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CME Dimming Region Recognition


  • Inputs: AIA images, in multiple wavelengths.

  • Outputs: Processed images showing locations of CME dimming regions.

  • Problem: Studies of dynamic events on the solar disk, such as dimmings, are based on 2 types of difference images: running difference (RD) images, which are obtained by subtracting the preceding image from the current one, or fixed difference (FD) images, which are produced by subtracting a single pre-event image from all subsequent images. In such difference images, dimmings appear as dark features with a reduced intensity.

There are important differences between FD and RD images.

  • RD images emphasis changes (in the brightness, localisation and structure of sources) that have occurred during the interval between successive heliographs.

  • However, many artifacts also appear in RD images. For example, spurious dimmings can occur if the intensity of a bright feature decreases.

  • In FD images, those changes that occur during an event are particularly clear.

  • In FD images, solar rotation can produce potentially spurious dimmings and brightenings unless solar rotation is taken into account, since the pre-event reference image may have been taken hours before subsequent frames.

Literature Search

  • K.P.Dere, G.E.Brueckner, R.A.Howard et al. Solar Physics. 175, 601-612 (1997).
    • Use running difference images to analyse evolution of CMEs.

  • I.M.Chertok and V.V.Grechnev. Astronomy Reports. 47, 139-150 (2003).

  • I.M.Chertok and V.V.Grechnev. Astronomy Reports, 47, 934-945 (2003).

Routines and Libraries

Test Data

SOHO EIT data in multiple wavelengths.


  • In SOHO EIT images, periodic vertial and horizontal light strips due to the CCD matrix in the instruments are often observed. Rotation of the solar image in fixed difference images tends to suppress the horizontal strips and enhance the vertical ones. However, this will not necessarily occur in SDO/AIA images.

  • According to Chertok et al, dimmings are relatively faint phenomena so they limited the intensity range in the difference images in order to make the features sufficiently pronounced.

  • It's relatively easy to create the difference images, but actual CME dimming region recognition is another matter. When does a dim region become a CME dimming region rather than just being an artifact of processing? What temporal and spatial scales are involved? What changes in intensity might we expect?

  • When using the FD, one needs to be able to specify an image (or a time so that a suitable image can be selected) to use as a reference frame.

  • One approach that has come during discussions is the idea of using difference images. For example, if you subtract the previous image from the next image, then you can show unchanged regions as grey, areas where brightness has reduced as white, and regions where the brightness has increased as black (for example).

-- SimonMartin - 19 Apr 2005

-- ElizabethAuden - 11 Jan 2005

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Topic revision: r6 - 2005-04-19 - SimonMartin
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