Magnetism plays a critical role in various solar phenomena such as flares, mass ejections, flux ropes, and coronal heating. Sunspots are areas of concentrated magnetic fields. A sunspot usually consists of a circular dark core (the umbra) with a vertical magnetic field and radially-elongated fine threads (the penumbra) with a horizontal field.

The penumbra harbors an outward flow of gas along the horizontal threads. The darkness of the umbrae is generally correlated with the magnetic field strength. Hence, the strongest magnetic field in each sunspot is located in the umbra in most cases.

Joten Okamoto (NAOJ Fellow) and Takashi Sakurai (Professor Emeritus of NAOJ) were analyzing data taken by the Solar Optical Telescope onboard HINODE, when they noticed the signature of strongly magnetized iron atoms in a sunspot. Surprisingly the data indicated a magnetic field strength of 6,250 gauss .

This is more than double the 3,000 gauss field found around most sunspots. Previously, magnetic fields this strong on the Sun had only been inferred indirectly. More surprisingly, the strongest field was not in the dark part of the umbra, as would be expected, but was actually located at a bright region between two umbrae.

HINODE continuously tracked the same sunspot with high spatial resolution for several days. This is impossible for ground-based telescopes because the Earth's rotation causes the Sun to set and night to fall on the observatories. These continuous data showed that the strong field was always located at the boundary between the bright region and the umbra, and that the horizontal gas flows along the direction of the magnetic fields over the bright region turned down into the Sun when they reached the strong-field area.

This indicates that the bright region with the strong field is a penumbra belonging to the southern umbra (S-pole). The horizontal gas flows from the southern umbra compressed the fields near the other umbra (N-pole) and enhanced the field strength to more than 6,000 gauss.

Okamoto explains, "HINODE's continuous high-resolution data allowed us to analyze the sunspots in detail to investigate the distribution and time evolution of the strong magnetic field and also the surrounding environment. Finally, the longtime mystery of the formation mechanism of a stronger field outside an umbra than in the umbra, has been solved."

Research paper

Related Links
National Institutes of Natural Sciences
Solar Science News at SpaceDaily

Tweet

Thanks for being here; We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain. With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords. Our news coverage takes time and effort to publish 365 days a year. If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor $5 Billed Once credit card or paypal		SpaceDaily Monthly Supporter $5 Billed Monthly paypal only

What's behind the most brilliant lights in the sky
Madison WI (SPX) Feb 01, 2018
Space physicists at University of Wisconsin-Madison have just released unprecedented detail on a bizarre phenomenon that powers the northern lights, solar flares and coronal mass ejections (the biggest explosions in our solar system). The data on so-called "magnetic reconnection" came from a quartet of new spacecraft that measure radiation and magnetic fields in high Earth orbit. "We're looking at the best picture yet of magnetic reconnection in space," says Jan Egedal, a professor of physics and ... read more