1. Particle energization by substorm dipolarizations
Konstantin Kabin
Royal Military College of Canada
Eric Donovan, German Kalugin, and Emma Spanswick
University of Calgary

2. Introduction
Substorm injection “creates” a population of electrons with energies of tens to hundreds of keV during the substorm expansion phase
To model the energization process we use a simple magnetotail model with few adjustable parameters, controlling magnetotail thickness and transition from dipole to tail-like fields (Kabin et al. JGR 2011, 2017)
We view dipolarization as a tailward retreat of this transition area
We also consider electron energization by an earthward propagating EM pulse

3. Example of a dipolarization

4. Particle trajectories
We trace electrons in the calculated dipolarization fields using Guiding Center equations.
For equatorial electrons GC simplifies dramatically

5. Electron trajectories

6. Energy gain by electrons

7. Energy gain by electrons

8. Electron density enhancements
Assuming uniform initial distribution of 5 keV electrons

9. Parameters used: E0=87.5 mV/m, V0=125 km/s,
Model of the EM pulse
Similar to Li et al 1998, Sarris et al, 2002, Zaharia et al, 2000, Gabrielse et al., 2016, etc, but 3D
Parameters used: E0=87.5 mV/m, V0=125 km/s,
b=1.5 RE, h=0.7 RE, =0.2 rad

10. Earthward propagating pulse

11. Equatorial electrons: optimizing ti for max energization

12. Equatorial electrons: radial transport and energization
Dependence on the initial position

13. Equatorial electrons: radial transport and energization
Dependence on the initial energy

14. Non-equatorial electrons (pitch angle dependence)
Co-longitude of the mirror points as a function of the equatorial pitch angle

15. Non-Equatorial electrons: radial transport and energization
Dependence on the initial equatorial pitch angle,
10 keV initial energy

16. Non-Equatorial electrons: pitch angle changes
Dependence of the final pitch angle on the initial one

17. Conclusions
We considered electron energization by two different processes: a tailward retreat of the near-earth transition region, and by an earthward propagating Electromagnetic impulse
In both cases we observed substantial electron energization factors of 10-25
Energization factors are the largest for equatorial electrons and decrease for other initial pitch angles
Azimuthal electric field drives electron pitch angles towards 90