New research maps the secret structure of the sun

[Buster's Uncle]

New research maps the secret structure of the sun
A discovery that could help explain everything from solar storms to sunspots
By Alexander Thompson on December 5, 2013 02:02 pm



The phenomenon of solar flares, as seen above, might be better understood thanks to the discovery of giant cells.

Nearly half a century ago, scientists started to unravel the structure of the sun and determine how solar material flowed on its surface. At the time, they predicted that the star should have massive cell structures, some 16 times the width of Earth, that carry currents across its surface. But these giant cells, despite their size, have remained elusive. Now, a researcher who 30 years ago worked on the problem as an intern has managed to solve the puzzle — moving this phenomenon from theory to reality.

Our sun, like many stars, is in part comprised of a convective layer that transports heat from its core to its surface. This transportation, in turn, creates pockets of solar currents that are constantly evolving (much like currents in the Earth's atmosphere). Scientists have known about some of the cells carrying these currents for centuries. Namely, they've been aware of relatively small "granules," which are about the size of Texas and only endure for about 10 minutes, as well as so-called "supergranules," which are about three times the width of Earth and last for about a day. Both discoveries led scientists to think that granules and supergranules were part of a hierarchy of currents, which pointed to the existence of giant cells.


If only those cells were easy to find

If only those cells were easy to find. In large part, they've eluded scientists because the motion caused by giant cells is relatively slow, and therefore tough to detect. Granules have flow velocities (a measure of how quickly the material within the cells move) of about 3,000 meters per second (almost double the speed of a X-51A scramjet) and supergranules flow at 500 meters per second. In contrast, giant cells have flow velocities of just 10 meters per second (about the speed of Usain Bolt), meaning the motion is subtle and difficult to tease out.



An illustration of giant-cell flow trajectories in 2010. Credit: Hathaway/NASA


But David Hathaway, a NASA scientist whose new paper in Science confirms the existence of giant cells, was able to find the structures by tracking supergranules over time. Hathaway and fellow researchers used NASA's Solar Dynamics Observatory to monitor the sun every 45 seconds for a few months. With careful averaging, they were able to determine that large groups of supergranules were being moved by an underlying presence — the long-sought giant cells.


These giant cells have a very visible consequence

They may have been tough to detect, but these giant cells have a very visible consequence: they cause the equatorial region of the sun to rotate faster than the poles. The cells are also important to understanding the sun's weather. "The analogy with Earth weather systems is very close," Hathaway says. "The same way weather systems carry moisture in the Earth's atmosphere, these things are carrying magnetic fields in the sun's surface and interior." Both granules and supergranules move magnetic fields around, and Hathaway thinks giant cells won't be any different. This phenomenon may have an impact on the strength of the magnetic field at the poles of the sun, which determines how intense the 11-year solar cycle of increasing and decreasing sunspots is going to be.

Hathaway also hopes that this finding yields a better understanding of where sunspots form. "The observation we're dying to get is whether there is any indication in these flows about where new sunspots are going to emerge," he says. Despite several theories on where sunspots might form with respect to these giants cells, pinning down the connection between won't be easy.


"Everything interesting about the sun is related to magnetic fields."

The next step for Hathaway and other experts will be to observe how magnetic fields respond to flows within the giant cells. "Everything interesting about the sun is related to magnetic fields — coronal heating, flares, coronal mass ejections," Hathaway says. Pinpointing the connection between flow and magnetism would allow scientists to better predict the behavior of solar storms and how they'll affect the solar system (like stripping away the Martian atmosphere), the Earth, and our satellites. "What does the solar wind look like? If you do produce a flare and a coronal mass ejection, how is it going to move through the interplanetary space? All of that is given by what this magnetic field does at the surface," Hathaway says. "I think we will get a better hand on that given the fact that we now see these flows."


http://www.theverge.com/2013/12/5/5178708/giant-cell-structure-of-the-sun

[Buster's Uncle]

Giant Plasma Spirals Found on the Sun
SPACE.com
By Charles Q. Choi, SPACE.com Contributor  27 minutes ago



This image depicts giant plasma cell flow paths on the sun for June 8, 2010



Colossal spiral-shaped flows of super-hot plasma have been discovered on the sun, completing a nearly 50-year quest to confirm their existence, scientists say.

These giant solar plasma spirals — each of which is at least 60,000 miles (100,000 kilometers) wide — could help spark the formation of strongly magnetic regions on the sun that have been linked with solar flares and other sun eruptions, researchers added.

The sun's internal heat causes matter to rise to its surface, where the material cools when near the cold of space, and then sinks back downward. This cycle of motion is altogether known as convection, and zones where it takes place are known as convection cells. [Solar Quiz: How Well Do You Know Our Sun?]


The rotation of the sun on its axis causes the largest convection cells to form circular, spiraling patterns.

"These are a lot like weather patterns seen on Earth — vortices that spiral and turn all over the place," study author Lisa Upton, a solar scientist at Vanderbilt University in Nashville, told SPACE.com. Convection in Earth's atmosphere is ultimately driven by heat from the sun; the rotation of the Earth then makes convecting air on Earth spiral.



This image shows the paths of giant cell flows on the sun for Aug. 30, 2010


Super cells on the sun

Convection was already evident on the surface of the sun in two kinds of structures — granules, which are about 600 miles (1,000 kilometers) wide, and supergranules, which are about 18,000 miles (30,000 km) across. Granules last about 10 minutes, and matter flows in them at speeds of about 6,700 mph (10,800 km/h); supergranules endure longer, surviving about 24 hours, but matter flows in them slower, at speeds of about 1,100 mph (1,800 km/h).

Scientists have suggested the sun might possess even larger convective cells for nearly five decades. These giant cells were expected to be about 120,000 miles (200,000 km) deep and wide, spanning the entire convection zone of the sun, the outermost third of the star's interior.

"You have to have something like these giant cells to help explain why the sun's equator rotates so rapidly,"study lead author David Hathaway, an astrophysicist at NASA Marshall Space Flight Center in Huntsville, Ala., told SPACE.com.

These giant cells are expected to each last months, helping transport incredible amounts of heat generated in the sun's core to its surface.

"They ultimately help drive the sun's 11-year sunspotcycle, and should also help active regions — highly magnetic areas — form," Hathaway said. These violently active regions underlie activity such as sunspots and explosions such as solar flares and coronal mass ejections, which drives space weather that can damage electronics on Earth and in orbit.


The hunt for giant sun cells

The problem in finding these giant cells is how slow they were expected to flow, making it difficult to identify their influence on the surface of the sun. Now, by using NASA's Solar Dynamics Laboratory, researchers detected these humongous structures.

The researchers followed the motions of supergranules for days. This helped them identify the patterns of flow caused by the giant cells.

"People have been looking for these cells for 45 years," Upton said. "A combination of having the right data and the right techniques ultimately led us to observe these features on the sun."

Matter flows in these cells at speeds of about 18 mph (30 km/h). The spirals are at least 60,000 miles (100,000 km) across, and can last for at least three months. As expected from the effects of the sun's rotation, these cells flow clockwise in the north and counterclockwise in the south — in both cases, around high-pressure regions.

"Now we have to figure out how big an effect these giant cells have on the emergence of active regions on the sun's surface, and what that means for space weather," Hathaway said.

Hathaway, Upton and their colleague Owen Colegrove detailed their findings in the Dec. 6 issue of the journal Science.


http://news.yahoo.com/giant-plasma-spirals-found-sun-235607972.html