Full-disk nonlinear force-free field extrapolation of SDO/HMI and SOLIS/VSM magnetograms T. Tadesse, T. Wiegelmann, B. Inhester, P. MacNeice, A. Pevtsov and X. Sun A&A, 550 (2013) A14 Published online: 18 January 2013 DOI: 10.1051/0004-6361/201220044