Auroral electron distributions within and close to the Saturn kilometric radiation source region

Abstract

[1] On 17 October 2008, Cassini observed for the first time the electron populations associated with the crossing of a Saturn kilometric radiation source region and its surroundings. These observations allow for the first time the constraint and quantification of the high-latitude acceleration processes, the current systems, and the origin of the low-frequency electromagnetic waves. Enhanced fluxes of field-aligned energetic electrons were measured by the Cassini electron plasma spectrometer in conjunction with unusual intense field-aligned current systems identified using the magnetometer instrument. In the region where downward field-aligned currents were measured, electron data show evidence of two types of upward accelerated electron beams: a broadband energetic (1-100 keV) electron population that is observed throughout the region and a narrow-banded (0.1-1 keV) electron population that is observed sporadically. In the regions where the magnetic field signatures showed evidence for upward field-aligned currents, we observe electron loss cone distributions and some evidence of shell-like distributions. Such nonthermal electron populations are commonly known as a potential free energy source to drive plasma instabilities. In the downward current region, the low-energy and energetic beams are likely the source of the very low frequency emissions. In the upward current region, the shell distribution is identified as a potential source for Saturn kilometric radiation generation via the cyclotron maser instability.

Search for Saturn's X‐ray aurorae at the arrival of a solar wind shock

“…We can compare the case discussed above with the crossing of the first SKR source on DOY 291 of 2008, at high southern latitudes, close to midnight and at 5 R S , which precisely followed a SW compression, revealing downward precipitating electrons with energies of 6–9 keV and upward travelling ions of more than 10 keV energy [ Bunce et al ., ; Lamy et al ., ; Schippers et al ., ]. This suggests that precipitating electrons may reach energies up to and above 20 keV.…”

Energetic Electron Pitch Angle Distributions During the Cassini Final Orbits

“…Energetic electron PADs were used in conjunction with other Cassini instruments to determine Saturn's polar cap boundary, mapped to the ionosphere, for (Jinks et al, 2014. Such electrons also exhibit bidirectional structures, and these are sometimes associated with field-aligned currents inferred from magnetometer measurements or with an instability region associated with Saturn kilometric radiation (Schippers et al, 2011(Schippers et al, , 2012. Similar investigations have been conducted for the lower energy electrons (E < 3 keV) using the Cassini Plasma Spectrometer (CAPS; Young et al, 2004).…”

Rotational modulation of Saturn Kilometric Radiation, narrrowband emission and auroral hiss

“…SKR is generated on auroral field lines in the upward current region whereas auroral hiss is generated by electrons moving up an auroral field line in the downward current region [Gurnett et al, 2009a and b;Schippers et al, 2011]. The upward and downward current regions should be separated by roughly 180…”