A global assessment of warm-phase convective invigoration from aerosol-cloud interactions. Part 1: Theory

Abstract. The theory of warm-phase convective invigoration from aerosol-cloud interactions posits that polluted cloud updrafts consume supersaturation more readily, causing them to release latent heat sooner and attain larger buoyancies and updraft speeds. An analytical model is developed to predict how much this mechanism changes cloud-updraft speeds when the cloud-droplet number concentration increases but the meteorological environment is fixed. For any perturbation in cloud-droplet number concentration, the model predicts an optimal updraft speed for warm-phase invigoration. Updrafts that are much slower than the optimal value experience invigoration that is directly proportional to the non-polluted updraft speed. In contrast, updrafts that are much faster than the optimal value experience a powerful feedback mechanism that resists invigoration due to changes in the drag force. For typical atmospheric conditions, shallow convective updrafts are generally closer to the optimal updraft speed than deep convective updrafts, making shallow convective clouds more susceptible to warm-phase invigoration. These predictions constrain the conditions under which substantial warm-phase invigoration can be expected to occur in nature.