Local time variation of the amplitude of geomagnetic sudden commencements (SC) and SC-associated polar cap potential

Local time (LT) variations of the averaged H-component amplitude of geomagnetic sudden commencements (SCs) observed at Memambetsu (geomagnetic latitude 35.4◦) are derived separately for the summer and winter season. The amplitude was found to be higher at nighttime than daytime in both seasons, and the LT variations showed a good agreement with calculated LT variations of the resultant magnetic field due to a pair of field-aligned currents (FACs) and ionospheric currents produced by the FACs. The DL- and DP-component of the disturbance field of SC can be separated based on a comparison of the observed and calculated LT variations. A method is introduced by which we can estimate the potential voltage difference associated with the FACs in the polar cap. Key words: Geomagnetic sudden commencement (SC), LT variation, field-aligned current, ionospheric current, interplanetary shock