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What does helicity mean ? (see also: Helicity in simple terms; Preprint of DOI: 10.1007/ s12036-008-0006-1) | Helicity on the Web

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(The Work of M. C. Escher)

Helicity in Solar Corona

Coronal observations from the Soft X-ray Telescope aboard the Yohkoh spacecraft provide a number of examples of sheared coronal structures in the shape of a forward or backward S. From our point of view these structures indicate electric currents flowing in the corona, whose direction determines the sense of the shear. A force-free field model gives a good example of that.

force-free field lines

Here is a model linear force-free field with alpha > 0 (left) and alpha < 0 (rigth). Electric currents are parallel to the magnetic field vector for the positive alpha and antiparallel for the negative alpha. Further discussion of that may be found here

Sigmoids in the Yohkoh soft X-ray observations.