DYNAMICS OF THE SOLAR GRANULATION .2. STATISTICAL-ANALYSIS - POWER SPECTRA, COHERENCE, PHASE

Granulation velocity fields provided by the Multichannel Subtractive Double Pass (MSDP) of the Coupole Tourelle (Pic du Midi Observatory) are analysed. Two methods of filtering have been applied in order to eliminate the 5-min oscillations. An inspection of the velocity maps, filtered for 5-min oscillations, confirms that the bright granules at the continuum level are well correlated with rising material and that the velocity fluctuations penetrate much higher into the photosphere than the intensity fluctuations. Both the velocity power spectrum and the coherence phase spectra (between velocity and intensity) indicate that the large granules (of size close to 3 arcsec) carry the major part of the convective energy, in this layer. The one-dimensional power spectrum exhibits a linear decrease in the high wavenumber side, not so distant to the -5/3 value which is expected for a purely Kolmogoroff spectrum. However the influence of 5-min filtering and the seeing corrections are not accurate enough for a definite conclusion about the nature of the solar granules.