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CME launch angle from 2021-04-19 AR2816 M1.1 flare

Drax Spacex

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I was surprised that the CME associated with the AR2816 M1.1 flare did not have an Earth-directed component.  SDO A1A 193 showed a circular halo-like shockwave across the surface of the sun after the CME eruption.  I was expecting so see the noisy full screen splatter on the LASCO coronographs soon thereafter (but there was none).

AR2816 coordinates at the time of the flare was S24E21.  If, like solar winds, CME launch direction is radial, I would have expected the center of its main lobe to be about 45° below horizon of the solar disk in the southeast quadrant.  Instead LASCO showed the CME propagation vector to be only about 10° below horizon.

How can this disparity be explained?


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CME launch angle from AR2816 2021-04-22 04:35

I think from this additional example we can conclude that CME launch direction is not radial (not along a vector from the center of the sun through the center of the active region on a spherical Sun producing the CME).

We're looking at a difference between radial and CME launch direction of 45° to 90° over a time span of only 3 hrs.  I don't think the Parker Spiral can explain this because there isn't much time lag, and the sun's rotation rate is only about 0.5 °/hr.  I guess the general answer regarding the direction, shape, width of a CME is "it's complicated" - and only grossly related to the solar geographic location of the AR that spawned the CME.

Perhaps the CME launch direction is related to the orientation of the sunspots, magnetic loops, and polarities of the active region (like the explosion of a shaped charge)?  Or the localized shape of the Sun at the region of the AR is curved, not ideally mapped to a sphere, but tilted, resulting in a launch angle that is askew, and variable between focused (narrow) or unfocused (wide).


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With the last CME of the C-flare, if you look closely at the difference images of the flare you can see the ejects leaving towards the east (left) so it does indeed have an influence on the magnetic loops where they break. Parker spiral has an effect as well but there are indeed multiple factors at play.

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Just a few of my thoughts:

- Low-level M-flares are often too weak to produce the massive wide CMEs that would cause significant storming on earth. There would need to be an active sunspot region in a perfect position (front and centre disk) for such a CME to be directly aimed at Earth and then be able to cause a G2+ storm. Although there have definitely been exceptions.

- The noisy splatter tends to require a 'proton event' and this happens mainly X-flares and some high-end M-flares. The X9.3 and X8.2 flares of 2017 are perfect examples - these were both proton events and caused radiation storms before causing geomagnetic storms at Earth.

- Sunspot regions in the ascending phase of the solar cycle (that we are in now) tend to be in the high latitudes of the sun (between 20 - 30 degrees on average), meaning that if they erupt, they are more likely to be directed either north or south of our planet, causing them to miss. So in a way, it is not surprising that we are having an increase of activity but it is missing earth. The M1.1 flare occurred at approx. 24 degrees south and 20 east, and along with the Parker spiral effect and random factors including magnetic field alignments, it is not surprising that it missed us. As we move past solar maximum in 2024-25, the active sunspot regions will be more equatorial, meaning that if they erupt they are much more likely to be geo-effective. The best example would be the high-end X-class flares of October 2003, which were front and centre disk, caused very large CMEs and resulted in extreme G5 storming at Earth.

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