Energetic particles and the solar cycle: Impact of solar magnetic field amplitude and geometry on SEPs and GCRs diffusion coefficient B. Perri1, A. Strugarek2, A. S. Brun2, V. Réville3 and E. Buchlin4 1 Centre for Mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200b-box 2400, B-3001 Leuven, Belgium 2 Université Paris Saclay and Unviersité de Paris, CEA, CNRS, AIM, F-91190 Gif-sur-Yvette, France 3 IRAP, Université de Toulouse III-Paul Sabatier, CNRS, CNES, Toulouse, France 4 Université Paris-Saclay, CNRS, Institut d’astrophysique spatiale, 91405, Orsay, France Abstract • Réville V, Velli M, Panasenco O, Tenerani A, Shi C, et al., 2020, ApJ, 246(2): 24 • Shalchi A, Bieber JW, Matthaeus WH, 2004, ApJ, 604(2): 675-686 • Spruit HC, 1981, vol. 450, Jordan S, (Ed.) NASA Special Publications, pp. 385-413 • Zank GP, Matthaeus WH, Bieber JW, Moraal H, 1998, J. Geophys. Res., 103(A2): 2085 • Bieber JW, Matthaeus WH, Shalchi A, Qin G, 2004, Geophys. Res. Lett., 31(10):L10, 805 • Chhiber R, Subedi P, Usmanov AV, Matthaeus WU, Ruffolo D, Goldstein ML, Parashar TN, 2017, ApJ, 230(2): 21 • Heber B, Potgieter MS, 2006, Space Sci. Rev, 127(1-4): 117 • Jokipii JR, Parker EN, 1970, ApJ, 160:735 • Mignone A, Bodo G, Massaglia S, Matsakos T, Tesileanu O, Zanni C, Ferrari A, 2007, ApJ, 170(1): 228 Get the article here! Hey, that’s me! doi/10.1051/swsc/2020057 SEPs (Solar Energetic Particles) are correlated with the 11-year solar cycle due to their production by flares and interaction with the inner heliosphere, while GCRs (Galactic Cosmic Rays) are anti-correlated with it due to the modulation of the heliospheric magnetic field. The solar magnetic field along the cycle varies in amplitude but also in geometry, causing diffusion of the particles along and across the field lines; the solar wind distribution also evolves, and its turbulence affects particle trajectories. We combine 3D MHD (magnetohydrodynamic) compressible numerical simulations to compute the configuration of the magnetic field and the associated polytropic solar wind up to 1 AU, with analytical prescriptions of the corresponding parallel and perpendicular diffusion coefficients for SEPs and GCRs. First, we analyze separately the impact of the magnetic field amplitude and geometry for a 100 MeV proton. By varying the amplitude, we change the amplitude of the diffusion by the same factor, and the radial gradients by changing the spread of the current sheet. By varying the geometry, we change the latitudinal gradients of diffusion by changing the position of the current sheets. We also vary the energy, and show that the statistical distribution of parallel diffusion is different for SEPs and GCRs. Then, we use realistic solar configurations, showing that diffusion is highly non-axisymmetric due to the configuration of the current sheets, and that the distribution varies a lot with the distance to the Sun, especially at minimum of activity. With this model, we are thus able to study the direct influence of the Sun on Earth spatial environment in terms of energetic particles. Fig. 1: Time evolution of the count rate of >70 MeV protons at Earth (black), by Voyager 1 (red) and Voyager 2 (green) (Heber & Potgieter 2006). We see the anti-correlation with the 22-yr cycle. Modeling the solar wind We solve the ideal MHD equations up to 1 AU using the multi- physics code PLUTO with a polytropic wind model (Mignone +2007, Réville+2015a, Perri+2018). Wind reference case D1 (dipole of low amplitude): Fig. 2: Meridional cut of the wind solution for case D1 (dipole of low amplitude). The colorscale represents the Mach number projected on the normalised magnetic field. The white lines are the poloidal magnetic field lines (Perri+2020). Modeling the cosmic rays diffusion We focus on the diffusivity term in the Fokker-Planck equation for cosmic rays (CRs) transport and implement them in post-processing (Parker 1965, Jokipii & Parker 1970, Zank+1998, Shalchi +2004): We also need to model the w