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Solar and geomagnetic field interaction with or without solar wind

  1. Apr 24, 2013 #1
    The usual story is that after a solar flair (coronal mass ejection) towards the earth the earth's magnetic field gets strongly deformed. It usually takes a few days from the solar event to when the earth is impacted. But I wonder if there is also a direct interaction: If there is drastic change of magnetic activity in connection with a large solar spot, should this not affect directly the earth's magnetic field? The change of these fields should propagate at light speed, so we should have some effect on the geomagnetic field 8 minutes later, and then if there is a major increase of solar wind, another and different impact 2-4 days later. Question is: Compared to the impact of solar wind, Is that first effect too small to actually matter or is it significant? And how could it be measured.
  2. jcsd
  3. Apr 24, 2013 #2


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    Hi rewnode

    Welcome to PF

    Solar Flare ;)
    The thing is with sunspots is that the magnetic field is primarily contained within the sunspot region .... you can see this when you look at images of the sun showing plasma loops tracing out the magnetic fields above the sunspot regions....


    its when these magnetic fields sometimes become complex and twisted and then "snap" that the energy and material contained within is released ( blasted out) into space as a CME. And if this region is Earth facing, then the Earth's magnetic field is in for some considerable compression.
    The avg emission speed of the Solar Wind is ~ 300 km/sec, this can increase up to 600 km/s or so during large CME's

    I'm not aware of the magnetic fields of individual spots, even when they snap, having much effect at any great distance from the sun. Because when the field snaps it collapses, only to reform again.
    Some one else my provide some furtherr info :)


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    Last edited: Apr 24, 2013
  4. Apr 27, 2013 #3
    Hi Davenn -

    thanks for the nice picture . I'm aware that the fields are enormously strong and mainly inside of solar spots. As you said, they snap and rebuild - which is probably in interaction with all the "crazy stuff" of magneto-hydro dynamics further down in the interior of the sun. My question is simply this: If the magnetic field "snaps" and reorganizes rapidly in a different way, it means to me that field strength and direction are rapidly changing. According to Maxwell, this should result in an electromagnetic wave that travels at light speed (at least once it's in free space, say a million km above the sun). Since the size of these fields is so enormous and since they can change polarity not in matters of seconds, but rather minutes (not sure about this - may be just my conjecture from watching many sun surface movies one can find for example at space weather dot com or all over on youtube) I would suspect that these are very low frequency waves with wavelengths of several million kilometers. But they should start off with quite a big initial field strength. These are the waves of disturbances I was speculating about. I figure they should reach earth within 8 minutes (earth sun distance of 8 light minutes). But for some reason I have never heard of those waves. One usually only hears of disturbances of the solar wind when it suddenly increases from a usual 300 km/s to 600 km/s or so, just like you describe. So I want to know more about the other waves that go at light speed, 1000 times faster than normal solar wind. My question is how strong such disturbances are by the the time they arrive at the earth, that is 8 minutes later, and in what way they interact with the geomagnetic field.

    p.s. I realize that my post would have been better in astrophysics. Moderator: can I move this somehow.
    Last edited: Apr 27, 2013
  5. Apr 27, 2013 #4


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    "The solar magnetic field extends well beyond the Sun itself. The magnetized solar wind plasma carries the Sun's magnetic field into space forming what is called the interplanetary magnetic field.[73]"

    "The plasma in the interplanetary medium is also responsible for the strength of the Sun's magnetic field at the orbit of the Earth being over 100 times greater than originally anticipated."

    "The heliospheric current sheet[1] is the surface within the Solar System where the polarity of the Sun's magnetic field changes from north to south. Magnetic field: The heliospheric current sheet rotates along with the Sun with a period of about 25 days, during which time the peaks and troughs of the skirt pass through the Earth's magnetosphere, interacting with it. Near the surface of the Sun, the magnetic field produced by the radial electric current in the sheet is of the order of 5×10−6 T.[5]"

    For lots of measurements of the sun’s magnetic field, visit Stanford University’s website for the “The Wilcox Solar Observatory (WSO) began daily observations of the Sun's global magnetic field in May 1975, with the goal of understanding changes in the Sun and how those changes affect the Earth; this is now called space weather.”
  6. Apr 28, 2013 #5
    Bobbywhy: Thanks for the helpful links.
    In one of the wikipedia links is already much of the answer to my question:

    "If space were a vacuum, then the Sun's magnetic dipole field, about 10^-4 teslas at the surface of the sun, would reduce with the inverse cube of the distance to about 10 ^ -11 teslas. " (10 to the power of minus 11) so - awfully weak

    It was kind of my suspicion that that it should be drastically weaker so far away. And certainly very weak compared to the earth's field. What surprised me was to learn from your Stanford link, where I could find tables that describe the field strength 1.5 radii from the core of the sun, that already so close the son's magnetic field isnt' all that hot and barely larger than that of earth.

