[1]
E. V. Liperovskaya, A. S. Silina, V. A. Liperovsky, C.-V. Meister, D. H. Hoffmann, and P. F. Biagi, “Midnight variations of spreading of ionospheric sporadic E-layers before earthquakes”, Ann. Geophys., vol. 55, no. 1, Apr. 2012.