Above: the most recent image from spaceweather.com shows two sunspot groups emerging. So far in 2010 there have been six spotless days. It’s on many solar physicists’ minds (not to mention climate scientists): What exactly is going on with the Sun? Or, more specifically: Where have all the sunspots gone? And, if they really are “missing” does that we’re in for another “mini ice age”….or worse? Or at least a “cooling Sun” interval?
I was fortunate to attend the 40th Meeting of the Solar Physics Division in June last year, where these questions took center stage at an entire morning session. At least five major papers confronting the mystery of Solar Cycle 24 were presented, and those who attended were well rewarded with clarifications from the top solar physics specialists.
First, some information that might be novel for many: Cycle 24 is actually an “interphase’ cycle with No. 23. That is, the two are mixed. The onset of Cycle 24 (estimated around 2001, according to the specialists at the solar cycles session) emerged with the tail end or wind down of No. 23. Technically, then, the current minimum is the minimum of cycles 23 AND 24. This is part of what’s engendered so much confusion.
In terms of numbers, at the time of the SPD Meeting, 2008 of Cycle 24 was trumped by only two others in terms of spotless days (not including the Dalton Minimum and Little Ice age): the 311 spotless days of 1913, and the 287 of 1911. Meanwhile, the 2009 total has come in at 260 days – tabulated by spaceweather.com, and so far in 2010 we’ve had 6 spotless days (up to this writing).
In addition, as I write this – glancing at www.spaceweather.com, two spot groups (1054 and 1055) are emerging with 1054 is growing so rapidly it poses a potential risk for C-class solar flares (the least energetic in the C-M-X categories- with “X” the x-ray flares.). (See image)
The decline of spotless days, in addition to the appearance of rapidly growing sunspot regions – informs us that it is wise not to jump to conclusions regarding Cycle 24, or to assume we are headed into a prolonged cooling period.
Indeed, in the paper ‘A Helioseismic Comparison of the Solar Minima Preceding Solar Cycles 23 and 24’ given by Prof. Frank Hill, we learned that while cycle 24 had the lowest irradiance in the modern (space) observation era, it was not as low as that recorded for cycles 13-14.
What about the large number of spotless days portending colder temperatures? As Prof. Hill noted, this argument also can’t be made since we already have the example of a very weak cycle (16) which led to a much more energetic and active one (17). Thus, Cycle 24 – following on the heels of the quiet Cycle 23- could actually turn out to be a very active cycle, with higher solar irradiance, that actually reinforces anthropogenic warming factors as opposed to neutralizing them.
What we do know is that Cycles 23 and 24 appear to pose special problems for solar dynamo theory. But that’s a whole separate topic.
Let’s now examine the irradiance issues at more length, given that solar irradiance (an indicator of solar heat energy received at Earth) is the whole solar radiance integrated over the entire solar disk in watts per square meter per second per steradian (solid angle – where the solid angle subtended by a sphere is 4pi sr).
See:
http://en.wikipedia.org/wiki/Steradian
This topic was covered in the session: ‘Solar Irradiance: Recent Results and Future Research Plans’ by Prof. Thomas Woods of the University of Colorado-Boulder. Woods began by noting the disparate periods wherein irradiance measurably varied, including: the Sporer Minimum(1400s), the Maunder Minimum (1600s) and the Dalton Minimum (1800s). He emphasized there was no single value to characterize a time interval or period- since the radiance itself van vary hugely on local scales. For example, large solar flares can propel radiance enhancements more than 50 times greater than normal, thereby affecting irradiance.
On average though, with such violent inputs smoothed over, the Earth’s temperature changes by about 0.07 K (Kelvin degrees) over a typical solar cycle. Compare this to the 0.6 K increase in mean global temperatures (measured at the same reference point) over the last 100 years from the Greenhouse effect (no – it’s not been disproven – despite the hacked emails!) and the latter component is roughly 8.5 times greater than the solar effect.
Even if solar forcing on climate is enhanced uniformly by positive feedback mechanisms, the amplification is no more than a factor of 2. So, the human warming factors are still greater (over 0.14K) by a factor of about 4.2. This was a point made by Woods- when he emphasized the recent(to that point) results of the University of Colorado SORCE project reinforced the hypothesis that anthropogenic greenhouse gases are the primary warming contributor.
As an aside here, or an extended footnote if you will, an interesting article by David Hathaway entitled: “What’s wrong with the Sun? (Nothing)”, appeared at the Nasa.gov site in June of 2008. Hathaway noted that examination of the interplanetary magnetic field (IMF) activity (to that time) supported the ‘nothing wrong’ conclusion and showed that while the sunspot number may be low, IMF activity this solar cycle appeared to be increasing as expected, with solar maximum predicted for 2010.
