An effect of charge exchange processes on the proton enhancement associated with a storm/substorm in the magnetosphere

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Energetic protons in the radiation belt of the earth's magnetosphere show energy density enhancement associated with geomagnetic storms/substorms, which observation with Explorer 45 evidently revealed as a nose structure in the E-t spectrogram inside the plasmasphere. An attempt has been made to explain this by an injection model in which energetic protons are injected around a nightside geosynchronous orbit with their subsequent inward motions due to a convection electric field possibly driven by the solar wind and a corotation electric field. It is also important to include a loss mechanism in the model inside the plasmasphere since the protons decay due to charge exchange loss processes with geocoronal neutral hydrogen. The loss rate of protons depends on the hydrogen density and charge exchange cross section. In this study, the effect of the charge exchange loss is examined by computer simulation of energetic proton trajectories in the magnetosphere; the hydrogen density being obtained by the Chamberlain model and the charge exchange cross section being adopted from the latest approximate formula. It is concluded that loss processes play an essential role in the energy density distributions of protons in the near earth radiation belts, especially inside L of about 4.
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