Atmospheric Precursors of and Response to Anomalous Arctic Sea Ice in CMIP5 Models

This study examines pre-industrial control simulations from eight Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models in an effort to better understand the complex two-way interactions between Arctic sea ice, the polar stratospheric vortex and surface temperatures over Eurasia. We present normalised regressions of Arctic sea ice area against several atmospheric variables at extended lead and lag times. Statistically significant regressions are found at leads and lags, suggesting both atmospheric precursors of and responses to low sea ice; but generally, the regressions are stronger when the atmosphere leads sea ice, including a weaker polar stratospheric vortex indicated by positive polar cap height anomalies. Significant positive mid-latitude eddy heat flux anomalies were also found to precede low sea ice. We argue that low sea ice and raised polar cap height are both a response to this enhanced mid-latitude eddy heat flux. The so-called "warm Arctic, cold continents" anomaly pattern is present one to two months before low sea ice, but is absent in the months following low sea ice, suggesting that the Eurasian cooling and low sea ice are driven by similar processes. Lastly our results suggest a strong dependence on the geographic region of low sea ice, with low Barents-Kara Sea ice correlated with a weakened polar stratospheric vortex whilst low Sea of Okhotsk ice is correlated with a strengthened polar vortex. Overall, the results support a notion that the sea ice, polar stratospheric vortex and Eurasian surface temperatures collectively all respond to large-scale changes in tropospheric circulation.