Skip to main content

Table 2 Table listing the major findings of this work. The explored parameters are period P = 24, 12, 8, 6, 4.8, 4 h; variance \(\sigma ^2 = 95 \%\) or \(99\%\) provided by PCA; total length of time series used for PCA (maximum—almost 1 year, minimum—2 weeks); selection of time series (separating them into sections); high latitude filtering by applying an SH filter of degree \(N_{cut}\); segment length along which a Fourier transform is applied (24, 48, 72 h); and latitude of observatory stations used for the estimation of the source coefficient. “N/A” stands for not applicable

From: Towards probing Earth’s upper mantle with daily magnetic field variations: exploring a physics-based parametrization of the source

Explored parameter Effect on the number of modes Effect on the spatial features \(R^2\) results
Period (P) Increases for decreasing P Long P show larger scale features
Short P show smaller and high latitude features
Increased agreement with increasing P
Variance Doubles when going from 95 to 99% Subsequent modes tend towards smaller scale features Improved when using higher variance
Length of time series Increases for longer time series Only a weak effect on the dominant modes Improved for longer time series
Selection of time series Increases for equinoctial months Only a weak effect on the dominant modes Weak improvement for equinoctial months
High latitude filtering Decreases (more prominent for lower \(N_{cut}\)) Features are blurred, but still present at high latitudes Worsens compared to unfiltered data
FT segment length Decreases for longer segment lengths Longer segment lengths show expected Sq pattern at short P Improved for short segment lengths
Observatory latitude N/A N/A Best agreement using only mid latitudes