Coupled atmosphere-ocean dynamics in the California Current System off the U.S. West Coast

Air-sea interactions substantially modulate oceanic and atmospheric mesoscale variability. Regions of particularly strong oceanic mesoscale activity and hence strong potential for these modulation effects are the highly productive eastern boundary upwelling systems (EBUS), such as the California Current System (CalCS). There, the interactions between atmospheric and oceanic processes can easily alter marine biogeochemical processes or force extreme events with highly anomalous conditions in ocean temperature, pH, and oxygen. Nevertheless, modeling this coupled variability remains challenging due to the small-scale nature of such interactions and the complexity of the system itself. In addition, the extent to which the interplay between atmospheric and oceanic processes impacts the spatial and temporal scales of mesoscale variability and affects the marine ecosystem and ocean biogeochemistry remains largely unknown.

Given these complex interactions between the atmosphere, the ocean, and marine biogeochemistry, we developed a coupled regional high-resolution Earth System Model (ROMSOC). For the atmosphere, ROMSOC uses the GPU-accelerated Consortium for Small-Scale Modeling (COSMO) model, and the Regional Oceanic Modeling System (ROMS) model for the ocean. ROMS in turn includes the Biogeochemical Elemental Cycling (BEC) model that describes the functioning of the lower trophic ecosystem in the ocean and the associated biogeochemical cycles. Our current model setup includes thermodynamical and mechanical coupling between the atmosphere and the ocean. Here, we present results from 10-year long coupled simulations for the CalCS at kilometer-scale resolution. We find that the inclusion of atmospheric feedbacks strongly affects oceanic dynamics such as upwelling strength, the advection of water masses and mixed layer depth. In a next step, we will test the hypothesis if this strong mesoscale coupling of the atmosphere and the ocean impacts the spatial and temporal scales of oceanic mesoscale variability such as marine heatwaves and can potentially act to shorten their duration.