Influence of Convective Entrainment on Climate Variability

Abstract:

Convective entrainment is known to impact the modelling of the mean climate, and in particular the pattern of mean tropical precipitation. Increasing convective entrainment suppresses convection in the margins of convergence zones and increases precipitation in the center of these convergence zones. This results from an interaction between convection and large-scale circulation. Results from the CNRM-CM5 model suggest that this sensitivity of the mean actually results from the synoptic variability: the larger the entrainment, the more intense the synoptic precipitating events, with drier periods between events. The changes in intensity and frequency of these events combine to explain the different sensitivities in the centers and margins of the convergence zones. In turn, it appears that the intensity of the synoptic precipitating disturbances is related to the mean stratification, as mesured by the Gross Moist Stability (GMS). The larger the entrainment, the smaller the GMS, because of a larger humidity stratification and a smaller potential temperature stratification, and the larger the dynamic feedback on precipitating disturbances. For large entrainment, the tropical mean GMS is even negative, implying a strong positive feedback of circulation onto precipitating disturbances.