Solar rotation as determined from OSO-4 EUV spectroheliograms

Abstract

Spectroheliograms obtained in extreme ultraviolet (EUV) lines and the Lyman continuum are used to determine the rotation rate of the solar chromosphere, transition region, and corona. A cross-correlation analysis of the observations indicates the presence of differential rotation through the chromosphere and transition region. The rotation rate does not vary with height. The average sidereal rotation rate is given by ω (deg day−1) = 13.46 - 2.99 sin2B where B is the solar latitude. This rate agrees with spectroscopic determinations of the photospheric rotation rate, but is slower by ∼ 1 deg day−1) = 13.46 - 2.99 sin2 than rates determined from the apparent motion of photospheric magnetic fields and from the brightest points of active regions observed in the EUV. The corona does not clearly show differential rotation as do the chromosphere and transition region.