Effects of Asymmetric Flows in Solar Convection on Oscillation Modes

TL;DR

This paper investigates how asymmetric flows in solar convection influence helioseismic oscillation measurements, revealing that asymmetries cause phase shifts that contribute to systematic errors in solar interior flow inferences.

Contribution

It proposes a physical explanation for center-to-limb effects in helioseismic data based on asymmetrical solar granulation flows, improving understanding of measurement biases.

Findings

Asymmetrical solar granulation causes apparent radial flows.

Phase shifts in oscillation modes depend on observation height and angle.

This explains some systematic errors in helioseismic measurements.

Abstract

Many helioseismic measurements suffer from substantial systematic errors. A particularly frustrating one is that time-distance measurements suffer from a large center to limb effect which looks very similar to the finite light travel time, except that the magnitude depends on the observable used and can have the opposite sign Zhao et al. (2012). This has frustrated attempts to determine the deep meridional flow in the solar convection zone, with Zhao et al. (2012) applying an ad hoc correction with little physical basis to correct the data. In this letter we propose that part of this effect can be explained by the highly asymmetrical nature of the solar granulation which results in what appears to the oscillation modes as a net radial flow, thereby imparting a phase shift on the modes as a function of observing height and thus heliocentric angle.