TY JOUR TI Impact of magnetic storms on the lower ionosphere within the auroral zone KW absorption KW ionosphere KW D-region KW sporadic Es KW magnetic storms JO Solnechno-Zemnaya Fizika AU Blagoveshchensky, D.V. AU Sergeeva, M.A. PY 2015 IS 1 PB Institute of Solar-Terrestrial Physics SB RAS