Harry warns that the Sun may have lost its spots

The Sun on 30 March 2009 with no spots, image courtesy SOHO/MDI

Sunspots may vanish is the eye-catching title of research by solar physicists Bill Livingston and Matthew Penn last year. Using sunspot field strengths and temperature data collected with the McMath-Pierce solar telescope they discovered systematic changes in both parameters that predict a spotless sun in 2015. Sunspots appear dark on the sun only because strong fields within the flux-rope from the sun’s core maintain a low temperature within the spot, so spots seem dark compared with their surroundings.

The important thing about the “Spots may vanish” paper is that extrapolation from the data shows field strengths dropping below 1500 gauss by about 2015. “So what?” you may ask, but we know when fields get this low spots are no longer seen – that is, they vanish.

The researchers remind us of the Maunder Minimum of the 17C when records say the Thames froze solid on a regular basis, and no sunspots were visible for decades. And the “Spots may vanish” paper suggests a similar event is possible!

Now, I am no “Chicken Little” alarmist, but two unexpected recent events support Livingston and Penn’s prediction, as I’ll briefly describe.

Solar flares over the last ~30 years

In “big picture” terms the sun has had two major anomalies over the past decade. The first anomaly is that flaring over Cycle 23 (C23) was much stronger than the two previous cycles, and anti-correlated with the sunspot count . That is, although the spot count strongly declined from C21 to C23, C23 had much stronger flares than the two previous cycles; an anti-correlation (Fig 1). Also these strong flares occurred over a much longer period than in the earlier cycles; C23 flaring peaked around 2003/4.

The second anomaly is that solar activity, as expected, has declined to solar minimum, BUT this is proving to be an unusually deep and prolonged minimum. In fact the current minimum is the deepest since 1913, the deepest for almost one hundred years.

The two events I believe are closely linked. It’s as if the sun, having had a “giant party” (i.e. hosted so many big flares), is now having a giant “hang-over” and does not want to get out of bed!

The trend in magnetic fields observed on the Sun

As a result, while we have had some new C24 activity, it’s much weaker than any solar modellers predicted. So weak in fact, that I am prompted to think it’s evidence that Livingston and Penn are correct. On their plot the last data recorded was in 2006, when maximum sunspot fields stood at 2300G, and their extrapolation has fields down to 1500G by 2015 (Fig 2). BUT it’s already 2009, and (if they are correct) spot fields will by now have weakened to about1900G. Is this the reason why new cycle activity appears to be so weak?

Of course all attempts to model solar activity involve extrapolation: i.e. predictive modelling is perilous. Can we really expect a spotless sun five years hence? Maybe. And remember all climate on Earth is driven by the sun (if we don’t count minor volcanism and CO2 effects) and with below par solar activity maybe the Gulf Stream will flow only fitfully: and maybe, just maybe, “sunspots may vanish”!

Keep a close watch for sunspots – it could be your last chance to see one!

Harry Roberts (expert Sun and Moon observer and member of the Sydney City Skywatchers)