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online365
2013-Nov-07, 11:54 AM
My understanding is that fluid dynamics in the convective zone generate electric fields and are what drives the magnetic fields which are then pushed up into the photosphere by differential rotation.

Question is are electric fields or currents also present in the plasma filled magnetic and coronal loops that can be seen on the surface?

If so,

1) can we detect the presence of them though some telescopic means or can they be expressed in formulas?
2) Do they have a positive/negative charge or does the plasma neutralize them?

Thanks!

tusenfem
2013-Nov-07, 01:06 PM
There is basically no way of measuring electric fields on the Sun unlike e.g. components of the magentic field on the surface of the Sun.

Electric fields and currents are present inside and outside of the surface of the Sun. The only way of having magnetic fields in a plasma is through electric currents. But as the process of the dynamo action is rather difficult to envision in electric fields and currents, the simpler view of magnetic loops and plasma velocities is used to show how magnetic fields can grow.

For magnetic fields we can use magnetograms, where we make use of the Zeemansplitting of certain spectral lines to obtain the strength of the magnetic field and the polarization of the emission (left- or right-handed) gives the direction of the magnetic field, into or out of the Sun.

The presence of currents we can deduce by looking at the structures we see in solar magnetic loops. Using the very good images from SDO of magnetic loops one can deduce how the field lines are twisted and that shows that there are currents flowing along the magnetic field.

Electric field also show themselves through accelerated particles in solar flares, where magnetic reconnection occurs.

For the last question, electric fields and current do not have positive/negative charge, the can be created by or are generated through different/moving charges. All in all, over the whole Sun the total electrical charge is zero (not completely zero probably, but that goes to deep into physics for these questions and I would have to look up the reference again). On smaller scales electric fields can exist and even charged regions can exist. However, the mobility of the different charges in the plasma will quickly try to make them disappear.

online365
2013-Nov-07, 02:38 PM
Thanks! Speaking of charged regions, do you know what the latest is on the mechanism responsible for SW acceleration ? There were a couple of older articles I came across: "LARGE-SCALE ELECTRIC-FIELDS IN SOLAR-FLARE REGIONS" and "CHROMOSPHERIC HEATING BY ELECTRIC CURRENTS INDUCED BY FLUCTUATING MAGNETIC ELEMENTS" which I believe were studies done to find a root cause for SW acceleration. However I ran across a new NASA press release titled "Solar Wind Energy Source Discovered" (March 8, 2013) which now heralds ion cyclotron waves as being responsible. Since these waves are essentially protons oscillating around a magnetic field, would that constitute an electric current?

tusenfem
2013-Nov-07, 04:00 PM
The solar wind acceleration mechanism(s), the eternal enigma ...

Alfvén waves, sound waves, nano-flares, cyclotron waves, .... and so you can go on.

The problem with the solar wind is definitely not "is there a mechanism" but "there are too many mechanisms" all of which can heat and accelerate the solar wind and many of which have been found, so in all I think it is a many-mechanism process, we only have to understand the energy distribution among those many processes.

So there I cannot give you a final answer, but often the problem is the person or group working on mechanism 1 and tweak it so that it can work, but then mechanism 2 of the other group can also be tweaked that it works (in simulations naturally) but how about 1 and 2 together etc.

All the serious mechanisms together have ample energy to heat the corona and accelerate the solar wind, several times the energy.

About the cyclotron waves, you have to be careful there, the waves themselves are not protons gyrating around the magnetic field, those are the source of the cyclotron waves. Whenever the perpendiclular temperature of the protons, with respect to the magnetic field, is greater than the parallel temperature, the plasma is unstable for cyclotron wave generation. The protons interact with the waves in the background turbulence at the right frequency, and then the protons lose energy whereas the wave gains energy and propagates along the field. Further out, in the frame of the wave, there can be "thermal" protons, which can take the energy of the wave again, thereby gaining perpendicular energy. That is a way of transporting energy from close to the Sun to further away.

The gyrational motion of the protons does contribute to a current perpendicular or around the magnetic field line, and will change the magnetic field strength around which they are gyrating.

online365
2013-Nov-07, 04:31 PM
Sounds much like the neutrino oscillation studies...many mechanisms... just have to understand the distribution.

So I take it you are using the terms temperature and energy interchangeably when describing cyclotron waves correct? eV, KeV, etc..?

What are the "waves" exactly? Waves of ions (electrons) or more like a heat wave? What frequencies do these wave operate at?

Jeff Root
2013-Nov-07, 09:37 PM
I just read the other day (probably in an article linked from a
post here on CQ) that pretty much all bodies are very slightly
positively charged, surrounded by a very slight excess of
negative electrons.

