(Alfvén's) heliospheric current circuit - real or not?

[DeiRenDopa]

The motivation for this thread comes from a post by Zeuzzz, in a lengthy Science, Mathematics, Medicine, and Technology thread, here is the post.

Here is the relevant part of that post:

I have not linked to the heliospheric current sheet, apart from the one quote in this post, I have always linked to the heliospheric current circuit, I only quoted the heliospheric current sheet in that post as it was highly relevant to Alfvens model, and is the principle the heliospheric current circuit is based on.

Maybe a picture would grab your, an others, attention more, since you so far have not commented on the links I provided before in various journals on this; (in the above link)

http://www.plasma-universe.com/index...urrent_circuit

Heliospheric current circuit with the Sun as a unipolar inductor.

I am curious:

Since Alfvén first proposed this heliospheric current circuit, many decades ago now, the interplanetary medium (IPM) has been explored, in situ, by many space probes.

For example, Pioneer 10, Pioneer 11, Voyager 1, and Voyager 2 checked out the IPM a long way out, more or less in the Sun's equatorial plane (and Galileo and Cassini too, but not quite as far out).

And Ulysses, which was shut down only recently, explored the IPM way above and below that plane.

To what extent is the data received from the instruments on these spacecraft consistent with Alfvén's heliospheric current circuit model?

In the community of scientists who study the IPM and the heliosphere, what's the current consensus on the viability of this model?

 

[Reality Check]

The motivation for this thread comes from a post by Zeuzzz, in a lengthy Science, Mathematics, Medicine, and Technology thread, here is the post.

Here is the relevant part of that post:I am curious:

Since Alfvén first proposed this heliospheric current circuit, many decades ago now, the interplanetary medium (IPM) has been explored, in situ, by many space probes.

For example, Pioneer 10, Pioneer 11, Voyager 1, and Voyager 2 checked out the IPM a long way out, more or less in the Sun's equatorial plane (and Galileo and Cassini too, but not quite as far out).

And Ulysses, which was shut down only recently, explored the IPM way above and below that plane.

To what extent is the data received from the instruments on these spacecraft consistent with Alfvén's heliospheric current circuit model?

In the community of scientists who study the IPM and the heliosphere, what's the current consensus on the viability of this model?

There is a Wikipedia article on the heliospheric current sheet but there is no comparison with a unipolar inductor. It is just the consequence of the Sun's rotating magnetic field. The sheet is "the surface within the Solar System where the polarity of the Sun's magnetic field changes from north to south". And the circuit is the path of electricity along this sheet - out wards from the poles and inward along the sheet.

 

[zosima]

I should start with the caveat that I work primarily on the earth's magnetosphere and not with the heliosphere, so feel free to tell me I don't know what I'm talking about, but...as I understand it there are some problems with the heliospheric current circuit idea.

First, I don't believe there is any evidence of inward current flows around the ecliptic. Evidence suggests that there are closed field lines that connect the poles, around which high energy particles gyrate; much like the ring current on the earth. This current passes through the plane of the ecliptic, it doesn't stop at it. There is also an ExB current within the current sheet that would be flowing into the diagram below; essentially around the sun. There isn't evidence that current flows inward at that point. That is not to say that an inward current doesn't exist, just that evidence has not been found that it exists.

Second, I believe there are also some theoretical problems with the idea that the sun's dynamo is driven by unipolar induction. Basically, a unipolar inductor model implies that the growth of the magnetic field is dependent on resistivity, but an MHD fluid is highly conductive. This resistivity dependence would also imply slow changes(more than billions of years) in the behavior of the dynamo, where we know that the period of reversal in the stellar dynamo is only 11 years. I don't know all the details of MHD with regard to stellar dynamos, though, so take this as you will.

Of course a unipolar inductor has served as a good approximation of the stellar dynamo in the past and it is still very useful for sun spots and many other phenomena, but there are better ways of treating the overall field in the sun. I'm not trying to exclude the heliospheric current circuit entirely, it's possible that a scientist with Alfvén's talents could find a way to update it to take into account the advances in theory and evidence of the last 30 years...but... As it stands I don't think it's credible.

