Quantifying the Transport of Radiation Belt Electrons due to Drift Orbit Bifurcation
Abstract
Recently a mechanism called Drift Orbit Bifurcation (DOB) has been suggested to play a major role in the loss and transport of radiation belt electrons. DOB violates both the second and third adiabatic invariants of electrons, which could lead to fast radial transport of electrons for them to be lost through the magnetopause and efficient pitch angle scattering of electrons for the precipitation loss. Therefore, it is critical to characterize the DOB effect and include it in radiation belt models. In our study, we use a guiding-center test particle code to simulate the DOB process since the first adiabatic invariant is conserved. The simulation is performed in the static Tsyganenko-1989c model with no electric field to isolate the DOB effect. Our simulation results show that DOB affects a broad region of outer radiation belt which could penetrate inside the geosynchronous orbit at Kp ≥ 3. Depending on the initial value of the second invariant or pitch angle, DOB can lead to either ballistic jumps (for large pitch angles) or diffusion (for smaller pitch angles) of the second invariant and radial distance of electrons after one drift. In the long-run over many drifts, we find the ballistic case only shows a ballistic jump in the first drift and then the transport becomes diffusive afterward. Our calculation of the radial diffusion rate (DLL) shows that the DLL due to DOB for the diffusive case at Kp=3 is small compared to the empirical DLL(Kp) from Brautigam and Albert [2000] due to interactions with ultralow frequency waves. While for the ballistic case, the DOB DLL after the first drift is comparable to DLL(Kp). The transport of electrons due to DOB also illustrates a strong dependence in L and Kp which will also be discussed in our study. It is significant to demonstrate that DOB could cause effective loss and transport of radiation belt electrons even in the absence of waves.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMSM0330010H
- Keywords:
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- 2722 Forecasting;
- MAGNETOSPHERIC PHYSICS;
- 2730 Magnetosphere: inner;
- MAGNETOSPHERIC PHYSICS;
- 2753 Numerical modeling;
- MAGNETOSPHERIC PHYSICS;
- 2774 Radiation belts;
- MAGNETOSPHERIC PHYSICS