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

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Abstract
Radial diffusion in planetary radiation belts is a dominant transport mechanism resulting in the energization and losses of chargedparticles by large-scale electromagnetic fluctuations. In this work we exploit the extensive radial diffusion coefficients (DLL) database createdin the framework of the Horizon 2020 SafeSpace project, which spans 9 years of hourly DLL coefficients, to investigate the spatiotemporaldistributions of the coefficients. Our results indicate that the radial distribution of the magnetic and electric component of theDLL, as well as their sum, the total DLL, 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. Weexamine the quasi-periodic behavior of the radial profiles of the DLL throughout most of the 24th Solar cycle, which the data cover, andfind an approximately 420 days dominant periodicity. This periodic behavior is linked (in terms of cross-wavelet analysis) with solaractivity, nevertheless, its origin remains unclear. The uncovered features are important for understanding DLL behavior and driversas well as for current and future modelling efforts.