Geomagnetic coast effect at two Croatian repeat stations

Eugen Vujić Eugen Vujić,Mario Brkić Mario Brkić

doi:10.4401/ag-6765

Abstract

<p>Knowledge of inductive effects is important for the reliability of geomagnetic surveys as well as reduction of measurements, and hence for the accuracy of models and maps of the Earth’s magnetic field. Detection of anomalous induced fields, due to the geomagnetic coast effect, was carried out by the transfer function method to estimate the induction arrows indicating areas of anomalous induced currents. To determine the transfer function at the two coastal Croatian repeat stations used in this study, the so-called geomagnetic plane-wave events from July 2010 were used. Analysis of transfer functions for Krbavsko polje and Sinjsko polje first order repeat stations, using observatories Grocka and Tihany as references, revealed the existence of the Adriatic coastal effect on periods of 10-65 minutes.</p>

Highlights

Following the establishment of the Croatian Geomagnetic Repeat Station Network, a series of geomagnetic surveys has been performed from 2004 to 2010, with the aim of obtaining reliable geomagnetic data over Croatia [Brkić et al 2013]
Csontos et al [2012] indicated the possible existence of geomagnetic effect of the coast in front of the Adriatic Sea, and this result was the reason for further investigation of inductive effects at the coastal Croatian repeat stations, here described and discussed
Each cross-spectra used in Equation (3) must be a mean value from a number of variation events [Schmucker 1970, Gough et al 1973], and in this case they were averaged over the events given in Table 1 for Krbavsko polje (KRBP) and Sinjsko polje (SINP), respectively

Summary

Introduction

Following the establishment of the Croatian Geomagnetic Repeat Station Network, a series of geomagnetic surveys has been performed from 2004 to 2010, with the aim of obtaining reliable geomagnetic data over Croatia [Brkić et al 2013]. Geomagnetic sounding methods are used to model subsurface electrical conductivity and, on a regional scale, they allow to determine lateral conductivity contrasts in the Earth’s crust and upper mantle Such contrasts produce anomalous induced magnetic fields, which need to be separated from the sum of the primary external magnetic fields produced in the Earth’s magnetosphere and ionosphere and of those they induce in the Earth’s interior (secondary) [Banks 1973, Gough et al 1973, Hitchman et al 2000]. An example of such anomalous induced fields, are those arising in proximity of coasts because of the contrast of electrical conductivity at the interface continent-ocean In this case, time variations of the vertical component of the Earth’s magnetic field have enlarged amplitudes, and correlate positively with the horizontal component at the close overland positions [Parkinson and Jones 1979]. Csontos et al [2012] indicated the possible existence of geomagnetic effect of the coast in front of the Adriatic Sea, and this result was the reason for further investigation of inductive effects at the coastal Croatian repeat stations, here described and discussed

Transfer function method and data

Results and discussion

Conclusion