Discovery of Alfven waves planetward of the Rings of Saturn
<p>Between April and September 2017 in the final stages of the Cassini Saturn Orbiter mission the spacecraft executed 22 orbits passing planetward of the innermost ring, the D-ring.&#160; During periapsis passes on all these orbits oscillations were detected in the azimuthal magnetic field components on typical time scales from a few minutes to 10 minutes. We argue that the time-varying signals detected on the spacecraft are also primarily time-varying in the plasma frame.&#160; Nonetheless, we show that nearly all signals exhibit a distinct spatial effect, namely a magnetic node near the effective field line equator.&#160; The oscillations thus have a standing structure along the background magnetic field and it follows that they are field line resonances associated with Alfv&#233;n waves.&#160; The form of the signals suggests that the local field line resonances are most likely pumped from global sources. &#160;This is the first detection in a giant planet magnetosphere of a phenomenon known to be important at Earth.</p>
Compressional wave events in the dawn plasma sheet observed by Interball-1
