Earth Planets Space, Vol. 61 (No. 4), pp. e13-e16, 2009E-LETTER
T. Araki1, S. Tsunomura2, and T. Kikuchi3
1SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai, China
2Japan Meteorological Agency, Tokyo, Japan
3Solar Terrestrial Environmental Laboratory, Nagoya University, Nagoya, Japan
(Received February 11, 2009; Revised March 16, 2009; Accepted March 21, 2009; Online published April 8, 2009)
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.