Patterns, Impacts, and Future Projections of Summer Variability in the Arctic from CMIP5 Models

Thirty models in phase 5 of the Coupled Model Intercomparison Project (CMIP5) are evaluated for their performances in reproducing two summertime atmospheric circulation patterns in the Arctic: the Arctic Oscillation (AO) and Arctic dipole (AD). The reference AO and AD are extracted from the ERA-Interim dataset (1979-2016). Model evaluation is conducted during the historical period (1901-2005). Models are ranked by a combined metrics approach based on two pattern correlation coefficients (PCCs) and two explained variances for the AO and AD, respectively. In the projected period (2006-2100), most models produce a positive trend for the AO index and a negative trend for the AD index in summer. The models ranked higher based on the combined metrics ranking show greater consistency and smaller values in the magnitudes of trends of AO and AD than the lower-ranked ones. The projected trends in the AO and AD contribute to a slight increase, if not a decrease, of the air temperature and an acceleration of precipitation increase in the twenty-first century over Arctic Alaska, which is the reverse of over the Barents and Kara Seas. Changes in the AO and AD are relatively minor contributing factors to the projected temperature and precipitation changes in the Arctic, among which the changes in the AD play a bigger role than those in the AO. The summer AO and AD have a stronger impact on the spatial asymmetry of the precipitation field than on the air temperature field.