Abstract
We study the properties of convective motions on the Sun by using Kitt Peak Doppler images. We remove the nonconvective components of the velocity images due to magnetic fields and the p-mode oscillations and obtain power spectra of convection. The power peaks at a scale of about 29,000 km and drops off smoothly with wavenumber. There is no evidence of apparent energy excess at the scale of the mesogranulation proposed by other authors. The power spectra can be expressed by a power law, E(k) ∝ k <sup>α</sup> , where k is the wavenumber and the index α is -0.66 for k < 1.05 rad Mm <sup>-1</sup> , and -2.67 for k > 1.05 rad Mm <sup>-1</sup> . By comparing power spectra at different heliocentric angles, we obtain the vertical and horizontal power for each wavenumber, from which we can calculate the vertical and horizontal velocities of the supergranulation. The amplitude of vertical and horizontal velocities of the supergranulation are 0.034 (±0.002) km s <sup>-1</sup> and 0.38 (±0.01) km s <sup>-1</sup> , respectively. The corresponding rms values are 0.024 (±0.002) km s <sup>-1</sup> and 0.27 (±0.01) km s <sup>-1</sup> .