Main patterns of the geomagnetic field: A case study using principal component analysis

The horizontal magnetic components observed by ground-based observatories belonging to the INTERMAGNET network have been used to analyze the global pattern of the geomagnetic field variation. The approach is based on the Principal Component Analysis method applied to magnetograms from 2000 to 2005. Quiet and disturbed days were geomagnetically distinguished. The pattern of the geomagnetic field variation fluctuates bewilderingly over time. In this work, we are interested in determining the geomagnetic field variability presenting in each principal component. The results suggest that the oscillation patterns of the first, second and third components could be explained respectively by the first one, two and three terms of the geomagnetic field spherical harmonic expansion. The principal components provide a meaningful way to appraise the overall space-time decomposition of the geomagnetic field.