From NASA’s website (h/t to David Archibald)
By Adam Voiland
NASA’s Earth Science News Team
Two satellite instruments aboard NASA’s Solar Radiation & Climate Experiment (SORCE) mission — the Total Solar Irradiance Monitor (TIM) and the Solar Irradiance Monitor (SIM) — have made daily measurements of the sun’s brightness since 2003.
The two instruments are part of an ongoing effort to monitor variations in solar output that could affect Earth’s climate. Both instruments measure aspects of the sun’s irradiance, the intensity of the radiation striking the top of the atmosphere.
Instruments similar to TIM have made daily irradiance measurements of the entire solar spectrum for more than three decades, but the SIM instrument is the first to monitor the daily activity of certain parts of the spectrum, a measurement scientists call solar spectral irradiance.
In recent years, SIM has collected data that suggest the sun’s brightness may vary in entirely unexpected ways. If the SIM’s spectral irradiance measurements are validated and proven accurate over time, then certain parts of Earth’s atmosphere may receive surprisingly large doses of solar radiation even during lulls in solar activity.
“We have never had a reason until now to believe that parts of the spectrum may vary out of phase with the solar cycle, but now we have started to model that possibility because of the SIM results,” said Robert Cahalan, the project scientist for SORCE and the head of the climate and radiation branch at NASA’s Goddard Space Flight Center in Greenbelt, Md.
Cahalan, as well as groups of scientists from the University of Colorado at Boulder and Johns Hopkins University, presented research at the American Geophysical Union meeting in San Francisco in December that explored the climate implications of the recent SIM measurements.
Cahalan’s modeling, for example, suggests that the sun may underlie variations in stratospheric temperature more strongly than currently thought. Measurements have shown that stratospheric temperatures vary by about 1 °C (1.8 °F) over the course of a solar cycle, and Cahalan has demonstrated that inputting SIM’s measurements of spectral irradiance into a climate model produces variations of that same magnitude.
Without inclusion of SIM data, the model produces stratospheric temperature variations only about a fifth as strong as would be needed to explain observed stratospheric temperature variations. “We may have a lot more to learn about how solar variability works, and how the sun might influence our climate,” Cahalan said.
Measuring Variation
As recently as the 1970s, scientists assumed that the sun’s irradiance was unchanging; the amount of energy it expels was even called the “solar constant.” However, instruments similar to TIM and SIM have made clear that the sun’s output actually fluctuates in sync with changes in the sun’s magnetic field.
Indeed, TIM and its predecessor instruments, whose records of irradiance began in 1978, show that the sun’s output varies by about 0.1 percent as the sun cycles through periods of high and low electromagnetic activity every eleven years or so. In practice, this cycling means the sun’s brightness, as measured by TIM, goes up a bit when large numbers of sunspots and accompanying bright spots called faculae are present on the sun, yet goes down slightly when sunspots and faculae are sparse, like they have been in the last few years as the sun has gone through an unusually quiet period.
However, there is a critical difference between the SIM and TIM, explains Jerry Harder, the lead SIM instrument scientist and a researcher at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado in Boulder. While the TIM lumps all wavelengths — including infrared, visible, and ultraviolet light — into one overall measurement, the SIM isolates and monitors specific portions of the spectrum.
Notably, this makes SIM the first space-based instrument capable of continuously monitoring the visible and near-infrared portion, parts of the spectrum that are particularly important for the climate. SIM also offers the most comprehensive view of the individual components that make up the sun’s total solar irradiance to date.
Some of the variations that SIM has measured in the last few years do not mesh with what most scientists expected. Climatologists have generally thought that the various part of the spectrum would vary in lockstep with changes in total solar irradiance.
However, SIM suggests that ultraviolet irradiance fell far more than expected between 2004 and 2007 — by ten times as much as the total irradiance did — while irradiance in certain visible and infrared wavelengths surprisingly increased, even as solar activity wound down overall.
The steep decrease in the ultraviolet, coupled with the increase in the visible and infrared, does even out to about the same total irradiance change as measured by the TIM during that period, according to the SIM measurements.
The stratosphere absorbs most of the shorter wavelengths of ultraviolet light, but some of the longest ultraviolet rays (UV-A), as well as much of the visible and infrared portions of the spectrum, directly heat Earth’s lower atmosphere and can have a significant impact on the climate.
