Speaker: Margaret Duffy, UC Berkeley
Title: Atmospheric Mechanisms of the Pattern Effect
Time: Wednesday, Oct 15 at 12:00pm PST
Location: EMS B210
Abstract: Climate feedbacks are expected to amplify over time due to the “pattern effect.” The pattern effect describes the influence of the pattern of surface warming on global climate feedbacks. In particular, delayed warming in the tropical east Pacific— as emerges several decades into abrupt4xCO2 simulations— causes climate feedbacks to amplify. Several explanations for the relationship between the pattern of sea surface temperature (SST) warming and climate feedbacks have been proposed, but previous literature has not reached a consensus. Previous literature has often highlighted the role of “tropospheric stability,” whose changes are highly correlated with changes in low clouds with warming. Relatedly, a “circus tent” model posits that in regions of deep atmospheric convection, convection communicates local SST anomalies vertically. The pattern of SST response also influences the “Walker circulation,” which is the zonal atmospheric circulation over the tropical Pacific region. We introduce a new ensemble of patch experiments and use it, along with observations and reanalysis of the historical period, to evaluate these three hypotheses, in isolation and their relationship to one another. The ensemble of patch experiments is created using the Community Atmosphere Model, version 6 (CAM6) by applying SST patches consistent with the Green’s Function Model Intercomparison Project (GFMIP) protocol. This ensemble uses a satellite simulator package, enabling enhanced cloud diagnostics. We find evidence that the circus tent and lower tropospheric stability hypotheses are closely related to one another, and largely explain the relationship between the pattern of SST warming and climate feedbacks in the ensemble of patch experiments and in interannual variability over the historical period.
