TY JOUR TI Electron density at F1-layer heights in the last solar minimum (2007–2009) KW semi-empirical model of electron density KW annual variations KW F1-layer heights JO Solnechno-Zemnaya Fizika AU Kushnarenko, G.P. AU Yakovleva, O.E. AU Kuznetsova, G.M. PY 2018 IS 4 PB INFRA-M Academic Publishing LLC.