On the electric current systems in the Earth's environment some historical aspects. Part II : external part/ ionosphere/ disturbed variation

Published in a book of History of geomagnetism and aeronomy, Solar varibility and Geomagnetism,lectures from the IAGA Assembly in Hanoï 2001, collected and edited by W. Schröder, pp 154-190, Science edition AKGGKP, Bremen-Rönnebeck, Postdam, 2002.International audienceIn this paper we present some historical aspects on ionospheric electric currents. Our attention is focused on the disturbed part of these currents at the origin of the Earth's magnetic field variation Dp. The steps described in this paper correspond to advances in fundamental physic, as well as in technology, data interpretation or other factors. The paper covers the period from 1870 up to now