1st Adiabatic Invariants and Phase Space Densities for the Jovian Electron and Proton Radiation Belts—Galileo and GIRE3 Estimates

Abstract:

The fluxes and phase space densities for a fixed 1^st adiabatic invariant for high energy electrons and protons provide important input data for a variety of scientific studies for determining the physics of particle diffusion and energization. This study addresses these issues for the jovian environment by providing estimates of the 1^st adiabatic invariant and phase space density based on the large data base available from the APL/JHU EPD charged particle detector on Galileo. 10 minute averages of the high energy EPD electron and proton data are used to compute electron and proton differential flux spectra versus energy between L=~8 and L=25 L over the Galileo mission. These spectra provide estimates of the differential fluxes and phase space density for constant 1^st adiabatic invariants between 10² MeV/G to 10⁵ MeV/G. As would be expected from previous studies, the electron and proton fluxes and phase space densities generally trend lower as the planet is approached. The results indicate that, whereas the overall trends for each orbit are consistent, the detailed orbit to orbit variations can be observed. Galileo orbit C22 is presented as a specific example of deviations from the mean downward trend. To validate the Galileo results and extend the findings into 3 L, the GIRE3 model, which is an amalgam of synchrotron measurements and Pioneer, Voyager, and Galileo in-situ data, was also used to compute the fluxes and phase space densities for constant 1^st adiabatic invariant versus L-shell. In addition, the GIRE3 flux contours at constant energy were converted to phase space densities to determine the applicable range of the results. Comparing the GIRE3 and Galileo findings demonstrates that, while the model adequately reproduces the EPD data trends, it shows additional variations near Io. Though the agreement between the data and model is not unexpected as the model is based in part on the Galileo data, it provides proof that the GIRE3 is a useful input for diffusion analyses and similar studies.