Distortions in Magnetotelluric Fields Possibly Due to ULF Activity at the South Atlantic Magnetic Anomaly Region.

Abstract

Several MT soundings carried out in different sites at the South Atlantic Magnetic Anomaly region in Brazil are distorted by severe incoherent noise. Apparent resistivity curves are displaced downwards showing local minima in frequencies around 0.1 Hz. On the other hand, power spectra analyses of pulsations in the Pc1-2 range observed at a ground station in the same region indicate the presence of linearly polarized Pi-bursts. These events may be related to the intensification of particle precipitation at localized low L values of the anomaly during magnetic disturbed periods with the characteristic polarization being probably associated with a local ionospheric current system driven by middle atmospheric ionization enhancement. It is speculated here that the mechanisms responsible for the Pi-bursts generation can introduce local spatial inhomogeneities in the external inducing field in the anomaly area generating the observed distortions in MT curves.