### Abstract

We present the results of three-dimensional direct numerical simulations of fully compressible polytropic turbulent convection in a very large aspect ratio ($\lambda=42.6$) cartesian box with $1024\times 1024\times 82$ mesh points. We investigate the general properties of this flow and discuss the similarities and differences between such an idealized experiment and the known properties of photospheric convection. We particularly focus on the emergence of large-scale coherent structures in the simulation and consider the potential implications of these results for the problem of the origin of mesogranular and supergranular flows and the large scale distribution of magnetic fields at the solar surface.