Subsequent missions have observed parts of the belts-including SAMPEX
, which observed the belts from below-but what causes such dynamic variation in the belts has remained something of a mystery.
measurements showed that, in the first days of November, 2003, the radiation belts-- and the magnetic field lines that confine them--were pushed inward to only half their usual distance, 6,000 miles from the equator.
results show that the cosmic-ray nuclei are located within the inner Van Allen belt at an altitude of roughly 6,000 kilometers at the equator and that they increase in number as the Sun's activity drops during its 11-year cycle.
circles the Earth at an altitude of 600 kilometers.