The Impact of Increased Vertical Resolution on Northern Hemispheric Wintertime Climatology, QBO and Teleconnections in the GISS E2.2 Model

Abstract The Quasi‐Biennial Oscillation (QBO) is the leading mode of interannual variability in the equatorial stratosphere, with important teleconnections to phenomena such as the polar vortex and subtropical jet, and an important source of subseasonal‐to‐seasonal predictability. However, most climate models struggle with its representation, particularly in the lower stratosphere, with an associated degradation in its teleconnections. To improve this, versions of the GISS E2.2 high‐top model with enhanced vertical resolution in different regions of the upper troposphere and lower stratosphere (UTLS) were run in a fully coupled atmosphere‐ocean CMIP6 preindustrial control configuration, and their resulting climatologies, QBO and associated teleconnections analyzed and compared to MERRA2 reanalysis data. Increasing resolution in the lower stratosphere improved extratropical climatological biases, QBO zonal wind anomalies and modulation of the polar vortex. Increasing resolution in the upper troposphere, in addition, enhanced these improvements, but reversed the relationship between the QBO and El Niño Southern Oscillation (ENSO)—a quasi‐periodic oscillation in sea surface temperatures and winds over the tropical Pacific—causing a deterioration of QBO tropical and subtropical teleconnections. Moreover, none of these experiments significantly improved tropical model climatology or QBO temperature signals and tropical teleconnections. Our results suggest that the impacts of increased vertical resolution on the QBO should be studied in both atmosphere‐only and coupled configurations, to enable one to distinguish between direct atmospheric impacts, and how they are modulated by oceanic feedbacks. In addition, a multi‐model ensemble is recommended to reduce the impacts of model biases.