Fig. 4.

Model–data comparison of variations in geomagnetic field intensity over the past 9,000 y in (A) North America and (B) the Middle East. The vertical gray shaded bands between 1000 and 500 BCE are added to highlight the large Northern Hemisphere asymmetry in the field during this time. Model predictions are represented by 100 samples from the posterior distribution (semitransparent black lines) and the 95% credible intervals (red lines). The archeomagnetic data (black dots; plotted on the maximum posterior probability ages) were selected from radii of 30${}^{°}$ and 10${}^{°}$, respectively, and relocated assuming an axial dipole field. The large radii used to select the data, chosen to obtain a reasonable amount of data for the comparison, can be justified on account that the model resolution is limited to spherical harmonic degree 5 (i.e., spatial wavelengths of 72${}^{°}$). Error bars represent 1-σ uncertainties. Note that the y-axes limits have been adjusted to highlight the main features of the field variation, thereby omitting four and three unusually high-intensity data, respectively.