-- Jeff, in Minneapolis

online365
2013-Nov-07, 11:43 PM
Jeff when you say "all bodies" what do you mean exactly? Magnetic features on the sun? Plasma?

Jeff Root
2013-Nov-08, 03:03 AM
Stars, planets, asteroids, rocks, spacecraft.

-- Jeff, in Minneapolis

tusenfem
2013-Nov-08, 07:39 AM
It rather depends on the environment the body is in.
A spacecraft around Earth in the sunlight will be positively charged, because of photoelectrons being kicked out of the surface by solar UV radiation.
A spacecraft around Earth in the shadow will be charged negatively because of inelastic collisions with electrons, which will stick to the surface.

tusenfem
2013-Nov-08, 07:48 AM
Sounds much like the neutrino oscillation studies...many mechanisms... just have to understand the distribution.


Ehhh what does sound like neutrino oscillations? I don't see the link.



So I take it you are using the terms temperature and energy interchangeably when describing cyclotron waves correct? eV, KeV, etc..?


Yes temperature or energy all "the same", naturally one can only talk about a temperature when the particle distribution is relaxed into a maxwellian.



What are the "waves" exactly? Waves of ions (electrons) or more like a heat wave? What frequencies do these wave operate at?


The waves are oscillations of the magnetic field, consider the magnetic field as a string that gets wiggled and the ions that rotate around it, drive one wiggle frequency up to higher amplitudes.
This is nothing like a heat wave, because that is something meteorological.
The frequencies of the waves are the ion cyclotron frequencies of the ions that gyrate around the magnetic field


f_{c,i} = \frac{q_i B}{m_i} \approx 0.01525 \frac{B {\rm [nT]}}{m_i {\rm [AMU]}}


see e.g. this paper of mine (http://esoads.eso.org/abs/2001JGR...10626033V) where cyclotron waves in the magnetic field data are used to identify the ion species that are coming from the surface of Europa.

Shaula
2013-Nov-08, 08:23 AM
Ehhh what does sound like neutrino oscillations? I don't see the link.
Indeed, there is only one mechanism for this in the Standard Model as far as I know. A mismatch between the eigenstates we observe and the mass eigenstate. So neutrinos are created in flavour eigenstates which are not pure mass eigenstates, meaning that they are superpositions of several mass eigenstates which can have different phases. As the neutrino wavefunction is propagated forwards the relative abundances of each flavour states changes with time, since different combinations of mass eigenstate will be observed as different combinations of flavour state.

online365
2013-Nov-08, 08:31 AM
Ehhh what does sound like neutrino oscillations? I don't see the link.

I was referring to your comment "The problem with the solar wind is definitely not "is there a mechanism" but "there are too many mechanisms" and how it reminded me of the research that went into neutrino oscillations. Not really referring to a particular study, just what I read about here http://www.talkorigins.org/faqs/faq-solar.html#_Toc430357863, Sorry about that..

I really appreciate all of the information you have presented to me here. It's a great help.

Shaula
2013-Nov-08, 09:22 AM
I was referring to your comment "The problem with the solar wind is definitely not "is there a mechanism" but "there are too many mechanisms" and how it reminded me of the research that went into neutrino oscillations. Not really referring to a particular study, just what I read about here http://www.talkorigins.org/faqs/faq-solar.html#_Toc430357863, Sorry about that..
OK I see where you are coming from. Originally when it was thought that neutrinos were massless there were several possible solutions to the Solar Neutrino Problem. It was not that there were loads of oscillation mechanisms, it was that oscillation was only one of many potential solutions to this problem. When oscillations were seen that pretty much won the argument - it was an observable mechanism that explained the deficit of electron neutrinos being seen. The major difference is that, as Tusenfem says, it si more likely for the Solar Wind that it is a combination of mechanisms. It is less likely that, as for the Neutrino Problem, there will be one solution.

online365
2013-Nov-08, 10:50 AM
OK I see where you are coming from. Originally when it was thought that neutrinos were massless there were several possible solutions to the Solar Neutrino Problem. It was not that there were loads of oscillation mechanisms, it was that oscillation was only one of many potential solutions to this problem. When oscillations were seen that pretty much won the argument - it was an observable mechanism that explained the deficit of electron neutrinos being seen. The major difference is that, as Tusenfem says, it si more likely for the Solar Wind that it is a combination of mechanisms. It is less likely that, as for the Neutrino Problem, there will be one solution.

Yes my initial comment on that was a very condensed version of how I understood it. Thanks for your insight's!