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Ann. Geophys., 25, 495-506, 2007
www.ann-geophys.net/25/495/2007/
© European Geosciences Union 2007
Solar wind-magnetosphere coupling functions on timescales of 1 day to 1 year
I. Finch1,* and M. Lockwood1,*
1Space Science and Technology Department, Rutherford Appleton Laboratory, Oxfordshire, UK
*also at: School of Physics and Astronomy, University of Southampton, Southampton, UK
Abstract. There are no direct observational methods for determining the total rate at
which energy is extracted from the solar wind by the magnetosphere. In the
absence of such a direct measurement, alternative means of estimating the
energy available to drive the magnetospheric system have been developed
using different ionospheric and magnetospheric indices as proxies for energy
consumption and dissipation and thus the input. The so-called coupling
functions are constructed from the parameters of the interplanetary medium,
as either theoretical or empirical estimates of energy transfer, and the
effectiveness of these coupling functions has been evaluated in terms of
their correlation with the chosen index. A number of coupling functions have
been studied in the past with various criteria governing event selection and
timescale. The present paper contains an exhaustive survey of the
correlation between geomagnetic activity and the near-Earth solar wind and
two of the planetary indices at a wide variety of timescales. Various
combinations of interplanetary parameters are evaluated with careful
allowance for the effects of data gaps in the interplanetary data. We show
that the theoretical coupling, Pα, function first proposed by
Vasyliunas et al. is superior at all timescales from 1-day to 1-year.
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