Signatures of photospheric convection throughout the solar atmosphere: the EVE Sun-as-a-star mHz continuum

Le résumé fourni par la source

Convectively driven motions in the solar photosphere can generate broadband Doppler variability across the chromosphere, transition region and corona. Here we investigate this variability using "Sun-as-a-Star" observations from the Extreme Ultraviolet Variability Experiment (EVE) aboard the Solar Dynamics Observatory, constructing high signal-to-noise Doppler power spectra from incoherently summed 3-hour sequences of the centroid wavelengths of emission lines that span wavelengths 35-104 nm. The spectra reveal a broad power-spectral continuum with two Harvey-like components, one of which extends to the Nyquist frequency at 50 mHz with a steep power-law tail. Lines formed in the corona, as compared with those of the chromosphere/transition region, have substantially less Doppler amplitude in the 5 mHz Harvey component associated with granulation-scale convection. Based on the observed continuum, there is no evidence (in any of the 26 lines studied) for Kolmogorov turbulence, which predicts a flat continuum component with Doppler variance ~ f^{-5/3) as a function of frequency f. The total inferred non-thermal RMS velocities (>0.1 mHz) are of order 15 km/s, consistent with previous coronal "microturbulence" estimates from non-thermal line widths. These observations provide the first clear detection of Sun-as-a-star EUV Doppler variability above about 10 mHz and demonstrate the potential of full-disk EUV spectroscopy to probe turbulent energy transport throughout the solar atmosphere.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.