Calculating Method on Charged Particles Motion in the Near-Earth Region

In this paper, based on the theory of magnetospheric particle dynamics, the charged particles motion character and the calculating method appropriate to these different energy particles in the near-earth region （L 〈 10） are discussed in detail, in terms of the single particle approach and dipole filed model. And then, it is analyzed quantitatively how the electric and magnetic field in the magnetosphere determined these particles drift motion. It is shown that, for the electron and proton with energy lower than 10^5 eV and 10^2 eV, respectively, the Guiding-Center Approximation Appoach （GCAA） is recommended; for 10^5 - 10^8 eV electron and 10^2 - 10^8 eV proton, GCAA or trajectory approach with adaptive step can be adopted in some regions. As for GCAA, the electric drift can be ignored when particle energy is higher than 10^5 eV, and the magnetic drift does not need to be taken into account when particle energy is lower than 10^3 eV. So the guiding-center equations are simplified and the efficiency of numerical calculation is improved.