Reflection and Refraction of the L‐O Mode 5 kHz Saturn Narrowband Emission by the Magnetosheath

The reflection-by-sheath mechanism of 5 kHz narrowband emissions (NB) at Saturn is confirmed by Cassini observations during several crossings of the magnetopause, which show that the 5 kHz NB can be prevented from escaping Saturn's magnetosphere. The L-O mode 5 kHz NB remained visible in areas of low plasma density but disappeared in regions of high plasma density. In three cases, NB disappeared immediately after the crossings of Saturn's magnetopause. A possible reflected NB event observed near the magnetosheath is discussed. This mechanism can help explain the 5 kHz NB observed at low latitudes outside the Enceladus plasma torus and their upper frequency limit variations. This mechanism significantly improves the current understanding of the 5 kHz NB. Plain Language Summary Very low frequency narrowband radio emissions have been observed at about 5 and 20 kHz by the Voyager and Cassini spacecraft at Saturn. Recently, a statistical survey of Saturn narrowband emissions indicated that the 5 kHz narrowband emissions could be reflected by Saturn's magnetosheath due to the high plasma density within. The work presents evidence to confirm the reflection and refraction of 5 kHz narrowband emissions by Saturn's magnetosheath. The observations of narrowband emissions near Saturn's magnetosheath show that sometimes the 5 kHz narrowband emissions cannot pass the magnetosheath when the plasma density is high enough, at other times the polarization reverses near the magnetosheath, which indicates a reflected signal. This survey confirms the reflection-by-sheath mechanism, and it is of special importance because this mechanism significantly improves the current understanding of the Saturn narrowband emissions and explains several features of them.