Analysis of Intense Z‐Mode Emission Observed During the Cassini Proximal Orbits. Issue 14 (20th July 2018)

• Record Type: Journal Article
• Authors: Menietti, J. D.; Averkamp, T. F.; Ye, S.‐Y.; Sulaiman, A. H.; Morooka, M. W.; Persoon, A. M.; Hospodarsky, G. B.; Kurth, W. S.; Gurnett, D. A.; Wahlund, J.‐E.
• Is Part Of: Geophysical research letters. Volume 45:Issue 14(2018)
• Page Start: 6766
• Page End: 6772
• Publication Date: 2018-07-20
• Subjects: Z‐mode emission -- Saturn proximal orbits -- wave source region; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2018GL077354
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The role of Z ‐mode emission in the diffusive scattering and resonant acceleration of electrons is believed to be important at Saturn. A survey of the "5 kHz" component of this emission at Saturn earlier reported strong intensity in the lower density regions where the ratio of plasma frequency to cyclotron frequency, f p / f c < 1. At Saturn this occurs along the inner edge of the Enceladus torus near the equator and at higher latitudes. Using the Cassini Radio and Plasma Wave Science instrument observations during the Cassini proximal orbits, we have now identified these emissions extending down to and within the ionosphere. Wave polarization measurements and unique frequency cutoffs are used to positively identify the wave mode. Analogous to the role of whistler mode chorus at Earth, Saturn Z ‐mode emissions may interact with electrons contributing to the filling or depleting of Saturn's inner radiation belts. Plain Language Summary: Very intense waves are observed near Saturn that have been identified as Z mode. These waves are unusual because they are observed in a narrow range of frequencies from uncertain source regions and generation mechanism. However, we know that these waves can scatter electrons or even accelerate them by a process that is observed at Earth due to similar waves (whistler mode chorus), causing the terrestrial radiation belts to fill with high energy electrons or to dump those electrons along magnetic field lines toward the polar auroral regions. At Saturn Z ‐mode waves may be a source of filling or depleting Saturn radiation belts that lie along magnetic field lines that are intercepted by the waves. We have used the Cassini wave instrument to measure wave properties such as polarization and unique wave cutoff frequencies to positively identify these waves along the orbit of Cassini extending from the polar auroral regions down to closest approach within the Saturn ionosphere. Key Points: Intense Z ‐mode emission is observed along Saturn proximal orbits down to and within the ionosphere Source regions may be along magnetic field lines that thread SKR source regions or along inner edge of Enceladus torus Z mode may interact with electrons to fill or deplete the inner radiation belts