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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, A05208, doi:10.1029/2006JA011853, 2008

A method for estimating the ring current structure and the electric potential distribution using energetic neutral atom data assimilation

S. Nakano

Institute of Statistical Mathematics, Research Organization of Information and Systems, Tokyo, Japan
Japan Science and Technology Agency, Saitama, Japan


G. Ueno

Institute of Statistical Mathematics, Research Organization of Information and Systems, Tokyo, Japan
Japan Science and Technology Agency, Saitama, Japan


Y. Ebihara

Institute for Advanced Research, Nagoya University, Nagoya, Japan


M.-C. Fok

NASA Goddard Space Flight Center, Greenbelt, Maryland, USA


S. Ohtani

Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA


P. C. Brandt

Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA


D. G. Mitchell

Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA


K. Keika

Space Research Institute, Austrian Academy of Sciences, Graz, Austria


T. Higuchi

Institute of Statistical Mathematics, Research Organization of Information and Systems, Tokyo, Japan
Japan Science and Technology Agency, Saitama, Japan


Abstract

We present a technique for estimating ring current ion distributions and electric potential in the inner magnetosphere by incorporating data from the High-Energy Neutral Atom (HENA) imager on the IMAGE satellite into a kinetic ring current model in the context of data assimilation. Data assimilation is an approach which adjusts a physics-based model according to differences with observations. We perform the data assimilation using the particle filter (PF) which is applicable to high-dimensional systems and observations with relatively low computational cost. In the present technique, the magnetospheric electric potential distribution is represented by the sum of a Volland-Stern field and a deviation, and the deviation is improved in the assimilation process. The ring current ion distribution is then determined from the electric potential distribution. The method is tested by assimilating artificial data generated by another simulation. The results demonstrate that the ring current ion distribution is successfully reconstructed by the proposed algorithm and that the distorted structures of the electric potential distribution are also well reproduced. An example to illustrate how the present technique could be applied for assimilating a real IMAGE/HENA data set is also demonstrated. This technique provides a useful tool for investigating the global dynamic structure of ring current and electric potential.

Received 15 May 2006; accepted 11 February 2008; published 10 May 2008.

Keywords: ring current; data assimilation; particle filter.

Index Terms: 2778 Magnetospheric Physics: Ring current; 3315 Atmospheric Processes: Data assimilation; 2730 Magnetospheric Physics: Magnetosphere: inner; 2753 Magnetospheric Physics: Numerical modeling; 2788 Magnetospheric Physics: Magnetic storms and substorms (7954).

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Citation: Nakano, S., G. Ueno, Y. Ebihara, M.-C. Fok, S. Ohtani, P. C. Brandt, D. G. Mitchell, K. Keika, and T. Higuchi (2008), A method for estimating the ring current structure and the electric potential distribution using energetic neutral atom data assimilation, J. Geophys. Res., 113, A05208, doi:10.1029/2006JA011853.