Scientists from the Naval Research Laboratory in Washington, DC, using images from NASA's two Solar Terrestrial Relations Observatory (STEREO-A and STEREO-B) spacecraft and Solar Dynamics Observatory (SDO) have found a previously unreported solar feature - coronal cells in the atmosphere of the Sun.

Solar Cells
© NASA / STEREO / NRLCoronal cells in the Sun's atmosphere.
The study, published online in the Astrophysical Journal, describes cells with bright centers and dark boundaries occurring in the Sun's atmosphere, the corona.

These cells look somewhat like a cell pattern that occurs on the Sun's surface - similar to the bubbles that rise to the top of boiling water - but it was a surprise to find this pattern higher up in the corona, which is normally dominated by bright loops and dark coronal holes.

The coronal cells occur in areas between coronal holes - colder and less dense areas of the corona seen as dark regions in images - and "filament channels" which mark the boundaries between sections of upward-pointing magnetic fields and downward-pointing ones. Understanding how these cells evolve can provide clues as to the changing magnetic fields at the boundaries of coronal holes and how they affect the steady emission of solar material known as the solar wind streaming from these holes.

"We think the coronal cells look like flames shooting up, like candles on a birthday cake," said Dr. Neil Sheeley, a solar scientist at the Naval Research Laboratory and a co-author of the study. "When you see them from the side, they look like flames. When you look at them straight down they look like cells. And we had a great way of checking this out, because we could look at them from the top and from the side at the same time using observations from SDO, STEREO-A, and STEREO-B."

The researchers used time-lapse sequences obtained from the SDO and the two STEREO spacecraft to track these cells around the Sun, and revealed the three-dimensional nature of the cells as columns of solar material extending upward through the Sun's atmosphere, like giant pillars of gas.

"Sometimes the cells were gone forever, and sometimes they would reappear exactly as they were," Dr. Sheeley said. "So this means we need to figure out what's blowing out the candles on the birthday cake and re-lighting them. It's possible that this coronal cell structure is the same structure that exists inside the coronal holes - but they're visible to us when the magnetic fields are closed, and not visible when the magnetic fields are open."

The discovery of coronal cells has already increased knowledge of the magnetic structure of the Sun's corona. Future studies of the evolution of coronal cells may improve scientists' understanding of the magnetic changes at coronal-hole boundaries and their effects on the solar wind and Earth's space weather.