Geomagnetic variation on decadal time scales: What can we learn from Empirical Mode Decomposition?

Abstract

The effects of core fluid dynamics are observable as variations in the geomagnetic field at time scales of decades to many thousands of years. A non-classical method, Empirical Mode Decomposition (EMD) is performed on globally distributed observatory records of declination and inclination to study decadal variations of the geomagnetic field. We use waveform analysis to test the robustness of EMD and find an 11.5 year signal consistent with the solar cycle. Periods of 30.5, 62 and 81 years are also identified in the observations and compared with results from core flow inversions. These signals are likely to be of internal origin, potentially the manifestation of torsional oscillations, in the fluid core. Finally, we analyse a new 600 year time series from Munich and suggest that a longer, 160 year period exists. © 2010 by the American Geophysical Union.