Longest Solar Minimum Since 1913
© 2009 by Linda Moulton Howe
“It's a fascinating time. It's the quietest sun in a century,
since the solar cycle of 1902 to 1913. ”
- Mark Miesch, Ph.D., NCAR's High Altitude Observatory
Spotless sun on April 7, 2009. Out of 365 days in 2008,
266 were without sunspots. So far in 2009, January had 25
sunspot free days; February had 23 sun spot free days; and
March had 28 sun spot free days. Image source: SOHO.
April 7, 2009 Huntsville, Alabama and Boulder, Colorado - A sunspot is a region of intense magnetic activity on the Sun's surface that are cooler than the rest of the sun. That's why they appear as dark spots. [ Sunspots are at temperatures of roughly 4,000 to 4,500 Kelvin surrounded by hotter solar material around 5,800 Kelvin.]
Many sunspots on the sun,
March 29, 2001. Image by SOHO.
Left: July 15, 2002, “the most detailed images ever of sunspots” on sun's granular surface
by solar telescope in La Palma, Canary Islands, off African coast. Resolution is 62 miles (100 km). Colorized image by Royal Swedish Academy of Sciences Institute for Solar Physics.
Right: Sunspot viewed close-up in ultraviolet light by the TRACE spacecraft.
Those dark sunspots appear in cycles of about eleven years. In between spots on the sun are quiet times called solar minimums. The last solar cycle minimum 23 began in May 1996. The next solar cycle 24 was expected to start some time in 2007 with a new crop of sunspots. But it is now April 2009, and this has been the most spotless sun in a century.
Scientists did not start numbering solar cycles until 1755, after a mini-ice age in Europe that was linked to a nearly spotless sun for seventy years, a period referred to as the Maunder Minimum.
Maunder Minimum of 1645 - 1715
Sunspots were at the lowest number for longest time of seventy years between 1645 and 1715,
in what was called the Maunder Minimum after solar astronomer Edward Maunder. During one
30-year-period within the Maunder Minimum, astronomers saw only about 50 sunspots compared
to modern sunspot cycles of 40,000 to 50,000 sunspots in a 30-year-period. Source of data: Solar
Influences Data Analysis Center (SIDC) at the Royal Observatory of Belgium.
The Maunder Minimum, named after solar physicist Edward Maunder, was a 70-year-long period roughly from 1645 to 1715, when sunspots became exceedingly rare. During one 30-year period within the Maunder Minimum, astronomers observed only about 50 sunspots compared to 40,000 to 50,000 sunspots in modern times.
Solar Cycle 24
On January 4, 2008, a patch of magnetism on the sun was declared by NASA to be the first official sunspot of the new Solar Cycle 24. The spot was in a high-latitude on the sun with reversed polarity from the previous Solar Cycle 23.
On January 4, 2008 , this new high-latitude active solar region was magnetically reversed
from sunspot magnetic directions in the previous Solar Cycle 23. So, this sunspot officially
marked the beginning of Solar Cycle 24. Images courtesy SOHO/NASA/ESA.
With that discovery, solar scientists expected 2008 would bring more sunspots as the new solar cycle developed intensity toward solar maximum in 2011 to 2012. But out of 365 days in 2008, 266 were without sunspots. So far in 2009, January had 25 sunspot free days; February had 23 sun spot free days; and March had 28 sun spot free days. Solar Cycle 23 began in a May 1996 minimum, so by April 2009, it's been thirteen years between minimums and still no increasing sunspots. The last time a solar cycle has gone thirteen years between minimums was Solar Cycle 15 in 1902 to 1913.
NASA reports that in 2008 (yellow in above graph), no sunspots were observed for 266
of the year's 365 days (73% of the time) - the most blank sun since 1913 when there were
311 spotless solar days (85%). Image credit: Spaceweather.com.
Recently I talked about the unusual thirteen years between solar cycle minimums 23 and 24 with John Davis, Ph.D., Manager of the Space Science Office at NASA's Marshall Space Flight Center in Huntsville, Alabama. Dr. Davis had planned to launch an instrument in September 2008 to measure the sun's magnetic fields. But he needs active sunspots in order to have fields to measure, so he and his fellow scientists are still waiting to launch. Frustrated, Dr. Davis now wonders if there will even be sunspots this summer of 2009?
John Davis, Ph.D., Manager, Space Science Office, NASA Marshall Space Flight Center, Huntsville, Alabama: “Six months ago, my prediction was that sunspots would have turned up by now because I was comparing it to other past cycles that Solar Cycle 23 seemed to be like. And there you had a fairly long decline and then the turn up would occur and I was saying by April 2009, we would have substantial activity.
