Solar Fireworks on July 2

The Solar Dynamics Observatory (SDO) captured this video of the M5.6 class solar flare that occurred on July 2, 2012. Credit: NASA/SDO. Play/Download video

On July 2, 2012, an M5.6 class solar flare erupted in the sun's southern hemisphere from large sunspot AR1515, peaking at 6:52 AM EDT.

From a different spot, but on that same day, the sun unleashed a coronal mass ejection (CME) that began at 4:36 AM EDT. Models from the NASA's Space Weather Center at Goddard Space Flight Center in Greenbelt, Md, describe the CME at traveling at nearly 700 miles per second, but do not show it heading toward Earth.

This view of the July 2, 2012 M5.6 class solar flare was captured by the Solar Dynamic Observatory (SDO) satellite. Credit: NASA/SDO. View larger

What is a solar flare? What is a coronal mass ejection?

For answers to these and other space weather questions, please visit the Spaceweather Frequently Asked Questions page.

Karen C. Fox
NASA Goddard Space Flight Center, Greenbelt, MD

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NRL Researchers Discover New Solar Feature

This shows the locations of the STEREO-A and -B spacecraft in 2011 relative to the Sun, Earth, and SDO spacecraft.

Scientists at the Naval Research Laboratory have discovered a previously unreported solar feature - Coronal Cells - where high-temperature coronal emission is confined to discrete plumes that extend upward from unipolar concentrations of magnetic flux. The NRL researchers think that future studies of these cellular regions will lead to an improved understanding of magnetic field line reconnection at the boundaries of coronal holes, and how these changes are transmitted outward into the solar wind. This research is published in the March 20 issue of the Astrophysical Journal. NASA provided financial support through their Heliophysics Guest Investigator Program and their Living With a Star Program.

Drs. Neil Sheeley and Harry Warren, researchers in NRL's Space Science Division, describe these Coronal Cells as appearing in discrete bundles "like candles on a birthday cake." The researchers discovered the cells in ultraviolet emission lines formed at temperatures around one-million degrees Kelvin. Although the researchers made their discovery using high-resolution images from the Atmospheric Imaging Assembly aboard the Solar Dynamics Observatory (SDO), they also observed the cells on ultraviolet images from STEREO-A and -B spacecraft recently, and from the Solar and Heliospheric Observatory (SOHO) in 2000 near the previous sunspot maximum. In addition, they used Doppler images, constructed from the Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft, to deduce that the outflow is faster at the centers of the cells than at their boundaries.

The researchers used time-lapse sequences of Fe XII 193 Å coronal images to follow these special regions as they were carried across the solar disk by the 27-day solar rotation. Near disk center, the Coronal Cells looked like photospheric granules with bright centers and dark, narrow intercellular lanes. But their 30,000 kilometer diameters were much larger than the 1,000 km dimension of granules. A comparison with magnetic maps of the photosphere, obtained with the Helioseismic Magnetic Imager aboard SDO, showed that the cells were centered on unipolar flux concentrations, but left doubt about whether the cellular emission was coming from the tops of closed loops near the Sun's surface, or from longer field lines that extend higher into the corona. This question was answered when observations were obtained away from disk center. Here, the cells appeared as long plumes of emission projecting toward the nearest solar limb. Moreover, simultaneous observations from the STEREO-B and SDO spacecraft, separated by about 90 degrees along Earth's orbit around the Sun, showed the same plumes projecting in opposite directions. Such stereoscopic views left no doubt that the Coronal Cells are columns of emission extending radially outward through the lower corona, like candles on a birthday cake.

The researchers addressed the question of how the Coronal Cells are lit and extinguished, and found that the visibility of the cells bears a close relation to the evolution of the adjacent coronal holes. The Coronal Cells appeared when the holes closed and disappeared when the holes opened. This behavior suggested that coronal holes have the same cellular magnetic structure as the newly observed Coronal Cells, but that this structure is not visible until the encroachment of opposite-polarity flux causes some of the open magnetic flux in the holes to close. For coronal holes at the north and south poles of the Sun, this happens during the approach to sunspot maximum, which is the present time in our current 11-year sunspot cycle.

