The Solar Series: I Background | II: The notch filter | III: The delay | IV: A new solar force? (You are here) | V: Modeling the escaping heat. | VI: The solar climate model | VII — Hindcasting | VIII — Predictions
Implacably, the discovery of a notch suggests a delay of anything from 10 to 20 years but most likely 11 years. (Don’t miss the delay post — two very big important concepts out in two posts). The big mystery is what could cause such a long delay in the correlation of solar radiation with temperatures on Earth?
David and I spent months wondering “what on Earth” could drive it. There were many possibilities though none of them seemed to be able to respond with the right timing: A resonant slop in ocean circulation could absorb extra energy, but it was difficult to see how the timing would be so tight with solar peaks. Likewise changes in ice or land cover. Then there are lunar cycles of 9 – 18 years, potentially generating atmospheric standing waves, but they were not synchronous with the sun.
Given that marine life can produce aerosol particles or carbonyl sulphide, we wondered if blue green algae or phytoplankton were the key. I particularly liked the idea that life on Earth would evolve to try to take advantage of the little extra energy arriving at regular intervals. But it’s unlikely, though not impossible, that microbiology would act after an 11 year delay. They could respond in weeks or months — but that type of response would not produce “a notch” in the transfer function. I spent most of 2013 spotting tantalizing 8 – 12 year cycles in papers on everything from arctic tundra to jet streams. All of which were interesting, but none of which would sit quietly for 10 years and then spring to life.
In the end, the answer was so prosaic, so beautiful – of course, the only possibility for a delay so perfectly timed with solar cycles was within the sun itself. Have we been fooled by a language slip? “Peak” solar activity doesn’t mean a “peak” in magnetic activity, actually it’s the other way around.
Think about the timing: At the peak of the sunspot cycle, while the sun is producing its maximum solar irradiation, it turns out that the Sun’s magnetic field is collapsing through its weakest moment. (Marvel at Figure 1 below.) The solar radiation only varies a little through the cycle, but the dynamo of the solar magnetic field is undergoing profound changes — flipping in polarity from North to South or back again. This causes the notch.
We don’t know exactly how this collapsing magnetic field reduces the effect of solar radiation on Earth. One obvious candidate is Svensmark’s cosmic ray hypothesis. He theorized that during the months of the weakest magnetic field the Earth loses its shield against cosmic rays, seeding clouds. But the mystery force might be electrical, or work through UV, or be something else entirely. Nonetheless, it was a leap to finally connect so many studies.
(This was a memorable “aha” moment — We did enjoy!.) – Jo
Physical Interpretation of the Notch and Delay
[Logically this post belongs a little later in the series, but some people seem so interested in the physical interpretation of the notch and the delay that we’ll jump forward in the story a little for a bit. So please excuse me for dragging a couple of things in from left field while I explain this, but I am under editor’s orders.]
The notch was observed in the data, and the delay was inferred from the notch. But what are the physical explanations for the notch and the delay?
The biggest clue lies in the delay, which we’ll take here to be the most likely value of about 11 years, though it could be as low as 10 years or as high as 20 years in the curve fitting.
The delay in the solar model says that today’s temperatures are more influenced by the level of solar radiation 11 years ago than by the level either 5 or 25 years ago. So something to do with climate has a memory of 11 years; the delay is not simply due to a dissipative element, like a store of heat in the ocean that declines at a certain rate.
(The heat store of the oceans is almost certainly the main element in the low pass filter, which is a dissipative element with a time constant, but that is quite separate from the delay. If a dissipative element dominated the response to TSI then today’s temperatures would be more influenced by the TSI of 5 years ago than of 11 years ago, but it’s the other way around.)
As far as we know there is nothing on Earth with a memory spanning multiple years. But there is one climate actor with an 11 year clock—the Sun.
The Sun’s sunspot cycle has an average length of 11 years, although it varies from 8 to 14 years. The Sun’s full cycle is actually 22 years long on average, consisting of two consecutive sunspot cycles, one with the Sun’s magnetic field in each orientation.
Also, the notching suggests that there is a countervailing force that counteracts the TSI peaks in the global surface temperature. This countervailing force would have to synchronized to the TSI peaks. While it might be a force that reacts to the onset of a TSI peak, a simpler explanation is that it originates on the Sun like the TSI and is thus synchronized to the TSI. *
We will soon deduce from the solar model that the notch and the delay work by affecting the albedo of the Earth (the fraction of solar radiation that is reflected straight back out to space by clouds, snow, ice etc. without warming the Earth, about 30%). We will also find by looking at the proportional changes in solar radiation and albedo that over the last few decades that the effect on temperature of albedo modulation has been at least six times greater than the immediate heating effect of variation in solar radiation. So it appears the notch and delay are associated with a powerful indirect solar influence that modulates the Earth’s albedo.
It is important not to prejudge what this influence is, so let us call this influence “force X” for now. Therefore the existence of “force X” is formally proposed:
- If force X is larger, the Earth gets warmer.
- Changes in force X lag behind changes in solar radiation by the delay, which is most likely half of the full solar cycle, or 180°—force X and TSI are in anti-cycle. The delay is the time between peaks in sunspots, which averages 11 years but varies from 8 to 14 years.
- Force X affects the Earth’s temperature by changing its albedo.
- Force X increases when the Sun’s magnetic field is stronger, and is weakest when the Sun’s magnetic field is reversing its polarity.
