7.4 Slanted contours

Although much of the debate in the early 1990s centered on discriminating between rotation constant on cylinders and rotation constant along radial lines, neither picture gave a complete description of the data. Gilman and Howe (2003) and Howe et al. (2005Jump To The Next Citation Point) pointed out that the differential rotation in the bulk of the convection zone, at least at low- to mid-latitudes, could be quite well described by saying that the contours of constant rotation lay at about a 25° angle to the rotation axis, as illustrated in Figure 19View Image.
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Figure 19: Mean rotation profile from GONG data; contours of constant rotation (left), showing lines at 25° to the rotation axis as dashed lines, after Howe et al. (2005Jump To The Next Citation Point), and cuts at constant latitude as a function of radius (right), after Howe et al. (2000bJump To The Next Citation Point).

Figure 20View Image compares idealized rotation profiles for the cylindrical, radial, and slanted-contour configurations.

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Figure 20: Idealized rotation profiles for rotation constant on cylinders (left), radial lines (middle), and lines at 25° to the rotation axis (right). The top row shows contours of constant rotation, while the lower row shows rotation rate as a function of radius at constant latitude for latitudes at 15° intervals from the equator (top) to 75° (bottom). The rotation rate is matched to the GONG inferences at 0.99 R ⊙ and smoothed to simulate the broadening effect of inversion resolution on the tachocline; the near-surface shear was not included.

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