered with navigational frequencies across the globe. Large portions Europe, Africa, Asia, and Australia experienced disruptions to low-frequency radio communications, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).

    As the flare jetted outward from the Sun’s surface, the star’s outer atmosphere, or corona, belched a huge cloud of ultrahot, electrically charged particles, known as a coronal mass ejection (CME) toward Earth. The CME prompted a warning from NOAA solar storm watchers of an impending strong (G3) geomagnetic storm or greater through today. An updated NOAA report at 1:57 p.m. Coordinated Universal Time (UTC) today revised the agency’s assessment to “G4 (Severe) geomagnetic storm levels” for the day-lit side of Earth.

    In addition to roiling communications and navigation signals, such geomagnetic storms can create surges or shutdowns in power grids and produce brilliant auroras visible at lower latitudes than usual.

    2
    Two solar flares exploded from the same region of the Sun within a few hours of each other. This time-lapse footage of the region, seen here in extreme-ultraviolet wavelengths, shows flares and CMEs many times larger than Earth. Credit: NASA/Goddard Space Flight Center/SDO

    According to NOAA’s Space Weather Prediction Center, the flare sprung from the Sun at 12:02 p.m. UTC on 6 September, accompanied by the CME, which arrived at Earth late last night and is expected to persist through today.

    A Blast amid the Calm

    NOAA heliophysicists identified Wednesday’s flare as the largest solar flare to date in the current solar cycle, which is an approximately 11-year cycle that tracks when solar activity increases and decreases. The current solar cycle began in December 2011. Although the Sun’s activity is declining on average, large flares such as these are not uncommon during this stage of the cycle.

    “Some of the strongest solar events occur near solar minimum,” Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate, explained on Twitter. “Space Weather matters during the entire solar cycle!”

    Heliophysicists associated with NASA’s Solar Dynamics Observatory (SDO) classified this event as an X9.3 solar flare, meaning it’s in the most intense class of flares. What’s more, the same region of the Sun had produced another X-class flare about 3 hours earlier on the morning of 6 September. Three other moderate-intensity flares have exploded from the region since 4 September, in addition to flares from other active areas on the Sun’s surface.

    3
    The Sun produced five strong solar flares from 4 to 7 September, including the X9.3 event that generated the large CME near time mark “2017/09/06 14:00.” CMEs are best observed when the bright disk of the Sun is blocked by a coronagraph, as seen in this sequence of images taken by the Large Angle and Spectrometric Coronagraph (LASCO) instrument on the NASA/ESA Solar and Heliospheric Observatory (SOHO). Credit: SOHO/LASCO/National Research Laboratory team

    “It’s the active region that keeps on giving!” tweeted Sophie Murray, a space weather scientist at Trinity College in Dublin, Ireland.

    NOAA’s Space Weather Prediction Center also reported a strong (R3) radio blackout on Wednesday at 9:10 a.m. UTC due to both flares that day.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

     
  • richardmitnick 11:25 am on May 8, 2017 Permalink | Reply
    Tags: , SDO - NASA’s Solar Dynamics Observatory, ,   

    From AAS NOVA: ” Escape for the Slow Solar Wind” 

    AASNOVA

    American Astronomical Society

    8 May 2017
    Susanna Kohler

    1
    This Solar Dynamics Observatory extreme ultraviolet image of the Sun reveals a coronal hole — a region of open magnetic field — surrounded by regions of closed magnetic field. A new study examines how plasma might escape from regions of closed magnetic field on the Sun. [SDO; adapted from Higginson et al. 2017]

    NASA/SDO

    Plasma from the Sun known as the slow solar wind has been observed far away from where scientists thought it was produced. Now new simulations may have resolved the puzzle of where the slow solar wind comes from and how it escapes the Sun to travel through our solar system.

    An Origin Puzzle

    The Sun’s atmosphere, known as the corona, is divided into two types of regions based on the behavior of magnetic field lines. In closed-field regions, the magnetic field is firmly anchored in the photosphere at both ends of field lines, so traveling plasma is confined to coronal loops and must return to the Sun’s surface. In open-field regions, only one end of each magnetic field line is anchored in the photosphere, so plasma is able to stream from the Sun’s surface out into the solar system.

    This second type of region — known as a coronal hole — is thought to be the origin of fast-moving plasma measured in our solar system and known as the fast solar wind. But we also observe a slow solar wind: plasma that moves at speeds of less than 500 km/s.

    The slow solar wind presents a conundrum. Its observational properties strongly suggest it originates in the hot, closed corona rather than the cooler, open regions. But if the slow solar wind plasma originates in closed-field regions of the Sun’s atmosphere, then how does it escape from the Sun?

    Slow Wind from Closed Fields

    A team of scientists led by Aleida Higginson (University of Michigan) has now used high-resolution, three-dimensional magnetohydrodynamic simulations to show how the slow solar wind can be generated from plasma that starts out in closed-field parts of the Sun.

    Motions on the Sun’s surface near the boundary between open and closed-field regions — the boundary that marks the edges of coronal holes and extends outward as the heliospheric current sheet — are caused by supergranule-like convective flows. These motions drive magnetic reconnection that funnel plasma from the closed-field region onto enormous arcs that extend far away from the heliospheric current sheet, spanning tens of degrees in latitude and longitude.