Given that there are zero spotless days so far this month (6 for the year), and rapidly growing spot groups emerging even as I write, this is something we need to attend to. However, I do think Hathaway is a bit premature in his maximum projection, which I don’t envisage until late 2012-early 2013 at the earliest. But who knows? Just about every solar physicist who’s made forecasts this cycle has been wrong thus far!
I was fortunate to attend the 40th Meeting of the Solar Physics Division in June last year, where these questions took center stage at an entire morning session. At least five major papers confronting the mystery of Solar Cycle 24 were presented, and those who attended were well rewarded with clarifications from the top solar physics specialists.
First, some information that might be novel for many: Cycle 24 is actually an “interphase’ cycle with No. 23. That is, the two are mixed. The onset of Cycle 24 (estimated around 2001, according to the specialists at the solar cycles session) emerged with the tail end or wind down of No. 23. Technically, then, the current minimum is the minimum of cycles 23 AND 24. This is part of what’s engendered so much confusion.
In terms of numbers, at the time of the SPD Meeting, 2008 of Cycle 24 was trumped by only two others in terms of spotless days (not including the Dalton Minimum and Little Ice age): the 311 spotless days of 1913, and the 287 of 1911. Meanwhile, the 2009 total has come in at 260 days – tabulated by spaceweather.com, and so far in 2010 we’ve had 6 spotless days (up to this writing).
In addition, as I write this – glancing at www.spaceweather.com, two spot groups (1054 and 1055) are emerging with 1054 is growing so rapidly it poses a potential risk for C-class solar flares (the least energetic in the C-M-X categories- with “X” the x-ray flares.). (See image)
The decline of spotless days, in addition to the appearance of rapidly growing sunspot regions – informs us that it is wise not to jump to conclusions regarding Cycle 24, or to assume we are headed into a prolonged cooling period.
Indeed, in the paper ‘A Helioseismic Comparison of the Solar Minima Preceding Solar Cycles 23 and 24’ given by Prof. Frank Hill, we learned that while cycle 24 had the lowest irradiance in the modern (space) observation era, it was not as low as that recorded for cycles 13-14.
What about the large number of spotless days portending colder temperatures? As Prof. Hill noted, this argument also can’t be made since we already have the example of a very weak cycle (16) which led to a much more energetic and active one (17). Thus, Cycle 24 – following on the heels of the quiet Cycle 23- could actually turn out to be a very active cycle, with higher solar irradiance, that actually reinforces anthropogenic warming factors as opposed to neutralizing them.
What we do know is that Cycles 23 and 24 appear to pose special problems for solar dynamo theory. But that’s a whole separate topic.
Let’s now examine the irradiance issues at more length, given that solar irradiance (an indicator of solar heat energy received at Earth) is the whole solar radiance integrated over the entire solar disk in watts per square meter per second per steradian (solid angle – where the solid angle subtended by a sphere is 4pi sr).
See:
http://en.wikipedia.org/wiki/Steradian
This topic was covered in the session: ‘Solar Irradiance: Recent Results and Future Research Plans’ by Prof. Thomas Woods of the University of Colorado-Boulder. Woods began by noting the disparate periods wherein irradiance measurably varied, including: the Sporer Minimum(1400s), the Maunder Minimum (1600s) and the Dalton Minimum (1800s). He emphasized there was no single value to characterize a time interval or period- since the radiance itself van vary hugely on local scales. For example, large solar flares can propel radiance enhancements more than 50 times greater than normal, thereby affecting irradiance.
On average though, with such violent inputs smoothed over, the Earth’s temperature changes by about 0.07 K (Kelvin degrees) over a typical solar cycle. Compare this to the 0.6 K increase in mean global temperatures (measured at the same reference point) over the last 100 years from the Greenhouse effect (no – it’s not been disproven – despite the hacked emails!) and the latter component is roughly 8.5 times greater than the solar effect.
Even if solar forcing on climate is enhanced uniformly by positive feedback mechanisms, the amplification is no more than a factor of 2. So, the human warming factors are still greater (over 0.14K) by a factor of about 4.2. This was a point made by Woods- when he emphasized the recent(to that point) results of the University of Colorado SORCE project reinforced the hypothesis that anthropogenic greenhouse gases are the primary warming contributor.
As an aside here, or an extended footnote if you will, an interesting article by David Hathaway entitled: “What’s wrong with the Sun? (Nothing)”, appeared at the Nasa.gov site in June of 2008. Hathaway noted that examination of the interplanetary magnetic field (IMF) activity (to that time) supported the ‘nothing wrong’ conclusion and showed that while the sunspot number may be low, IMF activity this solar cycle appeared to be increasing as expected, with solar maximum predicted for 2010.
Given that there are zero spotless days so far this month (6 for the year), and rapidly growing spot groups emerging even as I write, this is something we need to attend to. However, I do think Hathaway is a bit premature in his maximum projection, which I don’t envisage until late 2012-early 2013 at the earliest. But who knows? Just about every solar physicist who’s made forecasts this cycle has been wrong thus far!
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