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We present the results of complex obser-vationsof various parameters of the middle and upper atmosphere over Siberia in December 2012 \textendashJanuary 2013, during a major sudden stratospheric warming (SSW) event. We analyze variations in ozone concentra-tion from microwave measurements, in stratosphere and lower mesosphere temperatures from lidar and satellite measurements, in the F2-layer critical frequency (foF2), in the total electron content (TEC), as well as in the ra-tio of concentrations of atomic oxygen to molecular nitrogen (O/N2) in the thermosphere.To interpret the observed disturbances in the upper atmosphere, the ex-perimental measurements are compared with the results of model calculations obtained with the Global Self-Consistent Model of Thermosphere\textemdashIonosphere\textemdashProtonosphere (GSM TIP). The response of the upper atmosphere to the SSW event is shown to be a decreasein foF2 and TEC during the evolution of the warming event and a prolonged increase in O/N2, foF2, and TEC after the SSW maximum. For the first time, we observe the relation between the increase in stratospheric ozone, thermospheric O/N2, and ionospheric electron densityfor a fairly long time (up to 20 days) after the SSW maximum at midlatitudes.