Spatial incoherence of solar granulation: a global analysis using BiSON 2B data

TL;DR

This study analyzes the spatial coherence of solar granulation noise using BiSON 2B data, revealing largely incoherent granulation signals across atmospheric heights, which can be exploited to improve low-frequency p-mode detection.

Contribution

It provides the first detailed assessment of the spatial coherence of granulation noise at different atmospheric heights using BiSON data, suggesting new noise reduction techniques.

Findings

Granulation noise is largely incoherent across atmospheric heights.

Oscillation modes are almost fully coherent across heights.

Applying cross-spectrum reduces granulation noise effectively.

Abstract

A poor understanding of the impact of convective turbulence in the outer layers of the Sun and Sun-like stars challenges the advance towards an improved understanding of their internal structure and dynamics. Assessing and calibrating these effects is therefore of great importance. Here we study the spatial coherence of granulation noise and oscillation modes in the Sun, with the aim of exploiting any incoherence to beat-down observed granulation noise, hence improving the detection of low-frequency p-modes. Using data from the BiSON 2B instrument, we assess the coherence between different atmospheric heights and between different surface regions. We find that granulation noise from the different atmospheric heights probed is largely incoherent; frequency regions dominated by oscillations are almost fully coherent. We find a randomised phase difference for the granulation noise, and a near zero difference for the evanescent oscillations. A reduction of the incoherent granulation noise is shown by application of the cross-spectrum.