Radiative-convective disequilibrium

Radiative-convective systems inevitably seek a statistical equilibrium, but there is no reason to believe that this equilibrium must be steady. The obvious temporal variability of convection in nature, on many time scales, is clearly linked, at least in part, to forcing by transient large-scale dynamical processes (e.g. easterly waves) and transient radiative processes (e.g., the diurnal and seasonal cycles). The possibility remains, however, that under some conditions radiation and convection can interact nonlinearly to produce spontaneous temporal fluctuations on “large scales”. Recent numerical simulations with both parameterized and model-resolved two-dimensional convection provides evidence that this can, indeed, happen. Radiative-convective oscillations on both short (days) and long (weeks) time scales have been reported. Highly idealized models have been devised to interpret the results. Work is under way to determine to what extent such “free” radiative-convective oscillations are relevant to the transient convective activity that we see in nature.