 

[tusenfem]

It is interesting to see how Alfvén's heliospheric current circuit keeps popping up again now and then. I thought I would find the model in his books (cosmic electrodynamic or evolution of the solar system) but I could not find it (maybe I did not look well enough).

Now, there are some difficulties with this model, and that is why I wanted to find the original source. As mentioned above by Reality Check and zosima there is the heliospheric current sheet, which results from the necessity that the magnetic field in the north and in the south of the heliosphere have opposite directions, just like in the Earth's magnetotail. These currents flow perpendicular to the magnetic field. Now, the magnetic field is spiralling outward from the Sun and in a very simple dipole model of the solar magnetic field and wound up field lines (Parker spiral) one would find that then there is in the end a small net current flowing radially inward to the Sun. (see e.g. Prölls, Physics of the Earth's space environment (an introduction), Springer verlag, 2003) and in this simple model the only way of closing the current is through the polar region of "open field lines". However, this is not the whole story, because, only in the very simplest approximation, the Sun has a dipolar field.

Let's turn to e.g. Tom Cravens (Physics of solar system plasmas Cambridge University Press 1997) which enters deeper into the details of the heliospheric current sheet. There we find the following situation, that the polarity of the magnetic field in the source region of the solar wind is not constant, there are opposite polarities on the surface and usually this creates a sector structure in the solar wind, with radially inward and radially outward pointed magnetic field. This, naturally changes the whole situation, and in general there are four sectors in the solar wind. We need to dive into this a little more, but I have to go to a meeting, so I will need to come back later here, to finish the description of the heliospheric current sheet (and maybe circuit).

 

[zosima]

It is interesting to see how Alfvén's heliospheric current circuit keeps popping up again now and then. I thought I would find the model in his books (cosmic electrodynamic or evolution of the solar system) but I could not find it (maybe I did not look well enough).

Now, there are some difficulties with this model, and that is why I wanted to find the original source. As mentioned above by Reality Check and zosima there is the heliospheric current sheet, which results from the necessity that the magnetic field in the north and in the south of the heliosphere have opposite directions, just like in the Earth's magnetotail. These currents flow perpendicular to the magnetic field. Now, the magnetic field is spiralling outward from the Sun and in a very simple dipole model of the solar magnetic field and wound up field lines (Parker spiral) one would find that then there is in the end a small net current flowing radially inward to the Sun. (see e.g. Prölls, Physics of the Earth's space environment (an introduction), Springer verlag, 2003) and in this simple model the only way of closing the current is through the polar region of "open field lines". However, this is not the whole story, because, only in the very simplest approximation, the Sun has a dipolar field.

Let's turn to e.g. Tom Cravens (Physics of solar system plasmas Cambridge University Press 1997) which enters deeper into the details of the heliospheric current sheet. There we find the following situation, that the polarity of the magnetic field in the source region of the solar wind is not constant, there are opposite polarities on the surface and usually this creates a sector structure in the solar wind, with radially inward and radially outward pointed magnetic field. This, naturally changes the whole situation, and in general there are four sectors in the solar wind. We need to dive into this a little more, but I have to go to a meeting, so I will need to come back later here, to finish the description of the heliospheric current sheet (and maybe circuit).

I thought I'd note, as I understand it,
The behavior of the sun's magnetic field and the solar wind can vary wildly depending on whether you are at solar minimum or solar maximum. I see people using simpler models like the parker model to characterize things at solar minimum and then using the model where the field breaks up into a more multi-polar model closer to maximum. Although, close to maximum things are changing so quickly that it gets very hard to fit any particular model.

 

[robinson]

To what extent is the data received from the instruments on these spacecraft consistent with Alfvén's heliospheric current circuit model?

In the community of scientists who study the IPM and the heliosphere, what's the current consensus on the viability of this model?

If you really want an answer, it isn't that hard to look at the current papers and articles by the scientist involved.

