Whistler-mode waves upstream of Saturn

摘要: Whistler-mode waves are generated within and can propagate upstream of collisionless shocks. They known to play a role in electron thermodynamics/acceleration and, under certain conditions, markedly observed as wave trains preceding the shock ramp. In this paper, we take advantage Cassini's presence at ~10 AU explore importance whistler-mode parameter regime typically characterized by higher Mach number (median ~14) shocks, well significantly different IMF structure, compared near Earth. We identify electromagnetic precursors small subset bow crossings with properties which consistent waves. find these monochromatic, low-frequency, circularly-polarized have typical frequency range 0.2 – 0.4 Hz spacecraft frame. This is due lower ion cyclotron frequencies Saturn, between whistler develop. The also predominantly right-handed frame, opposite sense what attributed weaker Doppler shift, owing large angle solar wind velocity magnetic field vectors 10 AU. Our results on low occurrence Saturn underpins supercritical Saturn.