The effects of meridional motion on the determination of rotation by tracer tracking
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.
- Publication:
-
Solar Physics
- Pub Date:
- January 2000
- DOI:
- 10.1023/A:1005268323890
- Bibcode:
- 2000SoPh..191...21S
- Keywords:
-
- Systematic Error;
- Solar Activity;
- Series Expansion;
- Recent Analysis;
- Activity Cycle