Mid-latitude effects of “expanded” geomagnetic substorms: a case study Veneta Guineva, Irina Despirak, Rolf Werner, Rumiana Bojilova and Lyubomira Raykova EPJ Web Conf., 254 (2021) 01004 Published online: 08 November 2021 DOI: 10.1051/epjconf/202125401004