Disturbance diurnal electric field in Indian and American equatorial electrojet regions

The yearly mean Disturbance Daily (SD) variation, i.e., solar daily variati on on International Disturbed days (Sd) minus that on International Quiet d ays (Sq) of the geomagnetic H field at Huancayo, an equatorial electrojet s tation in American zone, for any of the years 1954-61 shows a dawn-maximum and a dusk-minimum as observed at any low and middle latitude station. Cont rary to this, the SD(H) variation at Kodaikanal, an equatorial station in t he Indian zone, shows a prominent minimum around noon hours besides the usu al dawn-maximum and dusk-minimum for any of these years. The amplitude of S D(H) at Huancayo or at Kodaikanal decreases with the decreasing solar activ ity. Seasonally, SD(H) is larger during equinoctial than during solsticial months. For any particular season, the SD(H) averaged for all hours of the day is lower at Huancayo than at Kodaikanal, while the Sq(H) at Huancayo is always greater than the corresponding amplitude of Sq(H) at Kodaikanal. Th us the sources of electrojet electric fields on quiet and on disturbed days seem to be different and need to be identified. (C) 1998 Elsevier Science Ltd. All rights reserved.