Physical explanation of the east–west center-to-limb effect

Explain the east–west antisymmetry, also termed the center-to-limb effect, observed in local helioseismic measurements of the solar rotation rate and establish a physics-informed basis for correcting or interpreting it.

Background

The ring-diagram measurements exhibit a statistically significant east–west antisymmetry in the inferred equatorial rotation rate. The paper attributes this effect principally to spatial variation in the observations and/or analysis and relates it to the center-to-limb effect reported in earlier local helioseismic studies.

Although a possible contribution from asymmetric solar granulation and height-dependent phase shifts has been proposed, the authors note that the effect has not been fully explained. They therefore refrain from applying the ad hoc corrections commonly used in other analyses because no physics-informed correction is currently established.