1 Outline 2 Local loss introduction 3 Local acceleration introduction

1. Richard Thorne / UCLAPhysical Processes Responsible for Relativistic Electron Variability in the Outer Radiation Zone over the Solar Cycle 1 Outline 2 Local loss introduction 3 Local acceleration introduction 4 Radial diffusion simulations 5 Explanation for slide 4 6 Local acceleration simulations 7 Explanation for slide 6 8 Future work

2. Dominant loss mechanismsand timescales • (Yellow) Plasmaspheric Hiss loss time on the scale of 5-10 days • (Blue) Chorus waves outside plasmapause provide fast losses on the scale of 0.5-1 day • (Red) EMIC waves mostly in plumes on the dusk side very fast localized losses on the scale of 1 hour 4) (Curved line) Combined effect of losses to magnetopause and outward radial diffusion on the scale of 1 hour at L>4

3. Dominant acceleration mechanisms • Inward radial diffusion driven by ULF waves very strong for higher L values. 2) Local acceleration due to energy diffusion driven by the chorus waves outside plasmapause. Will be especially effective when wpe/We is small just outside plasmapause.

4. Radial Diffusion Simulations comparison with observations. Comparison between 0.95 MeV electron fluxes (log cm-2 sr-1 s-1 MeV-1) computed by the radial diffusion model with empirical lifetimes (top), and electron flux measurements on CRESS (middle). The bottom panel shows the evolution of the Kp index used for calculation of the DLL and . [Shprits et al., 2005]

5. Explanation for the Radial diffusion simulations • Comparison of the radial diffusion simulations with observations show that radial diffusion can effectively redistribute radiation belt fluxes and can reproduce the inner boundary of the radiation belt fluxes and the location of the peak of fluxes. • Future improvement of the model should include local acceleration and loss and variable outer boundary conditions.

6. t=0 t=3 hours t=3 days Energy pitch angle, deg pitch angle, deg pitch angle, deg Evolution of phase space density obtained with the 2-D pitch-angle and energy diffusion code at L=3 during Halloween solar storms. [Shprits et al., 2005]

7. Explanation for the 2-D local acceleration simulations. • Simulations of the local acceleration and loss during the unprecedented Halloween supper storms show that the unusual behavior of the radiation belts and formation of the new radiation belt at L<3 (region usually devoid of high energy electrons) is due to the local acceleration driven by chorus waves. • ~100 keV electrons were accelerated locally to relativistic energies on the time scale of few hours, followed by a slow build up of fluxes. • Inclusion of local acceleration and loss is crucial for radiation belt modeling.

8. Future directions of the radiation belt research • Combine radial diffusion and local acceleration and loss into a 3D radiation belt code. • Use data assimilation tools to correct imperfect models and compensate for missing physics. • Couple radiation belt code with MHD and ring current models.