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Ann. Geophys., 25, 1465-1469, 2007
www.ann-geophys.net/25/1465/2007/
© European Geosciences Union 2007
ap-index solar wind driving function and its semiannual variations
A. A. Petrukovich and M. Y. Zakharov
Space Research Institute, 84/32 Profsoyuznaya st., Moscow, 117997, Russia
Abstract. Semiannual variation of geomagnetic activity and ap-index in
particular is supposed to consist of heliospheric factor (axial
hypothesis and Russell-McPherron effect) and
magnetospheric/ionospheric factor (equinoctical hypothesis).
In our investigation
we express ap-index as a magnetospheric response function to
solar wind and IMF input. Seasonal variation in ap-index on
average (1963–2003) is ~4 nT and consists of ~2.1–2.3 nT
of magnetospheric/ionospheric part, 0.6–1.3 nT of heliospheric
part (including 0.2–0.3 nT of R-M effect), 0.1–0.4 nT is due to
the non-linear term. 90% confidence range of all estimates is
~0.1–0.25 nT. While autumn/spring magnetospheric response
functions are almost identical, there is substantial difference
between winter and summer functions. The increase of solar wind
input in autumn and spring is also different by a factor of two.
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