It only took a few seconds to find this interesting web page.
http://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm

That you ask, "what's the current consensus" is revealing. I would rather know what is going on, than what the "current consensus" is. But that is just me.

 

[Third Eye Open]

That you ask, "what's the current consensus" is revealing. I would rather know what is going on, than what the "current consensus" is. But that is just me.

For the average person who hasn't spent years studying the subject, the 'current consensus' is usually a good way to judge 'what is going on.'

....Oh wait, I forgot, the majority of scientists are involved in a vast conspiracy to cover up *insert robinsons pet theory here*

 

[zosima]

If you really want an answer, it isn't that hard to look at the current papers and articles by the scientist involved.

It only took a few seconds to find this interesting web page.
http://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm

That you ask, "what's the current consensus" is revealing. I would rather know what is going on, than what the "current consensus" is. But that is just me.

Does anyone else appreciate the awesome pun opportunity we're going to have with alternate interpretations of the meaning of the word "current" as it is conjoined with consensus, in this thread?

 

[Tubbythin]

Does anyone else appreciate the awesome pun opportunity we're going to have with alternate interpretations of the meaning of the word "current" as it is conjoined with consensus, in this thread?

If only there was an alternative alternative theory utilising the energy stored in dried vine fruit.

 

[DeiRenDopa]

If you really want an answer, it isn't that hard to look at the current papers and articles by the scientist involved.

It only took a few seconds to find this interesting web page.
http://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm

Indeed.

However, as we have already discussed, many times, in many threads, PRs/popsci articles/etc are not necessarily representative of the relevant science.

That you ask, "what's the current consensus" is revealing. I would rather know what is going on, than what the "current consensus" is. But that is just me.

Indeed.

And how would you recommend that you, me, or anyone go about finding out 'what is going on'?

This is one form of a question that I (and others) have asked you many times robinson ... and I don't recall you ever having answered.

Oh, and on 'current consensus': perhaps it includes "there are several important, open questions; among them {list}"? Does your understanding of the meaning of the word 'consensus' include such a possibility?

 

[BeAChooser]

There is a Wikipedia article on the heliospheric current sheet but there is no comparison with a unipolar inductor.

I don't believe there is any evidence of inward current flows around the ecliptic.

I guess you folks missed the second paragraph of the Wikipedia article which states:

The underlying magnetic field is called the interplanetary magnetic field, and the resulting electric current forms part of the heliospheric current circuit.[4]

Reference number 4 is this:

http://cds.aanda.org/index.php?opti.../2001/34/aah2814/aah2814.html&access=standard

A&A 376, 288-291 (2001)
DOI: 10.1051/0004-6361:20010881

MHD simulation of the three-dimensional structure of the heliospheric current sheet

P. L. Israelevich1 - T. I. Gombosi2 - A. I. Ershkovich1 - K. C. Hansen2 - C. P. T. Groth2 - D. L. DeZeeuw2 - K. G. Powell3

... snip ...

Abstract
The existence of the radial component of the electric current flowing toward the Sun is revealed in numerical simulation. The total strength of the radial current is ~ 3 x 10⁹ A. The only way to fulfil the electric current continuity is to close the radial electric current by means of field- aligned currents at the polar region of the Sun. Thus, the surface density of the closure current flowing along the solar surface can be estimated as 4*A/m, and the magnetic field produced by this current is B ~ 5 x 10^-6 T, i.e. several percent of the intrinsic magnetic field of the Sun. This seems to mean that any treatment of the solar magnetic field generation should take into account the heliospheric current circuit as well as the currents flowing inside the Sun.

... snip ...

And take a look at Figure 1. It looks remarkably like Alfven's diagram ... with current flowing towards the sun on the plane of the ecliptic.

