Radial diffusion models of energetic electrons and Jupiter's synchrotron radiation: 2. Time variability

Abstract

We used a radial diffusion code for energetic electrons in Jupiter's magnetosphere to investigate variations in Jupiter's radio emission due to changes in the electron phase space density at L shells between 6 and 50, and due to changes in the radial diffusion parameters. We suggest that the observed variations in Jupiter's radio emission are likely caused by changes in the electron phase space density at some boundary L1 > 6, if the primary mode of transport of energetic electrons is radial diffusion driven by fluctuating electric and/or magnetic fields induced by upper atmospheric turbulence. We noticed an excellent empirical correlation, both in phase and relative amplitude, between changes in the solar wind ram pressure and Jupiter's synchrotron radiation if the electron phase space density at the boundary L1 (L1 ≃ 20‐50) varies linearly with the square root of the solar wind ram pressure, fnof; ∼ (Ns υs2)1/2. The calculations were carried out with a diffusion coefficient DLL = DnLn with n = 3. The diffusion coefficient which best fit the observed variations in Jupiter’s synchrotron radiation D3 = 1.3 ± 0.2 × 10−9 s−1 ≃ 0.041 yr−1, which corresponds to a lagtime of approximately 2 years. A comparison with previous estimates on diffusion coefficients in Jupiter's inner magnetosphere (L ≲ 10‐20) suggests that all estimates can be described by n = 2.5 and D2.5 = 4.5 × 10−9 s−1 ≃ 0.142 year−1. We further show that the observed short term (days‐weeks) variations in Jupiter’s radio emission cannot be explained adequately when radial diffusion is taken into account.