Climate Consequences?
Some climatologists, including Judith Lean of the United States Naval Research Laboratory, Washington, remain skeptical of the SORCE SIM measurements. “I strongly suspect the SIM trends are instrumental, not solar,” said Lean, noting that instrumental drift has been present in every instrument that has tracked ultraviolet wavelengths to date.
“If these SIM measurements indicate real solar variations, then it would mean you could expect a warmer surface during periods of low solar activity, the opposite of what climate models currently assume,” said Gavin Schmidt, a climate modeling specialist at NASA’s Goddard Institute for Space Studies in New York City.
It would also imply that the sun’s contribution to climate change over the last century or so might be even smaller than currently thought, suggesting that the human contribution to climate change may in turn be even larger than current estimates.
However, the surprising SIM measurements correspond with a period of unusually long and quiescent solar minimum that extended over 2007 to 2009. It may not be representative of past or future solar cycles, solar scientists caution.
Researchers will surely continue puzzling over the surprising SIM results for some time, but there is already considerable agreement on one point: that the need for continuous SIM and TIM measurements going forward has grown more urgent.
Modeling studies are showing that our climate depends critically on the true solar spectral variations. “If we don’t have the instruments up there to watch this closely, we could be arguing about spectral irradiance and climate for decades,” said Cahalan.
A new TIM instrument is slated to launch on the Glory satellite this February, but a replacement for the SORCE SIM instrument — called the Total and Spectral Solar Irradiance Sensor (TSIS) — likely won’t fly until 2014 or 2015. This could create a gap between the current SIM and its replacement, a situation that would present a significant obstacle to identifying any possible longer-term trend in solar spectral irradiances, and thus to nailing down the sun’s role in long-term climate change.
“Both instruments — TIM and SIM — are absolutely critical for understanding how climate works. We neglect either of them at our peril,” said Cahalan.
Solar activity – including sunspots and accompanying bright areas called faculae – vary over the course of a solar cycle and affect solar irradiance. Credit: NASA
Related Links:
SORCE Website
http://lasp.colorado.edu/sorce/index.htm
AGU Session: Solar Variability and Climate
http://www.agu.org/cgi-bin/sessions5?meeting=fm10∂=GC13E&maxhits=400
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Additional information:
Leif Svalgaard writes in email:
This is legit.
It is a confusing graph. It shows how much the spectral emission has
changed between 2004 and 2007. Since solar activity was decreasing one
expected UV to decrease. Instead it increased. The increase was offset
by a decrease in IR, leaving TSI almost constant. That the near UV
goes up when solar activity goes down I pointed out some time ago
[before the LASP people noticed it], see the lower two panels of
http://www.leif.org/research/Erl70.png (provided below)
There are all kinds of ramifications, see the talks in Session 4 at:
http://lasp.colorado.edu/sorce/news/2010ScienceMeeting/agendas.html#speakers
Ferdinand Engelbeen says:
December 22, 2010 at 2:42 pm
Next Steps:
Include stratospheric chemistry & circulation (see Haigh, also Stolarski)
Which are not included in the first runs???
There are models and models. The models discussed here are ad-hoc ‘what-if’ models trying to understand recent observations. Not the massive climate models that take months to run on super computers.
The issue is not if the models are any good, but just the claim by some that the models didn’t even try to include solar effects. I’m not defending the models as such, just pointing out that these things are not ignored.
BTW, here is Harder’s talk: http://www.agci.org/library/presentations/about/presentation_details.php?recordID=17442
It would be useful to see data of variance of all IR bands including thermal IR, as it provides as much heating as the visible band does. Heating from UV is small in comparison.
Ulric Lyons says:
December 22, 2010 at 3:35 pm
including thermal IR
What is ‘thermal IR’?
Leif Svalgaard says:
December 22, 2010 at 3:44 pm
What is ‘thermal IR’?
http://en.wikipedia.org/wiki/Infrared
http://ber.parawag.net/images/Atmospheric_Absorption_Bands.jpg
Ulric Lyons says:
December 22, 2010 at 4:15 pm
“What is ‘thermal IR’?”
http://ber.parawag.net/images/Atmospheric_Absorption_Bands.jpg
Thanks, one learns something new everyday.