WHICH IS NOW.
Yes, I know! (laughs) I’ve postponed my guess for sunspots starting again now until July 2009, but I don’t know if that’s going to be any better. My guess is that the spotless sun could go on for quite a long time – maybe another 12 months. Although within those 12 months, I would not be surprised to see one or two active rotations of the sun with sunspots and then it will drop back down again to spotlessness.
That’s what has happened in the past, but that’s no guarantee that that’s what is going to happen in the future.
AS AN EDUCATED GUESS, WHAT WOULD YOU EXPECT FOR THE SOLAR MAXIMUM? WHEN WOULD YOU EXPECT THERE TO BE X-40 FLARES AGAIN?
It would go on the same 11-year-cycle. That would not change. The maximum, if it comes – I cannot tell you if it is going to be a large or small cycle. The suggestion now is that it will be a fairly small cycle about three years from now (2012). If it doesn’t do that, I don’t know what the sun is doing! (laughs)
SO PERHAPS NOT AS INTENSE A SOLAR MAX AS ORIGINALLY EXPECTED?
Not as intense. But as soon as you say something, our sun knows what it’s going to do and it doesn’t tell us! (laughs) My guess is, if I were going to put money on it, I would say that the next two solar cycles are actually going to be quite small and that the next minimum will also be long, without sunspots like this solar cycle 24 because the sun has done that twice before in the past. And if you look at the second of those two long minimums, it can be followed by a fairly strong maximum cycle. Four of the last five solar cycles have been very big cycles. That’s somewhat unusual, and it's also unusual that this minimum in solar cycle 24 has gone so long without sunspots.
IS THE BOTTOM LINE HERE THAT THE SUN IS STILL BAFFLING TO OUR WORLD’S BEST SOLAR PHYSICISTS?
(laughs) It’s baffling to me! We can only say that the consensus opinion did not expect this.”
What's Going On Inside the Sun?
Astrophysicist Mark Miesch, Ph.D., Staff Scientist at the High Altitude Observatory (HAO) at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado studies the solar dynamo, which is how the sun generates the magnetic fields that make sunspots. He also wonders what's going on inside the sun? And how much longer before sunspots emerge again?
Mark Miesch, Ph.D., HAO/NCAR, Boulder, Colorado. Image © by NCAR/ICAR.
Mark Miesch, Ph.D., Staff Scientist at the High Altitude Observatory (HAO), National Center for Atmospheric Research (NCAR), Boulder, Colorado: “It's a fascinating time. It's the quietest sun in a century, since the solar cycle of 1902 to 1913. This relatively long minimum now by April 2009 – it was not predicted, but it’s not completely unprecedented. According to some computer models, a deep solar minimum implies that the upcoming solar maximum will be weaker than usual as well. But other models say differently, that the maximum in 2011 to 2012 could still be strong. So it could go either way.
WHAT DOES YOUR WORK IN STUDYING THE SUN INDICATE TO YOU?
Well, I wouldn’t want to go on the record with a prediction! (laughs) My work indicates it’s all rather random. I study how stars build magnetic fields. The sun and other stars we see in the galaxy – there are many stars that exhibit magnetic activity like our sun. And the one thing they all have in common is what we call convection. In the outer part of stars, we know that convection means warm stuff rises and cooler stuff sinks. If you heat a fluid from below like in the sun, energy is released by nuclear reactions in the core and that heats the fluid from below so you have over-turning motions and those fluid motions are what generate magnetic fields.
That constant churning motion inside the sun is what builds magnetic fields. The energy of motion of the fluids is converted into magnetic energy. The turbulent nature of those fluids is very chaotic, so that’s what gives you the chaotic part of the sun. That’s why each solar cycle is not the same as the last because there is a certain random element.
WHAT IS A SUNSPOT FROM YOUR POINT OF VIEW?
A sunspot is a manifestation of the magnetic field in the deep interior of the sun. In fact, it was 100 years ago that the American astronomer, George Ellery Hale, first detected magnetic fields on the sun and it was in sunspots. That was in 1908 to 1909. So, he was the first to show that sunspots are a magnetic phenomenon that come from magnetic fields. And we now think that those magnetic fields originate deep in the interior of the sun and then rise through something we call ‘magnetic buoyancy.’ There are tubes of magnetism that are less dense than their surroundings and they rise like a hot air balloon and then poke out of the surface of the sun. And that’s what we think a sunspot is. Sunspots are a way to probe the magnetism below the surface of the sun.
