CMIP6 model fidelity at simulating large-scale atmospheric circulation patterns and associated temperature and precipitation over the Pacific Northwest

The ability of a suite of models contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) to simulate observed large-scale atmospheric circulation patterns over the Pacific Northwest of North America is evaluated. Twelve representative patterns of 500-hPa geopotential height (Z500) anomalies are identified using the self-organizing map method applied to reanalysis. CMIP6 Z500 anomalies from simulations of the historical period are mapped to each reanalysis-derived pattern, and the resulting differences between patterns, as well as differences in frequency of pattern occurrence, are quantified. In general, models are able to simulate the range of Z500 patterns with reasonable fidelity, although model skill varies across the 25-member ensemble. Surface temperature and precipitation anomalies associated with each Z500 pattern are found to also be reasonably simulated by the models, with some biases noted. This boosts confidence that the models are simulating temperature and precipitation patterns for the correct physical reasons. The models exhibit a range of skill at simulating pattern occurrence frequency and pattern persistence, with more agreement in winter than summer. Results indicate that the CMIP6 models are appropriate for assessing future projections of key atmospheric circulation patterns and their impacts on temperature and precipitation over the region.