Characteristics, Occurrence and Decay Rates of Three-Belt events in the Earth's Radiation Belts.

A three-belt configuration of the electron radiation belts was reported at the beginning of the Van Allen Probes mission in September 2012, but an explanation of its formation has remained controversial. To explore this unique configuration we have identified and studied 30 events with a three-belt structure that occurred between September 2012 and November 2017 using data from the Van Allen Probes mission. We have determined the energy range of occurrence and the main geomagnetic conditions under which those three-belt events occurred, along with magnetopause location and the location of the remnant (middle) belt. We have found that the remnant belt location strongly correlates with the SYM-H minimum value measured around the time of the start of the events. We have also calculated the decay rates of the remnant belt for all 30 events, and have found that the lifetime of this intermediate belt gets longer as energy increases, ranging from a few days at E = 1.8 MeV up to months at E = 6.3 MeV.