Leif Svalgaard says:
December 22, 2010 at 4:53 pm
“What is ‘thermal IR’?”
http://ber.parawag.net/images/Atmospheric_Absorption_Bands.jpg
Thanks, one learns something new everyday.
Then, on the other hand, the solar input at those wavelengths is very small. The ‘thermal’ refers to what the Earth puts out.
Stephen Wilde says: December 22, 2010 at 11:16 am
I think I’m right in saying that the level of solar activity is in the models just as Leif says but it is limited to simple TSI which changes hardly at all.
What is not in the models is any accurate representation of changes in the composition of photons, wavelengths and particles coming from the sun. That is what this article is just beginning to consider.
I agree. What I find digestively unpalatable is Schmidts remark. If these data are contrary to the assumptions of the models, then he jumps to the illogical conclusion essentially, that it’s warming worse than expected. However, from what Willis observed in his recent post concerning the assumed factors in models, and the divergence in observations from the model output, I deduce an even greater increase in model uncertainty. In other words, the models incorrectly account for the differences in wavelength effect, probably with an inverted effect.
Tim Clark says:
December 22, 2010 at 5:40 pm
the assumed factors in models
Educate me about what those assumed factor are. As I understand it, the climate models integrate a set a differential equations describing the physics [as we know it] governing the climate. No factors need be assumed other than known fundamental physical constants. If I’m missing something, please tell me what those ‘factors’ might be and how you deduced that there are such factors. Did you study the source code carefully or what?
From Willis E.’s post on 12/20/2010. Excerpt:
To try to understand the GISSE model, I got the forcings used for the GISSE simulation. I took the total forcings, and I compared them to the GISSE model results. The forcings were yearly averages, so I compared them to the yearly results of the GISSE model. Figure 2 shows a comparison of the GISSE model hindcast temperatures and a linear regression of those temperatures on the total forcings.
And assumptions are exactly what this entire thread is all about. Model calculations based on assumed solar uv output.
“If these SIM measurements indicate real solar variations, then it would mean you could expect a warmer surface during periods of low solar activity, the opposite of what climate models currently assume,” said Gavin Schmidt, a climate modeling specialist at NASA’s Goddard Institute for Space Studies in New York City.
But then, who am I to argue with Gavin.
And closer to the point, if the models use physics as we know it and yet are demonstrably falsified by observations (there have been many, many threads here and elsewhere illustrating the divergence of temps and the model ensemble output), then you tell me what is incorrect in the models, the physics of CO2, adiabatic lapse rate, well-mixed atsmosphere, etc.
Tim Clark says:
December 22, 2010 at 6:23 pm
To try to understand the GISSE model, I got the forcings used for the GISSE simulation.
These are not ‘assumed factors’, but represent the values of the input variables describing the past, solar radiation, volcanism, etc.
Tim Clark says:
December 22, 2010 at 6:50 pm
then you tell me what is incorrect in the models, the physics of CO2, adiabatic lapse rate, well-mixed atsmosphere, etc.
Perhaps the notion that the climate is predictable at all.
Tim Clark says:
December 22, 2010 at 6:23 pm
“To try to understand the GISSE model, I got the forcings used for the GISSE simulation.”
Go here and read about GISS http://data.giss.nasa.gov/modelE/transient/climsim.html
LazyTeenager says:
December 22, 2010 at 8:45 am
“TSI is measured to be constant; no assumptions required.”
Top of atmosphere only. At the bottom of the column it fluctuates tremendously. Antarctica is the least variable. And even at TOA it is not constant but rather the measured variation is small and assumed to be insignificant. However, this data indicates that while TSI variation is small individual frequency bands vary out of phase with each other by a significant amount and where they mostly cancel each other due to being 180 degrees out of phase leaving TSI almost unchanged. Since different components of the atmosphere respond differently to different frequency domains it becomes significant in its effect on climate.
Mike Borgelt says:
December 22, 2010 at 2:59 pm
“I thought the mechanism was that the surface gets heated by that radiation which then heats the lower atmosphere by conduction and convection.”
The sun heats the ocean. The ocean heats the atmosphere. It heats it by conduction, convection, condensation, and radiation. Don’t forget the upwelling radiation is mostly all thermal infrared where water vapor absorbs very well and to a much lesser extent the non-condensing greenhouse gases CO2 and methane.
