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| Paper: |
Time-dependent Solar Modulation of GCRs Using a Monte Carlo Simulation |
| Volume: |
385, Numerical Modeling of Space Plasma Flows: Astronum-2007 |
| Page: |
31 |
| Authors: |
Li, G.; Webb, G.M.; le Roux, J.A.; Zank, G.P.; Wiedenbeck, M.E. |
| Abstract: |
In characterizing solar modulation of galactic cosmic rays, an often used parameter is the so called modulation parameter φ, whose value varies by a factor of more than 3 from solar maximum to solar minimum, reflecting the effects of different levels of solar activity on the modulation. This approach however, is based on the assumption that the current of GCRs is small and can be taken to be zero at all times, leading to a steady state solution of the transport equation. Recently, using data from CRIS/ACE and ground neutron monitor, Wiedenbeck et al. showed that for the declining phase of the solar cycle 23, the neutron monitor counting rate has been at a level of 4 percent higher than during the period when φ had comparable values during the rising phase of solar cycle 23. In this work, we examine this differences of neutron monitor counting rates (or alternatively, the difference of φ themselves) between the rising phase and declining phase of the solar cycle. We show that the modulation of low energy GCRs is more sensitive to the phase of the solar cycle than high energy GCRs. We present here, for the first time, using the framework of stochastic differential equation, to solve the time dependent transport equation and investigate the effect of a time dependent modulation. |
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