Experimental evidence of ELF plasma ducts in the ionospheric trough and in the auroral zone

Simultaneous measurements of the fine structure of the topside F-region electron density and the ELF hiss wave characteristics, carried out aboard the Aureol/Arcad 3 satellite, provide evidence of an efficient ducting mechanism produced by crests of ionization. The horizontal size of these plasma ducts lies, typically, in the range 5-50 km. The shape of the density structures as well as the wave propagation characteristics exhibit a well-marked difference between the inner and outer sides of the equatorward boundary of the mid-latitude ionospheric trough. Moreover, the observation of small scale plasma instabilities and electrostatic turbulence, occurring usually on the flanks of density enhancements, strongly suggests that the ducts are convecting structures assumed to be created in the auroral zone. 14 references.