During the course of their research, Drs. Sheeley and Warren observed the occasional disappearance of cellular regions when solar filaments erupted alongside them. As the chromospheric ribbon swept across the region signaling the reconnection of the field lines that were opened during the eruption, the same cells reappeared immediately behind the ribbon. This indicates that the plumes of material are established rapidly, in step with the reconnection of the associated magnetic fields. The discovery of Coronal Cells has already increased our knowledge of coronal magnetic structure. In the future, studies of the evolution of Coronal Cells may improve scientists' understanding of magnetic field line reconnection at coronal-hole boundaries and its effects on the solar wind and Earth's space weather.

The central part of the sun's disk on June 17, seen from SDO in a coronal emission line (top) and a map of the surface magnetic field (bottom). Coronal cells are sandwiched between a dark coronal hole and the polarity reversal line of the field. (Photo: top image - AIA instrument/bottom image - HMI instrument)

Coronal images during June 10-17, showing that the cells change to elongated plumes when seen in perspective. Progressing counter-clockwise from the upper left, cells are visible from STEREO-B on June 10 (panel 1), but appear as linear plumes, projecting to the right on June 13 (black arrows) (panel 2); they project to the left as seen from SDO at that time (white arrows) (panel 3), and appear again as cells on June 17 (panel 4). This variation with the viewing angle suggests that these million-degree features extend upward like candles on a cake and only appear as cells when seen from above. (Photo: Left side images - EUVI instrument/right side images - AIA instrument)

Movie showing the changes of a cellular region as solar rotation carries it across the solar disk. The camera is fixed on the region (panning with it) and shows the plumes change to cells and back to plumes again during the interval June 7-14, 2011, as seen from the Extreme Ultraviolet Imager aboard the STEREO-B spacecraft. (Photo: Fe XII images obtained from EUVI instrument aboard NASA STEREO-B spacecraft)

About the U.S. Naval Research Laboratory

The U.S. Naval Research Laboratory is the Navy's full-spectrum corporate laboratory, conducting a broadly based multidisciplinary program of scientific research and advanced technological development. The Laboratory, with a total complement of nearly 2,500 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 85 years and continues to meet the complex technological challenges of today's world. For more information, visit the NRL homepage or join the conversation on Twitter, Facebook, and YouTube.

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Second Biggest Flare Of the Solar Cycle

This movie of the March 6, 2012 X5.4 flare was captured by the Solar Dynamics Observatory (SDO) in the 171 Angstrom wavelength. One of the most dramatic features is the way the entire surface of the sun seems to ripple with the force of the eruption. This movement comes from something called EIT waves – because they were first discovered with the Extreme ultraviolet Imaging Telescope (EIT) on the Solar Heliospheric Observatory. Since SDO captures images every 12 seconds, it has been able to map the full evolution of these waves and confirm that they can travel across the full breadth of the sun. The waves move at over a million miles per hour, zipping from one side of the sun to the other in about an hour. The movie shows two distinct waves. The first seems to spread in all directions; the second is narrower, moving toward the southeast. Such waves are associated with, and perhaps trigger, fast coronal mass ejections, so it is likely that each one is connected to one of the two CMEs that erupted on March 6. Credit: NASA/SDO/AIA. Download video - Download still - Download multi-colored still

The sun erupted with one of the largest solar flares of this solar cycle on March 6, 2012 at 7PM EST. This flare was categorized as an X5.4, making it the second largest flare -- after an X6.9 on August 9, 2011 -- since the sun’s activity segued into a period of relatively low activity called solar minimum in early 2007. The current increase in the number of X-class flares is part of the sun’s normal 11-year solar cycle, during which activity on the sun ramps up to solar maximum, which is expected to peak in late 2013.

