The effects of lightning and impulse currents on the perturbations of the state of polarization (SOP) of optical beams transmitted on aerial cables are emulated in a laboratory environment. Submicrosecond-resolved measurements enable us to distinguish and quantify the magnetooptic contributions due to the discharge current. The maximum of Faraday-induced circular birefringence associated to natural strokes is estimated in /spl Delta/n/sub lr//spl ap/10/sup -7/ and may lead in a few microseconds to iterate swapping between orthogonal SOPs. The corresponding peak in relative phase delay, cumulated in transmission along a span, is evaluated as /spl Delta//spl tau//sub lr//spl ap/0.3 ps.