Gravity wave and sporadic- E echo signatures on VHF backscatter radar systems

Abstract

Wave-like features in range seen on the range/time/intensity (RTI) records of VHF backscatter radars operating in the South of New Zealand are interpreted as being the signature of gravity waves propagating in an ionospheric sporadic- E layer. The data show that, during midsummer in particular, sporadic- E ionisation which has been modified by the passage of a gravity wave can produce two distinct echo types : backscatter from field-aligned irregularities within the sporadic- E layer, probably generated by plasma waves, and a second type of echo resulting from energy backscattered from the surface of the sea after specular reflection in the ionosphere. The backscattering and reflecting region can exist at latitudes at least as low as 49° geographic (57° geomagnetic) latitude during quiet magnetic conditions. We confirm the patchiness of dense sporadic- E, and conclude that gravity waves at sporadic- E heights have amplitudes of the order of several tenths of a kilometre.