Estimation of the Transfer Function from Magnetic Variations of the Equatorial Electrojet Measured in Brazil

The Z/H-method uses the ratio of the vertical to the horizontal magnetic component of a non-uniform source field to determine a transfer function which equals the magnetotelluric (MT) impedance. At mid latidudes the Z/H-method can only be applied to the Sq-field with periods from 4 to 24 hours and to the On-field with even higher periods. In the vicinity of the dip equator the Equatorial Electrojet (EEJ) generates a non-uniform source field with periods from 100s to 10000s. Thus the transfer functions of the Z/Hmethod estimated from magnetic variations of the EEJ can be compared directly with the MT impedances. In this study the application of the Z/H-method to the EEJ-field and the comparison of the resulting transfer functions to MT impedances is investigated in numerical models and using electromagnetic data from the Northeast of Brazil.