WHEN THE SUN IS GOING SO LONG WITHOUT SUNSPOTS, WHAT DOES THAT SAY TO YOU ABOUT WHAT IS HAPPENING DEEP INSIDE OF THE SUN?
It says there are no magnetic fields strong enough to become buoyant like hot air balloons. The sun now is not generating these strong concentrations of magnetic field. But that does not mean that solar magnetism has stopped. A fascinating thing is just like the Earth has a magnetic field around it, the sun has a magnetic field around it that is pushed out by the solar wind and envelopes the whole solar system. There are cosmic rays that are generated by supernovae and other explosions in the galaxy that permeate the Milky Way galaxy, but the sun has a magnetic cage around all the planets that deflects those cosmic rays.
So, at times when the magnetic activity of the sun is small (like right now), more cosmic rays get in to Earth. When magnetic activity on the sun is high, less cosmic rays get into Earth. Those cosmic rays come to Earth and create isotopes in certain elements like beryllium and carbon. You can measure that back 10,000 years. Beryllium is in ice corers in Greenland and Antarctica. Carbon is contained in tree rings if you find an old tree.
By looking at the isotopes, we can trace sunspot cycles back a long time. That tells us that the solar cycle was still going on in the Maunder Minimum. The sun’s protective bubble around all the planets was going up and down every 11 years just like now, and yet there were no sunspots then. So, it’s a fascinating puzzle.
Some computer models say that sunspots are an integral part of why there is an 11-year-cycle, that the cycle cannot proceed without sunspots. But the isotope data during the Maunder Minimum suggest that might not be the case. So, us having a prolonged minimum now is exciting from a scientific point of view.
WHEN DO YOU EXPECT TO START SEEING A LOT OF SUNSPOTS AGAIN?
From what I study, I study turbulent fluids and turbulence is inherently random and unpredictable. So, from my experience it is unwise to predict what a chaotic system is going to do.
SO, ANYTHING COULD HAPPEN WITH THE SUN, INCLUDING ANOTHER MAUNDER MINIMUM?
Yes, that’s possible, but I think it’s unlikely.
WHY IS IT UNLIKELY?
Because the sun is a chaotic system and the Maunder Minimum was the only extended period like that in the last 400 years. It might never happen again.
Why Does Sun Have Cycles?
IF THE SUN IS A CHAOTIC SYSTEM, THEN WHY ARE THERE ANY 11 AND 22 YEAR CYCLES ON THE SUN AT ALL?
That is an excellent question. There are random processes superimposed on top of more ordered processes. Every star has a mixture of those. Our sun is particularly regular, compared to other stars. You can look at other stars and some have solar cycles like the sun and others are just completely chaotic and they have no rhyme or reason about what their magnetic activity is doing.
WHAT PRODUCES THE CYCLE IN OUR SUN?
That is a question that people have been asking for 200 years, or at least 150 years.
Well, there are models and it has to do with how the sun is stretched out. It has to do with differential rotation. The sun spins faster at its equator than at its poles. That tends to stretch out magnetic fields. If you have a magnetic field line that goes from the equator to the pole, but the equator spins around faster than the pole, that magnetic field line gets stretched out into an east and west direction and it gets stronger and stronger.
HOW DOES THE SUN GO FASTER AT THE EQUATOR THAN THE POLES?
That’s another question that people have been working on for centuries, but it has to do again with this convection, the fluid motions. As you heat the outer 30% of the sun, it has these turbulent convective motions in it. As these motions go up and down and overturn, they transport heat from the interior to the surface to make the sun shine. They create magnetic fields. And the convective motions also re-distribute angular momentum. The way the convective motions re-distribute angular momentum in a spinning star makes the equator spin faster than the poles.
Sun's Intensely Hot Nuclear Core,
Cool Surface and Hot Coronas
Core = 10 million degrees Kelvin, or 17,999,540.3 degrees Fahrenheit
Surface = 6,000 degrees Kelvin, or 10,340.33 degrees Fahrenheit
Corona Away from Sun = 2 million degrees Kelvin, or 3,599,540.33 degrees F.
The interior of the sun is hotter than the surface - it’s the nature of why a star is stable. Gravity pushes in, but you have to have an outward gradient of pressure. Pressure has to push out to balance gravity, so the center of the star has to have a higher pressure than the surface, or the star will implode.
The interior of the sun is about 10 million degrees Kelvin (17,999,540.3 degrees Fahrenheit). The surface is about 6,000 Kelvin (10,340.33 degrees Fahrenheit). So, the sun's surface goes down in temperature a lot compared to the core and that’s not so much a mystery. You expect that from the pressure balancing gravity.
