Speaker: Stephen Thomson (Exeter)
Title: Eddy feedback in atmospheric models – what is it, how are models deficient, and what can we do to fix it?
Abstract: The interaction between atmospheric jet streams and eddies is at the heart of many important problems in weather and climate science, including the response of jet streams to anthropogenic forcing, and their predictability on seasonal timescales. The role of ‘eddy feedback’ was examined in the influential work of Lorenz and Hartmann (2001), who used lead/lag analysis to differentiate between the midlatitude eddies leading the mean flow, and the mean flow leading the eddies, with the latter referred to as an ‘eddy feedback’. Recent studies have identified eddy feedback as one aspect where CMIP6 and seasonal-prediction models might be deficient. In this presentation I will examine the meaning of eddy feedback, discuss ways of quantifying the process, and identify ways in which models might be improved. In particular, we will compare the annual cycle of eddy feedback in both CMIP6 models and reanalysis, examine the role of atmospheric resolution in simple climate models, and discuss the role of large-scale biases.