Photospheric Velocities Measured at Mt. Wilson Show Rotational and Poleward Velocity Deviations Compose the Torsional Oscillations

Abstract

The methods for reducing the observations from the 150-foot tower telescope on Mt. Wilson are reviewed, and a new method for determining the poleward and rotational velocity deviations is described and applied. The flows we study are smaller than global and change with the solar cycle, so we describe them as poleward and rotational deviations rather than meridional circulation when we discuss solar surface flows. Due to a calibration problem with the data prior to 1983, only observations between 1983 and 2013 are presented at this time. After subtraction of latitude-dependent averages over the 30-year period of observation, the residual deviations in both the poleward and the rotational velocity are well synchronized and correspond to what is widely recognized as torsional oscillations. Both flow components need to be included in any model that replicates the torsional oscillations.