 

[Zeuzzz]

Maybe a few of the links I provided elsewhere on the heliospheric current circuit would be a good addition here aswell for anyone interested in this, as they went largely un-noticed previously, starting with Alfvens original model, and any later publications I have found that use it;


Electric Fields and Double Layers in Plasmas - Double Layers in Astrophysics, Proceedings of a Workshop held in Huntsville, Ala., 17-19 Mar. 1986

Double radio sources and the new approach to cosmical plasma physics Astrophysics and Space Science, vol. 54, no. 2, Apr. 1978

Cosmic plasma (Astrophysics and Space Science Library. Volume 82), 1981

Interstellar clouds and the formation of stars - Astrophysics and Space Science, vol. 55, no. 2, May 1978

Cosmic electric currents and the generalized Bennett relation Astrophysics and Space Science (ISSN 0004-640X), vol. 144, no. 1-2, May 1988

The 22-year solar cycle - A heliospheric oscillation - Planetary and Space Science, vol. 30, Mar. 1982

On the Quasi-ten-day periodicity of explosive processes on the sun - Advances in Space Research (ISSN 0273-1177), vol. 17, 1996

Does the solar wind affect the solar cycle? Space Physics Research Laboratory

Auroral Particle Acceleration Processes: The Legacy of Hannes Alfven - Physics and Chemistry of the Earth Part C, v. 26, 2001

MHD simulation of the three-dimensional structure of the heliospheric current sheet - Astronomy and Astrophysics, v.376, p.288-291 (2001)

The existence of the radial component of the electric current flowing toward the Sun is revealed in numerical simulation. The total strength of the radial current is ~ 3x10⁹ A. The only way to fulfil the electric current continuity is to close the radial electric current by means of field- aligned currents at the polar region of the Sun. [....]

Magnetic Flux Transfer By The Solar Wind and Heliospheric Current System - EGS XXVII General Assembly, Nice, 21-26 April 2002

We calculated the change of the magnetic flux through the surface encircled by the Earth’s orbit. This change is associated with the magnetic flux transfer by the solar wind flow and exhibits clear 22-year periodicity. The magnetic flux transferred by the solar wind is of the same order of magnitude as the flux of the main solar magnetic field through the northern hemisphere of the Sun. There seems to be a feedback between the solar wind and the solar magnetism. Indeed, the radial current of total strength of 3×10⁹ A exists in the heliospheric current sheet. The only way to fulfil the electric current continuity is to close the radial electric current by means of fieldaligned currents at the polar region of the Sun. [....]

And mentioned briefly in here; Certain problems of solar and heliospheric physics in the light of novel satellite data - Solar System Research, Volume 40, Issue 4, pp.265-271, 2006




I would recommend this one for an overview of Alfvens original model and other related subjects "Double radio sources and the new approach to cosmical plasma physics" http://articles.adsabs.harvard.edu/...GH&whole_paper=YES&type=PRINTER&filetype=.pdf

Heliospheric current system.

Of the heliospheric current sytem only the part of the circuit which is located in the equatorial plane has been explored by in situ measurements. These show that the radial component of the current flowing towards the sun must be closed by currents leaving the sun, which means that there must be high latitude outwards currents which, in case of symmetry, are 1.5x10⁹ A in each hemisphere. How close to the axis these currents flow is unknown, but it is likely that the 'polar plumes' in the solar corona mark their footprint (see further Alfven, 1977)

If we compare the heliospheric and the auroral current systems we find that they are similar in essential respects. In both cases the EMF is due to the integral in Equation (1) being different from zero. However, there are a number of modifications [....]

And these polar plumes that Alfven predicted were related to the heliospheric current circuit have been observed, and the author of this paper attributes it to the heliospheric current circuit proposed by Alfven; Polar Plumes in Coronal Expansion. We only just found huge currents connecting the Earth to the sun, transferring ~10⁶Amps into the Earths poles, so I would think that a similar current of approx 10⁹ Amps, like Alfven predicted, would be likely for the sun, it is a lot bigger than the Earth after all so you would expect it to be bigger as you scale the Amps needed for each current between the two. Also detection of these currents on the sun are a lot harder than they are on Earth, as the suns emissions tend to blur the picture, apart from the clear filaments we see lit up in the corona, and other less subtle events.

 

[Zeuzzz]

We need to dive into this a little more, but I have to go to a meeting, so I will need to come back later here, to finish the description of the heliospheric current sheet (and maybe circuit).

