Solar east-west flow correlations that persist for months at low latitudes are dominated by active region inflows

TL;DR

This study analyzes 19 years of solar flow data and finds that long-term east-west flow correlations at low latitudes are mainly caused by active region inflows, not giant convective cells.

Contribution

It extends previous correlation analyses with extensive data, demonstrating that active region inflows dominate long-term east-west flow correlations at low latitudes.

Findings

Correlations persist up to five solar rotation periods.

Flow features are linked to magnetic activity.

Long-term correlations are due to active region inflows, not giant cells.

Abstract

Context: Giant-cell convection is believed to be an important component of solar dynamics. For example, it is expected to play a crucial role in maintaining the Sun's differential rotation. Aims: We re-examine early reports of giant convective cells detected using correlation analysis of Dopplergrams. We extend this analysis using 19 years of space and ground-based observations of near-surface horizontal flows. Method: Flow maps are derived through local correlation tracking of granules and helioseismic ring-diagram analysis. We compute temporal auto-correlation functions of the east-west flows at fixed latitude. Results: Correlations in the east-west velocity can be clearly seen up to five rotation periods. The signal consists of features with longitudinal wavenumbers up to m=9 at low latitudes. Comparison with magnetic images indicates that these flow features are associated with magnetic activity. The signal is not seen above the noise level during solar minimum. Conclusions: Our results show that the long-term correlations in east-west flows at low latitudes are dominantly due to inflows into active regions and not to giant convective cells.