In 27 October 2012 the ULF wave in Pc4 range being Alfv'en wave was
observed with Van Allen Probe A. In the event the parallel Poynting flux
of the wave was directed towards the Northern ionosphere. Assuming that
this may be caused by the asymmetry of ionospheric conductivity between
the Northern and Southern hemispheres, its effect on the standing
structure of the Alfv'en wave was investigated in this paper. For this
purpose the analytical model with straight magnetic field lines was
used. As a result the method for estimation of the Northern and Southern
ionospheric conductivity was developed. It allows us to reconstruct the
parallel structure of Alfv'en waves under various conditions of the
ionospheric conductivity. With the method developed, the ionospheric
conductivity for the October 27, 2012 event was evaluated and compared
with ionosphere model IRI-2016.