Whistlers

Early on in the mission, each of the three Swarm satellites’ magnetometers was run temporarily in a higher frequency mode than normal. Data from this time have been reanalysed and revealed that, surprisingly, the instruments detected these waves. Converted into sound, they are known as whistlers. The whoosh of these lightning whistlers can be heard in the animation. Although few whistlers at such unusual frequencies have been measured from space before, Swarm detected some 4000 in just four days, which is a particularly rich dataset. This provides a unique opportunity to investigate the nature of the ionosphere and also see how lightning signals escape the atmosphere and propagate into space.