    The simulations by Higginson and collaborators demonstrate that closed-field plasma from coronal-hole boundaries can be successfully channeled into the solar system. Due to the geometry and dynamics of the coronal holes, the plasma can travel far from the heliospheric current sheet, resulting in a slow solar wind of closed-field plasma consistent with our observations. These simulations therefore suggest a process that resolves the long-standing puzzle of the slow solar wind.

    Citation

    A. K. Higginson et al 2017 ApJL 840 L10. doi:10.3847/2041-8213/aa6d72

    Related Journal Articles:
    See the full article for further research with links.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 9:51 am on April 27, 2017 Permalink | Reply
    Tags: Joint Japan Aerospace Exploration Agency NASA Hinode satellite, , Scientists Propose Mechanism to Describe Solar Eruptions of All Sizes, SDO - NASA’s Solar Dynamics Observatory, ,   

    From Goddard: “Scientists Propose Mechanism to Describe Solar Eruptions of All Sizes” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    April 26, 2017
    Lina Tran
    kathalina.k.tran@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    1
    A long filament erupted on the sun on Aug. 31, 2012, shown here in imagery captured by NASA’s Solar Dynamics Observatory. Credit: NASA’s Goddard Space Flight Center/SDO
    From long, tapered jets to massive explosions of solar material and energy, eruptions on the sun come in many shapes and sizes. Since they erupt at such vastly different scales, jets and the massive clouds — called coronal mass ejections, or CMEs — were previously thought to be driven by different processes.

    Scientists from Durham University in the United Kingdom and NASA now propose that a universal mechanism can explain the whole spectrum of solar eruptions. They used 3-D computer simulations to demonstrate that a variety of eruptions can theoretically be thought of as the same kind of event, only in different sizes and manifested in different ways. Their work is summarized in a paper published in Nature on April 26, 2017.


    Follow the evolution of a jet eruption in this video, which uses a 3-D computer simulation of the breakout model to demonstrate how a filament forms, gains energy and erupts from the sun.
    Credits: NASA’s Goddard Space Flight Center/ARMS/Genna Duberstein, producer

    The study was motivated by high-resolution observations of filaments from NASA’s Solar Dynamics Observatory, or SDO, and the joint Japan Aerospace Exploration Agency/NASA Hinode satellite.

    NASA/SDO

    JAXA/HINODE spacecraft

    Filaments are dark, serpentine structures that are suspended above the sun’s surface and consist of dense, cold solar material. The onset of CME eruptions had long been known to be associated with filaments, but improved observations have recently shown that jets have similar filament-like structures before eruption too. So the scientists set out to see if they could get their computer simulations to link filaments to jet eruptions as well.

    “In CMEs, filaments are large, and when they become unstable, they erupt,” said Peter Wyper, a solar physicist at Durham University and the lead author of the study. “Recent observations have shown the same thing may be happening in smaller events such as coronal jets. Our theoretical model shows the jet can essentially be described as a mini-CME.”

    Solar scientists can use computer models like this to help round out their understanding of the observations they see through space telescopes. The models can be used to test different theories, essentially creating simulated experiments that cannot, of course, be performed on an actual star in real life.

    The scientists call their proposed mechanism for how these filaments lead to eruptions the breakout model, for the way the stressed filament pushes relentlessly at — and ultimately breaks through — its magnetic restraints into space. They previously used this model to describe CMEs; in this study, the scientists adapted the model to smaller events and were able to reproduce jets in the computer simulations that match the SDO and Hinode observations. Such simulations provide additional confirmation to support the observations that first suggested coronal jets and CMEs are caused in the same way.

    “The breakout model unifies our picture of what’s going on at the sun,” said Richard DeVore, a co-author of the study and solar physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Within a unified context, we can advance understanding of how these eruptions are started, how to predict them and how to better understand their consequences.”

    The key for understanding a solar eruption, according to Wyper, is recognizing how the filament system loses equilibrium, which triggers eruption. In the breakout model, the culprit is magnetic reconnection — a process in which magnetic field lines come together and explosively realign into a new configuration.

    NASA Magnetic reconnection, Credit: M. Aschwanden et al. (LMSAL), TRACE, NASA

    In stable conditions, loops of magnetic field lines hold the filament down and suppress eruption. But the filament naturally wants to expand outward, which stresses its magnetic surroundings over time and eventually initiates magnetic reconnection. The process explosively releases the energy stored in the filament, which breaks out from the sun’s surface and is ejected into space.

    Exactly which kind of eruption occurs depends on the initial strength and configuration of the magnetic field lines containing the filament. In a CME, field lines form closed loops completely surrounding the filament, so a bubble-shaped cloud ultimately bursts from the sun. In jets, nearby fields lines stream freely from the surface into interplanetary space, so solar material from the filament flows out along those reconnected lines away from the sun.

    “Now we have the possibility to explain a continuum of eruptions through the same process,” Wyper said. “With this mechanism, we can understand the similarities between small jets and massive CMEs, and infer eruptions anywhere in between.”

    Confirming this theoretical mechanism will require high-resolution observations of the magnetic field and plasma flows in the solar atmosphere, especially around the sun’s poles where many jets originate — and that’s data that currently are not available. For now, scientists look to upcoming missions such as NASA’s Solar Probe Plus and the joint ESA (European Space Agency)/NASA Solar Orbiter, which will acquire novel measurements of the sun’s atmosphere and magnetic fields emanating from solar eruptions.

    NASA/SPP Solar Probe Plus

    NASA/ESA Solar Orbiter

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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.


    NASA/Goddard Campus

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: