The Response of the Large-Scale Tropical Circulation to Warming

Abstract:

Previous work has found that the large-scale tropical circulations weaken as the surface warms and as the atmospheric static stability increases. When the large-scale circulation is diagnosed with the vertical pressure velocity at 500 hPa, changes in the circulation are directly related to the degree of convective aggregation. Changes in the large-scale circulation inevitably lead to changes in the cloud fields which then influence the surface temperature. How do the changes in the overturning circulation influence the cloud feedback? Are there basic differences in the way that the large-scale circulation responds to warming in general circulation models and cloud-system resolving models?

This work uses data from the Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) to investigate the interaction between overturning circulations, surface temperature, and atmospheric moisture. RCEMIP provides a rich collection of data from an intercomparison of general circulation models (GCMs), cloud‐system resolving models (CRMs), and (large eddy simulation) LES models simulating radiative convective equilibrium (RCE) over a range of fixed surface temperatures. Results from eleven GCMs that participated in RCEMIP will be presented along with results from several of the CRMs. The wide range of models do not show a clear tendency of convective aggregation as the surface temperature changes and there are large differences among ensemble members in the mean profiles of temperature and humidity. We find that the circulation of the GCMs often responds to surface warming in the opposite direction as do the CRMs. In addition to the analysis of the multi-model ensemble we will present a more thorough documentation of the RCEMIP results from the CAM5 and CAM6 global models.