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.
Highlights
For more than 20 years, coordinated model intercomparisons have been undertaken in which simulations with consistent configurations have been performed with different models to assess whether different models behave and to aid in the understanding of relevant phenomenon
The results presented in the current paper are a small fraction of the topics that can be explored with the Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) ensemble, so, in addition to serving as a reference for the RCEMIP simulations, we hope that this paper will stimulate studies into more specific questions and process studies that may require additional experimentation
This paper has presented the first results of RCEMIP, the first model intercomparison to include cloud‐resolving models (CRMs), global cloud‐resolving models (GCRMs), large eddy simulations (LES), general circulation models (GCMs), and single column models (SCMs), with a focus on providing a broad overview with respect to each of the three themes of RCEMIP
Summary
For more than 20 years, coordinated model intercomparisons have been undertaken in which simulations with consistent configurations have been performed with different models to assess whether different models behave and to aid in the understanding of relevant phenomenon. RCE's status as the simplest representation of the climate system makes it an essential inclusion in such hierarchies (Jeevanjee et al, 2017; Maher et al, 2019) In addition to these formal issues, an intriguing result emerging from cloud‐resolving simulations of RCE is that the interaction between clouds and circulations can give rise to self‐aggregation of convection, but its importance for climate and the relative role of different driving mechanisms remain unclear and seemingly model dependent (Wing, 2019; Wing et al, 2017). As described in Wing et al (2018), RCEMIP was motivated by the absence of a common baseline in past simulations of RCE, the accessibility of RCE to a wide range of model types, and the utility of RCE as a framework in which to address some of the biggest open questions in climate science (Bony et al, 2015).
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