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- Title
Pitch Angle Scattering of Energetic Electrons by BBFs.
- Authors
Eshetu, W. W.; Lyon, J. G.; Hudson, M. K.; Wiltberger, M. J.
- Abstract
Field line curvature scattering by the magnetic field structure associated with bursty bulk flows (BBFs) has been studied, using simulated output fields from the Lyon‐Fedder‐Mobarry global magnetohydrodynamic code for specified solar wind input. There are weak magnetic field strength (B) regions adjacent to BBFs observed in the simulations. We show that these regions can cause strong scattering where the first adiabatic invariant changes by several factors within one equatorial crossing of energetic electrons of a few kiloelectron volts when the BBFs are beyond 10RE geocentric in the tail. Scattering by BBFs decreases as they move toward the Earth or when the electron energy decreases. For radiation belt electrons near or inside geosynchronous orbit we demonstrate that the fields associated with BBFs can cause weak scattering where the fractional change of the first invariant (μ0) within one equatorial crossing is small, but the change due to several crossings can accumulate. For the weak scattering case we developed a method of calculating the pitch angle diffusion coefficient Dαα. Dαα for radiation belt electrons for one particular BBF were calculated as a function of initial energy, equatorial pitch angle, and radial location. These Dαα values were compared to calculated Dαα for a dipole field with no electric field. We further compared Dαα values with that of stretched magnetic fields calculated by Artemyev et al. (2013, https://doi.org/10.5194/angeo-31-1485-2013) at r≈7RE. Results show that scattering by BBFs can be comparable to the most highly stretched magnetic field they studied. Key Points: Pitch angle scattering of energetic electrons by bursty bulk flow fields in MHD simulations with idealized solar wind input is demonstratedA method of calculating the equatorial pitch angle diffusion coefficient for general electromagnetic fields has been developedPitch angle diffusion coefficients are calculated for radiation belt electrons in realistic BBF fields for the first time
- Subjects
MAGNETIC fields; RADIATION belts; ELECTRIC fields; SOLAR wind; COMPUTER simulation
- Publication
Journal of Geophysical Research. Space Physics, 2018, Vol 123, Issue 11, p9265
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2018JA025788