Are the 1986-1988 Changes in Solar Free-Oscillation Splitting Significant?

The solar normal mode splitting coefficients for BBSO data differ between 1986 and 1988; inversions for equatorial rotation are slower at depth and faster near the surface in 1988 than in 1986. The significance of the change is disputed. The data sets overlap for 5 splitting coefficients {aj}>=, for 710 modes. On the assumption that rotation rate varies smoothly with radius, both data sets are satisfied (within the published uncertainties) by the same rotation model at all colatitudes except near 3040° and near 700 (and at their southern hemisphere reflections 140-150° and 1100). The evidence for equatorial changes is weak. Nonparametric tests show a significant offset in the magnitudes of a1, a2 and a4, and of linear combinations sensitive to rotation at colatitudes of 60°-80° (and 100°-120°). Nonparametric tests show significant radial trends in the changes to a2, a4, and (less significantly) a5. The evidence for radial trends in the changes to rotationally sensitive combinations of a1, a3 and a5 is weak. There is strong anticorrelation between a2 and a4, a1 and a3, and a3 and a5, suggesting the estimates are not independent. Individual coefficients aj show more evidence for change than do "physical" linear combinations, adding weight to this hypothesis. Some of the changes in splitting might be related to solar activity, which changed most near colatitude 700 from 1986 to 1988. Subject headings: Sun: rotation-Sun: oscillations-Sun: interior