Convective Inhibition, Subgrid-Scale Triggering Energy, and Stratiform Instability in a Toy Tropical Wave Model

Abstract

Abstract A toy model of large-scale deep convection variations is constructed around a radiative–convective equilibrium climate, with an observed mean sounding as its thermodynamic basic state. Vertical structure is truncated at two modes, excited by convective (one-signed) and stratiform (two-signed) heating processes in tropical deep convection. Separate treatments of deep and shallow convection are justified by observations that deep convection is more variable. Deep convection intensity is assumed to be modulated by convective available potential energy (CAPE), while occurrence frequency is modulated by the ratio of convective inhibition (CIN) to “triggering energy” K, a scalar representing the intensity of subgrid-scale fluctuations. Deep convective downdrafts cool and dry the boundary layer but also increase K. Variations of K make the relationship between convection and thermodynamic variables (CAPE, CIN, θe) nonunique and amplify the deep convective response to temperature waves of small (∼1°C) am...