Phases of the 5-Min Photospheric Oscillations above Granules and Intergranular Lanes

Abstract

The currently accepted excitation mechanism of solar oscillations is the stochastic excitation by turbulent convection with the acoustic energy output that scales as a high power of the Mach number of the convection (Goldreich and Kumar, 1988; Goldreich et al., 1994, and references therein). Acoustic events of large amplitudes might be observed with the help of high-resolution techniques as enhancements of the oscillatory amplitude localized in time and space (Brown, 1991). The analyses of observations performed by Rimmele et al. (1995) and Espagnet et al (1996) revealed that the amplitude amplification occurs mainly above the darkest intergranular lanes. This was attributed to the enhanced turbulence of downflows. But later Hoekzema et al. (1998) found no difference between oscillations above the granules and intergranular lanes. In this work we re-examine the links between the 5-minute oscillations and granulation using observations of the Fe I 5324 Å line obtained with high spatial and temporal resolution. In contradiction to the previous studies we show that oscillations above the brightest granules as well as above the darkest intergranular lanes occur with the smaller amount of radiative energy losses. This causes the amplitude amplification with the contrast of granulation.