Analysis of Ground-Level Enhancements: Strong events are hard Usoskin, I. ; Asvestari, E. ; Willamo, T. ; Gil, A. ; Kovaltsov, G. ; Mikhailov, V. ; Mayorov, A. Abstract Publication: 35th International Cosmic Ray Conference (ICRC2017) Pub Date: July 2017 DOI: 10.22323/1.301.0126 Bibcode: 2017ICRC...35..126U