Statistical analysis of ionospheric activity in the period of low solar activity using DPS-4 ionosonde data

In investigation of fundamental problems of ionosphere physics always large attention was given to the observational data during low solar activity, when there was a capability to minimize influence of external factors. On the basis of regular, continuous measurement of the Irkutsk ionospheric sounder the automated method of researches of ionospheric disturbances was designed. Statistical analysis of disturbances of an electron concentration during 2004 - 2009 was done. Main problem of the analysis was determination of total number of perturbed days and determination of total number of wave disturbances depending on a level of solar activity, season and time.