## ETNA RADIO OBSERVATORY

TOOLS AND TEST GALLERY

In 1976, Polyakov (1976) predicted the existence of ionospheric Alfvén resonator (IAR), equivalent to the ionospheric waveguide, but operating in vertical direction with shear Alfvén waves. According to the theory, further developed by Polyakov and Rapoport (1981), waves can be trapped between two altitudes characterized by large Alfvén velocity gradients: the lower limit occurs at ionospheric F-layer, the upper limit at about 3000 km. For a review, see, e.g., Lysak (1993).

In 1976, Polyakov (1976) predicted the existence of ionospheric Alfvén resonator (IAR), equivalent to the ionospheric waveguide, but operating in vertical direction with shear Alfvén waves. According to the theory, further developed by Polyakov and Rapoport (1981), waves can be trapped between two altitudes characterized by large Alfvén velocity gradients: the lower limit occurs at ionospheric F-layer, the upper limit at about 3000 km. For a review, see, e.g., Lysak (1993).

In 1976, Polyakov (1976) predicted the existence of ionospheric Alfvén resonator (IAR), equivalent to the ionospheric waveguide, but operating in vertical direction with shear Alfvén waves. According to the theory, further developed by Polyakov and Rapoport (1981), waves can be trapped between two altitudes characterized by large Alfvén velocity gradients: the lower limit occurs at ionospheric F-layer, the upper limit at about 3000 km. For a review, see, e.g., Lysak (1993).