Skip to main content
U.S. flag

An official website of the United States government

Pathways Linking Deep Convection, Circulation and Low Cloud Feedback

Presentation Date
Monday, December 14, 2020 at 8:38pm



It is well-established that low cloud feedback is a leading contributor to the inter-model spread in equilibrium climate sensitivity (ECS). Many previous studies examined local controlling factors for low cloud change in the subtropical descending regimes. In this study, we posit that deep convection and large-scale circulation changes in the tropical ascending regimes can modify subtropical low cloud fraction (LCF) through three pathways: (1) the temperature-stability pathway, through which tropospheric temperature anomalies propagated by wave dynamics subsequently modify lower tropospheric stability (LTS), (2) the moisture-mixing pathway that may depend on shallow ascent and sub-grid-scale mixing of moisture between the free troposphere and the planetary boundary layer (PBL), and (3) the radiation-subsidence pathway that involves longwave radiation mediated subsidence control on LCF. Hence, the differences in climate models’ deep convective parameterizations can drive a significant fraction of inter-model spread in low cloud feedback and thus ECS. We have analyzed a set of CESM1 perturbed physics experiments (PPEs) in which deep convective parameters were modified and found evidence of these pathways. Preliminary analysis of the CMIP6 simulations indicates the model differences in tropical deep convection and large-scale circulation changes are related to the model-spread in low cloud feedback via the above-mentioned pathways. Thus, improving deep convective parameterizations in climate models is critically important to reducing the uncertainty of ECS.

Funding Program Area(s)