Solar Science

A blog of solar physics

Posts Tagged ‘Maunder Minimum

NASA on the disappearing sunspots

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This just in from NASA:

September 3, 2009: The sun is in the pits of the deepest solar minimum in nearly a century. Weeks and sometimes whole months go by without even a single tiny sunspot. The quiet has dragged out for more than two years, prompting some observers to wonder, are sunspots disappearing?

“Personally, I’m betting that sunspots are coming back,” says researcher Matt Penn of the National Solar Observatory (NSO) in Tucson, Arizona. But, he allows, “there is some evidence that they won’t.”

Penn’s colleague Bill Livingston of the NSO has been measuring the magnetic fields of sunspots for the past 17 years, and he has found a remarkable trend. Sunspot magnetism is on the decline:

Above: Sunspot magnetic fields measured by Livingston and Penn from 1992 – Feb. 2009 using an infrared Zeeman splitting technique.

“Sunspot magnetic fields are dropping by about 50 gauss per year,” says Penn. “If we extrapolate this trend into the future, sunspots could completely vanish around the year 2015.”

Hmmm, yes they could. But the solar magnetic field could simply be in a cyclical downturn of which this is a part. We need an expert!

“This work has caused a sensation in the field of solar physics,” comments NASA sunspot expert David Hathaway, who is not directly involved in the research. “It’s controversial stuff.”

The controversy is not about the data. “We know Livingston and Penn are excellent observers,” says Hathaway. “The trend that they have discovered appears to be real.” The part colleagues have trouble believing is the extrapolation. Hathaway notes that most of their data were taken after the maximum of Solar Cycle 23 (2000-2002) when sunspot activity naturally began to decline. “The drop in magnetic fields could be a normal aspect of the solar cycle and not a sign that sunspots are permanently vanishing.”

Yes, what he said.

Penn himself wonders about these points. “Our technique is relatively new and the data stretches back in time only 17 years. We could be observing a temporary downturn that will reverse itself.”

The technique they’re using was pioneered by Livingston at the NASA-supported McMath-Pierce solar telescope near Tucson. He looks at a spectral line emitted by iron atoms in the sun’s atmosphere. Sunspot magnetic fields cause the line to split in two—an effect called “Zeeman splitting” after Dutch physicist Pieter Zeeman who discovered the phenomenon in the 19th century. The size of the split reveals the intensity of the magnetism

If the solar magnetism continues to decline what could this mean for the Earth?

If sunspots do go away, it wouldn’t be the first time. In the 17th century, the sun plunged into a 70-year period of spotlessness known as the Maunder Minimum that still baffles scientists. The sunspot drought began in 1645 and lasted until 1715; during that time, some of the best astronomers in history (e.g., Cassini) monitored the sun and failed to count more than a few dozen sunspots per year, compared to the usual thousands.

Note that of course, they don’t mention that this coincided with the coldest part of the Little Ice Age. But that would be politically incorrect, wouldn’t it?

“Whether [the current downturn] is an omen of long-term sunspot decline, analogous to the Maunder Minimum, remains to be seen,” Livingston and Penn caution in a recent issue of EOS. “Other indications of solar activity suggest that sunspots must return in earnest within the next year.”

I’d love to know what those other indications are, because the prognostications of future solar activity have been startlingly poor from practically everybody.

I leave the last words to David Hathaway, who dares to speak the truth to solar science:

Whatever happens, notes Hathaway, “the sun is behaving in an interesting way and I believe we’re about to learn something new.”

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Written by John A

September 3, 2009 at 10:13 am

Hathaway: “Sun’s contribution is small compared to volcanoes, El Nino and greenhouse gases”

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I’ve no objection at all and much praise when scientists actually make falsifiable predictions based on their understanding of the science. Thus when David Hathaway predicts that Solar Cycle 24 will be as large or larger than Solar Cycle 23, I applaud that boldness.

In this article on space.com, several aspects to the current solar minimum are discussed:

The sun’s surface has been fairly blank for the last couple of years, and that has some worried that it may be entering another Maunder minimum, the sun’s 50-year abstinence from sunspots, which some scientists have linked to the Little Ice Age of the 17th century.

Could a new sunspot drought plunge us into another decades-long cold spell?

It’s not very likely, says David Hathaway a solar physicist at NASA’s Marshall Space Flight Center in Huntsville, Ala.

Fair enough. Perhaps if I used IPCC-speak, we’d give that a 10-20% probability?

Hathaway continues to make bold observations and predictions:

The sun’s energy drives all climate and weather on Earth. And Hathaway does agree there are good indications that fluctuations in solar output related to sunspot cycles influence the Earth’s climate. And the Maunder minimum isn’t the only evidence — scientists have linked two smaller sunspot minimums (periods of time with very few sunspots) in the early 19th century to cold spells, as well as periods before the Maunder minimum deduced from tree ring records, he said.

But the sun isn’t the only thing that influences our climate: volcanic eruptions, large-scale phenomena such as El Nino, and, more recently, the accumulation of greenhouse gases in the atmosphere also affect the global climate.

Prior to the industrial revolution, the sun probably accounted for about 10 to 30 percent of climate variability, Hathaway told SPACE.com, but now that greenhouse gases have started to build up, “the sun’s contribution is getting smaller and smaller,” he added.

So the pre-industrial climate change on Earth was only 10-30% driven by solar variability. I wonder what the other 70-90% were.