About an hour later, at 8:14 PM ET, March 6, the same region let loose an X1.3 class flare. An X1 is 5 times smaller than an X5 flare.

These X-class flares erupted from an active region named AR 1429 that rotated into view on March 2. Prior to this, the region had already produced numerous M-class and one X-class flare. The region continues to rotate across the front of the sun, so the March 6 flare was more Earthward facing than the previous ones. It triggered a temporary radio blackout on the sunlit side of Earth that interfered with radio navigation and short wave radio.

In association with these flares, the sun also expelled two significant coronal mass ejections (CMEs), which are travelling faster than 600 miles a second and may arrive at Earth in the next few days. In the meantime, the CME associated with the X-class flare from March 4 has dumped solar particles and magnetic fields into Earth’s atmosphere and distorted Earth's magnetic fields, causing a moderate geomagnetic storm, rated a G2 on a scale from G1 to G5. Such storms happen when the magnetic fields around Earth rapidly change strength and shape. A moderate storm usually causes aurora and may interfere with high frequency radio transmission near the poles. This storm is already dwindling, but the Earth may experience another enhancement if the most recent CMEs are directed toward and impact Earth.

The Solar Heliospheric Observatory (SOHO) captured this movie of the sun's coronal mass ejection (CME) on the evening of March 6, 2012. The extremely fast and energetic solar particles associated with the solar flare caused the "noise" at the end of the movie. Credit: SOHO/ESA&NASA. Download video

In addition, last night’s flares have sent solar particles into Earth’s atmosphere, producing a moderate solar energetic particle event, also called a solar radiation storm. These particles have been detected by NASA’s SOHO and STEREO spacecraft, and NOAA’s GOES spacecraft. At the time of writing, this storm is rated an S3 on a scale that goes up to S5. Such storms can interfere with high frequency radio communication.

Besides the August 2011 X-class flare, the last time the sun sent out flares of this magnitude was in 2006. There was an X6.5 on December 6, 2006 and an X9.0 on December 5, 2006. Like the most recent events, those two flares erupted from the same region on the sun, which is a common occurrence.

What is a solar flare? What is a coronal mass ejection?

For answers to these and other space weather questions, please visit the Spaceweather Frequently Asked Questions page

Karen C. Fox
NASA Goddard Space Flight Center, Greenbelt, MD

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SDO Spots Extra Energy in the Sun's Corona

These jets, known as spicules, were captured in an SDO image on April 25, 2010. Combined with the energy from ripples in the magnetic field, they may contain enough energy to power the solar wind that streams from the sun toward Earth at 1.5 million miles per hour. Credit: NASA/SDO/AIA. View full disk

Like giant strands of seaweed some 32,000 miles high, material shooting up from the sun sways back and forth with the atmosphere. In the ocean, it's moving water that pulls the seaweed along for a ride; in the sun's corona, magnetic field ripples called Alfvén waves cause the swaying.

For years these waves were too difficult to detect directly, but NASA's Solar Dynamics Observatory (SDO) is now able to track the movements of this solar "seaweed" and measure how much energy is carried by the Alfvén waves. The research shows that the waves carry more energy than previously thought, and possibly enough to drive two solar phenomena whose causes remain points of debate: the intense heating of the corona to some 20 times hotter than the sun's surface and solar winds that blast up to 1.5 million miles per hour.

"SDO has amazing resolution so you can actually see individual waves," says Scott McIntosh at the National Center for Atmospheric Research in Boulder, Colo. "Now we can see that instead of these waves having about 1000th the energy needed as we previously thought, it has the equivalent of about 1100W light bulb for every 11 square feet of the sun's surface, which is enough to heat the sun's atmosphere and drive the solar wind."

McIntosh published his research in a Nature article appearing on July 28. Alfvén waves, he says, are actually fairly simple. They are waves that travel up and down a magnetic field line much the way a wave travels up and down a plucked string. The material surrounding the sun -- electrified gas called plasma – moves in concert with magnetic fields. SDO can see this material in motion and so can track the Alfvén waves.

