On Two Methods Using Magnetometer-array Data for Studying Magnetic Pulsations

Abstract

We present some recent progress in interpreting the results from the two powerful methods that analyze the magnetic pulsations observed by ground magnetometer arrays. The first method involves an inversion technique that requires the observations from a chain of magnetometer stations located on the same latitude. This method can estimate several factors that affect the pulsation amplitude on the ground, namely the magnitude of the wave ”event”, the local time distribution, and the ground conductivity effect. By analyzing several months of pulsation data, we present an alternative approach to estimate the statistical values of the ground conductivities. We confirm the conductivity structure obtained by one day of data presented by Chi et al. (1996). We also demonstrated the local time dependence of wave amplitude for different frequency bands using this method. The second technique is the ”the gradient method” that calculates the difference in phase or amplitude of the signals measured at two closely separated stations on the same meridian. This technique has been successful in ”observing” the eigenfrequencies of magnetospheric field lines. Although most studies to date analyze the phase difference in the H -component, we find that the phase difference was in fact largest in the Z-component. In order to interpret such difference quantitatively, we apply the conventional field line resonance theory to the condition in which the ground signals are induced by the Hall currents in the ionosphere. We also demonstrated that the same formulation can be used to understand the characteristics of field line resonance from the observations of phase differences.