Local and Remote Cloud Radiative Effect Impacts onto the Extratropical Atmospheric Circulation

Modern climate models are known to exhibit large positive biases in the annular mode timescale during certain seasons. Understanding the causes of these biases is an ongoing topic of study. Recent observational work has suggested that cloud radiative effects may act as a negative feedback on annular mode variability [Li and Thompson, 2016]. This study explores the possibility of an impact of cloud radiative effects on annular mode variability in a numerical model using the Clouds On-Off Klimate Intercomparison Experiment (COOKIE) framework [Stevens et al., 2012]. Performing this type of experiment with the GFDL AM2.1 model in a specified SST aquaplanet mode, it is shown that clouds can act to significantly increase the amplitude of meridional shifts of the eddy-driven jet. The causes for this change are explored. It is shown that cloud radiative effects in the tropics versus the extratropics cause competing effects on the latitude of the eddy-driven jet, but together they act to widen the climatological jet. Furthermore, eddy variability in the extratropics is strongly amplified by cloud radiative effects, and this is suggested to contribute to the stronger meridional shifts of the eddy-driven jet in the “clouds-on” model run. Finally, it shown that the impacts of cloud radiative effects in the tropics can have large impacts on the high-latitude atmosphere, and thus care must be taken when interpreting conventional COOKIE experiments for the understanding of cloud-circulation coupling in the extratropics.