Evaluating Springtime Atmospheric Ridging Over the Pacific Northwest in the HadAM3p Large Ensemble

Springtime atmospheric ridging over the Pacific Northwest can lead to anomalously dry conditions and an early end to the wet season as demonstrated in 2015 and 2018. Given the impacts of such events, it is important to understand how springtime atmospheric ridging will change under global warming. However, projections of future change rely on climate model ability to adequately simulate ridging climatology and associated characteristics such as frequency, persistence, and timing. To this end, we evaluate springtime atmospheric ridging over the Pacific Northwest in a large ensemble from the HadAM3p model. The ensemble contains 100 ten-year simulations of the early 21st century with small initial condition perturbations. An objective ridge identification algorithm is applied to the model simulations to compare ridge frequency, persistence, and timing to a reference climatology developed using reanalysis. Preliminary results suggest the model is capable of realistically capturing many features of springtime ridge climatology within a region shown to be important for anomalously low precipitation over the Pacific Northwest. This evaluation will help constrain uncertainty in future projections of springtime ridging over the region in follow on work using simulations of future climate under enhanced global warming.