Z mode waves as the source of Saturn narrowband radio emissions

Sheng-Yi Ye (1) , J. Menietti (1) , Georg Fischer (2) , Z. Wang (1) , Baptiste Cecconi (3, 4, 5) , Donald A. Gurnett (1) , William S. Kurth (1)

1 Department of Physics and Astronomy, Iowa State University
2 IWF - Institut für Weltraumforschung, Österreichische Akademie der Wissenschaften
3 Observatoire de Paris
4 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
5 Physique des plasmas

We report 5 kHz narrowband Z mode emissions observed by the Cassini Radio and Plasma Waves Science (RPWS) instrument during high latitude perikrone passes. The narrowband emissions observed below the local electron cyclotron frequency (f_ce) are >20 dB more intense than the usual L-O mode narrowband emissions observed above local f_ce. Polarization measurements show that the narrowband emissions observed below f_ce are oppositely polarized to those above f_ce, which identifies the emissions below f_ce with Z mode. We propose that the L-O mode narrowband emissions observed at 5 kHz are mode converted from the Z mode waves at a density gradient or density irregularity. The Z mode to L-O mode conversion via scattering off of density irregularities can also account for the direction finding results of 5 kHz narrowband emissions which point to a source in the auroral zone. We also present the first magnetic field measurements of Saturn narrowband emissions validating their electromagnetic nature.

Domaines: Astrophysique [astro-ph]

Sheng-Yi Ye, J. Menietti, Georg Fischer, Z. Wang, Baptiste Cecconi, et al.. Z mode waves as the source of Saturn narrowband radio emissions. Journal of Geophysical Research Space Physics, 2010, 115 (A08228), pp.8228. ⟨10.1029/2009JA015167⟩. ⟨hal-03733232⟩