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Improved outer boundary conditions for outer radiation belt data assimilation using THEMIS‐SST data and the Salammbo‐EnKF code
Author(s) -
Maget V.,
SicardPiet A.,
Bourdarie S.,
Lazaro D.,
Turner D. L.,
Daglis I. A.,
Sandberg I.
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021001
Subject(s) - data assimilation , van allen radiation belt , ensemble kalman filter , monte carlo method , van allen probes , physics , computer science , kalman filter , geophysics , computational physics , statistical physics , meteorology , magnetosphere , mathematics , extended kalman filter , magnetic field , statistics , artificial intelligence , quantum mechanics
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.