ABSTRACT
The first unambiguous report of whistlers was made by H. Barkhausen during World War I when it was common practice to eavesdrop on enemy telephone conversations at the front. He showed conclusive evidence that whistlers originated in lightning discharges in the opposite hemisphere and then propagated in the magnetosphere along the geomagnetic field lines to the hemisphere of the observer. When whistlers were explained as radiation from lightning that had traveled several Earth radii out into space, it became clear that they contained useful information about the medium through which they had propagated. There is evidence that whistlers interact with energetic electrons in the radiation belts during their traversal through the magnetosphere. The rocket observation of the wave normal direction of whistlers in the ionosphere, together with the simultaneous ground observation, experimentally confirmed the presence of this transmission cone, which was found to be slightly larger than the theoretical value.