Welcome to JREF

You seem to know a bit about the heliospheric current circuit, and your contributions i'm sure will be appreciated when you return.

It is interesting to see how Alfvén's heliospheric current circuit keeps popping up again now and then. I thought I would find the model in his books (cosmic electrodynamic or evolution of the solar system) but I could not find it (maybe I did not look well enough).

I dont think that it was proposed fully until the very late seventies, and it first gets a worthwhile mention in Alfvens book, "cosmic plasma", so wasn't included in his cosmical electrodynamics publication which was far earlier, I think.

As we have seen in Chapter II, it is advantageous to translate the traditional field description
of plasma phenomena in space into a current description . This gives a deeper understanding
of those phenomena in the following respects:

(1) The circuit representation demonstrates the importance of boundary conditions
which have often been forgotten.

(2) By studying the electromotive forces driving the current and the regions of dissipation,
the energy transfer from one region to another is more easily understood.

(3) Certain types of important current-produced phenomena, including the formation
of double layers, are difficult to understand without accounting for the current explicitly.

As an example, by simply translating the field description of the heliosphere into a
current description, we can demonstrate that there must be currents along the solar axis
(which had not been derived from the field description), and that coronal streamers and
polar plumes are likely to be due to filamentary currents (111 .4). [....]

And he elaborates on this later in more detail in chapter III, section four, under the heading "The Heliospheric Current System" and in the consequent subsections. I would quote the lot, but thats not looked upon favorably here due to copyright, etc. See here for a list of chapters; http://www.plasma-universe.com/index.php/Cosmic_Plasma_(Book)

* III.4. The Heliospheric Current System 53

* III.4.1. The .Sector Structure' and the Equatorial Current Layer 53
* III.4.2. Construction of the Heliospheric Current Model 54
* III.4.3. Properties of the Heliospheric Circuit 56
* III.4.4. Extrapolation to Galactic Dimensions: Double Radio Sources 56

I find it a fascinating subject and I think that many things indicate this could be correct, such as solar inflow events, coronal holes, polar plumes, electron depletion, backstreaming electrons, the equatorial plasma torus, and recent observations of the currents in our local proximity seem to imply that this current travelling towards the sun could indeed exist.

 

[zosima]

I guess you folks missed the second paragraph of the Wikipedia article which states:



Reference number 4 is this:

http://cds.aanda.org/index.php?opti.../2001/34/aah2814/aah2814.html&access=standard



And take a look at Figure 1. It looks remarkably like Alfven's diagram ... with current flowing towards the sun on the plane of the ecliptic.

MHD simulation is a useful tool, but it is not evidence. The results of MHD simulations often disagree and are often unrealistically unphysical. I've seen MHD results that show things a lot wackier than that.

Also, there definitely are 'circuits' in any magnetosphere. We know a huge amount of charge leaves from the poles of the sun, its well documented, I believe by the WIND spacecraft. For the most part the charge flows out along open field lines. The place that 'Alfven's current circuit' is unsupported is in whether that polar outflow is balanced by a radial inflow. It is not proven that polar outflows are closed by radial inflows along the Heliospheric Current Sheet. Evidence seems to show that energetic particles near the sun tend to thread the field lines from pole to pole like the ring current on earth. It *may* be that there is radial inflow, but it is just as possible that those currents are closed by flowing between poles or they may not close in the traditional sense at all.

Also, Zeuzzz in your link spam below the only recent article that seems to corroborate this Heliospheric current circuit is more simulation work done by the same people that did the MHD simulation: Israelevich, P.; Ershkovich, A.; Gombosi, T. Can you find any other MHD simulators that corroborate the results of this group? If two different MHD groups get the same results it is much more persuasive.

Also Alfven's paper seems to claim that spacecraft measured the current, but that paper was in 1977 and he doesn't even provide a citation as to what spacecraft measured the current. Do you have any spacecraft measurements of a radial inflow? Alfven's reasoning, Kirkoff's laws, does not constitute anything more than a suggestion in magnetospheric science today. For sure, their isn't a net charge build up in the Sun, but that doesn't mean the circuit needs to close the way he expected it to in 1977.

