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Aurora reliable data

  1. Mar 20, 2014 #1
    Hello, I am working in an experiment proposal for a contest at CERN, and I need reliable data about the Polar Aurora.

    The experiment consist in using a T9 beam to produce radiation similar to the Sun's radiation and irradiate with it a capsule with gas in conditions as close as possible to the atmosphere at the altitude where Auroras happen.

    The problem is the part of "similar to the Sun's radiation", because I can't find reliable data, every source has different information.

    Firstly it seems that nobody agrees if the ions take part in the Aurora or if it's just the electrons.
    Secondly the speed of the electrons, some sources say it is c/10, others 1000 km/s, other 400 km/s.
    And finally nobody agrees about the red auroras, some sources say they occur way higher in the atmosphere that the green ones, others say they happen after the green ones, and some people say that it only depends on the gases that are there.

    I have searched a lot but all the good articles are very expensive, besides they are kind of old and I don't even know if they will have the information I need.

    The reason I need this information is because I want to know how many GeVs the beam has to produce and what kind of target do we need to hit in order to produce the radiation needed, I don't want too energetic particles but also I don't want particles not energetic enough.

  2. jcsd
  3. Mar 20, 2014 #2


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    Hi Frigorifico! You have raised some interesting but complicated issues. Some scientists spend their entire lives studying and learning about Aurora. There are still many unanswered questions, so your experiment proposal just may help answer some of them.

    You haven’t created a public profile here on Physics Forums, so since I don’t know your educational level all I can do is guess. The below Wiki article gives a fairly good introductory overview of Aurora. I suggest you start with it: http://en.wikipedia.org/wiki/Aurora

    Now, as for the solar wind that is believed to cause the aurora, here is an excellent source to learn from: Kinetic Physics of the Solar Corona and Solar Wind, by Eckard Marsch at http://solarphysics.livingreviews.org/Articles/lrsp-2006-1/

    For a more in-depth study, here is a list you may find useful: http://en.wikipedia.org/wiki/List_of_plasma_(physics)_articles
  4. Mar 21, 2014 #3
    Thanks Bobbywhy, I haven't seen the benefits of having a public profile, but now that you mention it I probably will make it public.
    Also thanks for the links, they seem very trustworthy.
    Could you please tell me some of those unanswered questions?, I think maybe I could focus my proposal a little bit more on how to answer some of them.
  5. Mar 22, 2014 #4


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    Are you referring to only visible emissions from the Aurora, or do you intend to include the radio frequency emissions as well? What about infrared, ultraviolet, and X-ray emissions?

    In a solar magnetic storm, a large number of protons and electrons is energized and pushed earthward from the long tail of the Earth's magnetic field. These electrons and protons (plasma) interact with the earth’s magnetosphere. The electric currents that result produce the aurora.

    Both the Aurora and the Solar wind are types of plasma. Their interaction is governed by the laws of Magneteohydronamics (MHD). Auroras are now known to be caused by the collision of electrons, found in the magnetosphere, with atoms in the Earth's upper atmosphere (at altitudes above 80 km). These electrons are typically energized to levels between 1 thousand and 15 thousand electronvolts, far more than enough energy to ionize (elevate to excited states) atoms of air molecules such as oxygen and nitrogen. When atoms transition back to their ground (relaxed) states they emit visible light characteristic of the atoms. Some O+ ions ("conics") are accelerated by plasma waves in directions mainly perpendicular to the field lines. Both positive ions and negative electrons take some part in the Aurora.

    Operating the CERN T9 beam in the negative beam mode the fraction of electrons can be as high as 80% at 0.5 GeV/c but drops to ~5% at 5 GeV/c, for the electron enriched target. Are these momenta suitable to simulate the Auroral excitation modes?

    Students need to first register by the end of January, then submit a proposal for a research project to be conducted at the beam line by the end of March. Today, 22 March, seems a bit late to be so far away from a proposal.

    The first ionization energy of Nitrogen is 14.5 ev and of Oxygen is 13.6 ev.

