Abstract
We explore a systematic error that arises in feature-tracking measurements of time-average rotation. It stems from the flows of features across latitudes, and as these flows vary with the solar activity cycle, the error has a pattern of variation which mocks the torsional oscillation. We develop a series expansion for this error and evaluate the leading terms for the example case of cycle 21. It grows with the time lag; for a 30 day lag it is ≲1%, depending on how the correlations are done and interpreted. We conclude that the mock pattern cannot, however, account for the magnetic-rotation torsional oscillations pattern found in recent analyses of magnetograms from Kitt Peak and Mount Wilson. For the 1-day time lag in the Kitt Peak study, the error is negligible, and for the ∼30-day time lag in the Mount Wilson study, it represents at most about 30% of the signal.
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Birch, A. C. and Kosovichev, A. C.: Astrophys. J. 503, L187.
Howard, R. and LaBonte, B. J.: 1980, Astrophys. J. 239, L33.
Komm, R. W., Howard, R. F., and Harvey, J. W.: 1993, Solar Phys. 143, 19.
Kosovichev, A. G. and Shou, J.: 1997, Astrophys. J. 482, L207.
Latushko, S.: 1993, Solar Phys. 146, 401.
Latushko, S.: 1994, Solar Phys. 149, 231.
Smith, A. A.: 1999, B.A. Thesis, Lewis and Clark College (unpublished).
Smith, A. A. and Snodgrass, H. B.: 1999, Bull. Am. Astron. Soc. 31, 991.
Snodgrass, H. B.: 1983, Astrophys. J. 270, 288.
Snodgrass, H. B.: 1985, Astrophys. J. 291, 339.
Snodgrass, H. B.: 1991, Astrophys. J. 383, L85.
Snodgrass, H. B. and Dailey, S. B.: 1996, Solar Phys. 163, 21 (Paper I).
Snodgrass, H. B. and Smith, A. A.: 2000, Astrophys. J. (in press).
Stenflo, J. O.: 1992, in K. Harvey (ed.), The Solar Cycle, Proc. N.S.O./Sacramento Peak 12th Summer Workshop, Publ. Astron. Soc. Pacific Conf. Series, p. 421.
Ternullo, M.: 1990, Solar Phys. 127, 29.
Ulrich, R. K., Boyden, J. E., Webster, L., Snodgrass, H. B., Padilla, S. P., Gilman, P., and Shieber, T.: 1988, Solar Phys. 117, 291. ??
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Snodgrass, H.B., Smith, A.A. The effects of meridional motion on the determination of rotation by tracer tracking. Solar Physics 191, 21–35 (2000). https://doi.org/10.1023/A:1005268323890
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DOI: https://doi.org/10.1023/A:1005268323890