ONDRÁŠKOVÁ, A., ŠEVČÍK, S. and KOSTECKÝ, P. (2009) “A significant decrease of the fundamental Schumann resonance frequency during the solar cycle minimum of 2008-9 as observed at Modra Observatory”, Contributions to Geophysics and Geodesy, 39(4), pp. 345-354. doi: 10.2478/v10126-009-0013-5.