The Effect of Source Field Polarization on Geomagnetic Variation Anomalies in the British Isles

Abstract

Summary The published data on geomagnetic temporal variations in the British Isles are re-examined. The normalized complex amplitudes of the vertical component from place to place caused by the local channelling of regional current flow of given polarizations are computed. A contour map of the in-phase vertical component for a period of 40 mins caused by the channelling of regional NS current flow clearly demonstrates the existence of current concentrations in the shallow seas and in the Atlantic Ocean. A second map of the quadrature vertical component, at the same period, caused by the channelling of regional EW current flow shows current concentrations whose axes correlate remarkably well with Caledonian trends in England, Southern Scotland and Ireland. The Eskdalemuir Anomaly is an unusual special case. It is excited both by in-phase NS current flow due to current leaking between the North Sea and the Irish Sea and by quadrature EW current flow due to its location close to a major Caledonian feature. The Caledonian correlation may be caused by unusually low resistivity in rocks presently in the lower crust which formed part of a 'Proto-Atlantic' oceanic crust in the Late Palaeozoic.