Rapid Fluctuations in the Lower Solar Atmosphere

TL;DR

This study uses high-frequency solar atmospheric data to identify turbulent fluctuations and two distinct states of the lower solar atmosphere, revealing correlations with magnetic activity and oscillations.

Contribution

It provides new insights into the turbulent nature and dynamic states of the lower solar atmosphere through high-frequency spectral analysis.

Findings

Identification of turbulence-like power law in G-band spectra

Detection of two distinct atmospheric states based on fluctuation power

Correlation of UHF power peaks with magnetic bright points

Abstract

The Rapid Oscillations in the Solar Atmosphere (ROSA) instrument reveals solar atmospheric fluctuations at high frequencies. Spectra of variations of the G-band intensity (IG) and CaII K-line intensity (IK) show correlated fluctuations above white noise to frequencies beyond 300 mHz and 50 mHz, respectively. The noise-corrected G-band spectrum for f = 28 - 326 mHz shows a power law with exponent -1.21 \pm, 0.02, consistent with the presence of turbulent motions. G-band spectral power in the 25 - 100 mHz ("UHF") range is concentrated at the locations of magnetic bright points in the intergranular lanes and is highly intermittent in time. The intermittence of the UHF G-band fluctuations, shown by a positive kurtosis {\kappa}, also suggests turbulence. Combining values of IG, IK, UHF power, and {\kappa}, reveals two distinct states of the solar atmosphere. State 1, including almost all the data, is characterized by low IG, IK, and UHF power and {\kappa} \approx 6. State 2, including only a very small fraction of the data, is characterized by high IG, IK, and UHF power and {\kappa} \approx 3. Superposed epoch analysis shows that the UHF power peaks simultaneously with spatio-temporal IG maxima in either state. For State 1, IK shows 3.5 min chromospheric oscillations with maxima occurring 21 s after IG maxima implying a 150 - 210 km effective height difference. However, for State 2 the IK and IG maxima are simultaneous; in this highly magnetized environment sites of G-band and K-line emission may be spatially close together.