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[1] Layers of ionization that appear in the ionospheric E region sporadically in time have been named sporadic-E layers, or E s . These sporadic ionization layers play a crucial role in small-scale irregularity generation (as they guarantee a plasma density gradient necessary for gradient-drift processes to develop) and in providing reliability of radio communication and navigation. Despite the fact that E s layers have been studied since the late sixties, a method to visualize the E s horizontal structure was suggested for the first time only recently . In the present paper we propose a new type of experiment for the reconstruction of the patchy-type E s structure and dynamics using a combination of the above-mentioned method with the method of artificial periodic irregularities (API) [Belikovich et al., 1999]. This combined method allows us for the first time to carry out E s tomography, to trace the three-dimensional (3-D) dynamics of sporadic ionization clouds and their associated 3-D neutral motions, and to study the effects of high-frequency radio waves on the sporadic-E layers. The procedure includes recording of the E s horizontal structure and dynamics with an all-sky camera via radiowave-induced optical emissions in combination with measurements of the E s vertical structure and dynamics by the API method. Both methods complement each other and can be used simultaneously. The experiment is to be equipped with a powerful HF radio wave transmitter, all-sky cameras, an ionosonde, and an HF digital receiver. INDEX TERMS:2439 Ionosphere: Ionospheric irregularities; 6929 Radio Science: Ionospheric physics (2409); 6969 Radio Science: Remote sensing; 2437 Ionosphere: Ionospheric dynamics; 0310 Atmospheric Composition and Structure: Airglow and aurora; KEYWORDS: ionospheric structure, sporadic-E layer, radio-wave-induced optical emissions, artificial periodic irregularities, ionospheric interactions, HF powerful radio waves Citation: Kagan, L. M., N. V. Bakhmet'eva, V. V. Belikovich, A. V. Tolmacheva, and M. C. Kelley, Structure and dynamics of sporadic layers of ionization in the atmospheric E region,

We present the results of studying the sporadic layers of ionization in the lower ionosphere observed in the sunset-sunrise time during the summer months of 2000 and 2001. Measurements were performed at the "Sura" heating facility of the Radiophysical Research Institute (Nizhny Novgorod, Russia). Based on the analysis of the altitude-time dependences of the amplitude, relaxation time, and phase of the scattered signal, we obtain new data on the formation and dynamics of the evening and nighttime mid-latitude sporadic E layer, present the results of measuring the velocity of the plasma vertical motion, and estimate the relative molecular mass and total number density of metal ions whose pile-up due to the wind shear can cause the formation of the observed sporadic layers.

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UDC 551.510.536We report on the results of studying the lower ionosphere by a method based on the resonant scattering of radio waves by artificial periodic inhomogeneities of the ionospheric plasma. Different aspects of studying the sporadic E layer such as the influence of the vertical transfer on its formation, the possibility of examination of its ion composition, and the influence of the ionosphere heating on the layer characteristics are discussed. The results of determining the parameters of the E s layer and some characteristics of the lower ionosphere during the creation of artificial periodic inhomogeneities at two frequencies are presented.