Meridional Motions of Magnetic Features in the Solar Photosphere
Abstract
We cross-correlate pairs of Mt. Wilson magnetograms spaced at intervals of 24-38 days to investigate the meridional motions of small magnetic features in the photosphere. Our study spans the 26-yr period July 1967-August 1993, and the correlations determine longitude averages of these motions, as functions of latitude and time. The time-average of our results over the entire 26-yr period is, as expected, antisymmetric about the equator. It is poleward between ∼ 10° and ∼ 60°, with a maximum rate of 13 m s−1, but for latitudes below ±10° it is markedly equatorward, and it is weakly equatorward for latitudes above 60°. A running 1-yr average shows that this complex latitude dependence of the long-term time average comes from a pattern of motions that changes dramatically during the course of the activity cycle. At low latitudes the motion is equatorward during the active phase of the cycle. It tends to increase as the zones of activity move toward the equator, but it reverses briefly to become poleward at solar minimum. On the poleward sides of the activity zones the motion is most strongly poleward when the activity is greatest. At high latitudes, where the results are more uncertain, the motion seems to be equatorward except around the times of polar field reversal. The difference-from-average meridional motions pattern is remarkably similar to the pattern of the magnetic rotation torsional oscillations. The correspondence is such that the zones in which the difference-from-average motion is poleward are the zones where the magnetic rotation is slower than average, and the zones in which it is equatorward are the zones where the rotation is faster.
- Publication:
-
Solar Physics
- Pub Date:
- January 1996
- DOI:
- 10.1007/BF00165454
- Bibcode:
- 1996SoPh..163...21S
- Keywords:
-
- Nash;
- Solar Minimum;
- Polar Field;
- Differential Rotation;
- Torsional Oscillation