STRAT-MSB - Quantifying the Role of Stratospheric Mean State Bias on Representations of Climate

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The proposed work will seek to quantify the role of stratospheric mean state bias in driving inter-model spread in stratospheric andtropospheric sensitivity to temperature perturbations in the lower stratosphere. Previous literature has highlighted majorinadequacies in the ability of global circulation models to capture processes in the upper troposphere and lower stratosphere,including the transport of water vapor into the stratosphere. This has major implications for the radiative budget of the entireatmosphere and feeds back on stratospheric circulation and tropospheric dynamical variability. This project will leverage the outputsof a novel model inter-comparison project in which a temperature tendency has been fixed in the lower stratosphere of five state ofthe art climate models. Early results indicate that in spite of an equivalent perturbation, each model exhibits unique thermalresponses which result in differing surface climate responses. Motivated by these findings, this project will extend analysis tocharacterize both the stratospheric and tropospheric inter-model differences, including changes to water vapor transport and theoverturning circulation. The source of these differences will be explored using a novel idealized stratospheric model to identify whatfraction of the response may be attributed to a model's stratospheric mean state. Results will be constrained by observations of thestratospheric profile. Outcomes of this work will guide model development by quantifying the importance of mean state bias ascompared to process level parameterizations, or numerical methods. Understanding sources of uncertainty in model behaviorenables improved interpretation of current future warming projections with implications for national and global scale adaptation andmitigation planning.