Partly ducted whistlers over Europe

The ducted and nonducted whistlers observed at ground and aboard satellites respectively are briefly reviewed. Another type (one and two hop whistlers) named partly ducted whistlers is observed aboard satellites in a large area over Europe. Their spectrographic traces are always diffuse and their morphology is consistent with a theoretical study of partly ducted propagation through the magnetosphere of the VLF energy radiated by lightning. This mode of propagation seems to be a magnetospheric permanent feature during magnetic quiet conditions. It implies that: 1. (i) the wave is ducted by electron irregularities aligned along the Earth magnetic field lines in the vicinity of the equatorial plane between L = 2 and 2, 6; and 2. (ii) after leakage out of ducts, it propagates through an homogeneous medium in the nonducted mode and can reach the conjugate ionosphere over a very large area extending sometimes from L = 1, 2 to 3, 6 and over more than 50° in longitude.