2:00 PM - 2:15 PM
[PEM14-08] Numerical simulation on invasion process of galactic cosmic rays into the heliosphere: Particle orbits and statistics
Keywords:galactic cosmic rays, heliosphere
Galactic cosmic rays (GCRs) are produced in our galaxy. Some of them invade the heliosphere and reach the earth. The motion of GCRs in the heliosphere is very complicated because of the influence of solar wind flow and magnetic field. The transport processes of GCRs have been discussed by using convection-diffusion models. But the model does not tell us the information of GCRs trajectories. Our goal in this study is to understand the invading process of GCRs into the heliosphere in the level of particle trajectory.
We performed three-dimensional relativistic test particle simulations using electromagnetic fields reproduced by the global MHD simulation of the heliosphere ([1] Washimi et al. 2015). In the MHD simulation, the solar wind velocity, density, magnetic field strength and temperature at 1 AU are set to be 400 km/s, 5.0 /cc, 35 μG and 105 K, respectively. These quantities are assumed to be time stationary and simply extrapolated to the inner boundary of the simulation domain at 50 AU from the sun. For the outer boundary at 900AU, the corresponding parameters of the stationary interstellar plasma are 23 km/s, 0.1 /cc, 6,300 K, and 3 μG, respectively. In the test particle simulation, the motions of protons initially distributed outside the heliopause with Lorentz factor γ are solved. Their velocity distribution function is given by a mono-energetic shell distribution. We found various patterns of particle trajectories. They exhibit different characteristics depending on their initial energy. Some concrete trajectories will be discussed in detail. Furthermore, we will estimate some statistics of the particles reached at the inner boundary, such as distribution of arrival position, energy, momentum, etc.
We performed three-dimensional relativistic test particle simulations using electromagnetic fields reproduced by the global MHD simulation of the heliosphere ([1] Washimi et al. 2015). In the MHD simulation, the solar wind velocity, density, magnetic field strength and temperature at 1 AU are set to be 400 km/s, 5.0 /cc, 35 μG and 105 K, respectively. These quantities are assumed to be time stationary and simply extrapolated to the inner boundary of the simulation domain at 50 AU from the sun. For the outer boundary at 900AU, the corresponding parameters of the stationary interstellar plasma are 23 km/s, 0.1 /cc, 6,300 K, and 3 μG, respectively. In the test particle simulation, the motions of protons initially distributed outside the heliopause with Lorentz factor γ are solved. Their velocity distribution function is given by a mono-energetic shell distribution. We found various patterns of particle trajectories. They exhibit different characteristics depending on their initial energy. Some concrete trajectories will be discussed in detail. Furthermore, we will estimate some statistics of the particles reached at the inner boundary, such as distribution of arrival position, energy, momentum, etc.