The Impact of Enhanced Vertical Resolution on Seasonal Prediction Skill of the Quasi-Biennial Oscillation and Its Teleconnections in CESM2: A New Community Hindcast Dataset

Skillful seasonal forecasts of impactful climate events are in high demand yet remain a major challenge. Skill on seasonal timescales will arise from prediction of slowly varying predictable modes and their influence on the weather. The stratosphere provides one such mode, if it can be predicted, and if it exerts a sufficient influence on the troposphere below. Here we introduce a new seasonal hindcast data set with the Community Earth System Model version 2 (CESM2) with a raised atmospheric model lid and enhanced vertical resolution and compare with a companion hindcast set with CESM2's default vertical resolution. The enhanced vertical resolution enables considerably higher prediction skill of the Quasi-biennial Oscillation (QBO). We further use this data set to probe for associated skill in features that are thought to be influenced by the QBO and use it to inform on the uncertainties that could be present in observed QBO connections given the short observational record. This includes connections to the Northern Hemisphere polar vortex, the North Atlantic Oscillation, the Madden Julian Oscillation, the sub-tropical and mid-latitude westerlies in the Pacific sector, tropical precipitation, and the tropical easterly jet. The enhanced QBO skill has little impact on these phenomena. However, the hindcasts do indicate an improved representation of connections between the QBO and the stratospheric polar vortex and tropospheric zonal winds in the Pacific sector with higher resolution but there are indications of a low signal-to-noise problem in QBO teleconnections that, if addressed, could improve prediction skill in some of these features.