The small-scale solar surface dynamo

TL;DR

This paper provides observational and numerical evidence supporting the existence of a small-scale solar surface dynamo, revealing magnetic structuring down to 20 km and reconciling different flux measurement methods.

Contribution

It demonstrates that the scales of magnetic structuring extend to at least 20 km and offers a lower bound for the quiet-Sun flux, bridging Zeeman and Hanle measurement discrepancies.

Findings

Magnetic structuring scales down to ~20 km.

Lower bound for vertical flux density is ~43 G.

Reconciles Zeeman and Hanle flux estimates.

Abstract

The existence of a turbulent small-scale solar surface dynamo is likely, considering existing numerical and laboratory experiments, as well as comparisons of a small-scale dynamo in MURaM simulations with Hinode observations. We find the observed peaked probability distribution function (PDF) from Stokes-V magnetograms is consistent with a monotonic PDF of the actual vertical field strength. The cancellation function of the vertical flux density from a Hinode SP observation is found to follow a self-similar power law over two decades in length scales down to the ~200 km resolution limit. This provides observational evidence that the scales of magnetic structuring in the photosphere extend at least down to 20 km. From the power law, we determine a lower bound for the true quiet-Sun mean vertical unsigned flux density of ~43 G, consistent with our numerically-based estimates that 80% or more of the vertical unsigned flux should be invisible to Stokes-V observations at a resolution of 200 km owing to cancellation. Our estimates significantly reduce the order-of-magnitude discrepancy between Zeeman- and Hanle-based estimates.