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We measure the axisymmetric transport of magnetic flux on the Sun bycross-correlating narrow strips of data from line-of-sight magnetogramsobtained at a 96-minute cadence by the MDI instrument on the ESA/NASA SOHOspacecraft and then averaging the flow measurements over each synodic rotationof the Sun. Our measurements indicate that the axisymmetric flows varysystematically over the solar cycle. The differential rotation is weaker atmaximum than at minimum. The meridional flow is faster at minimum and slower atmaximum. The meridional flow speed on the approach to the Cycle 23/24 minimumwas substantially faster than it was at the Cycle 22/23 minimum. The averagelatitudinal profile is largely a simple sinusoid that extends to the poles andpeaks at about $35\degr$ latitude. As the cycle progresses a pattern ofin-flows toward the sunspot zones develops and moves equatorward in step withthe sunspot zones. These in-flows are accompanied by the torsionaloscillations. This association is consistent with the effects of the Coriolisforce acting on the in-flows. The equatorward motions associated with thesein-flows are identified as the source of the decrease in net poleward flow atcycle maxima. We also find polar counter-cells (equatorward flow at highlatitudes) in the south from 1996 to 2000 and in the north from 2002 to 2010.We show that these measurements of the flows are not affected by thenon-axisymmetric diffusive motions produced by supergranulation.

Variations in the axisymmetric transport of magnetic elements on the Sun: 1996-2010