33RD INTERNATIONAL COSMIC RAY CONFERENCE, RIO DE JANEIRO 2013 THE ASTROPARTICLE PHYSICS CONFERENCE Galactic cosmic ray modulation beyond the heliopause: When will Voyager 1 measure the LIS?

Abstract: With the Voyager 1 (V1) crossing of the heliopause (HP) believed to happen soon, this paper tries to answer the question: Are galactic cosmic rays (GCRs) modulated beyond the HP? Using a newly developed hybrid GCR modulation model, where the resulting heliospheric geometry and plasma flow fields from a 3D MHD model are coupled to a stochastic differential equation (SDE) based transport model, the modulation of GCRs beyond the HP is studied. We find that a considerable amount of modulation may occur beyond the HP and that, based on the assumed transport parameters, V1 may not measure the pristine LIS for GCRs soon. Moreover, we show that modulation beyond the HP is dependent on the modulation conditions inside the HP because of the GCRs ability to cross the HP multiple times. Due to the draping of the interstellar magnetic field lines along the HP, modulation beyond the HP is determined by the ratio of parallel to perpendicular diffusion