Event specific simultaneous estimates of loss, diffusion, and acceleration for MeV electrons

Abstract:

The most significant unknown in outer radiation belt electron dynamics is the relative contribution of loss, transport, and acceleration processes inside the inner magnetosphere. Detangling each individual process is critical to improve the understanding of radiation belt dynamics, but determining any single component is difficult due to sparse measurements of a large observation space. However, in the current era, an unprecedented number of spacecraft are taking measurements, and they are sampling different regions of the inner magnetosphere. With today’s observations, system dynamics can begin to be unraveled. In this work, we focus on in-situ measurements during a single outer belt enhancement event, which occurred on January 13-14, 2013. We use Van Allen Probe measurements of ULF wave activity to determine radial transport rates. We use Colorado Student Space Weather Experiment observations to model electron lifetimes from atmospheric precipitation caused by pitch-angle diffusion. To estimate the source rate, we use a data assimilative model. The Kalman filter method we use estimates the full radial phase space density profile, as well as the amplitude, location, and radial extent of a Guassian-shaped source region. The estimates are made by minimizing the residuals between a simple 1D radial diffusion model and Van Allen Probe phase space density observations for mu=750 MeV/G and K=0.11 G^(1/2)R_E. The model also quantifies electrons lost to the outer boundary, providing direct comparison between losses to the inner and outer boundaries. This work produces simultaneous, quantitative estimates of loss, transport, and acceleration mechanisms and the relative contribution from each.