Meridional Flow Variations: Implications for flux transport models
David H. Hathaway [David.Hathaway@msfc.nasa.gov], NASA Marshall Space Flight
Center, Huntsville, Alabama; and Lisa Rightmire, University of Memphis, Tennessee
Observations of the transport of magnetic elements across the Sun's surface indicate that,
in general, the meridional flow extends all the way to the poles. Furthermore, the speed of
this flow varies systematically over each solar cycle – faster at minimum and slower at
maximum. The flow speed on the approach to this (Cycle 24) minimum was substantially
faster than it was at the last minimum. This increased flow speed should have produced a
short Cycle 23 with strong polar fields in the flux transport dynamos used to predict Cycle
24. This is contrary to what we have seen. The increased flow speed does produce weak
polar fields in the surface flux transport models like those used to estimate past irradiance
variations. However, these surface flux transport models use meridional flow profiles that do
not agree with the observations. Both types of flux transport models are missing identifiable
components. We note that the observed changes in the structure of the meridional flow
profile are consistent with Spruit's model for the torsional oscillations - suggesting that there
may be associated irradiance variations.