The WIND and ACE spacecraft are currently collecting solar wind data, if it exists there should be papers documenting the phenomenon. So ya'll are so sure that this exists, why don't you get a publication from the WIND or the ACE teams that corroborate your claim. My bet is that if they saw anything it is not strong enough to power the sort of phenomena that you ascribe to it(ie electric stars)

My understanding is that Heliospheric Current Sheet(HCS) is similar to the Plasma Sheet(PS) on Earth. The major difference is that the PS is constrained by distortions from the solar wind while the HCS is close to radially symmetrical. Otherwise they are very similar. There is large plasma outflow within both. They are the region for their respective body that divides a dipolar magnetic field azimuthally. In the PS we see a cross-tail-current(also called the dawn-dusk current). It flows counter-clockwise across the tail and then reconnects at the magnetopause. If the analogy holds to the sun, then majority of current flow in the HCS should be traveling in a clockwise or counter clockwise direction not inward.

 

[Zeuzzz]

MHD simulation is a useful tool, but it is not evidence. The results of MHD simulations often disagree and are often unrealistically unphysical. I've seen MHD results that show things a lot wackier than that.

Indeed, there are problems with the MHD framework in general which is used by so many astrophysicists. A number of assumptions its based on can not be fully justified... often frozen in lines, but theres others....

Also, there definitely are 'circuits' in any magnetosphere. We know a huge amount of charge leaves from the poles of the sun, its well documented, I believe by the WIND spacecraft. For the most part the charge flows out along open field lines.

Pitnick: Not literally open, thats impossible, open for modelling convenience mainly.

The place that 'Alfven's current circuit' is unsupported is in whether that polar outflow is balanced by a radial inflow. It is not proven that polar outflows are closed by radial inflows along the Heliospheric Current Sheet. Evidence seems to show that energetic particles near the sun tend to thread the field lines from pole to pole like the ring current on earth. It *may* be that there is radial inflow, but it is just as possible that those currents are closed by flowing between poles or they may not close in the traditional sense at all.

All depends on where you consider the boundaries of the flow of the circuit I suppose. And I agree that there could be a radial inflow, its just that currently there is no real data to directly prove or disprove this idea, which is why I'm open to the possibility.

Also, Zeuzzz in your link spam below the only recent article that seems to corroborate this Heliospheric current circuit is more simulation work done by the same people that did the MHD simulation: Israelevich, P.; Ershkovich, A.; Gombosi, T. Can you find any other MHD simulators that corroborate the results of this group? If two different MHD groups get the same results it is much more persuasive.

The others links all have the exact phrase "heliospheric current circuit" in them and elaborate on it, the paper on polar plumes proposes uses it as an explanation for their formation, and the others all talk about it. But yes, the most modern ones are the MHD simulations by Israelevich et al. I dont know about independant confirmation. Maybe. I'll have a dig around.

Also Alfven's paper seems to claim that spacecraft measured the current, but that paper was in 1977 and he doesn't even provide a citation as to what spacecraft measured the current. Do you have any spacecraft measurements of a radial inflow? Alfven's reasoning, Kirkoff's laws, does not constitute anything more than a suggestion in magnetospheric science today. For sure, their isn't a net charge build up in the Sun, but that doesn't mean the circuit needs to close the way he expected it to in 1977.

I'm not sure what he was referring to, but it was back in 1977 so I presume nothing came of it.

The WIND and ACE spacecraft are currently collecting solar wind data, if it exists there should be papers documenting the phenomenon. So ya'll are so sure that this exists, why don't you get a publication from the WIND or the ACE teams that corroborate your claim. My bet is that if they saw anything it is not strong enough to power the sort of phenomena that you ascribe to it(ie electric stars)

Electric stars should not be associated with this, I feel. They change too much of the existing nuclear theory to be accepted, by PC proponents or standard astronomy. I would stick to the current fuel source of the sun in this thread, forget any mention of electrical power for now, just the potential current circuit....

