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

The fluxes and phase space densities for a fixed 1st 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 1st adiabatic invariant and phase space density based on the large data base available from the APL/JHU EPD charged particle detector on Galileo. This is the first time where the EPD high energy data set collected over the entire mission duration has been used for this purpose. Thus, this paper provides insight into the long term (~7 years) dynamics of the high energy electron and proton environment at Jupiter which has not been studied in its entirety before. To be specific, 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 1st 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, 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 1st adiabatic invariant versus L-shell. In addition, the GIRE3 flux contours at constant energy were converted to phase space densities to estimate the applicable range of the data and model. 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 starting point for diffusion analyses and similar studies.