Astronomy and Astrophysics – Astronomy
Scientific paper
May 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.5110k&link_type=abstract
American Astronomical Society, 180th AAS Meeting, #51.10; Bulletin of the American Astronomical Society, Vol. 24, p.815
Astronomy and Astrophysics
Astronomy
1
Scientific paper
We present results of an analysis of 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 mean sidereal rotation rate of small magnetic features is best fit by $omega = 2.913 (+/- 0.004) -0.405 (+/- 0.027) sin(2phi ) -0.422 (+/- 0.030) sin(4phi ) in \mu rad s^{-1} where \phi$ is the latitude. The small features 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. The magnetic torsional oscillation resembles the pattern derived from Doppler measurements, but is different in three respects. Its velocities are larger by a factor of more than 1.5, it lies closer to the equator, and leads the Doppler pattern by about two years. Motions in longitude and also in latitude are determined by a two-dimensional crosscorrelation analysis. The mean sidereal rotation rate of the two-dimensional analysis is in excellent agreement with the one-dimensional rate which assures the robustness of the two-dimensional analysis. In latitude, we find meridional motions of the order of 10 m/s which are poleward in each hemisphere.
Harvey John W.
Howard Robert F.
Komm Rudolf W.
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