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

Abstract

Emissions near 10 kHz are also reported (Menietti et al., 2009), but this needs further study. Case studies have shown that the Z-mode NB (at both 5 and 20 kHz) can be generated by temperature anisotropy and loss cone distributions in the low latitude region interior to the plasma torus, whereas the modulation analysis and direction finding results indicate a possible auroral source (Menietti et al., 2011(Menietti et al., , 2016(Menietti et al., , 2018. More events to check the plasma distribution near the source region will help to further explore the generation of the Z mode NB. According to the Z-mode dispersion relation, the initially generated Z-mode NB would be trapped in a "Channel" formed by the iso-surfaces of the f uh and f L = 0 (f uh upper hybrid frequency, f L = 0 Z-mode cut-off frequency; Sonwalkar et al., 2004). These "trapped" Z-mode NB can mode convert to the "free space" L-O mode NB at density gradients (Menietti et al., 2019;Ye, Menietti, et al., 2010). Due to the blockage of the high density plasma torus (centered at the equatorial plane) generated by the cryovolcanic activity of the moon Enceladus, the L-O mode NB originally generated interior to the plasma torus would propagate to high latitudes unhindered, creating a low latitude shadow zone outside the plasma torus (S. Ye, Menietti, et al., 2010). However, 5 kHz NB is still observed at low latitudes outside the plasma torus. How did these NB bypass the plasma torus?

Ray‐Tracing Analysis for the Propagation of Saturn Narrowband Emission Within the Saturnian Magnetosphere

“…The 5 kHz NB emission shows a cut‐off at the magnetopause, whereas the 20 kHz NB emissions can propagate into the magnetosheath with some attenuation, as previously discussed in Wu et al. (2022). The observations shown in Figure 3 Panels (a)–(b), including the wave electric field spectrogram and circular polarization, were obtained from measurements of the Cassini RPWS (Radio and Plasma Wave Science) High Frequency Receiver (Gurnett et al., 2004).…”

“…At 11 July and near 12:00 UT, Cassini is in the dayside magnetosheath (inferred from the boundary crossing list of Jackman et al, 2019) as marked by the text in Panel (a). The 5 kHz NB emission shows a cut-off at the magnetopause, whereas the 20 kHz NB emissions can propagate into the magnetosheath with some attenuation, as previously discussed in Wu et al (2022). The observations shown in Figure 3 Frequency Receiver (Gurnett et al, 2004).…”

“…For instance, the L-O mode NB emissions, originally generated by mode conversion from the Z mode waves near a density gradient interior to the plasma torus, are expected to propagate freely but are probably reflected by the dense plasma torus in the equatorial region, ultimately propagating toward high latitudes. Wu et al (2022) suggested that the 5 kHz L-O mode NB emissions may undergo reflection at the magnetosheath and be redirected back to the equatorial region outside the plasma torus, while the 20 kHz L-O mode NB emissions can escape from the magnetosphere, creating an equatorial shadow zone (Wu et al, 2021(Wu et al, , 2022.…”

“…Wu et al. (2022) suggested that the 5 kHz L‐O mode NB emissions may undergo reflection at the magnetosheath and be redirected back to the equatorial region outside the plasma torus, while the 20 kHz L‐O mode NB emissions can escape from the magnetosphere, creating an equatorial shadow zone (Wu et al., 2021, 2022).…”

Saturn Anomalous Myriametric Radiation, a New Type of Saturn Radio Emission Revealed by Cassini

“…Only 8 SAM cases are observed in the equatorial plane as shown in panel (a), which could be due to the reflection at the magnetosheath when the electron density in the magnetosheath is high enough, similar to the 5 kHz NB (Wu et al, 2022). This suggests that SAM emissions rarely undergo reflections at the magnetosheath as their frequency is mostly above the plasma frequency in the sheath (Wu et al, 2022). 3.…”