Characteristics of the Equatorial Electrojet determined from an array of magnetometers in N-NE Brazil

An array of 29 vector magnetometers was operated in N-NE Brazil from Novemb er 1990 until March 1991, We present the analysis of 16 selected quiet days , for which a simple model of an equivalent current distribution for the Sq and EEJ, fits the observed maximum amplitude of the daily variation at mid day. In equatorial regions the precise latitude profile of the Sq field is maske d by the EEJ, This uncertainty is resolved by assuming that the EEJ, obtain ed after subtracting the Sq from the daily ranges, should present a ratio o f 0.3 for the westward to eastward current. With this constraint, a combine d non-linear least squares inversion of Sq and EEJ was used to estimate the parameters of Onwumechili's model of the EEJ current distribution. The H a nd Z components of the EEJ are jointly inverted and good a,agreement obtain ed between the calculated and observed data for all 16 days. The EEJ's main parameters averaged for 16 quiet days were: A total positive current intensity equal to 67 +/- 20 (10(3) A) for diurnal range Mg (or 80 +/- 20 (10(3) A) for M-3) and a half-width of 403 +/- 67 km. The EEJ centr e was located at 21 +/- 16 km south of the dip equator. The Sq was estimate d from several permanent observatories and found to be centred at a mean la titude of 5.5 +/- 2 degrees south.