11
years
Hot gas flows cause sunspot lows

By Ron Cowen

Ne wly reported observations of gas flows on the solar surface may explain why the sun recently had such an extended case of the doldrums.

From 2008 through the first half of 2009, the sun had a puzzling lack of sunspots, flares and other storms, extending the usual lull at the end of the 11-year solar activity cycle for an extra 15 months. Data from the orbiting Solar and Heliospheric Observatory, or SOHO, indicate that gas flow affecting magnetic fields near the sun’s poles may have been responsible for the extended quiet. The findings also suggest a better way to forecast the intensity and duration of future solar cycles.

Scientists want to improve predic-
tions because some solar outbursts can
blast Earth with massive, magnetized
clouds of charged particles capable of
knocking out electrical power grids and
harming satellites.

Duration of an average solar cycle

14 years

Duration of longest solar cycle on record

The latest period of minimal solar activity
lasted longer than expected; data from
the SOHO spacecraft may explain why.

onal flow typically oppose much stronger flows of magnetized material on the surface, Hathaway says. The faster the meridional flow, the greater the opposition to other flows. As a result, the sun’s polar magnetic field can’t become as strong, the researchers propose.

“It is possible that the delayed start of the present cycle, 2009 to 2010, was caused by the relatively weak polar field in 2007 to 2009,” comments Neil Sheeley of the Naval Research Laboratory in Washington, D.C.

Polar magnetic field strength plays a crucial role in the onset of each solar cycle, Hathaway notes. These fields dive beneath the solar surface, building up deep sunspot-generating magnetic fields that signal the start of the next cycle. Weaker polar fields take more time to reach the strength required to produce sunspots, prolonging the lull in activity from the previous cycle. And weaker-than-usual polar fields are likely to produce less activity during the next solar cycle, Hathaway and Rightmire predict.

“The fact that the meridional flow plays a key role in setting up the sun’s polar fields for the next cycle suggests that future observations will help us predict” the duration and intensity of upcoming cycles, Hathaway says.