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__A forecasting model of the magnetosphere driven by optimal solar-wind coupling functions__

__N. A. Tsyganenko and V. A. Andreeva __
Saint-Petersburg State University, Saint-Petersburg, Russia.

__Abstract:__

A new empirical magnetospheric magnetic field model is described, driven by interplanetary parameters including a
coupling function by *Newell et al.* (2007) or, alternatively, by *Boynton et al.* (2011), termed henceforth as
“ N-index” and " B-index", respectively.
The model uses data from Polar, Geotail, Cluster, and Themis satellites, obtained in 1995–2013 at distances 3–60 RE.
The model magnetopause is based on *Lin et al.* (2010) boundary driven by the solar wind pressure, IMF Bz and the
geodipole tilt. The model field includes contributions from the symmetric ring current (SRC), partial ring current (PRC)
with associated Region 2 field-aligned currents (R2 FAC), tail, Region 1 (R1) FAC, and a penetrated IMF. Increase in the
N- or B-index results in progressively larger
magnitudes of all the field sources, the most dramatic growth being found for the PRC and R1 FAC. The solar wind dynamic
pressure P_{dyn} affects the model magnetotail current in proportion to the factor
[P_{dyn}/< P_{dyn} >]^{ζ}
where the exponent ζ on the order of 0.4–0.6 steadily decreases with increasing N-
or B-index. The PRC peaks near midnight at quiet N~0
or B~0 but turns duskward as the indices grow toward the high end of their range (~1–2).
At ionospheric altitudes, both R1 and R2 FAC expand equatorward with growing N- or
B- index and P_{dyn}, and the R2 zone rotates westward. Larger values of
N or B result in a more efficient penetration of the
IMF into the magnetosphere and larger magnetic flux connection across the magnetopause. Growth of the dipole tilt is
accompanied by a persistent and significant decrease of the total current in all magnetospheric field sources.

__References:__

Boynton, R. J., M. A. Balikhin, S. A. Billings, H. L. Wei, and N. Ganushkina (2011), Using the NARMAX OLS-ERR algorithm
to obtain the most influential coupling functions that affect the evolution of the magnetosphere, *J. Geophys. Res.
Space Physics*, 116, A05218, doi:10.1029/2010JA015505.
Lin, R. L., X. X. Zhang, S. Q. Liu, Y. L. Wang, and J. C. Gong (2010), A three-dimensional asymmetric
magnetopause model, *J. Geophys. Res. Space Physics*, 115, A04207, doi:10.1029/2009JA014235.

Newell, P. T., T. Sotirelis, K. Liou, C.-I. Meng, and F. J. Rich (2007), A nearly universal solar wind-magnetosphere
coupling function inferred from 10 magnetospheric state variables, *J. Geophys. Res. Space Physics*, 112, A01206, doi:10.1029/2006JA012015.

Tsyganenko, N. A., and V. A. Andreeva (2015), A forecasting model of the magnetosphere driven by an
optimal solar wind coupling function, *J. Geophys. Res. Space Physics*, 120, doi:10.1002/2015JA021641.

This work was supported by the Russian Science Foundation grant 14-17-00072.