A Data-Model Comparison Approach to Understand the Source and Transport Mechanisms of keV-Energy Electrons at Saturn

Friday, 19 December 2014
Daniel Santos-Costa, Southwest Research Institute San Antonio, San Antonio, TX, United States, George B Clark, Catholic University of America, Washington, DC, United States, Chris Paranicas, Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, John Douglas Menietti, University of Iowa, Physics and Astronomy, Iowa City, IA, United States and Wei-Ling Tseng, NTNU National Taiwan Normal University, Department of Earth Sciences, Taipei, Taiwan
We present results from a multi-instrument data analysis and interpretation of Cassini observations that is guided by a theoretical model. Through this analysis, we discuss the source and transport mechanisms of energetic electrons at Saturn and attempt to explain their spatial distributions inside 20 planetary radii (Rs). Using only data sets from equatorial orbits, a recent analysis of Cassini MIMI/LEMMS, CAPS, and MAG data sets by Clark et al. (2014; doi:10.1016/j.pss.2014.07.004) demonstrated how the angular profiles (i.e., ‘pancakes’, ‘isotropic’, ‘field-aligned’, and ‘butterfly’ PADs) of keV-energy electrons are statistically distributed at Saturn. Through a theoretical transport model, Clark et al. (2014) also demonstrated the role of Saturn’s neutral gas torus with adiabatic transport to explain the spatial distribution of electrons. However, their data/model comparison was limited to a case study analysis and the data-model comparison results still do not provide the full picture in understanding the source of keV-energy electrons and their radial evolution. Here we continue to refine our understanding of the spatial distributions of keV-energy electrons at Saturn with the use of a data-model comparison approach. Using the full set of MIMI/LEMMS particle data available for the period mid-2004 to mid-2014, we carefully reexamine the role of neutrals and adiabatic transport for the region ~10 to 15 Rs. Using PAD profiles deduced from data sets at 15 Rs, we build different boundary conditions for our computational model and discuss how angular profiles radially evolve throughout the region ~10-15 Rs and which PADs at our boundary condition can explain the Cassini observations near ~10 Rs. We also present the results from our ongoing investigation of the dominant processes inside ~10 Rs and focus on the impact of chorus emission on the energetic electron distributions.