[P-EM15] Heliosphere and Interplanetary Space

[PEM15-06] Statistical behavior of galactic cosmic rays in the steady heliosphere

*Kotaro Yoshida¹, Shuichi Matsukiyo^2,3, Haruichi Washimi³, Tohru Hada^2,3 (1.Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 2.Faculty of Engineering Sciences, Kyushu University, 3.International Center for Space Weather Science and Education, Kyushu University,)

Keywords:galactic cosmic rays, heliosphere, test particle simulation, MHD simulation

Most of the galactic cosmic rays (GCRs) coming from interstellar space are prevented from entering the heliosphere. Only a fraction of them can propagate deep inside the heliosphere and be observed on the Earth. Their motion in the heliosphere is strongly affected by the solar modulation effects.

In the last meeting, we mainly reported the trajectory analysis results of 10 GeV and 1TeV GCR protons in the heliosphere. The heliosphere is reproduced by an MHD simulation assuming the steady solar wind and its north polarity solar magnetic field with zero tilt angle. We showed that GCR trajectories could be characterized by the relative scale between particle gyroradii and heliospheric structures.

In this study, we perform large scale test particle simulations with an increased number of particles to discuss statistics of the GCRs reaching the inner boundary (at 50 AU from the Sun). Monoenergetic test particles in the range of 10 GeV to 1 TeV are uniformly distributed outside the heliosphere as an initial condition. We analyze the statistics of the GCRs reaching the inner boundary after a sufficiently long time, such as the arrival direction distribution and the arrival rate. Further, we estimate the GCR energy distribution outside the heliosphere and show how the heliospheric structures contribute to the GCRs statistics.