Convective quasi-equilibrium revisited

A theory for the rate of adjustment of large-scale atmospheric environments via convection is presented. Temperature perturbations are applied to upper and lower elevation layers of a single-column toy model and of a 3D cloud-resolving model in order to examine factors directing the return to radiative-convective equilibrium. The rainfall, specific moist entropy and a derived variable we call the adiabatic warming are examined. The latter variable, which is the dry entropy minus a scaled mixing ratio, captures combined changes in the temperature and mixing ratio which leave the moist entropy unmodified.

Buoyancy anomalies occurring in the moist, lower elevations of the modeled atmosphere are met with latent heating and subsequent changes in rainfall which alter the local temperature and ultimately drive the adiabatic warming back toward equilibrium levels on convective time scales. In the upper elevations, however, the lack of moisture precludes these heating effects so that adjustment is limited. Consequences of this theory for convective quasi-equilibrium are discussed.