Entrainment Makes Pollution More Likely to Weaken Deep Convective Updrafts Than Invigorate Them

Abstract

Are the results of aerosol invigoration studies that neglect entrainment valid for diluted deep convective clouds? We address this question by applying an entraining parcel model to soundings from tropical and midlatitude convective environments, wherein pollution is assumed to increase parcel condensate retention. Invigoration of 5%–10% and <2% is possible in undiluted tropical and midlatitude parcels respectively when freezing is rapid. This occurs because the positive buoyancy contribution from freezing is larger than the negative buoyancy contribution from condensate loading, leading to positive net condensate contribution to buoyancy. However, aerosol‐induced weakening is more likely when realistic entrainment rates occur because water losses from entrainment more substantially reduce the latent heating relative to the loading contribution. This leads to larger net negative buoyancy contribution from condensates in polluted than in clean entraining parcels. Our results demonstrate that accounting for entrainment is critical in conceptual models of aerosol indirect effects in deep convection.

Modulation of Tropical Convection‐Circulation Interaction by Aerosol Indirect Effects in Convective Self‐Aggregation Simulations of a Gray Zone Global Model

“…By acting as cloud condensate nuclei (CCN) or ice nuclei (IN), aerosols change cloud properties by influencing cloud microphysics and dynamics, meanwhile influencing cloud-radiation feedbacks (i.e., aerosol indirect effects (AIEs); see reviews of Fan et al (2016) and Tao et al (2012)). However, the underlying mechanisms of how the updraft speed of deep convection is influenced remain elusive and are often debated (Rosenfeld et al, 2008;Fan et al, 2018;Grabowski & Morrison, 2020;Igel & van den Heever, 2021;Peters et al, 2023;Romps et al, 2023). Varble et al (2023) argued that many studies have incorrectly conflated the response of updraft speed of deep convection to enhanced CCN concentrations with the response of cloud microphysical properties.…”

The Effects of Shallow Cumulus Cloud Shape on Interactions Among Clouds and Mixing With Near‐Cloud Environments

“…The adequate representation of the processes controlling moist convection remains one of the most challenging climate and weather modeling issues. Some of the uncertainty in Earth system models can be attributed to various convective processes that are poorly represented or neglected entirely, including cloud‐cloud interactions and turbulent entrainment‐mixing (Chen, Hagos, Feng, et al., 2023; Lasher‐Trapp et al., 2021; Lu, Liu, & Niu, 2014; Lu et al., 2018; Peters et al., 2023). Current convective parameterizations use mass flux schemes in a bulk manner (e.g., Tiedtke, 1989) or in a spectral formulation (e.g., Arakawa & Schubert, 1974), with particular focus on the sizes of clouds.…”