Extended Data Figure 6 : Further linear resolution analysis.

From: Broad plumes rooted at the base of the Earth's mantle beneath major hotspots

Extended Data Figure 6

This analysis is of a 400-km-width plume-like conduit extending from the CMB to 1,000-km depth, with a similar lateral profile (a cosine cap) and maximum amplitude (−2%) as the test structures in Extended Data Figs 4 and 5. The inherent limits of our spherical spline basis prohibit us from representing this narrow conduit with sufficient fidelity for the purposes of this test above 1,000 km. Upper panel, conduit-like input structure; lower panel, output structure resulting from resolution test. We observe that the output structure is at least 800 km in width, but is also significantly weaker than the input, exhibiting a maximum amplitude of −0.6% near its base, while only reaching −0.3 or −0.4% elsewhere in its core. As such, we can infer that the input-structure amplitudes would need to be increased by at least 10× in order to maintain amplitudes near −2.0% throughout the majority of the lower mantle. This latter observation has implications for effective excess temperature (see Methods).