But the mystery is that the temperature goes up again – that from the surface of the sun, it goes from 6,000 degrees Kelvin at the surface to 2 million degrees Kelvin (3,599,540.33 degrees Fahrenheit) in the corona. That’s one of the big mysteries of the sun – why is the corona hotter than the surface? The source of the heat in the sun is generated by nuclear processes in the core of the sun. Just as you have a heater in your house, as you go farther away from the heater, you expect the temperature to cool down and as you go closer to the heater, you expect it to be warmer. So, the corona is farther away from the heat source and yet, it is hotter.
WHAT IS THE ENERGY THAT WOULD CAUSE A RISE FROM 6,000 DEGREES KELVIN AT THE SURFACE TO 2 MILLION IN THE CORONA AWAY FROM THE SUN?
It all comes down to magnetism again. The magnetism that is generated in the convection zone in the interior of the sun and that magnetism threads through the surface of the sun and is spit out in eruption events such as solar flares and coronal mass ejections (CMEs) and the magnetic field threading the surface from the interior convection zone wiggles the magnetic field lines and that transports energy out into the corona. Then that energy is dissipated and converted to heat. So, it all has to do with magnetic energy. The turbulent fluid motions in the solar interior transform the energy of motion into magnetic energy that filters out to the sun’s surface and then in the corona – that magnetic energy is changed back to heat – a redistribution of energy.
More Cosmic Rays Getting to Earth
in Long Solar Minimum
IS THERE ANY POTENTIAL DANGER TO EARTH’S SURFACE LIFE IF THE SUN GOES FOR AN INDEFINITE PERIOD OF TIME WITHOUT SUNSPOTS?
Not really. There is still solar magnetism. The magnetic bubble that protectively surrounds the Earth, we call the magnetosphere. The similar magnetic protective bubble around the sun and al the planets in our solar system is called the heliosphere. There is still solar magnetism permeating the heliosphere, even during the Maunder Minimum and during solar minimums. So, if there were no sunspots for 70 years, there would still be a heliosphere.
BUT IT DOES SHRINK.
Yes, the amount of magnetism in the heliosphere does go down when solar activity goes down and lets more cosmic rays in.
WHAT IS THE DANGER OF MORE COSMIC RAYS COMING TO EARTH?
Not significant from a health perspective. The biggest impact that solar activity has is at times of strong solar activity. You would not want to take a trans-polar flight, like a flight from New York City to Beijing, China. They go at pretty high latitudes. If there is a lot of magnetic activity on the sun, it sends out particles in the solar wind and those get funneled towards the Earth’s polar magnetic fields and that’s what causes aurora. Aurora are nice to look at when you are safely standing on the Earth’s surface, but if you are in a plane in the stratosphere, you can get a significant dose of radiation if you fly through an aurora.
WHAT ABOUT THE ASTRONAUTS UP ON THE INTERNATIONAL SPACE STATION (ISS)?
Yes, the ISS itself is within the magnetosphere, it is within Earth’s protective bubble and its orbit is more towards the Equator in the lower latitudes. So, actually astronauts on the ISS would get less radiation than a high-altitude flight over the Earth’s poles. But if you went to the moon or Mars outside the Earth’s magnetosphere – astronauts on a deep space mission – would certainly get a lot of solar radiation if there were a lot of magnetic activity on the sun.
2011 - 2012 Solar Max Could Hurt Satellites
and Affect Airline Flights Over North Pole
If we kick into a strong maximum in 2011 to 2012, the sun could become a threat again. What usually happens is that it’s more an economic issue than health issue because if there is a significant threat of increased radiation, what the planes will do is fly lower. Flying lower means more atmospheric drag, which means more fuel consumption and possibly multiple stops to refuel.
It can potentially cost the airlines money and other economic impacts, too. High solar activity can disable satellites, so communication satellites in particular can be disabled. Telecommunication companies would have to repair them or launch new ones and that can be an economic impact. Also high solar activity can disrupt power grids underground. So, this all goes under the realm of what we call space weather.
The most exciting thing for me is this is the deepest minimum of the Space Age and now since we have instruments to monitor the sun and space weather and the whole magnetism and heliosphere and how the sun interacts with the planets – we have more instruments and telescopes now in space and on the ground monitoring this than ever before. This minimum will tell us a lot about how the sun generates magnetic fields and how those magnetic fields shape the solar corona and the heliosphere and how solar activity impacts the planets.
AND THAT EVEN OUT OF A LONG MINIMIUM LIKE THIS ONE, WE STILL COULD HAVE X-40 FLARES AS WE GET TO 2011 TO 2012?
It’s possible, yes.”http://www.earthfiles.com/news.php?ID=1545&category=Science