Measurement of Turbulence Injection Scale Down to the Chromosphere

TL;DR

This study measures the turbulence injection scale in the solar chromosphere using high-resolution eclipse images, revealing a scale of about 1.5 Mm linked to granule size and detailing how turbulence structures evolve with altitude.

Contribution

First direct measurement of turbulence injection scale in the chromosphere down to 0.33 Mm, linking it to granule size and magnetic field expansion.

Findings

Turbulence injection scale is approximately 1.5 Mm.

Correlation length remains constant up to 4 Mm then increases.

Magnetic field expansion influences turbulence structure with altitude.

Abstract

The solar atmosphere displays a sharp temperature gradient, starting from spicules in the chromosphere at $2 \times 10^4$ K, outward into the corona exceeding $10^6$ K. Plasma turbulence produced by the transverse motion of magnetic fields anchored in the photosphere is likely the energy source producing this gradient. However, very little is known about the turbulent structures near the solar surface. Using the highest spatial resolution white-light total solar eclipse image to date, we measure the transverse correlation length at distances ranging from 0.33 to 9 Mm above the solar surface-two orders of magnitude closer than previous estimates. Our results show that the turbulence injection scale in the chromosphere is ~1.5 Mm, which we associate with the size of granules since they are the only structured features of comparable size. Further, the change in perpendicular correlation length with distance from the solar surface exhibits a plateau in the first 4 Mm, followed by a rapid increase until 9 Mm where it becomes shallower thereafter. We associate this radial gradient with the expansion of the magnetic field in the transition region between the chromosphere and the corona.