Catalogue of events with cumulative fluxes below as well as comparable and exceeding those for RBSP discovered third radiation belt

Abstract

The formation of a temporary third radiation belt in the slot region of Earth’s magnetosphere was reported (Baker et al. in Science 340:186-190, 2013a) from the early data of the radiation belt storm probes (RBSP) mission. The cumulative flux of relativistic electrons in L = 3-3.5 for the third radiation belt of that study is calculated here and defined as threshold flux (TF) (105 cm−2 s−1 sr−1 MeV−1). A catalogue of 133 events during Sep 2012 – Feb 2019 is presented. Events are distributed into, below threshold flux (BTF), of the order of, one hundred and one thousand times the threshold flux, (OTF), (HTF), and (TTF) categories respectively. Finding high 2 MeV flux threshold at L = 3-3.5 is a way to find ideal condition for the possible formation of a third radiation belt, aware that attaining TF does not necessarily mean formation of the third radiation belt. It is found that BTF occurred 29 times and 105 times cumulative flux exceeded TF but TTF occurred very rarely. The effects of large scale solar wind structures (LSSS) and number of main phase Dst dips on BTF-TTF events are also studied. The findings of this study may be helpful for understanding the third radiation belt formation in the slot region of Earth’s magnetosphere.