TY JOUR TI Behavior of electron density in the ionosphere over Norilsk during the period of declining solar activity KW electron density KW annual variation KW semi-empirical model (SEM) JO Solar-Terrestrial Physics AU Яковлева, О.Е. AU Кушнаренко, Г.П. AU Кузнецова, Г.М. PY 2021 IS 7 PB Институт солнечно-земной физики СО РАН