RAPID FLUCTUATIONS IN THE LOWER SOLAR ATMOSPHERE

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.