It is shown that the amplitude of storm sudden commencement (SSC) at a station within the equatorial electrojet belt experiences daytime enhancement, latitudinal enhancement, and longitudinal enhancement just as do the similar characteristics of the strength of the equatorial electrojet current itself. It is concluded that the sudden commencements of geomagnetic storms are associated with an increase of electric fields in the dynamo region modifying primarily the equatorial rather than Sq currents. The V¿Bz electric field generated at the magnetopause due to the impact of the solar plasma is transmitted along the magnetic lines of force to polar latitude as dusk to dawn electric field which is instantaneously transmitted to the equatorial latitude as transverse magnetic waveguide mode between conducting ionosphere and Earth. The enhancements of SSC amplitude over the magnetic equator seem to be related to the basic ionospheric conductivity at the longitude concerned. ¿ American Geophysical Union 1993