The sensitivities of convection to large-scale temperature and moisture perturbations

The responses of convection to temperature and moisture perturbations has important implications in a number of aspects of atmospheric dynamics, such as convective coupled equatorial waves and the evaluation or improvement of convective parameterizations. The goal of this study is to explore the physical processes underlying such responses, using large-eddy-simulations and simple models. For shallow cumulus convection, we found that a positive temperature perturbation forms a buoyancy barrier, which preferentially eliminates parcels that start with lower equivalent potential temperature or have experienced heavy entrainment. Besides the amount of entrainment, the height at which parcels entrain is also important in determining their fate. Parcels entraining at higher altitudes are more likely to overcome the buoyancy barrier than those entraining at lower altitudes. Responses to environmental moisture perturbations are quite small compared to those to temperature perturbations, because changing environmental moisture is ineffective in modifying buoyancy in shallow cumuli. Responses of deep convection to perturbations at different heights will also be discussed.