Acoustic waves in the solar atmosphere at high spatial resolution II. Measurement in the Fe I 5434 Å line

Aims. We investigate the energy supply of the solar chromosphere by acoustic waves. Methods. A time sequence with high spatial and temporal resolution from the quiet Sun disc centre in Fe I 5434 angstrom (Lande factor g = 0) is analysed. We used models from a numerical simulation of granular convection and apply NLTE spectral line transfer to determine the height of formation. For estimates of acoustic energy flux, we adopted wave propagation with inclinations of the wave vector with respect to the vertical of 0 degrees, 30 degrees, and 45 degrees. For a granular and an intergranular model, the transmissions of the atmosphere to high-frequency waves were determined for the three inclination angles. Wavelet and Fourier analyses were performed and the resulting power spectra were corrected for atmospheric transmission. Results. We find waves with periods down to similar to 40 s. They occur intermittently in space and time. The velocity signal is formed at a height of 500 km in the granular model and at 620 km in the intergranule. At periods shorter than the acoustic cutoff (similar to 190 s), similar to 40% of the waves occur above granules and similar to 60% above intergranules. By adopting vertical propagation, we estimate total fluxes above granules of 2750-3360 Wm(-2), and of 910-1000 Wm(-2) above intergranules. The weighted average is 1730-2 060 Wm(-2). The estimates of the total fluxes increase by 15% when inclined wave propagation of 45 degrees is assumed.