Parameterization of the spatial and temporal distribution of radial diffusion coefficients in the outer Van Allen belt.

Radial diffusion in planetary radiation belts is a dominant transport mechanism resulting in the energization and losses of charged particles by large-scale electromagnetic fluctuations. In this work we exploit the extensive radial diffusion coefficients (D LL) database created in the framework of the Horizon 2020 SafeSpace project, which spans 9 years of hourly D LL coefficients, to investigate the spatio-temporal distributions of the coefficients. Our results indicate that the radial distribution of the magnetic and electric component of the D LL , as well as their sum, the total D LL , can be well described by a power law function of L* in the [4.3–7.7] range. We show that the L*-dependent spectral index varies significantly and is far from constant as assumed and implemented in many semi-empirical models. We examine the quasi-periodic behavior of the radial profiles of the D LL throughout most of the 24th Solar cycle, which the data cover, and find an approximately 420 days dominant periodicity. This periodic behavior is linked (in terms of cross-wavelet analysis) with solar activity, nevertheless, its origin remains unclear. The uncovered features are important for understanding D LL behavior and drivers as well as for current and future modelling efforts. [ABSTRACT FROM AUTHOR]