A Statistical Study on Photospheric Magnetic Nonpotentiality of Active Regions and Its Relationship with Flares During Solar Cycles 22  23
Abstract
A statistical study is carried out on the photospheric magnetic nonpotentiality in solar active regions and its relationship with associated flares. We select 2173 photospheric vector magnetograms from 1106 active regions observed by the Solar Magnetic Field Telescope at Huairou Solar Observing Station, National Astronomical Observatories of China, in the period of 1988  2008, which covers most of the 22nd and 23rd solar cycles. We have computed the mean planar magnetic shear angle (overline{Δφ}), mean shear angle of the vector magnetic field (overline{Δψ}), mean absolute vertical current density (overline{J_{z}}), mean absolute current helicity density (overline{h_{c}}), absolute twist parameter ( α _{av}), mean free magnetic energy density (overline{ρ_{free}}), effective distance of the longitudinal magnetic field ( d _{E}), and modified effective distance ( d _{Em}) of each photospheric vector magnetogram. Parameters overline{h_{c}}, overline{ρ_{free}}, and d _{Em} show higher correlations with the evolution of the solar cycle. The Pearson linear correlation coefficients between these three parameters and the yearly mean sunspot number are all larger than 0.59. Parameters overline {Δφ}, overline{Δψ}, overline{J_{z}},  α _{av}, and d _{E} show only weak correlations with the solar cycle, though the nonpotentiality and the complexity of active regions are greater in the activity maximum periods than in the minimum periods. All of the eight parameters show positive correlations with the flare productivity of active regions, and the combination of different nonpotentiality parameters may be effective in predicting the flaring probability of active regions.
 Publication:

Solar Physics
 Pub Date:
 September 2012
 DOI:
 10.1007/s1120701200612
 arXiv:
 arXiv:1206.2006
 Bibcode:
 2012SoPh..280..165Y
 Keywords:

 Active regions;
 Flares;
 Magnetic fields;
 Nonpotentiality;
 Photosphere;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 20 pages, 5 figures, 4 tables, accepted for publication in Solar Physics