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Thread: Alfven waves from Coronal Holes

  1. #1
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    Alfven waves from Coronal Holes

    Its fairly well known that Alfven waves are now responsible, at least to a certain extent, for heating the corona and propelling solar wind from Coronal Holes. However, we also now know that these waves travel to earth from these Coronal Holes. If we have an earth facing Coronal Hole, is it possible for the Alfven waves to reach earth faster than the actual stream of particles embedded in the solar wind from the Coronal Hole or does it all reach earth at the same time, which is typically 3-4 days?

  2. #2
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    Dear Gerald, welcome to CQ.

    With respect to your question. indeed Alfvén waves (turbulence) seems to be a source for heating.
    The Alfvén waves, however, will not arrive earlier at the Earth, because the solar wind is both super-sonic and super-Alfvénic.
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  3. #3
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    Thank you. And thank you for the welcome. These waves are obviously energetic. Has there been any documented studies or research done on how these Alfven waves interact/integrate with the earth? Something perhaps that details impact to the magnetoshpere, impact to lower layers, etc...i.e, the ionoshpere? Could these be destructive/disruptive forces, (if conditions are right), as they relate to earths geophysical state?

  4. #4
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    Put it this way-- there's a reason we knew about the solar wind long before we knew about the Alfven waves. The particles are way more important for the interactions with Earth. However, the way the particles couple to the magnetosphere depends somewhat on the field geometry, so there could be some interplay where the Alfven waves alter the impact that the particles have, if the Alfven waves have a large amplitude. I really don't know if it's a significant issue because I don't think the amplitude is generally that large.

    Incidentally, you might wonder how the Alfven waves could be important for heating something that ultimately ends up having a way higher energy flux in the particles. That's because the magnetic field weakens as you go out, so the Alfven waves either reflect, or are dissipated, before they get to us. Perhaps we should say that the Alfven wave energy gets converted into particle energy flux.
    Last edited by Ken G; 2015-Jul-18 at 02:00 AM.

  5. #5
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    There are a lot of waves and fluctuations in the solar wind. The Alfven waves that you mention will probably not reach the Earth because they are expected to heat up the corona. Basicaly there is Alfven turbulence which is heating the corona. Here is a paper bz Aert van Balllegooijen et al. on "Heating of the solar chromosphere and corona by Alfven wave turbulence". It is basically the turbulent cascade of the waves to smaller scales that is putting the energy into the particles at the dissipation scale.

    However in the fast solar wind from coronal holes there are lots of waves present, including Alfven waves, being one of the easiest waves to generate. Large amplitude waves were measured e.g. by Ulysses report Velli & Pruneti.

    However, the Alfven waves are generated also in the solar wind itself along its travels to the Earth. I just looked in the literature and I found a paper by Prikryl et al. where they discuss "Solar wind Alfven waves: a source of pulsed ionospheric convection and atmospheric gravity waves."

    Although, interestingly, there was a day in 1997 that the solar wind speed reduced below the Alfven speed, as reported by Gosling et al.

    Like Ken G above says, however, the main interaction of the solar wind with the Earth's magnetosphere is through dynamic pressure of the solar wind, which can let the magnetosphere compress or expand, and by the interaction of the solar wind magnetic field and the Earth's magnetic field. If the two are oppositely directed at the nose of the magnetosphere, then reconnection will take place and Earth field will be connected to solar wind field and be transported to the Earth's magnetotail. If they fields are equally directed, then at high latitudes there still can be so-called lobe reconnection, again also opening up the magnetosphere to solar wind plasma. This all then later results in an energized magnetotail, which reacts with reconnection within itself and a so-called substorm, which creates the beautiful aurorae borealis and australis (which is more my field of expertise).
    All comments made in red are moderator comments. Please, read the rules of the forum here, the special rules for the ATM section here and conspiracy theories. If you think a post is inappropriate, don't comment on it in thread but report it using the /!\ button in the lower left corner of each message. But most of all, have fun!

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