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Fickle. The predicted coming solar maximum (red line) compared with the past three solar maxima (blue line). Inset: The sun's face, showing dark sunspots.

Credit: NOAA Space Weather Prediction Center

Sun's Behavior Flummoxes Solar Scientists

By Robert Zimmerman
ScienceNOW Daily News
8 May 2009

For the past 3 centuries, the sun has followed a regular and reliable cycle. Every 11 years, it experiences a peak and a valley in its activity, called the maximum and minimum, respectively. During maxima, there are numerous sunspots (cool and dark areas on the sun's surface), the polarity of the sun's magnetic field weakens and then flips, and the solar wind fluctuates wildly. During minima, the sun is relatively placid, with no sunspots, a steady and strong magnetic field, and a more-or-less constant solar wind.

Although the solar cycle is regular, scientists have had a difficult time predicting exactly when the maxima and minima will occur. In 2006, for example, as the sun slowly settled down from its most recent maximum, scientists argued with great passion over the timing and strength of the next peak. Forty-five predictions were offered, based on a variety of techniques, from the theoretical to the purely statistical. These predictions generally fell into two camps, with one group forecasting an early and strong solar maximum whereas another group predicted a late and weak maximum.

In the end, the Solar Cycle 24 Prediction Panel, made up of scientists from both groups, published both forecasts. "It was amazing how split the community's predictions were," says panel chair Douglas Biesecker of the National Oceanic and Atmospheric Administration's Space Weather Prediction Center in Boulder, Colorado.

To everyone's surprise, the sun so far hasn't followed either prediction. Both camps expected that by March 2008, the sun would hit its minimum and begin ramping up its activity toward one of the predicted maximums. But the sun remained quieter than it has been in almost a century. It has now been more than a year, and the sun is still docile, in one of the deepest solar minimums on record.

So the Solar Cycle Prediction Panel is revising its 2007 predictions. And this time, three-quarters of the researchers are on the same page. Today's announcement comes to three main conclusions. First, the panel now believes that the ongoing minimum reached its lowest point in December 2008. Second, the scientists predict that the next maximum will be weak with relatively few sunspots, the weakest since 1928. And third, the panelists say that the maximum will peak in May 2013, 9 months later than previously predicted.

Whether this newly revised forecast comes true, however, still remains unknown. As of today, the solar minimum continues, as deep and as quiet as scientists have ever seen. And there remains significant disagreement within the panel, with a large minority still unconvinced that the new prediction is right.