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Last Post 3/20/2012 10:20 AM by  Claire Raftery
solar stroms
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Anonymous





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3/20/2012 6:33 AM

    Lexie (SA)

    When a CME happens how do you know it heads for earth?


    Emilia Kilpua



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    Posts:88
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    3/20/2012 9:22 AM

    Hi Lexie,

    It is sometimes quite difficult to predict whether a CME will hit the Earth! If in coronagraphs we see a halo CME, which means a CME that extends around the whole occulting disk of the coronagraph, we know that a CME is coming straight towards the Earth or in the opposite direction (see example e.g. from http://spaceweather.com/g...sary/halocmes.html). To find out whether the CME is Earth-directed one needs to investigate solar disk images taken for example in ultraviolet wavelenghts. They often show different types of activity related to CME eruption. But there are more complications! After a CME has been released it can deflect away from the Sun-Earth line and away or towards from the ecliptic plane (where the Earth is located). In particular, close to low solar activity conditions CMEs tend to deflect from high latitude source regions to the ecliptic plane.

    Emilia


    Claire Raftery



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    3/20/2012 10:20 AM
    Hi Lexie, The magnetic field of the Sun actually comes out in a big spiral called the Parker Spiral (http://en.wikipedia.org/wiki/Parker_spiral). Because we can estimate how the Sun and Earth are connected from following the spiral, we know that if a CME erupts from a particular part of the Sun then its more likely to hit the Earth. (have a look at this computer simulation to see what I mean http://www.youtube.com/watch?v=7L-YNGiCxXE). Like Emilia said, this is not the end of the story. There can be complications that we can't predict that may chance the path of a CME but this is certainly somewhere to start! Thats why last week there were so many nice aurorae. There was a Sunspot that was in the right location on the Sun that kept producing CMEs. Based on where on the Sun it was, the CMEs were mostly Earth directed. Claire
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