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Solar Physics

, Volume 143, Issue 1, pp 19–39 | Cite as

Torsional oscillation patterns in photospheric magnetic features

  • R. W. Komm
  • R. F. Howard
  • J. W. Harvey
Article

Abstract

We analyzed 689 high-resolution magnetograms taken daily with the NSO Vacuum Telescope on Kitt Peak from 1975 to 1991. Motions in longitude on the solar surface are determined by a one-dimensional crosscorrelation analysis of consecutive day pairs. The main sidereal rotation rate of small magnetic features is best fit byω = 2.913(±0.004) − 0.405(±0.027) sin2φ − 0.422(±0.030) sin4φ, in µrad s−1, whereφ is the latitude. Small features and the large-scale field pattern show the same general cycle dependence; both show a torsional oscillation pattern. Alternating bands of faster and slower rotation travel from higher latitudes toward the equator during the solar cycle in such a way that the faster bands reach the equator at cycle minimum. For the magnetic field pattern, the slower bands coincide with larger widths of the crosscorrelations (corresponding to larger features) and also with zones of enhanced magnetic flux. Active regions thus rotate slower than small magnetic features. This magnetic torsional oscillation resembles the pattern derived from Doppler measurements, but its velocities are larger by a factor of more than 1.5, it lies closer to the equator, and it leads the Doppler pattern by about two years. These differences could be due to different depths at which the different torsional oscillation indicators are rooted.

Keywords

Solar Cycle Torsional Oscillation Field Pattern Cycle Minimum Slow Rotation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Kluwer Academic Publishers 1993

Authors and Affiliations

  • R. W. Komm
    • 1
  • R. F. Howard
    • 1
  • J. W. Harvey
    • 1
  1. 1.National Solar ObservatoryNational Optical Astronomy ObservatoriesTucsonUSA

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