Helioseismic Determination of the Solar Rotation Axis

Abstract

Time-distance helioseismology analysis of Dopplergrams from the Michelson Doppler Imager instrument on board the Solar and Heliospheric Observatory spacecraft provides a very accurate measurement of meridional flows. This shows a sinusoidal variation with a period of 1 yr and was identified by P. Giles to be due to an error in the determination of the solar rotation axis. The phase and amplitude of the annual variation of meridional flows are used to determine the error in the Carrington elements. After comparing with other recent estimates of the Carrington elements, we suggest the following values: i=7.155d+/-0.002d and Ω=-73.5d+/-0.1d.