Leif Svalgaard says on December 22, 2010 at 6:58 pm
Surely it is predictable within a reasonably narrow range, say ~20 C.
Dave Springer says:
December 22, 2010 at 8:56 pm
Yes Dave I know that but the way the sentence read it implied that incoming shortwave visible and IR was directly absorbed by the atmosphere, thus heating it which isn’t the major mechanism in the lower tropopause.
Richard Sharpe says:
December 22, 2010 at 9:06 pm
Surely it is predictable within a reasonably narrow range, say ~20 C.
To be useful, the range must be much narrower, say ~1 C. Your 20 C is not reasonable.
@Tim Clark says:
December 22, 2010 at 6:40 pm
We have a problem with the definition of low solar activity, the solar wind speed and temperature gets overlooked.
@Leif Svalgaard says:
December 22, 2010 at 5:01 pm
My original point was about variation of all bands of IR, not just thermal.
And what happens to the plasma heat at the Earth`s bowshock ?
Leif Svalgaard says: If they mean that, then there would be nothing earth-shaking about the UV, it just behaved as expected. What do y’all think?
I think we need a better understanding of what they are saying vs what they are graphing. Is there a way BOTH can be right?
So I followed the link in the screencap you made to:
http://lasp.colorado.edu/lisird/sorce/sorce_ssi/ts.html
and played with it a little. At the 308.5 you used, UV rises. BUT, at 300 it is darned near flat. And, at 250, it’s dropping like a rock.
So, my take on things is:
1) You are right, lousy job of presentation of findings.
2) Don’t use 308.5 to test his words 😉 It’s 250 that drops…
footnote: Need to learn to do screencaps on PC with MS Windoz…
Given this, I’d say that UV does drop and in part of the band where your chart shows absorption / heating (IFF I’ve read it correctly and the “O3 band” is showing warming via that whiter spot). I’d further speculate that this has implications for ozone, but don’t know what those would be…
I was about to assert that 308+ would show rises, but did a ‘spot check’ on 400 just to make sure I wasn’t leaping to unwarranted conclusions, and fell off a cliff of conclusion… 400 is also dropping while 700 makes a “hump’ of rising then falling.
OK, we’ve got a complex distribution of variation by frequency. So the paper is correct to say “UV Dropped” but very unclear about exactly WHICH UV and does the average as a whole drop (and in what bands and with what ‘shapes’ and…)
BTW, this is in keeping with what my skin has reported. I’ve had a much lower incidence and severity of sunburn the last couple of years. ( I have ‘the Redhead Gene’, so I sunburn if I’m out at high noon for more than 20 minutes in the summer. I’ve been out MUCH longer with no issue in the last couple of years. The UV that causes me to burn is definitely reduced.)
Hope this helps, and may folks have fun playing with different wavelengths and making a proper 3 D chart out of things…
E.M.Smith says:
December 23, 2010 at 3:15 am
At the 308.5 you used, UV rises. BUT, at 300 it is darned near flat. And, at 250, it’s dropping like a rock.
1) You are right, lousy job of presentation of findings.
2) Don’t use 308.5 to test his words 😉 It’s 250 that drops…
You need to pay attention to the amount of UV at each frequency. For 308.5 nm it is 0.650 W/m2/nm, but for 250 nm the energy is 11 times less, only 0.056 W/m2/nm. So it doesn’t matter much that that tiny bit is dropping.
What heats the atmosphere is the band between 242 and 310 nm:
http://www.leif.org/research/Solar-Heating-UV.png
It is a bit tedious but you have to add up the energy for each nm going up from 242 to 310, and look at how that varies: http://www.leif.org/research/Erl70.png
This is then the trend in the UV that heats the atmosphere.
Ulric Lyons says:
December 23, 2010 at 2:37 am
And what happens to the plasma heat at the Earth`s bowshock ?
Slides off down the tail. Does not heat the Earth.
It is not about what heats the atmosphere…this is just a smokescreen.
EUV (26-34nm) is where the action is. EUV is the major contributor when considering Thermsophere height and ozone creation. However small this part of the spectrum is in relation to TSI, it has huge climate ramifications.
EUV is not rising like the graphs shown, in fact the levels this minimum are 15 % lower than the previous minimum…at present the EUV levels are very low which correlate with the negative ocean and atmosphere oscillations.