The photospheric convection spectrum

Spectra of the cellular photospheric flows are determined from observations acquired by the MDI instrument on the SOHO spacecraft. Spherical harmonic spectra are obtained from the full-disk observations. Fourier spectra are o btained from the high-resolution observations. The p-mode oscillation signa l and instrumental artifacts are reduced by temporal filtering of the Doppl er data. The resulting spectra give power (kinetic energy) per wave number for effective spherical harmonic degrees from 1 to over 3000. Significant p ower is found at all wavenumbers, including the small wavenumbers represent ative of giant cells. The time evolution of the spectral coefficients indic ates that these small wavenumber components rotate at the solar rotation ra te and thus represent a component of the photospheric cellular flows. The s pectra show distinct peaks representing granules and supergranules but no d istinct features at wavenumbers representative of mesogranules or giant cel ls. The observed cellular patterns and spectra are well represented by a mo del that includes two distinct modes - granules and supergranules.