The Spatial Distribution of Charge Exchange Loss Contributions to Storm
Time Ring Current Decay: Van Allen Probes Observations
Abstract
Charge exchange between hot ions and cold neutral atoms is an important
effect in ring current loss processes on magnetized planets. In this
letter, we investigate the spatial distribution of charge exchange loss
contributions to terrestrial ring current decay using data from the Van
Allen Probes. These contributions were calculated by dividing local
energetic neutral atom energy density escape rates by local ring current
energy density decay rates. The results exhibit clear MLT and L
dependence, with larger contributions observed nightside during the
recovery phase of geomagnetic storms. The contribution of H+; peaked at
L~4 during early recovery phases and was stronger at
higher L shells during late recovery phases, while O+; decreased
slightly with L shell. Possible explanations for this inhomogeneous
distribution are also discussed. The asymmetric exospheric hydrogen
density distribution may cause the inhomogeneous distribution in the
MLT, while the L dependence may be related to the charge exchange
cross-section and the ion energy flux. These results provide the first
spatial distribution of charge exchange contributions, which is helpful
for understanding local terrestrial ring current evolution.