In the PS we see a cross-tail-current(also called the dawn-dusk current). It flows counter-clockwise across the tail and then reconnects at the magnetopause. If the analogy holds to the sun, then majority of current flow in the HCS should be traveling in a clockwise or counter clockwise direction not inward.

I accept your reasoning, analogies between the two must certainly be drawn, but a deviation of just 0.1 degrees from this direction would make this current travel inwards towards the sun, for whatever reason, so I'm neither here nor there on this on falsifying the current circuit.

 

[zosima]

@Zeuzz
I think I agree with your comments overall.

I've got a couple little points.

WRT the idea of magnetic field lines only being open for 'modeling purposes'.
I see what your saying, and while technically true. A magnetic field line is really only an abstraction when it is not threaded with plasma. When it is it can be closed in a lot of ways that don't even come close to directly reconnecting to the sun. For all intents and purposes it really is open, in that we don't know how it closes and its impossible to tell and there might be numerous small contributing sources.

My other point of contention is with respect to a .1 degree deviation. Theoretically an even smaller deviation would constitute a 'technical inflow' but that wouldn't be an inflow capable of closing the circuit.

 

[Reality Check]

I was surprised at just how variable the Sun's magnetic field is. Not only does it reverse polarity at frequent intervals but it can even change to 2 north poles (A Star with two North Poles) with a south pole smeared around the equator. The article mentions another spcaecraft that is studying the Sun - Ulysses - which is currently above the Sun's north pole There is a fascinating web site about the data that this probe is collecting here. The instruments are

• Vector Helium Magnetometer / Flux Gate Magnetometer
• Solar Wind Ion Composition Experiment
• Unified Radio & Plasma Wave Investigation
• Energetic Particle Investigation
• Interstellar Neutral Gas Experiment
• Heliosphere Instrument for Spectra, Composition & Anisotropy at Low Energies
• Cosmic Ray and Solar Particle Investigation
• Gamma Ray Burst Experiment
• Gravitational Wave Experiment
• Cosmic Dust Experiment
• Coronal Sounding Experiment

 

[zosima]

I was surprised at just how variable the Sun's magnetic field is. Not only does it reverse polarity at frequent intervals but it can even change to 2 north poles (A Star with two North Poles) with a south pole smeared around the equator. The article mentions another spcaecraft that is studying the Sun - Ulysses - which is currently above the Sun's north pole There is a fascinating web site about the data that this probe is collecting here. The instruments are

• Vector Helium Magnetometer / Flux Gate Magnetometer
• Solar Wind Ion Composition Experiment
• Unified Radio & Plasma Wave Investigation
• Energetic Particle Investigation
• Interstellar Neutral Gas Experiment
• Heliosphere Instrument for Spectra, Composition & Anisotropy at Low Energies
• Cosmic Ray and Solar Particle Investigation
• Gamma Ray Burst Experiment
• Gravitational Wave Experiment
• Cosmic Dust Experiment
• Coronal Sounding Experiment

It tends to switch polarity every 11 years. I think I mentioned above that most of the models we're discussing are only particularly accurate at solar minimum. At it approaches maximum 'all hell breaks loose' basically, the solar dipole(or quadrapole depending on your model) breaks up into a bunch of little dipoles that are oriented around sun-spots. One sunspot will be magnetic north and an opposing sunspot will be magnetic south.

 

[tusenfem]

(Note I have to cheat with urls because I am New Blood, sorry for the inconvenience)

Okay, I did a quick search at ADS and I could not find any peer reviewed papers that discuss radially inward flowing current in the heliospheric current sheet. Also, as far as I know, the measurements of Wind, ACE, Geotail, Cluster in the solar wind have not shown any indication of a net radial current flow.

To go back to the sector stuff that I was discussing. There are basically always sectors in the solar wind, which have opposite polarity of the magnetic field. There is a nice figure in Tom Cravens' book (Figure 6.27) adapted from a paper by (esoads.eso.org/abs/1970SoPh...15....3S) Severny et al (complete paper available from ADS for free) where it is the figure on page 6, where one nicely sees that over a solar rotation the field changes polarity.