Alfvén waves are part of a much more complex system of magnetic fields and plasma surrounding the sun. Understanding that system could help answer general questions such as what initiates geomagnetic storms near Earth and more focused questions such as what causes coronal heating and speeds of the solar wind – a field of inquiry in which there are few agreed-upon answers.

"We know there are mechanisms that supply a huge reservoir of energy at the sun's surface," says space scientist Vladimir Airapetian at NASA's Goddard Space Flight Center in Greenbelt, Md. "This energy is pumped into magnetic field energy, carried up into the sun's atmosphere and then released as heat." But determining the details of this mechanism has long been debated. Airapetian points out that a study like this confirms Alfvén waves may be part of that process, but that even with SDO we do not yet have the imaging resolution to prove it definitively.

Looking almost like seaweed waving in the water, these giant jets shooting off the sun's surface may hold enough energy to heat the sun's atmosphere, the corona, to well over a million degrees Fahrenheit. Credit: NCAR/Scott McIntosh. Play/Download video

When the waves were first observed in 2007 (more than six decades after being hypothesized by Hannes Alfvén in 1942), it was clear that they could in theory carry energy up from the sun's surface to its atmosphere. However, the 2007 observations showed them to be too weak to contain the great amounts of energy needed to heat the corona so dramatically.

This study says that those original numbers may have been underestimated. McIntosh, in collaboration with a team from Lockheed Martin, Norway's University of Oslo, and Belgium's Catholic University of Leuven, analyzed the great oscillations in movies from SDO's Atmospheric Imagine Assembly (AIA) instrument captured on April 25, 2010.

"Our code name for this research was 'The Wiggles,'" says McIntosh. "Because the movies really look like the sun was made of Jell-O wiggling back and forth everywhere. Clearly, these wiggles carry energy."

The team tracked the motions of this wiggly material spewing up -- in great jets known as spicules – as well as how much the spicules sway back and forth. They compared these observations to models of how such material would behave if undergoing motion from the Alfvén waves and found them to be a good match.

Going forward, they could analyze the shape, speed, and energy of the waves. The sinusoidal curves deviated outward at speeds of over 30 miles per second and repeated themselves every 150 to 550 seconds. These speeds mean the waves would be energetic enough to accelerate the fast solar wind and heat the quiet corona. The shortness of the repetition – known as the period of the wave – is also important. The shorter the period, the easier it is for the wave to release its energy into the coronal atmosphere, a crucial step in the process.

Earlier work with this same data also showed that the spicules achieved coronal temperatures of at least 1.8 million degrees Fahrenheit. Together the heat and Alfvén waves do seem to have enough energy to keep the roiling corona so hot. The energy is not quite enough to account for the largest bursts of radiation in the corona, however.

"Knowing there may be enough energy in the waves is only one half of the problem," says Goddard's Airapetian. "The next question is to find out what fraction of that energy is converted into heat. It could be all of it, or it could be 20 percent of it – so we need to know the details of that conversion."

In practice, that means studying more about the waves to understand just how they impart their energy into the surrounding atmosphere.

"We still don't perfectly understand the process going on, but we're getting better and better observations," says McIntosh. "The next step is for people to improve the theories and models to really capture the essence of the physics that's happening."


Karen C. Fox
NASA's Goddard Space Flight Center

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NASA’s Solar Dynamics Observatory Catches “Surfer” Waves on the Sun

Cue the surfing music. Scientists have spotted the iconic surfer's wave rolling through the atmosphere of the sun. This makes for more than just a nice photo-op: the waves hold clues as to how energy moves through that atmosphere, known as the corona.

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Surfer waves -- initiated in the sun, as they are in the water, by a process called a Kelvin-Helmholtz instability -- have been found in the sun's atmosphere. Credit: NASA/SDO/Astrophysical Journal Letters

Since scientists know how these kinds of waves -- initiated by a Kelvin-Helmholtz instability if you're being technical -- disperse energy in the water, they can use this information to better understand the corona. This in turn, may help solve an enduring mystery of why the corona is thousands of times hotter than originally expected.

