The Rapid Transition From Shallow to Precipitating Convection as a Predator–Prey Process

Abstract

Properly predicting the rapid transition from shallow to precipitating atmospheric convection within a diurnal cycle over land is of great importance for both weather prediction and climate projections. In this work, we consider that a cumulus cloud is formed due to the transport of water mass by multiple updrafts during its lifetime. Cumulus clouds then locally create favorable conditions for the subsequent convective updrafts to reach higher altitudes, leading to deeper precipitating convection. This mechanism is amplified by the cold pools formed by the evaporation of precipitation in the sub-cloud layer. Based on this conceptual view of cloud–cloud interactions which goes beyond the one cloud equals one–plume picture, it is argued that precipitating clouds may act as predators that prey on the total cloud population, such that the rapid shallow–to–deep transition can be modeled as a simple predator–prey system. This conceptual model is validated by comparing solutions of the Lotka-Volterra system of equations to results obtained using a high-resolution large-eddy simulation model. Moreover, we argue that the complete diurnal cycle of deep convection can be seen as a predator–prey system with varying food supply for the prey. Finally, we suggest that based on the present conceptual model, new unified cloud-convection parameterizations can be designed which may lead to improved representations of the transition from shallow to precipitating continental convection.