Magnetic Waves Excited by Newborn Interstellar Pickup Ions Measured by the Voyager Spacecraft from 1 to 45 au. II. Instability and Turbulence Analyses

Abstract

In this companion paper, we describe low-frequency magnetic waves observed in 637 intervals of Voyager   1 and 2 data from launch late in 1977 through 1990. By the end of 1990 the Voyager   1 spacecraft reached 43.5 au, while the Voyager   2 spacecraft reaches 33.6 au. The waves are attributed to newborn interstellar pickup He + and H + . In this analysis we follow the idea put forward by Cannon et al. and followed by Fisher et al. and Aggarwal et al. wherein the necessary condition for the observation of the waves is that the wave growth rate exceeds the background turbulence rate. We explore this idea and build on the conclusion in our companion paper that the waves are typically observed in rarefaction regions where the turbulence level is low and noise-dominated signals sometimes distort the computed background turbulence spectra.