Jovian whistler waves propagate at audio frequencies along closed field lines in Jupiter's magnetosphere. Like Earth whistlers, the higher frequency components of the Jovian whistler propagate faster than the lower frequency components, resulting in a descending whistling tone. Also like Earth whistlers, Jovian whistlers are generated by lightning discharges in the atmosphere. It was the detection of these signals by the Voyager 1 spacecraft that provided the first indirect evidence of lightning on the giant planet.