A Computational Study of Cross Field Diffusion of Energetic Particles Caused by their Interaction with Magnetic Decreases in Interplanetary Space

Edio da Costa Junior1, Bruce T. Tsurutani2, Maria Virgania Alves1, Ezequiel Echer1

1National Institute for Space Research - INPE, Brazil
2Jet Propulsion Laboratory - NASA, USA

There are regions in the interplanetary space where the strength of the magnetic field is low as compared to around regions. These structures are nowadays usually called Magnetic Decreases (MDs). MDs are probably created by a diamagnetic effect caused by the heating of particles that are accelerated preferentially perpendicular to B. The particle acceleration is associated with the dissipation of phase-steepened Alfven waves, presumably through the ponderomotive force. Our main intent in this work is to investigate non-resonant cross-field diffusion particles due to their interactions with MDs at large heliospheric latitudes and at the ecliptic plane. In order to perform that we start using analytical expressions for the distributions of magnetic field decreases and sizes of the MDs at large heliospheric latitudes. These expressions were obtained from analytical fits of Ulysses data. In order to have an statistical representation of these distribution functions we use Monte Carlo method (Amar, Computing in Science and Engineering, 8(2), 9, 2006). A theoretical model for particle diffusion has been presented by Tsurutani et al. (Nonlinear Processes in Geophys., 6, 235, 1999). We use this model in our calculations by letting a particle with an specific energy interacts with an MD to which field decrease and thickness are attributed by the respective Monte Carlo representation of the distribution functions. This process can go on until all particles have been scattered. Besides that, we have also obtained results for the coefficient diffusion using particles (protons) within a large range of energy (100 keV to 100 MeV) interacting with MDs of constant features to find out what would be the influence of MDs parameters on the diffusion. Nowadays, we are analyzing Ulysses magnetic field data corresponding to the ecliptic plane to derive distribution functions for MD properties to calculate the cross-field diffusion of energetic particles in low latitudes.