Hathaway hints that volcanic eruptions have an effect, but as far as I am aware such eruptions only cool for perhaps 2 or 3 years, hardly causing a blip in a climate trend [unless we’re talking about supervolcanic events which can cause climate cooling for decades, but we haven’t had one of those for 70,000 years with the Toba explosion]. Is the rest caused by the ENSO cycle?

What of the current solar minimum and the sputtering start to Solar Cycle 24?

Signs of the current, new solar cycle (which actually overlaps with the last cycle) showed up in November 2006, and its first sunspots were seen in January of this year, and again in April, Hathaway said. So already that rules out another Maunder minimum, Hathaway says, since this solar cycle has already begun producing spots, even if there haven’t been many of them yet.

This cycle is just simply “off to a slow start,” Hathaway said.

The last three solar cycles were also what Hathaway calls “big cycles,” meaning they had more than the average number of sunspots (the average is around 110 to 120 sunspots on any given day during the cycle’s maximum). It’s not unusual for such a spate of prolific cycles to be followed my more muted solar cycles (such as the cycle that preceded the last three biggies).

Hathaway says that solar physicists are divided on their predictions of this new solar cycle — some say it will be small, others say it will be another doozy. Predictions have ranged anywhere from 75 to 150 maximum spots during its peak. “There really are two camps,” Hathaway said. Whatever the number ends up being, though, “it’s not zero,” he added.

That depends on whether the Maunder Minimum was really devoid of sunspots or had sporadic “Tiny Tim” spot groups which were not seen because of the technology used at the time.

It’s doubtful that it was really zero during that time.

Here’s the clincher:

Why the sun is so fickle in its sunspot production is still something of a quandary. “We still don’t fully understand how the sun does this,” Hathaway noted.

Now that statement I regard as the most important of the article. It might not be a popular statement with people on either side of the argument, but as far as solar cycle prediction is concerned, nobody knows for sure what will happen with the Solar Cycle next week, never mind next year or five or ten years hence.

The science of the variation of the Sun’s solar cycle is in its vary early stages. No-one, not even David Hathaway, knows what will happen next. That’s why he’s checking the Sun every day.

As Kenneth Tapping has already reported (and I blogged his observation) long solar cycles are not that unusual historically and are not in themselves indicative of how powerful are the succeeding cycles. Tapping noted that the long and weak Solar Cycle 20, (which occurred during a global cool period on Earth), was succeeded by Solar Cycles 21, 22 and 23 all of which were relatively powerful (and coincided by chance with a global warming on Earth).

Little Ice Age

But on the point of whether even a Maunder Minimum style collapse would cool the Earth, Hathaway admirably sticks with the IPCC-derived consensus:

One idea springs from the fact that the sun emits much more ultraviolet radiation when it is covered in sunspots, which can affect the chemistry of Earth’s atmosphere. The other is that when the sun is active, it produces tangled magnetic fields that keep out galactic cosmic rays. Some scientists have proposed that a lack of sunspots means these cosmic rays are bombarding Earth and creating clouds, which can help cool the planet’s surface.

But these ideas aren’t yet proven, and anyway, the sun’s contribution is small compared to volcanoes, El Nino and greenhouse gases, Hathaway notes.

Even if there were another Maunder minimum, he says, we would still suffer the effects of greenhouse gases and the Earth’s climate would remain warm. “It doesn’t overpower them at all,” Hathaway said.

So according to Hathaway, greenhouse gases are warming the Earth to such an extent that solar variation becomes unimportant. Never mind whether I agree with him (and who am I to disagree with an expert?), I applaud David Hathaway for making such scientifically falsifiable statements.

I hope he’s right about the warming. So far, during the current warming, we’ve had the major deserts contract, the tropics expand and possibly a general reduction in hurricane frequency globally during the 20th Century.

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Written by John A

June 12, 2008 at 1:38 am

A very good question

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OK, so I’ve recently bemoaned my fortune in actually seeing an SC24 spot “live”. But there’s a much more serious question which Anthony Watts has brought up:

Galileo, Wolf, and other solar observers of the past would likely never have seen it. So with these Tiny Tims coming and going so quickly, that begs the question; was the Maunder Minimum, Dalton Minimum and other minimums not simply a period of Tiny Tim sunspots that nobody could detect with the observing equipment of the time?

THAT is a very good question.

History of sunspot number observations showing the recent elevated activity.

Above is the record of the Solar Cycle right back to the Maunder Minimum. As you can see Galileo reported sunspots just before the Maunder Minimum, which was fortunate because with the instrumentation available at the time, he would not have seen the “Tiny Tims” similar to the current SC24 ones.

I hope this isn’t what we’re seeing. If the Earth’s climate is dominated by variations in Solar luminosity and magnetic field strength as is believed by some, then that would mean cooling.

And that would be a global disaster as deserts expand, storms increase, glaciers expand and wipe out towns and villages in places like Switzerland and Nepal, a shorter growing season with more variability in precipitation, an increase in the number of droughts and failed harvests leading to mass starvation in certain regions.

I hope its just a hiccup in global warming, because there’s very little to be scared of in a warming climate.

Before the current scare began, climatologists talked of warm periods as “Optimums” or “Optima”, a time of plenty and societal growth and prosperity. With the advent of political supplication to climate models and the pronouncements of some climate modellers, we have been taught to fear warming and try to reverse it as wholly undesirable even at the expense of every modern device that keeps us from being victims of climate change, howsoever caused.

I really hope for global warming. At the moment, I’m pessimistic about whether it will continue.

Written by John A

May 6, 2008 at 8:23 am