So, when the field changes polarity, this will have consequences for the heliospheric current sheet, as now we do no longer have the simple dipole model that Prölls was talking about and the net inward flow of current, created by the necessity of the current sheet and the Parker spiral, will be changed. I will let you ponder on how this will work. But keep in mind, this still is a very simplified model!

We only just found huge currents connecting the Earth to the sun, transferring ~10⁶ Amps into the Earths poles, so I would think that a similar current of approx 10⁹ Amps, like Alfvén predicted, would be likely for the sun, it is a lot bigger than the Earth after all so you would expect it to be bigger as you scale the Amps needed for each current between the two. Also detection of these currents on the sun are a lot harder than they are on Earth, as the suns emissions tend to blur the picture, apart from the clear filaments we see lit up in the corona, and other less subtle events.

Oh, now I have to start digging and find what exactly was in this press release, I think I found (science.nasa.gov/headlines/y2007/11dec_themis.htm) here about THEMIS. (mmmm time I start working on Themis data). This was an interaction of a flux rope in the solar wind with the Earth's magnetosphere (not atmosphere like the press release keeps on saying) Flux ropes are well known, and have also been measured by e.g. Cluster (so Themis is not the first multi-spacecraft mission to measure their structure). This was a very big flux rope, and a flux rope carries current, otherwise is cannot be a flux rope, something has to twist the magnetic field into a rope. However, this happens all the time in the solar wind, but basically the currents that start flowing towards the poles of the Earth ARE NOT from this flux rope. Those currents are driven by the changes in the magnetotail of the Earth, when it reconfigures. The two current systems are not connected to eachother. zosima can correct me, if (s)he thinks I am wrong here, but I know my way around substorms and magnetotail physics. And I fail to see how such an event could somehow "prove" that a heliospheric current system must exist.

Also, I am not aware that Ulysses measured any signature that any collimated current from the Solar pole would create. I looked for that a long time ago, when the same discussion was on the BAUT forum. Ulysses found slow and fast flows, but in the data I looked at then, I did not see the tell-tale signature of twisted magnetic field lines. However, if you can show me some indication of this I can always have another look.

Then the talk by Isrealevich at the EGU meeting in Nice only shows us an abstract of what might be an interesting calculation. However, (adsabs.harvard.edu/abs/2001A%26A...376..288I) here is the published version of the paper, free from ADS. I need to read it, first.

Then one last thing here, and zosima also commented on that, and that is about:

Not literally open, thats impossible, open for modelling convenience mainly.

Indeed, literally "open field lines" are impossible, because of Maxwell. However, in magnetospheric physics "open field lines" have a different meaning. It means that they are not closed. Duh!!! you might say, but with closed we mean that they do not return to the Earth. So there is the magnetosphere with the dayside and the night tail, where all the field lines start at Earth and end at Earth, but then there is the region of the cusp/cleft at the magnetic poles of the Earth, and there the field lines start, but do not return to Earth, they get connected to the solar wind magnetic field and thus this region "is open with respect to the solar wind" and therefore we call these field lines "open field lines", which basically has nothing to do with numerical modeling.

 

[zosima]

@Tusfenem
I've only really got some details about this event.

The event with the flux rope that they are talking about was actually on the day side. Since the THEMIS launch got delayed until feb 2007, they missed the 2006-2007 storm season for the northern hemisphere almost entirely. Instead they were put into a configuration so that they would enter useful conjunctions on the day side. So what they saw was one end of a flux rope connected up to the day side of the magnetosphere. Technically they never actually saw if it connected up with the sun, thats just some unproven supposition that made it into the press release. It was only in the sunward direction. Moreover it isn't really evidence of a persistent current because they just saw it during that event.

I think the big thing that makes THEMIS different than CLUSTER is scale. As you are probably already aware, the CLUSTER satellites are kept much closer together than THEMIS so that they can study smaller scale dynamics. So probably what was novel about this particular rope was the size.

ETA: It wasn't until October/September of 2007 that THEMIS was put into a tail configuration.