Linking the Quasi-Biennial Oscillation and Projected Arctic Sea-Ice Loss to Stratospheric Variability in Early Winter

Observations and climate model simulations have shown potential linkages between Arctic sea-ice loss and mid-latitude climate variability. However, there remain large uncertainties in understanding the complex troposphere-stratosphere mechanisms. Using an atmospheric general circulation model with a well-resolved stratosphere (SC-WACCM4), we assess the role of the Quasi-Biennial Oscillation (QBO) on the atmospheric response to projected Arctic sea-ice loss. We perform two 200-ensemble member simulations prescribed with either historical or late-21^st century sea-ice fields (concentration and thickness). The QBO in the model is prescribed based on observed radiosonde data. To assess the significance of the “Holton-Tan” effect, we composite years by easterly (QBO-E) and westerly (QBO-W) phases of the QBO in each of our numerical experiments.

We find that the polar stratospheric response to sea-ice anomalies is larger coinciding with the QBO-E phase. Moreover, this response shows a weakening of the polar vortex during QBO-E and a strengthening during QBO-W. The opposite-signed responses are associated with differences between the phasing of the anomalous and climatological stationary waves in early winter. Here we also investigate the influence of the QBO on the tropospheric response to sea-ice anomalies. We find a negative NAO response during the QBO-W phase, while under QBO-E the NAO response is insignificant. Instead, we observe a larger circulation response in the North Pacific coinciding with the QBO-E phase. Additional diagnostics, such as differences in the probability of mid-latitude cold extremes, will also be discussed. Overall, our results suggest that the QBO can modulate the response of the large-scale atmosphere to Arctic sea-ice loss.