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Last Post 21 Mar 2013 11:47 AM by  Yan Li
CME / Solar Storm
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Anonymous





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17 Mar 2013 10:10 PM

    Stephanie C

    How can the speed of a solar CME be predicted?

    Thanks.

    Tags: CME, space weather, forecast, space storm

    Emilia Kilpua



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    Posts:88
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    17 Mar 2013 11:09 PM

    Hi Stephanie!

    CME speeds are usually calculated from coronagraph images. CME height is calculated at different times. However, such speed estimates are not very reliable if the spacecraft carrying the coronagraph is in the Sun-Earth line (like SOHO) because Earth-coming CMEs appear as halos around the coronagraph disk. Two STEREO spacecraft can view CMEs from different angle and they provide better speed estimates. Also, coronagraph images taken nearly at the same time by SOHO and STEREO can be used to model CMEs in 3-dimensions and using such modeling one gets more reliable speed estimations towards the Earth.

    Emilia


    Emilia Kilpua



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    Posts:88
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    18 Mar 2013 01:19 AM

    Below is an illustration of a 3-dimensional model used to fit CMEs with STEREO and SOHO (from http://stereo.gsfc.nasa.gov).
    Note that after CME leaves the coronagraph field of view (about 30 solar radii) the speed can change significantly before it arrives to the Earth.
    Fast CMEs decelerate and slow CMEs accelerate approximately to the speed of the surrounding solar wind. With STEREO CMEs can be viewed all the way to the Earth by heliospheric imagers. Fast CMEs drive also shock waves and they emit radiation that can be detected and the speed can be also estimated from this emission.

    Emilia

    3D_CME_shot_03_nolabels_thumb.jpg


    Pat Reiff



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    Posts:83
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    21 Mar 2013 10:17 AM
    There are special 3D models of the solar wind that try to model the CME and its speed (it can slow down if it runs into a slower blob of solar wind). We have an upstream monitor at ACE, which gives us about 45 minutes warning of a CME hitting. We can use that data to predict solar storms, like the one last weekend. We would love to have a solar monitor upstream that would give us 4 hours of warning... maybe using a solar sail!

    Here is our space weather forecast page:
    http://mms.rice.edu/realtime/forecast.html

    You can send us email to get onto our space storm warning email list:
    spacalrt-subscribe@mailman.rice.edu

    ..Doctor Pat

    Yan Li



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    Posts:55
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    21 Mar 2013 11:47 AM

    Hi, Scientists cannot really predict CME speed at this point. But we understand most fast CMEs accompany large solar flares and from strong active regions/large sunspots. CME speed can be measured soon after it leaves the Sun using coronagraph images. If the measurements can be done quick enought, it'll still be helpful to space weather predictions. CMEs take about one to five days to reach the Earth.

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