Abstract

RBSPA observations suggest that the inner radiation belt high energy proton fluxes drop significantly during the storm main phase and recover in parallel to as the SYM-H index [Xu et al., 2019]. A natural problem arises: are these storm‐time proton flux variations in response to the magnetic field modifications adiabatic? Based on Liouville's theorem and conservation of the first and third adiabatic invariants, the fully adiabatic effects of high energy protons in the inner radiation belt have been quantitatively evaluated. Two case studies show that theoretically calculated, adiabatic flux decreases are in good agreement with RBSPA observations. Statistical survey of 67 geomagnetic storms which occurred in 2013–2016 has been conducted. The results confirm that the fully adiabatic response constitutes the main contribution 90 % to the changes in high energy protons in inner radiation belt during the storm main and recovery phases. It indicates that adiabatic invariants of the inner belt high energy protons are well preserved for majority of storms. Phase space density results also support adiabatic effect controls the varication of high energy protons especially for small and medium geomagnetic storms. Non-adiabatic effects could play important role for the most intense storms with fast changes in magnetic configuration.

Highlights

  • Later measurements confirmed that significant changes in these fluxes have been observed in the outer boundary of the inner radiation belt (1.7

  • We found that sharp descent in high energy proton fluxes is accompanied by the corresponding depression of SYM‐H

  • In contrast to previous belief the outer zone of the inner radiation belt is very sensitive to the geomagnetic activities

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Summary

Introduction

NOAA15, NOAA16, and NOAA17 satellites observations show the responses of the inner radiation belt high‐ energy protons to large geomagnetic storms (|Dst| > 200) [Zou et al, 2011]. The proton loss mechanisms mentioned above consist of non-adiabatic processes, while the fully adiabatic effect could account for the flux dropout during magnetic storms Those adiabatic flux changes known as the “Dst effect” have been applied mostly for relativistic electron flux decreases in the outer radiation belt [Li et al, 1997; Kim and Chan, 1997]. The main purpose of this work is to evaluate quantitatively the extent to which fully adiabatic changes can account for the sharp descent and recovery in proton fluxes in the inner radiation belt observed during magnetic storms. For adiabatic process the storm time proton flux is given in terms of the prestorm time proton flux multiplied by the magnetic field strength ratio, Bm⁄Bp

Magnetic Field Models
Findings
Analysis on phase space densities during 2013-2016

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