Sigmoid

Sigmoid is S-shaped coronal structure observed during the preflare phase of a solar flare.


Appearacne of sigmoidal structure is related to saturation observed in the temporal development of relative magnetic helicity.

References

Canfield, R. C., Hudson, H. S., & McKenzie, D. E. 1999, GRL, 26, 357
Lee, H. H. & Magara, T. 2014, PASJ, 66, 39
Magara, T. & Longcope, D. W. 2001, ApJ, 559, L55
Rust, D. M. & Kumar, A. 1994, SP, 155, 69