Five-minute oscillations above granules and intergranular lanes

Abstract

We discuss the links between the photospheric 5–min oscillations and the granulation pattern using a 30-min time series of CCD spectrograms of solar granulation recorded with high spatial (0′′5) and temporal (9.3 s) resolution. The observed images contain the Fe i 5324 A spectral line with good height coverage from the low photosphere up to the temperature minimum region. Amplitudes, phases and periods of the 5–min oscillations are found to be different above granules and intergranular lanes. Strong oscillations occur well separated temporally and spatially. Many features of this different behaviour can be described in the frame of a relatively simple model of wave propagation in the solar atmosphere. To that aim, we have introduced oscillations into a 3D snapshot of a theoretical time dependent solar model atmosphere. NLTE synthesis of the time series of the Fe i 5324 A line profiles was performed taking into account granular and oscillatory components of the velocity field. Both, observations and theoretical modeling, lead to similar results: (i) oscillations above granules and intergranular lanes occur with different periods; (ii) the most energetic intensity oscillations occur above intergranular lanes; the most energetic velocity oscillations occur above granules and lanes with maximum contrast, i.e. above the regions with maximum convective velocities; (iii) velocity oscillations at the lower layers of the atmosphere lead oscillations at the upper layers in intergranular lanes. In granules the phase shift is nearly zero. We conclude that differences in oscillations above granules and lanes are caused mainly by variations of the physical conditions in