A study of ionospheric absorption events at very high latitudes

International audience; Riometer recordings at Dumont d'Urville station (Antarctica) show very often absorption events characterized by an irregular and slowly varying absorption of about 0.2 to 1 dB.Analysis of these data and of simultaneous ionograms allows the separation of these events into three homogenous populations, one of which is associated with F-lacuna, i.e. the disappearance on the ionograms of all or part of echoes from the F-region.This paper describes the method of separation of these populations and describe the properties of occurrence of each of them.