Abstract: The possibility of triggering the geomagnetic disturbances by the northward B_z component of the IMF is discussed using some typical events and statistical analyses. The coupling coefficient of the IEF E_y component to the large scale magnetospheric convection electric field is given. The response of the magnetosphere to the solar wind effects is analysed from the coupling equation of these two fields. The results show that the magnetosphere does not act as the half-wave rectifier to the solar wind effects, hence the classical recon-nection scheme of the magnetosphere is proposed to be somewhat modified.