Spherical harmonic analysis of geomagnetic variations observatory data up to degree 4 in the range of periods from 5 to 40 days

Magnetic observatory daily means from the years 1965 and 1980 were analysed using the techniques of discrete Fourier analysis in the time domain and s pherical harmonic analysis (SHA) in the spatial domain to obtain spherical harmonic coefficients (SHCs) at significant periods between 5 and 40 days f rom X, Y data up to degree 4 and from Z data up to degree 2, Synthetic test s indicate that there is not significant power at degrees higher than 4, bu t there is a high level of random noise in the data which causes high uncer tainty estimates for SHCs. A table of SHCs with their uncertainty estimates is presented. (C) 1999 Elsevier Science B.V, All rights reserved.