Response of high-energy protons of the inner radiation belt to large magnetic storms

Abstract

[1] The responses of the high-energy protons (35–70 MeV, 70–140 MeV and 140–500 MeV) below L = 3 to the large geomagnetic magnetic storms (|Dst| > 200 nT) during 1998 to 2005 have been investigated with the measurements by three NOAA POES satellites (NOAA-15, 16 and 17). The losses of protons in the outer region of the inner radiation belt are found during the large storms. Similar loss events were also measured by the HEO-3 satellite for lower energy protons (8.5–35 MeV, 16–40 MeV and 27–45 MeV). However, the response of higher energy protons to the storms observed by NOAA satellites is different from that of the lower energy protons. It is shown that some aspects of the loss event and energy dependence during large storms can be accounted for by the trapping limit of the field line curvature scattering mechanism. The maximal L shells of the observed trapped protons are consistent with the critical L shells of the field line curvature scattering. The modeling results based on the storm-time geomagnetic field model (TS04c) and the radiation belt model (AP8) show the inward motion of the outer boundary of trapped protons is caused by the distortion of geomagnetic field during the magnetic storms and depends on proton energy. The additional proton loss in the lower energy channel (35–70 MeV) could be attributed to the storm-caused weakening of geomagnetic field combined with L dependent lifetimes induced by curvature scattering during magnetic storms.