Cause of the Minimum in the Earth's Radiation Belt

It has been argued that both radiation belts (1.5 and 3 to 4 earth radii) may be of solar origin with the minimum at 2R/sub E/ due to some other cause. In order to decide among the various possibilities on the cause of the minimum, the expected altitude dependence of the cosmic-ray belt was calculated by incorporating in more detail the breakdown of the adiabatic condition. (W.D.M.)