Understanding the acceleration of solar wind particles

[Michael Mozina]

I would like to understand the "standard" explanation for the acceleration of solar wind particles as they leave the solar surface. Could someone help me out? I'm specifically interested in explaining this sort of image from the European Space Agency.

http://a1862.g.akamai.net/7/1862/14448/v1/esa.download.akamai.com/13452/qt/Atmospheric_drag.mov
http://www.esa.int/esaCP/SEMS9773R8F_index_1.html#subhead1

I can think of a way to explain this behavior using a non standard model, but I was curious how one might try to explain the observation of solar wind acceleration in standard theory.

 

[pixel01]

Light can exert pressure on objects. The intensity of light on the surface of the Sun is enormous so it exerts pressure on charged particles, thus accelerate them out.

 

[Garth]

There is also an enormous amount of energy contained by MHD in the magnetic field lines associated with sun spots and prominences. When the field lines disconnect, because the build up of energy has grown too strong, then plasma previously constrained by those field lines burst out with great speed and energy.

Garth

 

[Astronuc]

There's certainly radiative pressure (i.e. interaction with photons) and MHD effects (magnetic pressure proportional to B² and accelerations due to $\frac{\partial{B}}{\partial{t}}$).

 

[Michael Mozina]

Light can exert pressure on objects. The intensity of light on the surface of the Sun is enormous so it exerts pressure on charged particles, thus accelerate them out.

Hmmm. I'm skeptical of that idea. The solar wind is composed of a lot of protons, non ionized hydrogen atoms, helium atoms, carbon atoms, oxygen atoms, and even heavier elements. I'm in the middle of finishing some programming for a corporate client at the moment, but I think if you sit down with the math, you won't come up with anywhere near enough energy that way to offset the force of gravity. It seems to me that any photon force of that magnitude would dislodge electrons galore.

 

[Michael Mozina]

There is also an enormous amount of energy contained by MHD in the magnetic field lines associated with sun spots and prominences. When the field lines disconnect, because the build up of energy has grown too strong, then plasma previously constrained by those field lines burst out with great speed and energy.

Garth

Well, there are certainly bursts of energy that cannot ever be explained by photon pressure such as this event.

http://www.space.com/scienceastronomy/050524_solar_flare.html

Pretty much all of the mathematical presentations of electron flow treat magnetic lines as a complete continuum. They can't make and break connection. Hannes Alfven was quite outspoken against the idea of magnetic reconnection as an energy source for such flare type events. Could you briefly explain the physics behind that kind of any event, and how it might differ from say an electrical reconnection event? How would that physically play out inside the plasma flows of the atmosphere, and how would you use a magnetic reconnection theory to explain say a single coronal loop that contains plasma in the millions of degrees?

I will grant you that the magnetic field strengths of these loops are quite large.

 

[pixel01]

Hmmm. I'm skeptical of that idea. The solar wind is composed of a lot of protons, non ionized hydrogen atoms, helium atoms, carbon atoms, oxygen atoms, and even heavier elements. I'm in the middle of finishing some programming for a corporate client at the moment, but I think if you sit down with the math, you won't come up with anywhere near enough energy that way to offset the force of gravity. It seems to me that any photon force of that magnitude would dislodge electrons galore.

The solar wind as I know, consists of mainly charged particles (plasma), of which, mainly protons. Hydrogen is more than 70% of the Sun afterall. Photons are not considered 'solar wind'. My idea is just one guess. There are other things such as magnetics driven bursting etc.. that scientists do not know for sure.

 

[Michael Mozina]

The solar wind as I know, consists of mainly charged particles (plasma), of which, mainly protons. Hydrogen is more than 70% of the Sun afterall. Photons are not considered 'solar wind'. My idea is just one guess. There are other things such as magnetics driven bursting etc.. that scientists do not know for sure.

http://prola.aps.org/abstract/PRD/v22/i1/p93_1

I've been trying to figure out how a photon would even begin to interact with a proton. The more I read, the more skeptical I become about the idea of photons 'pushing' the charged particles and causing them to accelerate. I can understand how the charged particles like protons could be attracted to something external, like a more negatively charged heliosphere, and thereby pickup momentum. I can't see how photons (mostly low energy photons in the visible spectrum) could "push" a proton out into space and cause them to accelerate.

 

[pixel01]

http://prola.aps.org/abstract/PRD/v22/i1/p93_1

I've been trying to figure out how a photon would even begin to interact with a proton. The more I read, the more skeptical I become about the idea of photons 'pushing' the charged particles and causing them to accelerate. I can understand how the charged particles like protons could be attracted to something external, like a more negatively charged heliosphere, and thereby pickup momentum. I can't see how photons (mostly low energy photons in the visible spectrum) could "push" a proton out into space and cause them to accelerate.

Light can exert pressure of course. Perhaps you have heard about 'solar sail'. The Sun gives off not only visible light but light at shorter wavelength as well. What's more, the pressure depends mostly on the flux of light or intensity which must be very high right on the Sun's surface.
After all, a star is in a stable condition (not colapses) only because of this pressure, which balances the gravity, I think.

 

[Wallace]

I've been trying to figure out how a photon would even begin to interact with a proton.

Compton scattering for one. Usually Compton Scattering refers to interactions between electrons and photons but there is no reason that photons shouldn't scatter off free protons, it's just that it's more common to have free electrons, so we normally deal with that situation.

I'm not sure why you think that photons shouldn't interact with protons?

 

[Michael Mozina]

Compton scattering for one. Usually Compton Scattering refers to interactions between electrons and photons but there is no reason that photons shouldn't scatter off free protons, it's just that it's more common to have free electrons, so we normally deal with that situation.

Doh! You're absolutely right. I forgot about Compton scattering because I typically associate that phenomenon with scattering from electrons, but there is in fact a wealth of information about Compton scattering involving protons.

I'm not sure why you think that photons shouldn't interact with protons?

I guess my primary concern with this idea is that a proton is a relatively massive object. It's not nearly as easy to "push" a proton as it would be to accelerate an electron that way. I just can't imagine that there is enough pressure from something like Compton scattering to explain how protons not only escape the gravity well of the sun, but accelerate as well.

You are correct however about Compton scattering being an obvious method of interaction. Thanks for pointing that out.

 

[SpaceTiger]

I would like to understand the "standard" explanation for the acceleration of solar wind particles as they leave the solar surface.

I don't think this is a solved problem, but the following paper reviews some of the theories:

http://arxiv.org/abs/astro-ph/0409724"

 

[Michael Mozina]

http://science.nasa.gov/headlines/y2007/06dec_xrayjets.htm?list20332
http://www.npr.org/templates/story/story.php?storyId=16981177

It seems we're on a very timely topic. New data from the Hinode program tends to point us toward a very different energy source behind some of the solar wind acceleration we observe.