Variations of the Levels of the Vlf/lf Radio Signals on the Middle-Latitude Traces during the Deep Solar Minimum

Statistical characteristics of the levels of the VLF/LF radio signals from the different European radio stations are presented. The regular observations were been carried out by the test receiver Rohde & Shwarz ESH-3 on the geophysical observatory of IDG RAS Michnevo (54.94°N, 37.73°E) during the period of the deep solar minimum (2007-2009). The radio signals from the radio stations Le Blanc (France, 18.3 kHz), GBZ (Great Britain, 19.6 kHz), HBG (Switzerland, 75 kHz), DCF-77 (Germany, 77.5 kHz) and RBU (Russia, 66.6 kHz) have been chosen for the analysis. In the amplitudes of observable signals the diurnal variations, the seasonal and secular trends were observed. In spite of the absence of the external drivers from above the variations of the radio signal amplitude can obtain 5 - 20 dB and have duration of 2-3 hours. The obtained data can testify that processes from below can make independent strong impact on the ionosphere condition.