Permalink : http://hdl.handle.net/2115/20425

JaLCDOI : 10.14943/gbhu.70.85

The radiation belts are the region that energetic charged particles are trapped by Earth’s magnetic field. It is well known that the energetic particles flux are varied during geomagnetic disturbances. Many researchers have studied about the flux variation of radiation belt, but the mechanism of the variation has not been understood in detail. A radial diffusion model can reproduce a basic structure of the radiation belts. Radiation belt particles are supplied from the outer boundary of the radiation belt, and the flux is arranged by the balance of intensity of the diffusion and the loss due to pitch-angle scattering. An intensity and a distribution of the electrostatic field and the whistler waves which determine the magnitude of the diffusion and the loss of radiation belt particles are uncertain. Cornwall (1968) derived the radial diffusion coeffcient due to substorm convection electrostatic field. Brautigam and Albert (2000) derived the root mean square of electrostatic field which is a linear function of Kp index from observations. Lyons et al. (1972) calculated the pitch-angle diffusion within the plasmasphere and the lifetime of the particles. Solving the radial diffusion equations using these functions, the slot region is not formed and the flux near the Earth region is too large. Diffusion coeffcient is reduced by 1/100 at L < Lpp, the slot is formed and too much flux injection from outer belt is suppressed. The change of radial diffusion coeffcient at the plasmapause location may affect the structure of radiation belts.