Theoretical modeling of convection I. Key physical processes

If one strives for a reliable description of "Turbulent Mixing in Stars" one must account for a large variety of physical processes. These include non-locality, that is needed in unstably stratified regimes, overshooting, which occurs in a stably stratified regime, double-diffusion processes (semi-convection and salt-fingers), transport of angular momentum, the Li⁷ problem, compressibility, and magnetic fields. While phenomenological models are manifestly inadequate, LES are too computer intensive to tackle this large variety of processes. Since the requirement of completeness of the description of these processes must also result in models that are usable in stellar structure-evolution codes, we conclude that only the RSM (Reynolds Stress Model) can do so and a description of the state of the art in that field is presented in Part 2.