Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh51a..03g&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SH51A-03
Astronomy and Astrophysics
Astrophysics
7500 Solar Physics, Astrophysics, And Astronomy, 7509 Corona, 7524 Magnetic Fields, 7529 Photosphere
Scientific paper
Despite its extreme importance, the calculation of the total magnetic helicity in solar active regions remains an unresolved problem in solar physics. On the other hand, the helicity variations in an active region can be calculated partially, for longitudinal magnetograms, or in full, for vector magnetograms, but only by using coarse, uncertain velocity field maps, calculated by means of correlation tracking techniques. Whether one should apply correlation tracking to magnetograms or white-light continuum images is also unclear, as the two inputs do not yield identical outputs. We present a technique that provides a lower limit of the total magnetic helicity in active regions, without using any velocity fields. The temporal variation of the total helicity can also be calculated in full if a series of vector magnetograms is available. The method relies on a comparison between the best linear force-free approximation and the potential approximation for a given photospheric boundary and begins by demonstrating that a commonly used formula for the magnetic helicity density in the linear force-free approximation is, in fact, erroneous. We have tested our method on vector magnetograms acquired by the Imaging Vector Magnetograph (IVM) of the University of Hawaii. We discuss the pros and cons of our approach and we compare our results for the magnetic helicity variations with results obtained when classical methods are employed.
Georgoulis Manolis K.
LaBonte Barry J.
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