POWER SPECTRA OF MEDIAN-SCALE AND SMALL-SCALE SOLAR CONVECTION

We study the properties of convective motion on the Sun for the scales smaller than supergranules by using the high-resolution Doppler images from the Big Bear Solar Observatory and the Huairou Solar Observatory. By removing the p-mode oscillatory power, we obtain spatial power spectra of convection. The spatial power spectra of convection from both sets of data show an energy excess in the range of about k = 0.6-2.8 rad Mm-1, corresponding to 2200-10,000 km. This might correspond to the mesogranulation proposed by other authors. The rms velocity (line-of-sight component) of the mesogranulation is 0.079 +/- 0.001 km s-1 for the scales 2500-9000 km, and 0.056 +/- 0.001 km s-1 for the scales 5000-10,000 km. We also obtain temporal power spectra of convection for various scales, from which we can determine the lifetime of convective motion. Both sets of data show the fact that the lifetime of convective motion increases with the scale. But the lifetimes of the mesogranulation from two sets of data are different: about 30 minutes from Big Bear and 2 hr from Huairou.