    I suspect then that the local aberrations in the solar near solar spots would even drop off with distance even faster than the dipole component. Which should make them practically irrelevant. Would you agree?

    It's also confirmed in theses links that the main reason the solar field influences the earth's mainly because the interactions between the magentic field and the plasma surrounding the sun (and earth): The above citation from the above wiki about the interplanetary magrnetic field continues as follows

    " ... But satellite observations show that it is about 100 times greater at around 10^-9 teslas. Magnetohydrodynamic (MHD) theory predicts that the motion of a conducting fluid (e.g. the interplanetary medium) in a magnetic field, induces electric currents which in turn generates magnetic fields, and in this respect it behaves like a MHD dynamo."
  7. Apr 28, 2013 #6


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    Yup Bobbywhy's links back up what I said in my earlier post....
    I'm not aware of the magnetic fields of individual spots, even when they snap, having much effect at any great distance from the sun.

    The overall magnetic field of the sun is a different thing.

    well from the flares you have a burst of light, radio waves, Xrays all that get here in that 8 and a bit minute period
    Its the X-rays that cause the main initial effects namely shortwave ( 1 - 30 MHz ) black outs (SW fadeouts)
    This is caused by enhancement of the D layer of the Ionosphere by the incoming X-Rays, it enhances VLF propagation but stops the HF (~ 1 - 30MHz) signals from reaching and being reflected by the F1/F2 layers.
    The term for this phenomena is called a SID, Sudden Ionospheric Disturbance.
    the other event that is directly related to this is a PCA, a Polar Cap Absorption. This affects HF radio signals using the polar paths.....
    A polar cap absorption event results from the ionisation of the D-layer of the polar ionosphere by high energy protons ( X-rays). A PCA causes a HF radio blackout for trans polar circuits (polar paths) and can last several days. PCAs are almost always preceded by a major solar flare with the time between the flare event and the onset of the PCA ranging from few minutes to several hours.

    Solar activity is one of my fav subjects and has been for some 40 years since I first started observing and drawing sunspot groups. Then went on to giving lectures on solar activity, aurora and also the effects of those on radio propagation

    Last edited: Apr 28, 2013
  8. Apr 28, 2013 #7
    You're right, there is a lot more to learn about solar activity and solar-earth interactions than I have even heard of, and I'm only beginning to look into this. I was in part motivated to ask these questions - about sun-earth direct interaction with the geomagnetic field - by the frequently repeated rumors on the internet, in particular on youtube, about solar flares purportedly being able to trigger earthquakes. There are hundreds of internet "experts" who push this story together with all kinds of other doomsday scenarios. Regularly, if there is a larger solar event, plenty of toothsayers predict the next deadly seismic event to follow foot. Even though many attempts have been made to actually verify this connection, it could never be really proven, and basically all serious studies came up negative, showing no statistically significant correlations between solar spot activity and earthquake activity. Still, it always made me a little nervous to not know for sure: I figure that what is missing in this debate are real arguments not just based on statistics, but more based on first principle and measurement. If it then turns out, which I'm now convinced it does, that impact forces by interplanetary magnetism on the earth are way too small compared for example to the tidal forces of the moon (which are very unlikely but not entirely impossible trigger forces), and really forget about the toothsayers' alarms. Good reason to look in other directions to find out one day how earthquakes might actually be better predicted.
  9. Apr 28, 2013 #8


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    Yup a good path to follow :)
    There is just so much unsubstantiated garbage out there on the net about the end of the world, mega quakes and the reasons for .. etc It takes some reasonable discernment to sift out the rubbish and start delving into the known facts

    Solar astronomy is a great subject, and I am, by no means an expert. Just some one who has followed the subject passionately for many years doing lots of observations and some study.

    Earthquakes and geology in general is another of my major interests. I did manage to do a BSc in geology some years ago. I dont work in that area, again its just a passionate following .... see the Earth section in Other Sciences on PF for some of my postings.

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