Investigating the Effects of Changing Atmospheric Forcing Resolution in a Regional Ocean Model of the Northwest Atlantic

Regional, uncoupled ocean models require atmospheric forcing data to properly simulate the impact of atmospheric variability on the ocean. When downscaling seasonal to decadal predictions and climate change projections with a regional ocean model, the available atmospheric forcing data often has low resolution (on the order of 1 degree). Would higher-resolution atmospheric forcing result in better quality of the simulation? If so, why don’t we use it? Does it take longer to run? While studies have been done on the effects of atmospheric resolution, they largely focus on global ocean-atmosphere coupled models and not regional, uncoupled models. To explore the impacts of atmospheric forcing resolution on a regional ocean model, we ran and compared a suite of 30-year simulations using GFDL’s 1/12-degree regional ocean and biogeochemical model of the Northwest Atlantic Ocean (MOM6-COBALT-NWA12): 5 ensembles with 1-degree atmospheric forcing from GFDL’s SPEAR_LO global coupled model and 5 ensembles with 0.5-degree atmospheric forcing from GFDL’s SPEAR_MED coupled model. The greatest difference we found between SPEAR_LO and SPEAR_MED was the distribution of winds, since higher resolutions better capture spatial heterogeneity. For diagnostics sensitive to shifts in wind, like chlorophyll concentration in the Gulf of Maine, medium-resolution forcing showed discernible improvement compared to low-resolution forcing. For more robust diagnostics like the northward position of the Gulf Stream, there was little difference between low and medium-resolution forcing. Overall, our results suggest that, when available, higher resolutions provide slightly better output when used to force regional, uncoupled models.