An idealized atmospheric state where the ensemble average equals both the time and spatial averages. While most turbulence theories are based on the ensemble average, most calculations of averages in the real atmosphere are averages over time of a fixed point, or averages over a line or a volume at an instant in time (i.e., a snapshot). By making the assumption ergodic, values measured in the real atmosphere can be utilized within the Reynolds averaged equations for turbulent flow.