ULF waves are a common occurrence in the inner magnetosphere and they contribute to particle motion, significantly, at times. We used the magnetic and the electric field data from the Electric and Magnetic Field Instrument Suite and Integrated Sciences (EMFISIS) and the Electric Field and Waves instruments (EFW) on board the Van Allen Probes to estimate the ULF wave power in the compressional component of the magnetic field and the azimuthal component of the electric field, respectively. Using L∗, Kp, and magnetic local time (MLT) as parameters, we conclude that the noon sector contains higher ULF Pc-5 wave power compared with the other MLT sectors. The dawn, dusk, and midnight sectors have no statistically significant difference between them. The drift-averaged power spectral densities are used to derive the magnetic and the electric component of the radial diffusion coefficient. Both components exhibit little to no energy dependence, resulting in simple analytic models for both components. More importantly, the electric component is larger than the magnetic component by one to two orders of magnitude for almost all L∗ and Kp; thus, the electric field perturbations are more effective in driving radial diffusion of charged particles in the inner magnetosphere. We also present a comparison of the Van Allen Probes radial diffusion coefficients, including the error estimates, with some of the previous published results. This allows us to gauge the large amount of uncertainty present in such estimates.
Bibliographical noteFunding Information:
The electric field measurements were obtained from the EFW instrument data repository located at http://www.space.umn.edu/rbspefw-data/. The magnetic field measurements were obtained from the EMFISIS instrument data repository located at http://emfisis.physics.uiowa.edu/data/index. The ephemeris data are available as an RBSP-ECT data service provided by the Los Alamos National Laboratory at http://www.rbsp-ect.lanl.gov/science/DataDirectories.php. This work was supported by the NASA grants NNX15AF59G, NNX14AC04G, NNX13AE39G, NNX15AI93G, and NNx14AN55G and the NASA Earth and Space Science Fellowship (NESSF) grant NNX13AO43H. Authors Ashar Ali and Scot Elkington would like to thank Louis Ozeke, Yuri Shprits, and Mary Hudson for their valuable remarks which aided this study. Ashar Ali would like to thank Alexander Drozdov, Ksenia Orlova, and Kyle Murphy for many helpful discussions.
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- electric and magnetic components
- radial diffusion