Data assimilation strategy developed to reproduce the dynamics of the Earth radiation belts

We propose to present here the developments conducted at ONERA to define and develop a data assimilation strategy to reproduce the dynamics of the Earth radiation belts. This is a very different system than the typical ones implementing data assimilation schemes. Constraints as well as available data may differ a lot from other research fields.

The natural energetic electron environment in the Earth's radiation belts is of general importance as dynamic variations in this environment can impact space hardware and contribute significantly to background signals in a range of other instruments flying in that region. The most dramatic changes in the relativistic electron populations occur during enhanced periods of geomagnetic activity. The relative importance of all competing physical processes involved in the radiation belt dynamics changes from storm to storm and the net result on particle distribution might then be very different. Many orders of magnitude are spanned during such period and the related dynamics have strong non-linear components requiring considering adequate data assimilation technics.

Modeling Earth's radiation belts still constitutes an active field of research. The most common practice is to deduce empirical formulae of physical processes amplitudes versus one or more proxies from statistical studies. Although this allows us to reproduce the mean dynamics of the radiation belts, this may introduce uncertainties in the system, which becomes even more important for high magnetic activity conditions for which statistics are usually poor. In parallel, it has been shown in the recent years that a data assimilation scheme based on an Ensemble Kalman Filter (EnKF) may lead to great improvements in (1) the accuracy of modeling the different regions of Earth's radiation belts, (2) the possibility to accurately predict the state of the radiation belts, and (3) in accurately reanalyzing a long time period as a basis for specification model and climatology.

We would like to present a global overview of the efforts undergone at ONERA concerning data assimilation in the radiation belts based on the Salammbô code and an EnKF. We would in particular focus our attention on the uncertainties estimation of the physical processes modeled and how it is taken into account in the implement EnKF. We would also present our ongoing efforts to improve our data assimilation strategy to gain in performance and accuracy.