Sunspots and their relationship to active regions.

[michaelmozina]

While there is not necessarily a one to one relationship between sunspots and coronal loops, there does seem to be a strong correlation between the two. The mainstream theories suggest however that sunspots are *cooler* regions in the photosphere (and there is evidence this is true). The problem however is that sea temperatures on Earth *increase* during active phases with lots of sunspot activity, and coronal loop activity also increases significantly. This would suggest that the excess heat received on Earth is directly or indirectly related to these million degree coronal loop events, not the sunspots themselves. I'm also curious about where folks believe the base of the coronal loops begin, underneath or above (or both) of the photosphere. There seems to be some debate about this based on the images I've found on NASA websites, and articles I've read related to "solar moss" activity.

The one thing I find most "hard to understand" about mainstream theory is the notion that magnetic fields somehow cause the photosphere to "cool" and form a "sunspot', but at the same time these active regions generate more energy outside of the sunspot (and more energy reaches Earth), and these loops heat plasma to 10's of millions of degrees in the corona. How does that work exactly?

 

[Saiph]

The idea behind sunspots, in mainstream theory, is that is the location of a 'tangle' in the magnetic field. This could very well be the source of many coronal loops, as the sunspots are believed to be a place where the magnetic field pops out (or into) the photosphere in unusually high densities.

The reason the sunspot itself is cooler than the surrounding region is dependent upon how the photosphere gets it's energy from the interior. This is believed to be via convection (helio-siesmology supports this idea btw). When the convection current rises and finds this magnetic tangle, it gets diverted, shut down, disturbed, etc. The end result is less efficient energy transport to that particular region, so it cools slightly compared to it's surroundings.

This cooling mechanism is independent from any heating mechanism any coronal loops may have on the corona. And we don't entirely understand how the coronal loops heat the corona in the first place, but my guess is that's it's due in part to the loops moving rapidly through it, due to the suns rotation and the loop's changing geometry.

 

[michaelmozina]

The idea behind sunspots, in mainstream theory, is that is the location of a 'tangle' in the magnetic field.

That would technically be true as I see things as well.

This could very well be the source of many coronal loops, as the sunspots are believed to be a place where the magnetic field pops out (or into) the photosphere in unusually high densities.

I tend to agree that the loop originate beneath the photosphere. This brings me I suppose the the notion of 'solar moss', and articles I've read on this topic. It seems to me that the base of the loops, and also the solar moss activity begin underneath the photosphere.

When you talk about "density" here are you referring to the strength of the magnetic field, the density of the plasma in the loops, or a combination of both of these things?

The reason the sunspot itself is cooler than the surrounding region is dependent upon how the photosphere gets it's energy from the interior. This is believed to be via convection (helio-siesmology supports this idea btw).

I agree that convection is bringing heat to the surface of the photosphere, but those same heliosiesmology studies suggest that the plasma flows "flatten out" about 4800KM, and show a "stratification subsurface" located about about .995R which varies with the solar cycle.

http://arxiv.org/abs/astro-ph/0510111

When the convection current rises and finds this magnetic tangle, it gets diverted, shut down, disturbed, etc. The end result is less efficient energy transport to that particular region, so it cools slightly compared to it's surroundings.

I suppose the part that doesn't seem to "add up" to me is the fact that the higher energy wavelengths require that these loops reach millions (sometimes up to 20 million) degrees Kelvin to be able to emit such photons. That seem consistent with 'hot' plasma, but not cooler regions. From a visual perspective, the sunspots themselves also seem to have a distinct edge (seen in penumbral filaments) that stop emitting light at particular depth, including all the edges of the sunspot. I have however seen plenty of evidence that these regions do show evidence of cooler plasma, and that must be "explained" in some way shape or form.

This cooling mechanism is independent from any heating mechanism any coronal loops may have on the corona.

Hmm. It might make sense to suggest that coronal loops "carry away" some of the heat and distribute it in the corona, so I'm not sure how you're certain that they are "independent" processes.

And we don't entirely understand how the coronal loops heat the corona in the first place, but my guess is that's it's due in part to the loops moving rapidly through it, due to the suns rotation and the loop's changing geometry.

The one thing that seems clear to me about this sunspot/coronal loop relationship is that there are many times where "activity" can be observed in 195A, and nothing much is happening as it relates to sunspot activity. All sunspots however tend to be congregated, in and around these active regions. The may not be directly related, but there is an "indirect" relationship between them. The other thing that seems rather clear is that these active regions are emitting energy that is consistent with plasma that has been heated to millions of degrees, and the energy received on Earth *increases* during sunspot activity and active solar cycles. There is excess energy being released in the active part of the solar cycle, and the sunspots are somehow related to this high energy activity.

 

[Saiph]

Hmm. It might make sense to suggest that coronal loops "carry away" some of the heat and distribute it in the corona, so I'm not sure how you're certain that they are "independent" processes.

That may be part of what's happening, but it may not. The sunspots may be more of a side effect of coronal loops, not an integral part of the energy transport. It all depends on where the energy for the loops is coming from. If they're created by the gyrations of the plasma currents in the photosphere and deeper in the sun...their energy has nothing to do (directly anyway) with sunspot temperature.

As for cool regions and million degree coronas, don't forget there is a distinct difference between 'heat' and 'temperature' in physics. The corona is incredibly hot, but there isn't much heat (actual energy) there because it's such a low pressure area (few atoms).

 

[michaelmozina]

That may be part of what's happening, but it may not. The sunspots may be more of a side effect of coronal loops, not an integral part of the energy transport. It all depends on where the energy for the loops is coming from. If they're created by the gyrations of the plasma currents in the photosphere and deeper in the sun...their energy has nothing to do (directly anyway) with sunspot temperature.

I would tend to agree with you on all those points. In fact I do not personally believe that they are directly related either, and sunspot temperatures are not directly related to the coronal loop activity either IMO.

As for cool regions and million degree coronas, don't forget there is a distinct difference between 'heat' and 'temperature' in physics. The corona is incredibly hot, but there isn't much heat (actual energy) there because it's such a low pressure area (few atoms).

Well, keep in mind that the total energy inside the filaments of an ordinary plasma ball is related to the total circuit energy, not necessarily the heat of the plasma in the ball. The same is true of lightening here in the Earth's atmosphere. Something, some energy source is capable of making plasma emit gamma and x-rays in the Sun's atmosphere. Such emissions in the Earth's atmosphere are directly related to electrical discharges in the Earth's atmosphere. The atmosphere itself may not have much heat, and the temperature outside the discharge may be quite cool. I certainly would not want to be standing inside the discharge however.
http://www.nasa.gov/vision/universe/sol ... i_tgf.html

 

[michaelmozina]

This is a very interesting early paper on this topic

http://articles.adsabs.harvard.edu//ful ... 5.000.html

I recently ran across this early paper on the topic of coronal loops and high energy emissions. I think you'll appreciate it too.

 

[michaelmozina]

FYI, today's SOHO images show the rather tenuous link between active regions seen in 195A and other iron ion wavelengths and sunspots. Two new active regions have formed in the southern hemisphere over the last few days and a couple of small sunspots can now be observed near only one of the two active regions, whereas the other one is currently not generating any sunspots. This could obviously change over time.

http://sohowww.nascom.nasa.gov/data/rea ... t_195/512/
http://sohowww.nascom.nasa.gov/data/rea ... i_igr/512/