This last property is because peaks in solar radiation and sunspots coincide with reversals in the Sun’s magnetic field, as shown in Figure 1.
The Sun’s magnetic field reverses polarity every sunspot cycle, about every 11 years, and it occurs just as the TSI and the number of sunspots are peaking. In the reversal, the Sun’s north pole gets swapped with its south pole, so the magnitudes of some aspects of the solar magnetic field go briefly to zero, and presumably all aspects of the various solar magnetic fluxes are at a minimum. For example, the magnitude of the solar polar magnetic shown in Figure 1 field drops to zero before rebounding as the polar field reverses polarity.
This synchronicity of peaks in solar radiation with troughs in force X accounts for the observed notching. Just as the TSI peaks the warming from force X is at a minimum, so the peak in the direct warming effect of TSI is counteracted by the trough in warming from force X. Presumably the combined influence of the peak in TSI and the trough in force X is less than the precision of the temperature record.
(By the way, it was Joanne who noticed the synchronicity of TSI peaks with magnetic field reversals and made the connection to the notch and delay.)
Although we can deduce its presence in the datasets, at this stage it is not known what force X is. We cannot measure some signal on an antenna pointed somewhere and say “that is force X”. Conversely, nearly every measured variable has been compared to temperature, so if someone was measuring force X they probably would have noticed by now.
The obvious candidate for force X is some aspect of the solar magnetic field that is responsible for deflecting cosmic rays so that they do not hit the Earth as often as they would otherwise. More cosmic rays hitting the Earth may create more microscopic cloud nuclei, which form more clouds, which reflect more solar radiation back into space, lowering the unreflected TSI entering the climate system and thus cooling the Earth’s surface. When the appropriate component of the solar magnetic field is stronger, it warms the Earth by protecting it from cooling cosmic rays. Thus, a solar magnetic field could modulate the albedo of Earth. When solar radiation peaks, force X is momentarily weak and the cosmic ray shields are down.
It is possible that force X is not related to cosmic rays. For instance force X might be electric and modulate the ozone in the Earth’s stratosphere, or otherwise affect the Earth’s atmosphere by some electrical connection. Solar magnetic fields are known to directly influence weather near the Earth’s poles, and may influence mid-latitudes via the global atmospheric electric circuit (Lam et al 2013). Or there may be solar influences which are not explainable yet (e.g. Sober 2010). Or it might be that solar UV modulates algae or plankton which in turn modulate albedo (Watts, 2014). Yoshimura in 1996 found that the TSI leads some index of the solar magnetic field by 10.3 years, and posited that the Sun could affect the Earth’s climate “through two channels”.
Or it might be more than one of the above.
While the effects on temperature of the tiny changes in the immediate heating effects of TSI are too small to explain the recent global warming, those tiny changes are a leading indicator of force X. Tremors in the near-constant level of solar radiation foretell what force X will do in 11 years’ time. Because TSI indicates what force X will do in about 11 years, the TSI record is also a record of future force X.
Force X has ten to twenty times more influence on temperatures on Earth than changes in the direct heating effect of TSI (a result we will show later). TSI no doubt has vastly more energy than force X, but the changes in TSI are proportionally very small. Indeed, the level of TSI was thought to be constant until satellites were able to measure it more closely and found minor variations, and it used to be called “the solar constant”.
Force X affects the albedo of Earth, affecting how much solar radiation gets reflected straight back out to space. Force X is like a tap, a small force controlling the much larger flow of solar radiation into the Earth’s climate system.
I know that “force X” sounds speculative, but this is where the trail has taken us. We observed the notch, deduced the delay, and the 11 year clock leads us to the Sun. We find some confirmation in the synchronicity of the peaks in TSI with the troughs in the Sun’s magnetic field, so force X has something to do with the solar magnetic field. The story isn’t complete until we know what force X is.
This is logical, but otherwise unsatisfactory because we have not actually found force X. Before “force X” can be named properly, we need a graph of something we can measure and that correlates very well with temperature. Until then we can only speculate with complicated higher-tech tools like transfer functions, delays, signals, and models.
Notch-delay solar project home page, including links to all the articles on this blog, with summaries.
* This paragraph added 23 June 2014.
Lam, M M; Chisham, G; Freeman, M P, “The interplanetary magnetic field influences mid-latitude surface atmospheric pressure”, Environmental Research Letters, 2013
Stober, Dan, The strange case of solar flares and radioactive elements, Stanford News, August 2010, http://news.stanford.edu/news/2010/august/sun-082310.html
Watts, Anthony, 2014, http://wattsupwiththat.com/2014/04/22/new-paper-finds-solar-uv-b-output-is-correlated-to-global-mean-temperature/
Svensmark, H., Bondo, T. and Svensmark, J. 2009. Cosmic ray decreases affect atmospheric aerosols and clouds. Geophysical Research Letters 36: 10.1029/2009GL038429. [Discussion CO2Science]
Svensmark, H. and Friis-Christensen, E. (2007) Reply to Lockwood and Fröhlich – The persistent role of the Sun in climate Forcing, Danish National Space Center, Scientific Report 3/2007 [PDF]
Yoshimura, H. (1996). Coupling of Total Solar Irradiance and Solar Magnetic Field Variations with Time Lags: Magneto-thermal Pulsation of the Sun. Astronomical Society of the Pacific, ASP Conference Series, Vol 95, pp. 601 – 608. [Article]