Quantifying and Understanding Forced Changes to Unforced Modes of Atmospheric Circulation Variability over the North Pacific in eight Large Ensembles

Understanding how unforced modes of climate variability are projected to change under increasing greenhouse gases is important for understanding changing climate impacts. This work extends a previous study that investigates forced changes to unforced modes of wintertime atmospheric circulation variability and associated impacts on precipitation over the North Pacific and adjacent regions in the CESM1 Large ensemble to 7 additional single model initial condition large ensembles (LEs). We apply an empirical orthogonal function to each LE at individual time steps across the ensemble to isolate how patterns of variability change in the future scenario (either SSP370 or 585). This method leverages the size of the LEs and allows for the time-evolving forced response to be isolated. While the patterns of wintertime atmospheric circulation variability are similar across models there are large differences in their projected changes in both the circulation itself and its impacts. Although some consistencies exist such as a strengthening of the Aleutian Low and associated Californian rainfall impacts in the Pacific North American Pattern (PNA). Model differences in the PNA and North Pacific Oscillation (NPO) are found to be linked to model differences in the Tropical Pacific, suggesting that models would behave more similarly in their North Pacific future projections if we improve tropical Pacific biases.