SPACE.com -- Key Found to Why Sun's Magnetic Poles Flip

ANIMATION: A coronal mass ejection erupted from the Sun on Nov. 18. It is aimed directly at Earth and could arrive sometime Nov. 19.

A major solar eruption early on Nov. 3, 2003, flung a cloud of expanding, hot gas into space. The myriad white spots are protons ahead of the storm slamming into the spacecraft's imager. Credit: NASA/ESA/SOHO

Three Sunspots Return, First Storm En Route

Latest Sun Flare Put at X28, Strongest on Record

Starspots Act as Glue, Star Does the Twist


	Key Found to Why Sun's Magnetic Poles Flip By Robert Roy Britt Senior Science Writer posted: 09:30 am ET 20 November 2003

EMBARGOED FOR

Every 11 years the Sun's magnetic field flips, but scientists don't know what triggers it. A new study shows that big eruptions of superheated gas, called coronal mass ejections, may play an important role.

The coronal mass ejections (CMEs) tend to be most common during a period of maximum solar activity, the peak in a known 11-year cycle. The outbursts typically wane for a few years and reach a low point at solar minimum.

The current cycle is in the waning phase, about two or three years past maximum.

In a magnetic reversal, north becomes south and south becomes north. They occur amid each solar maximum. The new study of more than seven years of data show CMEs blast billions of tons of electrified gas into space, causing the Sun to shed its old magnetic field and making conditions right for the new one.

"The Sun is like a snake that sheds its skin," Nat Gopalswamy of NASA's Goddard Space Flight Center said in a statement Wednesday. "In this case, it's a magnetic skin. The process is long, drawn-out and it's pretty violent. More than a thousand coronal mass ejections, each carrying billions of tons of gas from the polar regions, are needed to clear the old magnetism away.

Gopalswamy is lead author of the new report, which appears in the Astrophysical Journal. The study was based on observations by the Solar and Heliospheric Observatory (SOHO) spacecraft, a joint project between NASA and the European Space Agency.

The study used seven years of SOHO data, plus records of CMEs from 1979-85 recorded by a US Air Force satellite.

CMEs are like brooms, sweeping away untidy magnetic fields created by sunspots, Gopalswamy and his colleagues explain. The research affirmed a direct connection between the number of sunspots and the number of CMEs, which often emanate from the spots. Importantly, though, a large number of CMEs originate near the solar poles where there are no sunspots.

By clearing the polar regions of remnants of magnetic activity, high-latitude CMEs "groom the polar magnetic fields in a new configuration," the study concludes.

The research comes to light during a stretch of unusual solar activity. Though past its peak on this cycle, the Sun coughed up 10 major solar flares, from three huge sunspots, in late October and early November.

Flares are radiation events, their light and X-rays arriving at Earth about 8 minutes later. Several of the recent flares had associated coronal mass ejections. The billowing clouds of charged particles take anywhere from 18 hours to about 3 days to arrive. The most powerful among them can rattle satellites and power grids.

Another round of severe space weather appears in the offing, and all three sunspots rotated back to the solar surface in recent days. One apparently moderate CME was en route mid-day Wednesday when the new research was announced.