# The effect of turbulence strength on meandering field lines and Solar Energetic Particle event extents

Laitinen, Timo Lauri mikael ORCID: 0000-0002-7719-7783, Effenberger, Frederic, Kopp, Andreas and Dalla, Silvia ORCID: 0000-0002-7837-5780 (2018) The effect of turbulence strength on meandering field lines and Solar Energetic Particle event extents. Journal of Space Weather and Space Climate, 8 (A13).

However, adding cross-field transport of SEPs as spatial diffusion has been shown to be insufficient in modelling the SEP events without use of unrealistically large cross-field diffusion coefficients. Recently, Laitinen et al.\ (2013b, 2016) demonstrated that the early-time propagation of energetic particles across the mean field direction in turbulent fields is not diffusive, with the particles propagating along meandering field lines. This early-time transport mode results in fast access of the particles across the mean field direction, in agreement with the SEP observations. In this work, we study the propagation of SEPs within the new transport paradigm, and demonstrate the significance of turbulence strength on the evolution of the SEP radiation environment near Earth. We calculate the transport parameters consistently using a turbulence transport model, parametrised by the SEP parallel scattering mean free path at 1 AU, $\lambda*$, and show that the parallel and cross-field transport are connected, with conditions resulting in slow parallel transport corresponding to wider events. We find a scaling $\sigma\propto (1/\lambda*)^{1/4}$ for the Gaussian fitting of the longitudinal distribution of maximum intensities. The longitudes with highest intensities are shifted towards the west for strong scattering conditions. Our results emphasise the importance of understanding both the SEP transport and the interplanetary turbulence conditions for modelling and predicting the SEP radiation environment at Earth.