Altitude–time variations in electron number density in the ionospheric E layer

We present the results of measuring the electron number density in the ionospheric E layer by a method based on the creation of artificial periodic irregularities of the ionospheric plasma with two different spatial scales. Artificial periodic irregularities were created by the radiation of the Sura heating facility at frequencies 4.7 and 5.6 MHz. The electron number density was determined by the ratio of relaxation times of the signals backscattered by artificial periodic irregularities during their sounding by probing radio waves at the mentioned frequencies. Features of the electron-density profiles obtained in 2006 and 2007 in the altitude range 95–115 km are discussed and their altitude–time variations are analyzed.