Characteristic of Downslope Wind Along the California Coast with and without the Coupled Models

Downslope winds, such as the Santa Ana Winds, are a significant meteorological phenomenon affecting the California coast particularly during the fall and winter months. These winds are characterized by their strong and dry nature as they descend from higher elevations to the coastal areas and could have significant impacts on weather, fire risk, and air quality. Previous numerical studies on downslope wind over the coastal areas generally just involves the standalone atmospheric model, which don’t account for the physical processes and feedback mechanism between the ocean and wave. Therefore, using the fully three-way coupled (atmospheric-ocean-wave) model could potentially provide a more accurate representation and impact assessment of the downslope winds by considering the complex interactions between atmosphere, ocean and wave.

In this study, the goal is to investigate the characteristic of downslope wind by simulating a real-world significant wind event with and without the coupled models. The Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling system is used to investigate the coupled processes of the atmosphere (WRF), ocean (ROMS), and waves (WAVEWATCH III). The impact from individual and coupled model on the offshore flow are examined by comparing simulations between different model configurations and validating against the National Data Buoy Center (NDBC) buoy observations along the California coast. This evaluation will help quantify model errors, identify conditions under which the model physics works and areas where it may need improvement. Additionally, it will help determine the impact of the different coupling modes on simulating significant wind events and assess the potential benefits of using the coupled mesoscale-modeling approach for wind energy.