D. Sokoloff, H. Zhang, K.M. Kuzanyan, V.N.
Obridko, D.N. Tomin, V.N. Tutubalin Current Helicity and Twist as Two
Indicators of the Mirror Asymmetry of Solar Magnetic
Fields Solar Phys (2008) 248:
17–28
N.G.Bludova, V.N.Obridko, O.G.Badalyan The relative umbral area in spot groups as an index of cyclic variation of solar activity Solar Physics, 2014, v. 289, pp. 1013-1028
Yu.A.Nagovitsyn, V.N.Obridko, A.I.Kuleshova The upper limit of sunspot activity as observed
over a long time interval Solar Physics, 2015, v. 290, 1285-1294