On the Relationship Between ULF Wave Power and Changes of Relativistic Electron Fluxes in the Outer Radiation Belt

Abstract

We performed a statistical study on the correlation between electromagnetic Ultra Low Frequency (ULF) waves and the evolution of relativistic electron fluxes in the outer radiation belt for 3.1L∗6.0 during 101 geomagnetic storms that occurred between January 2013 and November 2018. We used the Van Allen Probes MagEIS and REPT instruments to study electron fluxes from 0.47 MeV to 5.2 MeV, and we utilized magnetic field data from EMFISIS to calculate magnetic field fluctuations parallel and perpendicular to the background magnetic field direction and obtain the ULF integrated power between 1 mHz and 10 mHz. We analyzed the data during the following three different time intervals: the main phase, the recovery phase, and the entire storm. We computed the Pearson’s correlation coefficient and mutual information score between the ratio of fluxes before and after each given phase and the total integrated ULF power during the same time interval. Our results show a significant correlation between ULF wave power and changes in fluxes of hundreds of keV electrons during the main phase of the storms and for MeV electrons during the recovery phase of the storms. By studying fluxes at independent L∗, the largest correlations correspond to changes in fluxes before and after the entire storm and ULF fluctuations parallel to the field, especially for L∗4.6. We evaluated the drift resonance frequency for azimuthal wavenumber 1≤m≤10 and found that for all considered energies and frequencies, the drift resonance with Pc5 ULF waves may occur in our region of study, which is consistent with the statistical results.

Keywords

• ULF waves
• geomagnetic storms
• relativistic electrons
• Van Allen Probes