a_p-index solar wind driving function and its semiannual variations

A. A. Petrukovich (1) , M. Y. Zakharov (1)

1 IKI - Space Research Institute of the Russian Academy of Sciences

Semiannual variation of geomagnetic activity and a_p-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 a_p-index as a magnetospheric response function to solar wind and IMF input. Seasonal variation in a_p-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.

Domaines: Océan, Atmosphère; Sciences de la Terre

A. A. Petrukovich, M. Y. Zakharov. a_p-index solar wind driving function and its semiannual variations. Annales Geophysicae, 2007, 25 (7), pp.1465-1469. ⟨hal-00318343⟩