Improved outer boundary conditions for outer radiation belt data assimilation using THEMIS‐SST data and the Salammbo‐EnKF code

Abstract

Over the last decade, efforts have been made in the radiation belt community to develop data assimilation tools in order to improve the accuracy of radiation belts models. In this paper we present a new method to correctly take into account the outer boundary conditions at L* = 8 in such an enhanced model of the radiation belts. To do that we based our work on the Time History of Events and Macroscale Interactions during Substorms/Solid State Telescope data set. Statistics are developed to define a consistent electron distribution at L* = 8 (in both equatorial pitch angle and energy), and a variance‐covariance matrix is estimated in order to more realistically drive the Monte Carlo sampling required by the Ensemble Kalman Filter (EnKF). Data processing is first described as well as caveats avoided, and then the use of these information in a machinery such as the EnKF is described. It is shown that the way the Monte Carlo simulations are performed is of great importance to realistically reproduced outer boundary distribution needed by the physic‐based Salammbô model. Finally, EnKF simulations are performed and compared during September 2011 in order to analyze the improvements gained using this new method of defining outer boundary conditions. In particular, we highlight in this study that such a method provides great improvement in the reconstruction of the dynamics observed at geosynchronous orbit, both during quiet and active magnetic conditions.

Particle Dynamics in the Earth's Radiation Belts: Review of Current Research and Open Questions

“…With a full Fokker‐Planck code, one can solve today simultaneously the following processes: radial diffusion, pitch angle diffusion, energy diffusion, cross energy and pitch angle diffusion, Coulomb collision, and anomalous diffusion. Among the most well‐established Fokker‐Planck codes are the ONERA Salammbô code (e.g., Beutier & Boscher, ; Bourdarie et al, , , ; Pugacheva et al, ; Beutier et al, 2005; Varotsou et al, , ; Maget et al, ; Herrera et al, ), the British Antarctic Survey (BAS) Radiation Belt Code (e.g., Glauert et al, , ; Glauert & Horne, ; Horne et al, ; Meredith et al, , ), the VERB 3‐D code (e.g., Subbotin & Shprits, ; Shprits et al, ; Subbotin et al, , ; Kim et al, 2011, Kim et al, ; Drozdov et al, ) recently extended to a 4‐D version (e.g., Aseev et al, ; Shprits et al, ) to soon incorporate models of nonlinear wave‐particle interactions, the University of California, Los Angeles (UCLA) 3‐D diffusion code (e.g., Tao et al, ; Li et al, ; Li, Ma, et al, ; Ma et al, , , , Ma et al, that incorporates the (UCLA) Full Diffusion Code (e.g., Ni et al, 2008, Ni et al, ; Shprits & Ni, 2009) in order to compute diffusion coefficients (similarly to VERB 3‐D/4‐D), the radiation belt code of the Space Vehicles Directorate of the U.S. Air Force Research Laboratory (AFRL) (e.g., Albert, , ; Albert et al, ; Albert & Young, ; Selesnick, Albert, & Starks, ), the LANL Dynamic Radiation Environment Assimilation Model (DREAM) 1‐D (e.g., Tu et al, 2009; Reeves et al, ; Welling et al, ) and 3‐D codes (Camporeale et al, , ; Cunningham, ; Cunningham et al, ; Tu et al, ), the Commissariat à l'Energie Atomique (CEA) CEVA code (Réveillé, ; Ripoll & Mourenas, 2012; Ripoll, Chen, et al, , Ripoll, Reeves, et al, , Ripoll et al, , ), and the STEERB code developed in China (e.g., Su et al, …”

Accounting for Variability in ULF Wave Radial Diffusion Models

“…In reality the gradient across the outer boundary will not be 0, and many radiation belt models either determine the outer boundary from electron flux data observed by spacecraft (e.g., Drozdov et al., 2017; Glauert et al., 2018; Shin & Lee, 2013) or use plasmasheet characteristics (Christon et al., 1988, 1991) and magnetic activity dependencies (Bourdarie & Maget, 2012) for analytic fits (Maget et al., 2015).…”

Infer Electron Space Environment Along EOR Mission Profile From LEO Measurements: Application to EUTELSAT 7C

“…THEMIS is a scientific mission with three probes (A, D and E) on a HEO 470 km x 87330 km inclined at 16°, since 2007, equipped with SST detector which measures differential electron flux in the slot from 30 keV to 700 keV with a time resolution of 3 s [14,15].…”