Slow Earth-directed Halo CME

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This time a CME is headed directly for us!

Around 5:24 UT (1:24 EDT), the SOHO/LASCO C2 instrument caught a first glimpse at a CME leaving the sun directly for Earth. The CME is traveling at a fairly slow ~610 km/s or ~1.3 million mph. This is around the speed of the fast solarwind. It is a halo CME. It looks like an expanding smoke ring because it is headed straight for us. When we see halo CMEs in SOHO it means that they are either headed straight for us or away from us. By using the SDO and STEREO spacecrafts we can then determine if it is front-sided (towards Earth) or back-sided (away from Earth). SDO lets us see if there is an obvious eruption on the solar disk and STEREO allows us to see the CME from the side. In the case of this CME we can only get the necessary information from STEREO because we are currently experiencing ~10 hours data gap with SDO but a look at SDO 193 angstrom data right before the event seems to show some stirring just below disk center. This means that we don’t know actually where on the sun it is coming from yet. We will know as soon as data is available. Here is a video of combined SOHO/LASCO C2 and C3 images.

The ring of the halo CME is faint but it is there. You can also see lots of speckle on the images from a small solar energetic particle event. This event, though headed directly towards us, is fairly slow.

It is expected 8/23/2013 at 23:59 UT (8 pm EDT) give or take 7 hours according to NASA models.

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Estimates are for a minor or at most moderate geomagnetic storm. But that could mean aurora for high latitude observers.

credit: NASA/ESA/SOHO/SWRC and helioviewer

2 Comments

  1. Awesome!!! Thank you for sharing & breaking it down! So exciting!

  2. tim washburn says:

    Dr. Young,

    Would a very large CME headed directly for Earth be visible to the naked eye? I know of the increased activity of the Aurora Borealis, but would the space matter slamming into our atmosphere trigger other visible events?

    Thanks much,
    Tim

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