    Very high in the ionosphere (above 180 miles), oxygen is the most common atom. The incoming energetic charged particles raise most of the oxygen atoms to their first excited state, creating the rare red (630.0 nm ) aurora. The strong yellowish-green light which is most common in auroras, is produced by excitation of oxygen atoms to their second excited state (557.7 nm) at a lower altitude, between 60 and 180 miles. Around 60 miles, oxygen atoms are few and nitrogen molecules produce a red light that often seems to form the lower fringes on Auroral curtains. Other colors appear, especially those emitted by atomic and molecular nitrogen (blue and purple), respectively.

    You need to decide if the CERN T9 beam will be an appropriate simulator of the Auroral process. There may be far simpler and less expensive ways to perform your experiment.

    As for unexplained Auroral mechanisms, no good explanations exists as yet for "poleward arcs" stretching sunward across the polar cap, the related "theta aurora", and "dayside arcs" near noon. These are relatively infrequent and poorly understood. Also other effects such as flickering aurora, "black aurora" and sub visual red arcs need explanations. In addition to all these, a weak glow (often deep red) has been observed around the two polar cusps, the "funnels" of field lines separating the ones that close on the day side of Earth from lines swept into the tail. The cusps allow a small amount of solar wind to reach the top of the atmosphere, producing an Auroral glow. Since solar activity is directly connected to our global climate, a more thorough understanding of the interaction between the solar wind and the earth’s magnetosphere.

    Some of the data above was taken from "The Exploration of the Earth's Magnetosphere" at http://www.phy6.org/Education/index.html and “Plasma Universe” at http://www.plasma-universe.com/Aurora
  6. Mar 23, 2014 #5


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    The CERN beam is nice for GeV protons, muons, pions and so on, but if you want fast electrons there are easier sources (beta decays, or direct electron beams). Low-energetic protons (sub-MeV to ~25 MeV) are available elsewhere, too.

    If you want to mimic the upper atmosphere, you need a very low gas density - probably so low that it will be hard to see any aurora effects within your small volume.
  7. Mar 26, 2014 #6
    As someone who sees his fair share of northern lights I can tell you that green is the most common. When red colors appear, they are always above the green. The winter of 2013-2014 has had very poor aurora showing, compared with prior years. I usually get my aurora forecast from Alaska Weather Watch - Astronomy, but that site pulls its information from NOAA's OVATION Aurora.

    The University of Alaska at Fairbanks, Geophysical Institute is another good source for aurora information.

    As I understand it, the green color is produced by exited oxygen ~60 miles up. The less common red color is also produced by oxygen, but ~200 miles up. Nitrogen produces blue or purple and is very rare. I have never seen a blue or purple aurora in the 23 years I have lived in Alaska. I cannot tell you if they are composed of protons or ions, all I know is that they are "charged particles," a plasma. So it could be either, or both. As to their speed, that depends on the speed of the Coronal Mass Ejection that produces the aurora. CME speeds vary from 20 km/s to 3,200 km/s with an average speed of 489 km/s.
  8. Mar 17, 2015 #7


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    Some new experiments, both in the lab and in space, have come along to add to this knowledge. Magnetic energy is seen to be converted to particle energy over spatial scales that greatly exceed previous theories and simulations. Theta aurora appears to be explained. The MMS mission is now underway to expand this knowledge.







    Illustration of the Earth’s magnetosphere showing it complexity. The Theta Aurora are now confidently linked to magnetic reconnection events in the lobes of the magnetotail. (Credit: NASA)

    The science paper explains that what was previously observed by only lower altitude spacecraft was captured by Cluster within the magnetotail lobes. The southerly lobe’s plasma – ionized particles – was very energetic. The measurements revealed that the southern lobe of the magnetotail was acting as a bottle and the particles were bouncing between twomagnetic mirrors, that is, the lobes were close due to reconnection. The particles were highly energetic.
    Last edited: Mar 17, 2015
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