"One of the biggest questions about the solar corona is the heating mechanism," says solar physicist Leon Ofman of NASA’s Goddard Space Flight Center, Greenbelt, Md. and Catholic University, Washington. "The corona is a thousand times hotter than the sun's visible surface, but what heats it up is not well-understood. People have suggested that waves like this might cause turbulence which cause heating, but now we have direct evidence of Kelvin-Helmholtz waves."

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On April 8, 2010, SDO recorded images of gas erupting through the sun's atmosphere that formed the froth covered, curly waves that look like surfing waves. Look for them rolling around the edges of the expanding dark spots. Credit: NASA/Goddard Space Flight Center


Ofman and his Goddard colleague, Barbara Thompson, spotted these waves in images taken on April 8, 2010. These were some of the first images caught on camera by the Solar Dynamics Observatory (SDO), a solar telescope with outstanding resolution that launched on February 11, 2010 and began capturing data on March 24 of that year. The team's results appeared online in Astrophysical Journal Letters on May 19, 2011 and will be published in the journal on June 10.

That these "surfer" waves exist in the sun at all is not necessarily a surprise, since they do appear in so many places in nature including, for example, clouds on Earth and between the bands of Saturn. But observing the sun from almost 93 million miles away means it's not easy to physically see details like this. That's why the resolution available with SDO gets researchers excited.

"The waves we're seeing in these images are so small," says Thompson who in addition to being a co-author on this paper is the deputy project scientist for SDO. "They're only the size of the United States," she laughs.

Kelvin-Helmholtz instabilities occur when two fluids of different densities or different speeds flow by each other. In the case of ocean waves, that's the dense water and the lighter air. As they flow past each other, slight ripples can be quickly amplified into the giant waves loved by surfers. In the case of the solar atmosphere, which is made of a very hot and electrically charged gas called plasma, the two flows come from an expanse of plasma erupting off the sun's surface as it passes by plasma that is not erupting. The difference in flow speeds and densities across this boundary sparks the instability that builds into the waves.

In order to confirm this description, the team developed a computer model to see what takes place in the region. Their model showed that these conditions could indeed lead to giant surfing waves rolling through the corona.

Ofman says that despite the fact that Kelvin-Helmholtz instabilities have been spotted in other places, there was no guarantee they'd be spotted in the sun's corona, which is permeated with magnetic fields. "I wasn't sure that this instability could evolve on the sun, since magnetic fields can have a stabilizing effect," he says. "Now we know that this instability can appear even though the solar plasma is magnetized."

Seeing the big waves suggests they can cascade down to smaller forms of turbulence too. Scientists believe that the friction created by turbulence – the simple rolling of material over and around itself – could help add heating energy to the corona. The analogy is the way froth at the top of a surfing wave provides friction that will heat up the wave. (Surfers of course don't ever notice this, as any extra heat quickly dissipates into the rest of the water.)

Hammering out the exact mechanism for heating the corona will continue to intrigue researchers for some time but, says Thompson, SDO's ability to capture images of the entire sun every 12 seconds with such precise detail will be a great boon. "SDO is not the first solar observatory with high enough visual resolution to be able to see something like this," she says. "But for some reason Kelvin-Helmholtz features are rare. The fact that we spotted something so interesting in some of the first images really shows the strength of SDO."

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K-H waves in the clouds Credit: Danny Ratcliffe

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The iconic surfer wave appears in between the bands of Saturn.
Credit: NASA/Cassini

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This computer simulation shows how the conditions of erupting gas flowing by stationary gas in the sun's atmosphere could give rise to Kelvin-Helmholtz instabilities. Credit: Ofman/Thompson/Astrophysical Journal Letters.

Karen C. Fox
NASA's Goddard Space Flight Center

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