LONGITUDINAL VARIATION OF SUDDEN COMMENCEMENT OF GEOMAGNETIC STORM ATEQUATORIAL STATIONS

It is shown that the amplitude of storm sudden commencement (SSC) at a station within the equatorial electrojet belt experiences daytime enh ancement, latitudinal enhancement, and longitudinal enhancement just a s do the similar characteristics of the strength of the equatorial ele ctrojet current itself. lt is concluded that the sudden commencements of geomgnetic storms are associated with an increase of electric field s in the dynamo region modifying primarily the equatorial rather than Sq currents. The V x Bz electric field generated at the magnetopause d ue 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 transver se magnetic waveguide mode between conducting ionosphere and Earth. Th e enhancements of SSC amplitude over the magnetic equator seem to be r elated to the basic ionospheric conductivity at the longitude concerne d.