HR: 08:35h
AN: SH51A-03 [PDF]
TI: Calculation of a Minimum Total Magnetic Helicity in Solar Active Regions
AU: * Georgoulis, M K
EM: manolis.georgoulis@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723
AU: LaBonte, B J
EM: barry.labonte@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723
AB:
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.
DE: 7500 SOLAR PHYSICS, ASTROPHYSICS, AND ASTRONOMY
DE: 7509 Corona
DE: 7524 Magnetic fields
DE: 7529 Photosphere
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting