Stochastic mixing of protons from chaotic orbits in the nightside geomagnetosphere

Abstract

The stochastic mixing of protons in the energy range from 1 to 30 keV in the night‐side magnetosphere is studied by calculating the local divergence rate of neighboring orbits and the two‐time velocity correlation function. The rate of divergence of neighboring bundles of trajectories is shown to have large bursts with average separation times of order 1 minute per e ‐folding during the crossing of the central plasma sheet in the region beyond −50 R e . For the Tsyganenko magnetosphere the net amount of orbit divergence is 15 to 20 e ‐foldings in one hour. The velocity correlations are shown to decay as power laws τ −m with a distribution of m values. These results indicate that for short time (<1 hour) there is reversibility and memory for the protons but for longer times there is no memory for protons in the nightside magnetosphere.