Observations in the downward auroral current region of Saturn's magnetosphere by Cassini: Electron and ion beams and their relation to the Low-frequency waves

Details Observations in the downward auroral current region of Saturn's magnetosphere by Cassini: Electron and ion beams and their relation to the Low-frequency waves Observations in the downward auroral current region of Saturn's magnetosphere by Cassini: Electron and ion beams and their relation to the Low-frequency waves

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm23a1919s&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM23A-1919

Physics

[2721] Magnetospheric Physics / Field-Aligned Currents And Current Systems, [2756] Magnetospheric Physics / Planetary Magnetospheres, [2772] Magnetospheric Physics / Plasma Waves And Instabilities, [5737] Planetary Sciences: Fluid Planets / Magnetospheres

Scientific paper

On day 291 of year 2008, while Cassini was crossing the auroral regions, magnetospheric instruments onboard the spacecraft measured unusual strong signals: 1) a very intense field-aligned current system was identified using the magnetometer (MAG), 2) strong electron and ion flux were measured by the detectors of charged particles (CAPS-Cassini plasma spectrometer; MIMI-Magnetospheric imaging instrument), and a strong enhancement of the radio (ie. Saturn Kilometric Radiation) and plasma waves in the low-frequency range was identified by the electric antennas (RPWS; Radio and plasma wave science). Our analysis focuses on the observations in the downward auroral current region. In this region, CAPS measured upward directed field-aligned electron flux and ion flux within the 100eV-100keV energy range. While the upward electron fluxes are expected, the observation of upward-directed ion beams is surprising but has been previously observed at Earth and was explained by the so-called Pressure-cooker effect. RPWS measured strong enhancement of low-frequency waves below the electron cyclotron frequency. 3 types of plasma wave emissions were identified: a) Broadband extremely low frequency waves (BBELF), b) Whistler-mode (WM), and c) Electrostatic/Electromagnetic ion cyclotron wave (ICW) harmonics. In this work, we investigate the origin of WM and ICW in terms of beam-plasma instability, for which we calculate the growth rates. We then discuss the origin of BBELF in terms of turbulence. Finally we will discuss the origin of the heating of the ions by wave-particle interaction (WPI) with the identified low-frequency waves and the effectiveness of pressure-cooker effect.

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