Research into the fine structure of coherent echo spectra using data from the Irkutsk incoherent scatter radar

Research into the formation process of different-scale inhomogeneities is an actual problem of ionospheric physics. Plasma instability is one of physical mechanisms responsible for formation of a small-scale inhomogeneity. E-layer instabilities comprise the two-stream and gradient-drift ones. Inhomogeneities they form lead to abnormally intensive radio scattering of different wavelengths (known as coherent echo (CE) or radio aurora) in the E-layer. Thus the radio wave back-scattering technique is among the much used methods for studying such inhomogeneities. CE was mostly investigated at high and equatorial latitudes providing conditions for the CE occurrence. Over the last decade CE has been investigated at middle latitudes, where it is seldom observed and has unstudied conditions of occurrence. Research into peculiarities (especially coherent properties) of the mid-latitude CE was carried out at the Irkutsk incoherent scatter radar in 1998-2006. Spectra of some data sets were found to have fine comb-shaped structure forming single-humped CE spectra due to the static averaging. Original coherent methods of processing some data sets of CE signals were developed within the framework of this research. These methods enabled investigation into peculiarities of unaveraged CE-signal spectra. The new model of the inhomogeneity spectrum was offered to describe these peculiarities. Being superposition of the discrete set of spatial harmonics with close wave numbers, the model describes scattered-signal characteristics observed experimentally.