Clouds and Convective Self‐Aggregation in a Multimodel Ensemble of Radiative‐Convective Equilibrium Simulations

Abstract

The Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) is an intercomparison of multiple types of numerical models configured in radiative‐convective equilibrium (RCE). RCE is an idealization of the tropical atmosphere that has long been used to study basic questions in climate science. Here, we employ RCE to investigate the role that clouds and convective activity play in determining cloud feedbacks, climate sensitivity, the state of convective aggregation, and the equilibrium climate. RCEMIP is unique among intercomparisons in its inclusion of a wide range of model types, including atmospheric general circulation models (GCMs), single column models (SCMs), cloud‐resolving models (CRMs), large eddy simulations (LES), and global cloud‐resolving models (GCRMs). The first results are presented from the RCEMIP ensemble of more than 30 models. While there are large differences across the RCEMIP ensemble in the representation of mean profiles of temperature, humidity, and cloudiness, in a majority of models anvil clouds rise, warm, and decrease in area coverage in response to an increase in sea surface temperature (SST). Nearly all models exhibit self‐aggregation in large domains and agree that self‐aggregation acts to dry and warm the troposphere, reduce high cloudiness, and increase cooling to space. The degree of self‐aggregation exhibits no clear tendency with warming. There is a wide range of climate sensitivities, but models with parameterized convection tend to have lower climate sensitivities than models with explicit convection. In models with parameterized convection, aggregated simulations have lower climate sensitivities than unaggregated simulations.

Understanding the Extreme Spread in Climate Sensitivity within the Radiative‐Convective Equilibrium Model Intercomparison Project

“…In this study, we analyzed the variability of climate sensitivities across 31 models, run at three fixed SSTs (295, 300, and 305 K) that participated in the RCEMIP (Wing et al, 2018, 2020). Estimates of the climate feedback parameter ( λ ) have an extremely large range across the RCEMIP models, from −6 to 3 W m −2 K −1 .…”

“…In addition to homogeneous surface conditions, the insolation is everywhere equal to the tropical annual mean (409.6 W m −2 ), and all trace-gas concentrations are fixed and spatially uniform. More details on the boundary conditions and RCEMIP model setup are described in Wing et al (2018Wing et al ( , 2020.…”

Characterizing Convection Schemes Using Their Responses to Imposed Tendency Perturbations

“…All rights reserved. Rennó et al, 1994;Sobel & Bretherton, 2000;Wing et al, 2020). The RH values of the SCMs range between 56% and 88% at the surface levels and between 6% and 85% in the midtroposphere.…”

Investigating the impact of cloud-radiative feedbacks on tropical precipitation extremes

“…Climate models have lately been adapted for RCE experiments, and show similar convective organization (although on larger scales) as the high-resolution models [20][21][22] . Some of these studies have pointed to different mechanisms of convective aggregation than the CRM studies; for example, Coppin and Bony 23 show how low-level cloud effects drive aggregation at cooler surface temperatures.…”