Characterizing anomalous geomagnetic induction from coastal effects with transfer functions and gradient measurements

Abstract. The occurrence of anomalous subsurface currents in a region is of significant geophysical importance. Several geomagnetic methods have been developed to characterize the effects of geomagnetic induction. Typically, the intensity and direction of the inducing processes are determined using simplified transfer functions that relate corresponding horizontal and vertical geomagnetic components. The geomagnetic field associated with nearby anomalous currents is expected to be inhomogeneous. Additionally, the distortion of the measured geomagnetic field's geometrical structure, as indicated by the magnetic gradient, is a relevant parameter in this context. In this comprehensive study, both methods are applied to simultaneous measurements of geomagnetic induction and magnetic gradient conducted at two geomagnetic repeat stations near the Adriatic Sea. Furthermore, a novel concept for a magnetic gradiometer is introduced. A strong correlation was observed between the direction and intensity of the calculated Parkinson vectors and the strike directions and intensities of the horizontal geomagnetic gradient during periods influenced by the seaside effect. The primary conclusion is that geomagnetic gradient measurements are highly effective for characterizing the effects of geomagnetic induction and/or quasi-stationary subsurface currents.